Portrait of Professor Steven Gao

Professor Steven Gao

Professor of RF/Microwave Engineering
Director of Graduate Studies (Research)

About

Professor Steven (Shichang) Gao is Chair of RF and Microwave Engineering, and the Director of Postgradudate Research at School of Engineering and Digital Arts, University of Kent, UK.

He started his career since 1994 while at China Research Institute of Radiowave Propagation (China). Then he worked as a Post-doctoral Research Fellow at National University of Singapore (Singapore), a Research Fellow at Birmingham University (UK), a Visiting Scientist at Swiss Federal Institute of Technology (ETH Zurich, Switzerland), a Visiting Fellow at Chiba University (Japan), and a Visiting Scientist at University of California at Santa Barbara (US). He was a Senior Lecturer, Reader and Head of Antenna and Microwave Group at Northumbria University (UK) during 2002-2007, and the Head of Satellite Antennas and RF System Group at Surrey Space Centre, University of Surrey (UK) during 2007-2012. He joined the University of Kent as a Professor in 2013. He also held short-term visiting appointments at some institutes including as a Visiting Professor at Northwestern Polytechnic University (China) and the University of Calabria (Italy).

He authored, co-authored and co-edited 2 books including Space Antenna Handbook (Wiley, 2012) and Circularly Polarized Antennas (Wiley-IEEE, 2014), over 300 refereed papers in international journals and conferences, and 4 patents.

He is an Associate Editor of several international Journals (IEEE Transactions on Antennas and PropagationRadio Science; IEEE Access; IET Circuit, Devices and Systems; Electronics Letters), and the Editor-in-Chief for Wiley Book Series on "Microwave and Wireless Technologies". He was a Distinguished Lecturer of IEEE Antennas and Propagation Society (2014-2016), General Chair of 2013 Loughborough Antenna and Propagation Conference, Lead Guest Editor of Proceedings of the IEEE for Special Issue on "Small Satellites"(2018), Lead Guest Editor of IEEE Trans on Antennas and Propagation for Special Issue on "Antennas for Satellite Communication"(2015), Guest Editor of IET Circuits, Devices & Systems for Special Issue in “Photonic and RF Communications Systems” (2014), Chair of Special Session on “Satellite Communication Antennas” in CSNDSP'2012, Chair of Workshop on "New Technology Development for Space" in 2015 IEEE Microwave Symposium, etc. He is a member of the editorial boards of International Journal of RF and Microwave CAE (US),  International Journal of Space Science and Engineering (US),Chinese Journal of Electronics (China), Chinese Journal of Radio Science (China), etc. He was a Plenary/Invited Speaker of some international conferences and workshops (IEEE APWC'2017, UCMMT'2017, AES'2014, IWAT'2014, SOMIRES'2013, APCAP'2014, etc). He is a Fellow of Institute of Engineering and Technology (IET), UK, and a Fellow of the Royal Aeronautical Society, UK.

He received many research grants and was Principal Investigator for "Millimeter-wave intelligent array antennas for Ka-band satellite communications on the move" (FLEXWIN, funded by EU FP7), “Advanced reflectarray antennas for space-borne synthetic aperture radars” (funded by the Royal Academy of Engineering, UK), “Gallium Nitride integrated millimeter-wave active phased array multi-beam transceivers for SATellites" (GaNSat, funded by EU FP7 Space Programme), etc. Currently he is a Principal Investigator for Several Research Projects including "Adaptive multi-band small MIMO antennas for next-generation smart phones" (funded by Huawei), "Low-cost THz wideband smart antennas design and fabrication using 3D Printing" (WISDOM, funded by EPSRC), "Lead Niobate-based Tunable Dielectrics for Smart Microwave and Millimeter-wave Systems" (EPSRC), "Digital Beamforming Synthetic Aperture Radars onboard satellites constellations "(DIFFERENT, funded by EU FP7 Space Programme), etc.

Research interests

Lead Niobate-based Tunable Dielectrics for Smart Microwave and Millimeter-wave Systems" (EPSRC);

Millimeter-wave intelligent array antennas for Ka-band satellite communications on the move (FLEXWIN, funded by European Union FP7 ICT Program);

Low-cost THz wideband smart antennas design and fabrication using 3D Printing" (funded by EPSRC),;

Advanced reflectarray antennas for space-borne synthetic aperture radars (funded by the Royal Academy of Engineering, UK);

Gallium Nitride integrated millimeter-wave active phased array multi-beam transceivers for SATellites (GaNSat, funded by European Union FP7 Space Programme);

Digital Beamforming Synthetic Aperture Radars onboard satellites constellations (DIFFERENT, funded by EU FP7 Space Programme);

Adaptive multi-band small MIMO antennas for smart phones (funded by industry);

Low-cost small smart antennas for wireless communications (funded by industry);

Ultra-wideband antennas and arrays for through-wall imaging radars;

Antennas and RF front ends for multi-band Global Navigation Satellite Systems Receivers onboard small satellites (funded by CEOI, UK, and industries);

GaN HEMT-based high-efficiency RF/microwave power amplifiers (HEFCE and industries);

Air-borne synthetic aperture radar RF payload (funded by industries).

Teaching

Satellite and Optical Communication;

Communication Systems;

Electronic and RF Circuits;

Antennas and Propagation;

Microwave Engineering

Supervision

His main areas of expertise are in antennas, smart antennas, phased arrays, MIMO, satellite antenna, deployable antennas, RF/microwave/millimetre-wave/THz circuits and RF front ends (high-efficiency RF/microwave power amplifiers, filters), 5G mobile communications, satellite communications, wireless power transfer, UWB radars, GNSS reflectometry, synthetic-aperture radars, electromagnetic modelling and small satellites.

He is looking for potential PhD students. Ideally he/she has completed MSc study and may be funded by his/her government scholarship (e.g., China Scholarship Council or similar government scholarships in other countries) or other sources.

Professional

He received URSI Young Scientist Award from International Union of Radio Science (URSI), 2002, Japan Society of Promotion Science (JSPS) Fellowship Award, Japan, 2005, Best Paper Award, LAPC, 2012, JSPS Award, Japan, 2013, Royal Academy of Engineering Visiting Fellow Award, UK, 2013, IET Premium Award for the Best Paper in IET Microwave, Antennas and Propagation, 2016, CST University Publication Award, 2017, etc.

Publications

Article

  • Mao, C. et al. (2018). Integrated Dual-Band Filtering/Duplexing Antennas. IEEE Access [Online] 6. Available at: https://doi.org/10.1109/ACCESS.2018.2805224.
    In this paper, the state-of-the-art integrated filtering antennas with dual-band operation are first reviewed. Then, two designs of dual-band microstrip filtering antennas with a low frequency-ratio are presented. The 1st design is a dual-band dual-polarization (DBDP) antenna with a frequency ratio of 1.2 on a single patch, by employing the coupled resonator technique. Two bands at each polarization are achieved by vertically coupling a hairpin resonator with a patch through a slot in the ground plane and then coupled to a dual-mode stub loaded resonator (SLR). Each band exhibits a 2nd-order filtering performance with improved bandwidth and out-of-band rejection. Such an integration technique could significantly reduce the dimension and complexity of traditional DBDP antennas/arrays. In the 2nd design, a novel dual-port dual-band antenna (with a frequency ratio of 1.38) with the integrated filtering and duplexing functions is proposed. The frequency duplexing function is implemented by coupling a single patch with two sets of resonator-based filtering channels via a U-slot resonator inserted in the ground. This device seamlessly integrates the functions of duplexers, filters and antennas in a very compact structure.
  • Duan, Z. et al. (2018). Integrated Design of Wideband Omnidirectional Antenna and Electronic Components for Wireless Capsule Endoscopy Systems. IEEE Access [Online] 6:29626-29636. Available at: https://doi.org/10.1109/ACCESS.2018.2840689.
    This paper presents a wideband antenna with
    omnidirectional radiation pattern for wireless capsule endoscopy
    (WCE) systems. The proposed antenna radiates as a slot structure
    formed between a central copper cylinder and a copper strip
    attached to the interior surface of biocompatible polyimide shell.
    Main features of the antenna include: 1). An integrated design of
    the antenna and electronic components in the capsule is employed.
    And, by utilizing the entire inner space of the capsule, the
    radiating aperture of antenna is increased to the maximum; 2).
    The copper cylinder can be used to house electronic components,
    therefore the potential electromagnetic interferences (EMI)
    brought by battery and electronic circuits are reduced to the
    minimum; 3) The antenna in tissue has a wide bandwidth from
    0.721 to 1.705 GHz, covering both 0.902-0.928 GHz Industrial,
    Scientific, and Medical (ISM) band and 1.395-1.4 GHz Wireless
    Medical Telemetry Service (WMTS) band. This is achieved by
    optimizing the stepped width of copper strip; 4). The antenna
    inside human tissues has stable omnidirectional radiation patterns
    across all operating frequencies. This is an indispensable
    characteristic due to the unpredictable orientation of capsule in
    the gastrointestinal (GI) tract. Stable patterns are achieved by
    having strong electric fields concentrated within the top substrate
    pointing at the same direction. The integrated design concept,
    wideband impedance matching and stable omnidirectional
    radiation patterns make the proposed antenna a promising
    candidate for future WCE system.
  • Wan, W., Geyi, W. and Gao, S. (2018). Optimum Design of Low-Cost Dual-Mode Beam- Steerable Arrays for Customer-Premises Equipment Applications. IEEE Access [Online] 6:16092-16098. Available at: https://doi.org/10.1109/ACCESS.2018.2813299.
    Two novel designs of dual-mode beam-steerable array antennas are proposed for customer-
    premises equipment applications. To obtain the optimal distribution of excitations for the arrays, the gain
    and front-back ratio of the array systems are optimized by using the method of maximum power transmission
    efficiency. The first design operates at 2.45 GHz and uses four folded monopoles of height<1/10 wavelength
    and a sleeve of height of 1/4 wavelength underneath the monopoles. The peak gain and the front-to-back ratio
    are 6.7 dBi and 7.8 dB respectively. The second design operates at 830MHz and uses four Yagi monopoles as
    elements with a common reflector and four directors. The peak gain and the front-to-back ratio for the second
    design are 6.0 dBi and 16.8 dB respectively. The proposed antennas have advantages including: low cost
    and compact size; dual-mode operation including the modes of omnidirectional radiation and directional
    radiation; and in the mode of directional radiation, the beam can be electronically steered to achieve the full
    coverage of the azimuthal plane. It achieves higher gain than the traditional electronically steerable passive
    array radiator antenna.
  • Gao, S. et al. (2018). Issue Small Satellites. Proceedings of the IEEE [Online] 106:339-342. Available at: https://doi.org/10.1109/JPROC.2018.2805267.
    Small satellite is a disruptive technology in space industries. Traditionally, space industries were dominated by satellites which have thousands of kilograms and are bulky and expensive. Small satellites denote a new generation of miniaturized satellites which, by taking advantages of modern technologies (e.g., integrated circuits, digital signal processing, MEMS, and additive manufacturing), can achieve a significant reduction in volume, mass, development time, and cost of satellites. During recent decades, small satellites, including CubeSats, NanoSats, MiniSats, and MicroSats, have undergone rapid developments, and are playing an increasingly larger role in exploration, technology demonstration, scientific research, and education. These miniature satellites provide a low-cost platform for missions, including planetary space exploration, Earth observations, fundamental Earth and space science, and developing precursor science instruments like laser communications and millimeter-wave communications for intersatellite and intrasatellite links, and autonomous movement capabilities. They also allow educators an inexpensive means to engage students in all phases of satellite development, operation, and exploitation through real-world, hands-on research and development experience on rideshare launch opportunities. A number of miniaturized satellites can form spaceborne wireless sensor networks in the space, which are also going to play an important role in Internet of Space (IoS) of the future
  • Zhang, L. et al. (2018). Wideband Circularly Polarized Tightly Coupled Array. IEEE Transactions on Antennas and Propagation [Online]. Available at: http://dx.doi.org/10.1109/TAP.2018.2867031.
    Tightly coupled arrays (TCA) have received considerable
    interests recently. Although various TCAs have been reported, they are
    limited to single or dual linear polarizations. Considering the importance of
    circular polarization (CP) in various wireless systems, it is meaningful to
    design a CP TCA with a simple configuration. This paper presents a
    circularly polarized tightly coupled crossed dipole array (CP-TCCDA) with
    wide overlapped impedance bandwidth and axial ratio (AR) bandwidth. A
    tightly coupled crossed dipole unit cell is investigated and the comparison
    with an isolated crossed dipole of the same size indicates that the VSWR<3
    bandwidth is increased from 3:1 to 7.1:1 while the 3-dB AR bandwidth is
    increased from 1.3:1 to 2.1:1. Analysisis given to explain the principles of AR
    bandwidth improvement and is verified by the comparison of radiated Efields
    between a CP-TCCDA and a conventional crossed dipole array. To
    verify the design concept, a 4×4 CP-TCCDA with feeding network is
    fabricated and measured. The measured results confirm that the proposed
    array achieves VSWR<3 bandwidth from 2.06GHz to 6.46 GHz (3.14:1) and
    3-dB AR bandwidth from 2.35GHz to 5.6GHz (2.38:1), which are much
    wider than the bandwidth of an isolated element and a conventional array
    using the same element.
  • Qin, F. et al. (2018). A High-Gain Transmitarray for Generating Dual-Mode OAM Beams. IEEE Access [Online]. Available at: http://dx.doi.org/10.1109/ACCESS.2018.2875680.
    This paper proposes a novel transmitarray antenna which can achieve high gain and
    produce dual-mode orbital angular momentum (OAM) beams in Ku band. Two back-to-back wideband
    dual-polarized microstrip antennas are employed as the unit cells, which are connected using metalized
    via holes. Full 360 o phase ranges can be obtained by varying the length of feeding lines in two
    orthogonal polarizations. Due to high isolation between the two orthogonal polarizations, dual-mode
    OAM beams can be formed simultaneously by tuning phase distributions in x- and y-polarizations,
    respectively. The approach for generating OAM beams is explained. To verify this concept, one
    prototype carrying 0 and +1 mode OAM beams is designed, fabricated and measured. Experimental
    results demonstrate that the both 0 and +1 mode OAM beams can be generated successfully, and the
    measured results agree well with the simulated results. Because of high directivity and focusing effects
    of transmitarray, the proposed +1 mode OAM beam has stable performance at a long propagation
    distance. The maximum gain reaches 26 dBi and 20 dBi in 0 and +1 mode OAM beams, respectively.
    Meanwhile, a narrow divergence angle of +/-5 o is obtained in +1 mode OAM beam. Compared to other
    OAM antennas reported, main advantages of the proposed antenna include high gain, narrow divergence
    angle,low cost, planar structure and the capability of producing dual-mode OAM beams.
  • Mao, C. et al. (2018). Planar Sub-Millimeter-Wave Array Antenna with Enhanced Gain and Reduced Sidelobes for 5G Broadcast Applications. IEEE Transactions on Antennas and Propagation [Online]. Available at: http://dx.doi.org/10.1109/TAP.2018.2874796.
    In this paper, a compact, broadband, planar array
    antenna with omnidirectional radiation in horizontal plane is
    proposed for the 26 GHz fifth-generation (5G) broadcast
    applications. The antenna element is composed of two dipoles and
    a substrate integrated cavity (SIC) as the power splitter. The two
    dipoles are placed side-by-side at both sides of the SIC and they
    are compensated with each other to form an omni-directional
    pattern in horizontal plane. By properly combing the resonant
    frequencies of the dipoles and the SIC, a wide impedance
    bandwidth from 24 to 29.5 GHz is achieved. To realize a large
    array while reducing the complexity, loss and size of the feeding
    network, a novel dual-port structure combined with radiation and
    power splitting functions is proposed for the 1st time. The
    amplitude and phase on each element of the array can be tuned,
    and therefore, the grating lobes level can be significantly reduced.
    Based on the dual-port structure, an 8-element array with an
    enhanced gain of over 12 dBi is designed and prototyped. The
    proposed antenna also features low profile, low weight and low
    cost, which is desirable for 5G commercial applications. Measured
    results agree well with the simulations, showing that the proposed
    high-gain array antenna has a broad bandwidth, omni-directional
    pattern in horizontal plane, and low side-lobes.
  • Wen, L. et al. (2018). Compact Dual-Polarized Shared-Dipole Antennas for Base Station Applications. IEEE Transactions on Antennas and Propagation [Online]. Available at: https://doi.org/10.1109/TAP.2018.2871717.
    Crossed dipole antennas have been widely employed for dual-polarization in wireless communication systems in recent years. In this paper, a novel design concept of dual-polarized shared-dipole (DPSD) antenna is presented. Different from the traditional crossed dipole (CD) antennas, the arms of the DPSD antenna are shared for two orthogonal polarizations. This design technique leads to significant size reduction and high isolation compared to the traditional CD antennas. The operation principle of the proposed antenna is theoretically analyzed. To validate the presented design concept, two novel DPSD antennas are designed, fabricated and measured. The first design is a four-port DPSD antenna, which is a straightforward demonstration of the operation principle of the DPSD antenna. The second design is a highly integrated DPSD antenna, which avoids the use of feed network and provides a simple configuration to design the dual-polarized antenna. Both of the DPSD antennas are designed to operate at 1.7-2.7 GHz for base station applications. The simulated and measured results confirm that the two DPSD antennas have wide bandwidth with VSWR<1.5 and isolation>35 dB. In addition, stable gain and HPBW are obtained with the variance less than ±0.55 dB and ±3.5° respectively.
  • Yu, F. et al. (2018). Polarization-insensitive wide-angle-reception metasurface with simplified structure for harvesting electromagnetic energy. Applied Physics Letters 113:123903.
    This paper reports the design, fabrication, and measurement of a metasurface with wide-angle-reception and polarization-insensitive characteristics for harvesting electromagnetic energy. Unlike the metasurface unit cell with multiple vias reported in the literature, it realizes polarization-insensitive characteristics using a single via, which reduces the complexity of the structure significantly. The harvesting and absorption efficiencies at the normal and oblique incidences, energy distribution, and the surface current for different polarization angles are investigated. The simulation results show that the maximum harvesting efficiency is 88% at the center frequency of 5.8 GHz for the arbitrary polarization at the normal incidence of 0°. Within the oblique incidence range of 75°, the maximum efficiency remains higher than 77% for the random polarization. A 5 × 5 array has been fabricated and measured, and the good agreement with the simulated results is obtained.
  • Santosa, C. et al. (2018). Development of a Low Profile Wide-Bandwidth Circularly Polarized Microstrip Antenna for C-Band Airborne CP-SAR Sensor. Progress In Electromagnetics Research C [Online] 81:77-88. Available at: http://www.jpier.org/PIERC/pierc81/08.17110901.pdf.
    In this paper, a low-profile wide bandwidth circularly polarized microstrip antenna is
    proposed as element for a C-band airborne circularly polarized synthetic aperture radar sensor. Several
    bandwidth improvement techniques were proposed and implemented. In order to increase impedance
    bandwidth, the antenna is constructed using double-stacked substrate with low dielectric constant,
    modified radiating shape for multi-resonant frequency, and a circle-slotted parasitic patch. Generation
    of the circularly polarized wave employs a simple square patch with curve corner-truncation as radiating
    element. The asymmetric position of the feeding is attempted to improve the axial-ratio bandwidth.
    To avoid a complicated feed network, the antenna is fed by single-feed proximity-coupled microstrip
    line. The effect of copper-covering on the upper layer for decrease undesired radiation wave emitted by
    the feeding is also studied and presented. Measurement results show that the impedance bandwidth
    and axial ratio bandwidth are 20.9% (1,100 MHz) and 4.7% (250 MHz), respectively. Meanwhile the
    measured gain is 7 dBic at the frequency of 5.3 GHz.
  • Zhou, Y. et al. (2018). Tightly Coupled Array Antennas for Ultra-Wideband Wireless Systems. IEEE Access [Online]. Available at: http://dx.doi.org/10.1109/ACCESS.2018.2873741.
    Tightly coupled array (TCA) antenna has become a hot topic of research recently, due to its
    potential of enabling one single antenna array to operate over an extremely wide frequency range. Such an
    array antenna is promising for applications in numerous wideband/multi-band and multi-function wireless
    systems such as wideband high-resolution radars, 5G mobile communications, satellite communications,
    global navigation satellite systems, sensors, wireless power transmission, internet of things and so on. Many
    papers on this topic have been published by researchers internationally. This paper provides a detailed
    review of the recent development on TCA that utilizes the capacitive coupling. The basic principles and the
    historical evolution of the TCAs are introduced firstly. Then, recent development in the analysis and design
    of TCAs, such as equivalent circuit analysis, bandwidth limitation analysis, array elements, feed structures,
    substrates/superstrates loading, etc., are explained and discussed. The performances of the state-of-the-art
    TCAs are presented and a comparison amongst some TCAs reported recently is summarized and discussed.
    To illustrate the practical designs of TCA, one case study is provided, and the detailed design procedures of
    the TCA are explained so as to demonstrate the TCA design methodology. Simulated results including the
    VSWR at different angles of scanning, patterns and antenna gain are shown and discussed. A conclusion
    and future work are given in the end.
  • Wen, Y. et al. (2018). Dual-Polarized and Wide-Angle Scanning Microstrip Phased Array. IEEE Transactions on Antennas and Propagation [Online]. Available at: https://doi.org/10.1109/TAP.2018.2835521.
    In this paper, a novel microstrip phased array with dual-polarized and wide-angle scanning in the 2-dimensional (2D) space is proposed. The element antenna consists of a mushroom-shaped patch and two circular patches. Each circular patch is connected with one feeding port. The mushroom-shaped patch is excited via capacitive coupling through the gaps between the mushroom-shaped patch and the circular patch. The zeroth-order resonance (ZOR) and TM010 mode resonance are simultaneously generated in the mushroom-shaped patch. The 3dB beamwidth of the element antenna in the 2D space is in the range between 110° and 125°. One 6×6 phased array based on the antenna element is designed, fabricated and measured. The phased array shows dual-polarized wide-angle beam scanning in a range of ±66° in both x-z and y-z planes with the scan loss of 3.5dB.
  • Gao, S. et al. (2018). Advanced Antennas for Small Satellites. Proceedings of the IEEE [Online] 106:391-403. Available at: https://doi.org/10.1109/JPROC.2018.2804664.
    Antenna is one of the key components onboard small satellites as its design determines the performance of all the wireless systems including telemetry, tracking and control, high-speed data downlink, navigation, intersatellite communications, intrasatellite communications, wireless power transfer, radars and sensors, etc. This paper presents a review of recent development in advanced antennas for small satellites (MiniSat, MicroSat, NanoSat, CubeSat, etc.). A number of recent examples of antennas for small satellite applications are shown and discussed. A conclusion and future development in antennas for small satellites are given in the end.
  • Mao, C., Gao, S. and Wang, Y. (2018). Dual-Band Full-Duplex Tx/Rx Antennas for Vehicular Communications. IEEE Transactions on Vehicular Technology [Online] PP:1-1. Available at: https://doi.org/10.1109/TVT.2017.2789250.
    This paper proposes a novel dual-band full-duplex antenna/array for intelligent transport systems (ITS) applications. Different from traditional single-port single-band antennas, the two ports of the antenna are highly isolated and designed to operate at different frequency bands simultaneously. Such a property could support the full-duplex operation-mode, which significantly simplifies the complexity of the RF frontend subsystem. The other contribution of this work is that multiple functions such as filtering, duplexing and radiation are combined into one single device, resulting in a simplified RF frontend. This co-design multifunctional device could also remove the separate filters, duplexers and interfaces between them, resulting in the reduction of the size, weight and cost. In addition, cross-coupling is investigated and employed to generate additional transmission zeros so as to improve the channel isolation and out-of-band interference. To verify the concept, an antenna element and two 2 × 2 arrays at C-band are designed, prototyped and tested. All the measurements agree well with the simulations, showing two full-duplex channels of 4.58 - 4.83 GHz and 5.86 - 6.2 GHz for transmitting and receiving, respectively. The proposed antennas also exhibit excellent performance in terms of channel isolations, frequency selectivity, out-of-band rejections and gains.
  • Cai, Y. et al. (2018). A Low-Profile Frequency Reconfigurable Grid-Slotted Patch Antenna. IEEE Access [Online] 6:36305-36312. Available at: https://doi.org/10.1109/ACCESS.2018.2850926.
    This paper presents a novel low-profile high gain frequency reconfigurable patch antenna with unidirectional radiation pattern by using a grid-slotted patch with tunable varactors loading. The antenna consists of two stacked substrates and three metal layers. A grid-slotted patch with two tunable varactors is placed on the top layer, a microstrip line is placed in the middle of two substrates, and the ground plane is on the bottom layer. A single dc voltage applied on two varactors is used to control the working frequencies of the proposed antenna. By altering the bias voltage, the working frequency of the proposed antenna can be continuously changed within a wide range from 2.45 to 3.55 GHz. The antenna maintains broadside radiation and stable radiation pattern in all the operating modes. The measured antenna gain of the proposed antenna rises from 4.25 to 8.49 dBi with the working frequency increases from 2.45 to 3.55 GHz. Compared to other frequency-reconfigurable antennas available in the literature, the proposed antenna has advantages of a wide frequency tuning range over a bandwidth of 1.45:1, high frequency selectivity, low profile (0.016 free-space wavelength at 2.45 GHz), high gain, stable unidirectional pattern, simple structure, and low cost. These advantages make it a promising candidate for cognitive radio and future wireless communication systems
  • Gu, C. et al. (2018). Wideband high-gain millimetre/submillimetre wave antenna using additive manufacturing. IET Microwaves, Antennas & Propagation [Online] 12:1758-1764. Available at: https://doi.org/10.1049/iet-map.2018.5412.
    This paper presents a novel design of a wideband high-gain resonant cavity antenna (RCA) for millimetre and
    submillimetre wave bands, and its fabrication using additive manufacturing. The proposed RCA antenna consists of a partially
    reflecting surface and three impedance matching layers fed by a waveguide. Additive manufacturing (AM) techniques are
    utilized to fabricate the design operating at 30 GHz. Two fabrication techniques are assessed for printing the antenna. The
    first technique is based on printing a dielectric material and fully coating the parts with a metallic layer, while the second
    technique involves printing the parts in a single process using metal 3D printing. The first technique offers a lightweight
    solution while the second technique can print the whole model in one run. The antenna design is investigated by both
    simulations and experiments. The measured results show an 3dB gain bandwidth of about 10%, and high gain over 15 dBi
    for all the three resulting antennas. Good agreement between simulation and measurement is obtained. The antenna has a
    low cost and achieved good performance in terms of wide bandwidth and high gain, thus it is potentially useful for highspeed
    wireless communications at millimetre-wave and sub-millimetre-wave frequencies.
  • Luo, Q. et al. (2018). Wideband Transmitarray With Reduced Profile. IEEE Antennas and Wireless Propagation Letters [Online] 17:450-453. Available at: https://doi.org/10.1109/LAWP.2018.2794605.
    This letter presents a wideband transmitarray (TA) with reduced profile. A novel unit cell based on a wideband bandpass filter is developed and applied to the design of the TA. The TA consists of two identical tri-layer frequency selective surfaces (FSS), thus it has a lower profile compared to traditional designs which use at least four FSS layers separated by quarterwavelength air gaps to obtain the 360o phase shift range. The FSS has a pair of square patches printed on the top and bottom
    layers, and a square slot loaded by four microstrip lines printed on the middle layer. The phase shift is achieved by simultaneously adjusting the size of the square patches. Within the frequency band of interest, the developed unit cell shows low insertion loss and sufficient phase shift range. An equivalent circuit model is
    developed to better understand the operating principles of the FSS. To validate the design concept, one prototype operating at 13.5 GHz is designed, fabricated and measured. The measurement results show that the designed TA achieves 16% 1-dB gain bandwidth and 60% aperture efficiency. The developed unit cell has symmetric configurations so it can also be applied to the design of dual-polarized or circularly polarized TAs.
  • Liu, G. et al. (2018). Bandwidth enhancement of three-device Doherty power amplifier based on symmetric devices. IEICE Electronics Express [Online] 15. Available at: https://doi.org/10.1587/elex.15.20171222.
    This paper proposes a method for extending the bandwidth of
    a three-device Doherty power amplifier (DPA) based on symmetric devices.
    λ/4 transmission lines are inserted between each peaking amplifier output
    and carrier amplifier output to compensate load impedance of carrier amplifier.
    In order to achieve perfect load modulation, carrier amplifier output
    circuit total electrical length is designed to 90 degrees, and the peak amplifier
    output total electrical length is designed to 180 degrees. The proposed
    method is demonstrated by designing a three-device broadband DPA using
    three 10-W packaged GaN HEMT devices. Measurement results show that
    over 40% drain efficiency is achieved at 9-dB back-off power, over the
    frequency band of 1.45–2.35 GHz, accounting for 46% fractional bandwidth.
  • Wen, L. et al. (2018). A Wideband Dual-Polarized Antenna Using Shorted Dipoles. IEEE Access [Online]. Available at: http://dx.doi.org/10.1109/ACCESS.2018.2855425.
    A novel design method of wideband dual-polarized antenna is presented by using shorted dipoles, integrated baluns, and crossed feed lines. Simulation and equivalent circuit analysis of the antenna are given. To validate the design method, an antenna prototype is designed, optimized, fabricated and measured. Measured results verify that the proposed antenna has an impedance bandwidth of 74.5% (from 1.69 GHz to 3.7 GHz) for VSWR<1.5 at both ports and the isolation between the two ports is over 30 dB. Stable gain of 8.0-8.7 dBi and HPBW of 65-70° are obtained for 2G/3G/4G base station frequency bands (1.7-2.7 GHz). Compared to the other reported dual-polarized dipole antennas, the presented antenna achieves wide impedance bandwidth, high port isolation, stable antenna gain, and half-power beamwidth (HPBW) with a simple structure and compact size
  • Zhang, L. et al. (2017). Single-Layer Wideband Circularly Polarized High-Efficiency Reflectarray for Satellite Communications. IEEE Transactions on Antennas and Propagation [Online]. Available at: https://dx.doi.org/10.1109/TAP.2017.2722824.
    This paper presents a single-layer circularly polarized (CP) reflectarray which achieves large bandwidth in terms of axial ratio (AR), gain, aperture efficiency and radiation pattern. By using a novel wideband S-shaped phasing element, an offset-fed reflectarray with 20° offset beam is designed based on the element angular rotation method. Theoretical analysis is given to analyze the effect of angular rotated elements on the performance of the reflectarray, which indicates that the AR bandwidth of the reflectarray can exceed the AR bandwidth of the feed horn. Furthermore, the influence of the differential spatial phase delay is analyzed quantitatively, and the performance of S-element-based reflectarrays with different aperture sizes are investigated and discussed. To verify these concepts, a 180mm×180mm prototype with 15×15 elements is fabricated and measured. The measured results confirm that the proposed reflectarray achieves a 68.5% 3-dB AR bandwidth (7.0 GHz to 14.3 GHz) and a 47.8% 3-dB gain bandwidth (8.6 GHz to 14 GHz). Moreover, the aperture efficiency is larger than 50% in a 33% bandwidth and larger than 30% in a 64% bandwidth.
  • Xu, H. et al. (2017). Multimode Decoupling Technique with Independent Tuning Characteristic for Mobile Terminals. IEEE Transactions on Antennas and Propagation [Online] 65:6739-6751. Available at: https://doi.org/10.1109/TAP.2017.2754445.
    The isolation between antenna elements is a key metric in some promising 5G technologies such as beamforming and in-band full-duplex (IBFD). However, multimode decoupling technology remains a great challenge especially for mobile terminals. One difficulty in achieving multi decoupling modes is that the operating modes of closely-packed decoupling elements have very strong mutual effect, which makes the tuning complicated and even unfeasible. Thus, in physical principle, a novel idea of achieving the stability of the boundary conditions of decoupling elements is proposed to solve the mutual effect problem; in physical structure, a metal boundary is adopted to realize the stability. One distinguished feature of the proposed technique is that the independent tuning characteristic can be maintained even if the number of decoupling elements increases. Therefore, wideband/multiband high isolation can be achieved by using multi decoupling elements. To validate the concept, two case studies are given. In a quad-mode decoupling design, the isolation is enhanced from 12.7 dB to > 21 dB within 22.0% bandwidth by using a 0.295λ0 × 0.059λ0 × 0.007λ0 decoupling structure. The mechanism of decoupling technique and the mutual effect between decoupling elements are investigated.
  • Jun, S. et al. (2017). Circular polarised antenna fabricated with low-cost 3D and inkjet printing equipment. Electronics Letters [Online]. Available at: https://doi.org/10.1049/el.2016.4605.
    The fabrication of a patch antenna using low-cost 3D printing equipment is presented. A circular polarised (CP) patch antenna is manufactured by combining inkjet printing and stereolithography (SLA) technology. The substrate has been fabricated by curing photosensitive resin while the patch element of the antenna has been inkjet printed using silver ink. The printed antenna satisfies the required reflection coefficient, axial ratio and radiation pattern at 1575 MHz. The aim is to demonstrate an inexpensive technology that could be used for the fabrication of antennas on customised 3D printed substrates. The performance of the antenna is summarised through simulations and experimental results.
  • Cheng, Z. et al. (2017). High efficiency broadband GaN HEMT power amplifier based on three-frequency point matching method. Microwave and Optical Technology Letters [Online] 59:1850-1855. Available at: https://doi.org/10.1002/mop.30634.
    To cover the working frequency bands of the three mobile carriers of China Mobile, China Telecom, and China Unicom, power amplifiers (PAs) are required to own broadband. A PA with bandwidth 1.3–2.7 GHz is designed (fully covers the operating bands of the three mobile carriers). Measured results show that greater than 68% efficiency is attained over a 75% bandwidth from 1.3 to 2.7 GHz. The output power is larger than 40.2 dBm with gain varying from 10 to 13 dB across the band. In this article, three-frequency point matching method is applied in order for broadband matching. High-efficiency is achieved by a specially designed impedance matching topology which realizes short-circuits of the second harmonics and open-circuits of the third harmonics at different frequencies. The designed broadband high-efficiency GaN PA provides a new approach and method for the development of PAs in 4G base stations.
  • Li, W. et al. (2017). Polarization-Reconfigurable Circularly Polarized Planar Antenna Using Switchable Polarizer. IEEE Transactions on Antennas and Propagation [Online] 65:4470-4477. Available at: https://dx.doi.org/10.1109/TAP.2017.2730240.
    A novel polarization-reconfigurable planar antenna is presented. The antenna consists of an electronically reconfigurable polarizer integrated with a printed slot. By changing the states of the PIN diodes on the polarizer, the linearly polarized (LP) waves radiated by the slot can be converted to either right-hand circularly polarized (RHCP) or left-hand circularly polarized (LHCP) waves. The polarizer contains 16 unit cells arranged as a 4 × 4 array. The antenna radiates RHCP waves if the PIN diodes on the top side of the polarizer are switched ON, while LHCP waves are radiated if the PIN diodes of the bottom side of the polarizer are switched ON instead. The physical mechanisms of the antenna are discussed and the parametric study is carried out by full-wave simulations. To verify the concept, one prototype at 2.5 GHz is designed, fabricated and measured. Good agreement between the measured and simulated results is obtained. The antenna achieves a gain ≥ 8.5 dBic in both RHCP and LHCP with aperture efficiency of 70%. Advantages of the proposed design include electronicallyreconfigurable polarizations for RHCP or LHCP, low profile, low cost, high isolation between the DC bias circuit and RF signals, high power handling capability and easy extension to large-scale arrays without increasing the complexity of the DC bias circuit. To the best knowledge of the authors, this is the first report of an electronically polarization-reconfigurable circularly polarized antenna with a single-substrate polarizer.
  • Mao, C. et al. (2017). X/Ka-Band Dual-Polarized Digital Beamforming Synthetic Aperture Radar. IEEE Transactions on Microwave Theory and Techniques [Online] 65:4400-4407. Available at: http://dx.doi.org/10.1109/TMTT.2017.2690435.
    This paper presents a digital beamforming (DBF) synthetic aperture radar (SAR) for future spaceborne earth observation systems. The objective of the DBF-SAR system is to achieve a low cost, lightweight, low-power consumption, and dual-band (X/Ka) dual-polarized module for the next-generation spaceborne SAR system in Europe. The architectures and modules of the proposed DBF-SAR system are designed according to a realistic mission scenario, which is compatible with the future small/microsatellites platforms. This system fills an important gap in the conception of the future DBF-SAR, facilitating a high level of integration and complexity reduction. The proposed system is considered not only the first demonstrator of a receive-only spaceborne DBF system, but also the first X/Ka-band dual-polarized SAR system with shared aperture. This paper presents a description of the proposed instrument hardware and first experimental validations. The concept and design of the DBF multistatic SAR system are discussed and presented first, followed by the design of subsystems such as DBF networks, microwave integrated circuit, and antennas. Simulated and measured results of the subsystems are presented, demonstrating that the proposed SAR instrument architecture is well-suited for the future SAR applications.
  • Mao, C. et al. (2017). A Shared-Aperture Dual-Band Dual-Polarized Filtering-Antenna-Array with Improved Frequency Response. IEEE Transactions on Antennas and Propagation [Online] 65:1836-1844. Available at: http://dx.doi.org/10.1109/TAP.2017.2670325.
    In this paper, a novel dual-band dual-polarized (DBDP) array antenna with low frequency ratio and integrated filtering characteristics is proposed. By employing a dual-mode stub-loaded resonator (SLR) to feed and tune with two patches, the two feed networks for each polarization can be combined, resulting in the reduction of the feed networks and the input ports. In addition, owing to the native dual resonant features of the SLR, the proposed antenna exhibits 2nd-order filtering characteristics with improved bandwidth and out-of-band rejections. The antenna is synthesized and the design methodology is explained. The coupling coefficients between the SLR and the patches are investigated. To verify the design concept, a C/X-band element and a 2 × 2 array are optimized and prototyped. Measured results agree well with the simulations, showing good performance in terms of bandwidth, filtering, harmonic suppression and radiation at both bands. Such an integrated array design can be used to simplify the feed of a reflector antenna. To prove the concept, a paraboloid reflector fed by the proposed array is conceived and measured directivities of 24.6 dBi (24.7 dBi) and 28.6 dBi (29.2 dBi) for the X-polarization (Y-polarization) are obtained for the low- and high-band operations, respectively.
  • Qin, F. et al. (2017). A Tri-Band Low-Profile High-Gain Planar Antenna Using Fabry-Perot Cavity. IEEE Transactions on Antennas and Propagation [Online] 65:2683-2688. Available at: http://dx.doi.org/10.1109/TAP.2017.2670564.
    A tri-band high-gain antenna with a planar structure and low profile is proposed. The principle of operation is explained. It is based on Fary-Perot cavity antenna (FPCA) with two frequency selective surface (FSS) layers. Two different resonant frequencies are generated by the two resonant cavities formed by the ground plane and each of the two FSS layers, respectively. A third resonant frequency is produced by combining the two FSS layers together. Advantages of this tri-band antenna includes low profile, high gain, easy fabrication and low cost. Low
    profile is achieved by designing the combined FSS layers as an artificial magnetic conductor (AMC) with a reflection coefficient having 0o phase shift and high magnitude. In addition, a large frequency ratio, which is often a problem for multiband array antennas, can be achieved here. To verify this concept, a C/X/Ku band FPCA is designed and one prototype is fabricated and tested. Experimental results agree well with the simulated results. High gain performance with good impedance matching in three bands is obtained, which reaches a peak gain of 14.2 dBi at 5.2 GHz, 18.9 dBi at 9.6 GHz and 19.8 dBi at 14.7 GHz, respectively. The overall height of antenna is only 20.2 mm, which is about 1/3 wavelength at its lowest operating frequency, which means a reduction of 30% compared to the height of traditional FPCA antenna.
  • Zheng, S. et al. (2017). A Broadband Dual Circularly Polarized Conical Four-Arm Sinuous Antenna. IEEE Transactions on Antennas and Propagation [Online] 66:71-80. Available at: https://doi.org/10.1109/TAP.2017.2772301​.
    A novel wideband four-arm sinuous antenna with dual circular polarizations (CPs) and unidirectional radiation is proposed. Different from the conventional designs, this sinuous antenna is realized in a conical form and no ground plane or absorptive cavity is required to obtain unidirectional radiation. The beamforming network for dual circularly polarized operations consists of a wideband quadrature coupler and two wideband baluns, and an auxiliary feeding patch is introduced to facilitate the connection between baluns and sinuous arms. The design of baluns and coupler is inspired from the printed exponentially tapered microstrip balun and broadside-coupled microstrip coupler, respectively. The dynamic differential evolution algorithm is employed to optimize the geometry of coupler for optimal performance. For both polarizations, the presented antenna has wide impedance bandwidth, good axial ratio, moderate realized gain, and front-to-back ratio within 2–5 GHz. An antenna prototype is fabricated and tested. The agreement between simulation and measurement results validates the proposed antenna framework. The demonstrated antenna has advantages of wide bandwidth, dual CPs, unidirectional radiation, lightweight, and low cost, and is promising for applications in wireless systems.
  • Gu, C. et al. (2017). 3D-Coverage Beam-Scanning Antenna Using Feed Array and Active Frequency Selective Surface. IEEE Transactions on Antennas and Propagation [Online] 65:5862-5870. Available at: http://dx.doi.org/10.1109/TAP.2017.2754400.
    This paper presents the design of a smart antenna that can achieve three-dimensional beam scanning coverage. The antenna consists of a novel planar feed array and a cylindrical active frequency selective surface (AFSS). First, an array fed metallic reflector is studied as a reference antenna to validate the beam scanning characteristics in the elevation plane. Then the AFSS is assessed through simulation and measurement results. Finally, the complete structure containing the planar collinear array and the AFSS is analyzed. A prototype at S-band has been designed, manufactured and measured. The resulting antenna is shown to be able to operate at the 2.4 – 2.5 GHz frequency band and switch beams in both the azimuth and elevation planes. In the azimuth plane, the proposed antenna is capable of sweeping beams towards different directions to cover a full range of 360˚. In the elevation plane, it can achieve beam steering within an angle range of +16˚/-15˚. The measured maximum gain of the antenna is 9.2 dBi. This is the first report of a low-cost 3D coverage beam scanning antenna based on AFSS.
  • Mao, C. et al. (2017). Compact Broadband Dual-Sense Circularly Polarized Microstrip Antenna/Array With Enhanced Isolation. IEEE Transactions on Antennas and Propagation [Online] 65:7073-7082. Available at: https://doi.org/10.1109/TAP.2017.2766440.
    This paper presents a novel method of designing the compact dual-sense circularly polarized (CP) microstrip antenna/array with improved impedance bandwidth, axial ratio (AR) bandwidth, and interpolarization isolation. The left-hand and right-hand CP characteristics are achieved simultaneously by conceiving a vertically coupled resonant structure for the first time. Different from traditional methods, the antenna shows a compact size but exhibits the wide impedance and 3 dB AR bandwidths. For each input, two coupling paths are purposely designed to excite the TM10 and TM01-mode of the patch, respectively. By composing different coupling units in the two paths, an intrinsic ±90° phase difference over a broadband can be obtained, resulting in the broadband CP characteristics. In addition, a novel method of using the neutralization line between the two feeds is investigated to improve the isolation between the polarizations. Based on the dual-sense CP element, a 1×4 dual-sense CP array is composed to exemplify its potential applications in large arrays. Compared with traditional CP antennas, the proposed antennas have the advantages of compact size, simplified feed, broad impedance and 3 dB AR bandwidths, and improved isolation. Experimental results verify the predictions.
  • Gu, C. et al. (2017). Dual-Band Electronically Beam-Switched Antenna Using Slot Active Frequency Selective Surface. IEEE Transactions on Antennas and Propagation [Online] 65:1393-1398. Available at: http://dx.doi.org/10.1109/TAP.2016.2647578.
    Abstract—A dual-band electronically beam-switching antenna using a cylindrical active frequency selective surface (AFSS) is presented. The antenna structure consists of a slot AFSS and an omnidirectional dual-band feed antenna. The PIN diodes of half the AFSS are switched ON and OFF respectively to reconfigure the surface as transparent and opaque to the incident EM waves. Thus by controlling the bias voltages to different columns, the directive beams can be swept in 4 steps covering the whole azimuth plane. A design validation based on a metallic reflector antenna is performed to predict the performances of the proposed AFSS antenna. To validate the design concept, the transmission coefficients of the active FSS sheet are experimentally examined. Then an antenna prototype operating at 2.5 GHz and 5.3 GHz frequency bands is fabricated and measured. Simulation and measurement results of the fabricated antenna are presented to verify the design principle. A comparison between this work and previous (single-band) designs is given to better interpret the characteristics of the dual-band AFSS antenna.
  • Gu, C. et al. (2017). Frequency-Agile Beam-Switchable Antenna. IEEE Transactions on Antennas and Propagation [Online] 65:3819-3826. Available at: https://doi.org/10.1109/TAP.2017.2713978.
    A novel antenna with both frequency and pattern reconfigurability is presented. The reconfigurability is achieved by integrating an active frequency selective surface (AFSS) with feed antenna. The smart FSS comprises a printed slot array loaded by varactors. A novel dc biasing arrangement is proposed to feed the slots vertically so that the unwanted effects caused by bias lines are minimized. A monopole antenna is designed to illuminate the AFSS. The resulting structure can operate in a frequency tuning range of 30%. By reconfiguring the different sections of active FSS cylinder into a transparent or reflector mode, the omnidirectional pattern of the source antenna can be converted to a directive beam. As an illustration, half of the AFSS cylinder is successively biased, enabling the beam switching to cover the entire horizontal plane over a range of frequencies. An antenna prototype was fabricated and measured. Experimental results demonstrate the capability of providing useful gain levels and good impedance matching from 1.7 to 2.3 GHz. The antenna offers a low-cost, low-power solution for wireless systems that require frequency and beam reconfigurable antennas. The proposed design consumes about 1000 times less dc power than the equivalent narrowband beam-switching antenna design using p-i-n diode-loaded AFSS.
  • Wenting, L. et al. (2017). An Ultra-wide-band Tightly Coupled Dipole Reflectarray Antenna. IEEE Transactions on Antennas and Propagation [Online] PP:1-1. Available at: http://dx.doi.org/10.1109/TAP.2017.2772311.
    A novel ultra-wide-band tightly coupled dipole reflectarray (TCDR) antenna is presented in this paper. This reflectarray antenna consists of a wide-band feed and a wide-band reflecting surface. The feed is a log-periodic dipole array antenna. The reflecting surface consists of 26×11 unit cells. Each cell is composed of a tightly coupled dipole and a delay line. The minimum distance between adjacent cells is 8mm, which is about 1/10 wavelength at the lowest operating frequency. By combining the advantages of reflectarray antennas and those of tightly coupled array antennas, the proposed TCDR antenna achieves ultra-wide bandwidth with reduced complexity and fabrication cost. A method to minimize the phase errors of the wideband reflectarray is also developed and a concept of “equivalent distance delay” is introduced to design the unit cell elements. To verify the simulations, a prototype operating from 3.4 to 10.6 GHz is simulated and fabricated. Good agreement between simulated and measured results is observed. Within the designed frequency band, the radiation pattern of the TCDR antenna is stable and the main beam of the antenna is not distorted or split. The side lobe levels of the radiation patterns are below -11.7 dB and the cross-polarization levels are below -20 dB in the entire operating band. This TCDR antenna combines the reflectarray and tightly coupled arrays for the 1st time and achieves the widest bandwidth (in terms of stable radiation patterns and low sidelobes) reported so far. This work is expected to have significant impact on antenna development for broadband satellite communications and the base stations in 5G mobile communications.
  • Yang, X. et al. (2017). Low-Profile Frequency-Scanned Antenna Based on Substrate Integrated Waveguide. IEEE Transactions on Antennas and Propagation [Online] 65:2051-2056. Available at: http://dx.doi.org/10.1109/TAP.2017.2669961.
    A beam scanning flat antenna array with the frequency that covers about the whole X/Ku-band is proposed in this paper. The radiation element is the continuous transverse stub (CTS) constituted by the substrate integrated waveguide (SIW). The CTS array is fed by a linear source which is a SIW parabolic reflector, and good impedance matching characteristics within a broad bandwidth are obtained. The beam steering direction is tunable with the frequency increasing within the operation band. The design principles of the SIW based CTS array and the feed structure are explained in details. One 16-element array is simulated, designed and fabricated. The measurement results show a scanning angle range from 52.2° to -16.8° with the 3-dB gain decreasing within the operation band from 8.5 GHz to 14.1GHz. At the center frequency of 12 GHz, it achieves a maximum gain of 18.1 dBi with an array size of 11.7λ0×1.28λ0, the first sidelobe level is -11.4 dB and the 3-dB beamwidth is 6.5°.
  • Cheng, Z. et al. (2017). Design of 0.8–2.7 GHz High Power Class-F Harmonic-Tuned Power Amplifier with Parasitic Compensation Circuit. Active and Passive Electronic Components [Online] 2017:1-8. Available at: https://doi.org/10.1155/2017/2543917.
    The design, implementation, and measurements of a high efficiency and high power wideband GaN HEMT power amplifier are presented. Package parasitic effect is reduced significantly by a novel compensation circuit design to improve the accuracy of impedance matching. An improved structure is proposed based on the traditional Class-F structure with all even harmonics and the third harmonic effectively controlled, respectively. Also the stepped-impedance matching method is applied to the third harmonic control network, which has a positive effect on the expansion bandwidth. CGH40025F power transistor is utilized to build the power amplifier working at 0.8 to 2.7 GHz, with the measured saturated output power 20–50 W, drain efficiency 52%–76%, and gain level above 10 dB. The second and the third harmonic suppression levels are maintained at −16 to −36 dBc and −16 to −33 dBc, respectively. The simulation and the measurement results of the proposed power amplifier show good consistency.
  • Mao, C., Gao, S. and Wang, Y. (2017). Broadband High-Gain Beam-Scanning Antenna Array for Millimeter-Wave Applications. IEEE Transactions on Antennas and Propagation [Online] 65. Available at: https://doi.org/10.1109/TAP.2017.2724640.
    A novel method of achieving low-profile, broadband microstrip array antennas with high antenna gain is proposed for millimeter-wave (mm-wave) applications. The element employs a novel 3rd-order vertically coupled resonant structure that a U-slot resonator in the ground is used to couple with the feeding resonator and the radiating patch, simultaneously. This proposed structure can significantly improve the bandwidth and frequency selectivity without increasing the thickness of the antenna. Then, to achieve the subarray, a new wideband power divider with loaded resonators is employed, which can be used to further improve the bandwidth. To demonstrate the working schemes of broadside radiation and scanned beam, two 4 × 4 array antennas are implemented on the same board. Measured results agree well with the simulations, showing a wide bandwidth from 22 to 32 GHz (FBW = 37%) with the gain of around 19 dBi. The beam scanning array can realize a scanning angle of over 25 degrees over a broadband. In addition, due to the filtering features are integrated in the design, the proposed antenna could also reduce the complexity and potential cost of the frontends.
  • Zhang, L. et al. (2017). Wideband dual circularly polarized beam-scanning array for Ka-band satellite communications. Microwave and Optical Technology Letters [Online] 59:1962-1967. Available at: https://doi.org/10.1002/mop.30655.
    This article presents a wideband dual circularly polarized (CP) array which has two independent beams in orthogonal circular polarizations and the two beams can scan to ±23° individually. The proposed array consists of stacked patches fed by 90° hybrid couplers. To achieve two independent beams, the beam-forming networks (BFNs) for the left-hand circular polarization (LHCP) beam and right-hand circular polarization (RHCP) beam are printed on two separate layers with ground plane between them. This arrangement facilitates the integration of the BFNs and reduces the fabrication complexity. Two prototypes with different beam-scanning angles are fabricated and measured. The measured results confirm that the array achieves good impedance matching, larger than 20 dB isolation and smaller than 3 dB axial ratio (AR) from 27 to 30 GHz when the array scans to ±23°. Due to the independent beam-scanning ability, high isolation between the LHCP and RHCP beams and the wide bandwidth, the proposed array is promising for high data-rate Ka-band satellite communications which utilize polarization diversity.
  • Mao, C. et al. (2016). An Integrated Filtering Antenna Array With High Selectivity and Harmonics Suppression. IEEE Transactions on Microwave Theory and Techniques [Online]:1798-1805. Available at: http://doi.org/10.1109/TMTT.2016.2561925.
    In this paper, a new design of an antenna array with integrated functions of filtering, harmonics suppression, and radiation is proposed. The device employs a multi-port network of coupled resonators, which is synthesized and designed as a whole to fulfill the functions of filtering, power combination/division, and radiation. The 50-Ω interfaces between the cascaded filter, power divider, and antenna in traditional RF front-ends are eliminated to achieve a highly integrated and compact structure. A novel resonator-based four-way out-of-phase filtering power divider is proposed and designed. It is coupled to the patch array, rendering a fourth-order filtering response. The coupling matrix of the resonator network is synthesized. The physical implementations of the resonators and their couplings are detailed. Compared to a traditional patch array, the integrated filtering array shows an improved bandwidth and frequency selectivity. In addition, the harmonic of the antenna array is suppressed due to the use of different types of resonators. To verify the concept, a 2x2 filtering array at S-band is designed, prototyped, and tested. Good agreement between simulations and measurements has been achieved, demonstrating the integrated filtering antenna array has the merits of wide bandwidth, high frequency selectivity, harmonics suppression, stable antenna gain, and high polarization purity.
  • Cai, Y. et al. (2016). Compact-Size Low-Profile Wideband Circularly Polarized Omnidirectional Patch Antenna With Reconfigurable Polarizations. IEEE Transactions on Antennas and Propagation [Online] 64:2016-2021. Available at: http://doi.org/10.1109/TAP.2016.2535502.
    A compact-size low-profile wideband circularly polarized (CP) omnidirectional antenna with reconfigurable polarizations is presented in this communication. This design is based on a low-profile omnidirectional CP antenna which consists of a vertically polarized microstrip patch antenna working in TM01/TM02 modes and sequentially bended slots etched on the ground plane for radiating horizontally polarized electric field. The combined radiation from both the microstrip patch and the slots leads to a CP omnidirectional radiation pattern. The polarization reconfigurability is realized by introducing PIN diodes on the slots. By electronically controlling the states of the PIN diodes, the effective orientation of the slots on ground plane can be changed dynamically and the polarization of antenna can be altered between left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP). The proposed antenna exhibits a wide-operational bandwidth of 19.8% (2.09-2.55 GHz) with both axial ratio below 3 dB and return loss above 10 dB when radiates either LHCP or RHCP waves. Experimental results show good agreement with the simulation results. The present design has a compact size, a thickness of only 0.024λ and exhibits stable CP omnidirectional conical-beam radiation patterns within the entire operating frequency band with good circular polarization.
  • Wang, Y., Zhu, F. and Gao, S. (2016). Design and Investigation of Differential-Fed Ultra-Wideband Patch Antenna with Polarization Diversity. International Journal of Antennas and Propagation [Online] 2016:1-6. Available at: https://doi.org/10.1155/2016/4254830.
    A novel single- or dual-polarized ultra-wideband (UWB) patch antenna fed by coupled feeding mechanism is proposed. The single-polarized antenna consists of a square ring patch and two Γ-shaped patches which are coupled to the radiating patch. The vertical portions of the Γ-shaped patches are connected to the microstrip lines which are printed on the bottom layer of the grounded FR4 substrate. To realize the differential feeding mechanism for enhancing the polarization purity, a tapered balun is employed to excite the antenna. Further to provide dual linear orthogonal polarizations, another pair of Γ-shaped patches is added in the single-polarized UWB antenna. The dual-polarized UWB antenna prototype can achieve two orthogonal polarizations with an impedance bandwidth ( dB) of 113% and isolation of over 25 dB across the entire frequency band.
  • Zhang, L. et al. (2016). Wideband Loop Antenna with Electronically Switchable Circular Polarization. IEEE Antennas and Wireless Propagation Letters [Online]:1-1. Available at: http://doi.org/10.1109/LAWP.2016.2570859.
    This paper presents a novel printed antenna with wide bandwidth, high gain and reconfigurable circular polarizations. A loop antenna is printed on both sides of a dielectric substrate: a dual PIN diode loaded loop is printed on one side while a dual gap loaded smaller loop is printed on the other side. By controlling the ON/OFF states of the PIN diodes, the polarization of the proposed antenna can be switched electronically to right-hand circular polarization (RHCP) or left-hand circular polarization (LHCP) over a wideband frequency range. A prototype is fabricated and measured to verify the performance of the antenna. The measured results indicate that the antenna achieves an impedance bandwidth of over 30%, and a 3-dB axial ratio (AR) bandwidth of 12.7% and 14.9% for RHCP and LHCP, respectively. The measured gain is around 8 dBic for LHCP state and 7 dBic for RHCP state. Due to advantages of wide overlapped bandwidth, simple feeding structure and high gain, this antenna is promising for applications in dual-CP wireless communication systems.
  • Mao, C. et al. (2016). Dual-Band Patch Antenna with Filtering Performance and Harmonic Suppression. IEEE Transactions on Antennas and Propagation [Online] 64:4074-4077. Available at: http://dx.doi.org/10.1109/TAP.2016.2574883.
    A novel design of dual-band antenna with integrated filtering performance is proposed. A low-profile aperture-coupled U-slot patch antenna is employed for dual-band operation with a uniform polarization, which is fed by a dual-mode stub-loaded resonator (SLR). The U-slot patch works as a dual-mode resonator of the dual-band filter as well as the radiation element. The odd- and even-mode of the SLR are coupled and tuned with the U-slot patch, generating two 2nd-order operation bands at 3.6 and 5.2 GHz. Compared with the traditional patch antenna, the proposed antenna exhibits improved bandwidth and frequency selectivity. In addition, the bandwidths can be controlled by adjusting the coupling strength between the SLR and the patch. Furthermore, the higher-order harmonics can be suppressed over a broadband without increasing the footprint of the design. Measured and simulated results agree well with each other, showing an excellent performance in terms of impedance matching, bandwidths, 2nd-order filtering, out-of-band rejection, cross polarization discrimination (XPD) and gains at both bands.
  • Xu, H. et al. (2016). A Compact and Low Profile Loop Antenna with Six Resonant Modes for LTE Smart phone. IEEE Transactions on Antennas and Propagation [Online]. Available at: http://dx.doi.org/10.1109/TAP.2016.2582919.
    In this paper, a novel six-mode loop antenna covering 660-1100 MHz, 1710-3020 MHz, 3370-3900 MHz, and 5150-5850 MHz has been proposed for the application of Long Term Evolution (LTE) including the coming LTE in unlicensed spectrum (LTE-U) and LTE-Licensed Assisted Access (LTE-LAA). Loop antennas offer better user experience than conventional Planar Inverted-F Antennas (PIFA), Inverted-F Antennas (IFA), and monopole antennas because of their unique balanced modes (1λ, 2λ, …). However, the bandwidth of loop antennas is usually narrower than that of PIFA/IFA and monopole antennas due to these balanced modes. To overcome this problem, a novel monopole/dipole parasitic element, which operates at an unbalanced monopole-like 0.25λ mode and a balanced dipole-like 0.5λ mode, is first proposed for loop antennas to cover more frequency bands. Benefiting from the balanced mode, the proposed parasitic element is promising to provide better user experience than conventional parasitic elements. To the authors’ knowledge, the balanced mode for a parasitic element is reported for the first time. The proposed antenna is able to provide excellent user experience while solving the problem of limited bandwidth in loop antennas. To validate the concept, one prototype antenna with the size of 75×10×5 mm3 is designed, fabricated and measured. Both simulations and experimental results are presented and discussed. Good performance is achieved.
  • Qin, F. et al. (2016). A Simple Low-Cost Shared-Aperture Dual-Band Dual-Polarized High Gain Antenna for Synthetic Aperture Radars. IEEE Transactions on Antennas and Propagation [Online]:1-1. Available at: http://doi.org/10.1109/TAP.2016.2559526.
    This paper presents a novel shared-aperture dual-band dual-polarized high-gain antenna for potential applications in synthetic aperture radars (SAR). To reduce the complexity of SAR antennas, a dual-band dual-polarized high gain antenna based on the concept of Fabry-Perot resonant cavity is designed. This antenna operates in both C and X bands with a frequency ratio of 1:1.8. To form two separate resonant cavities, two frequency selective surface (FSS) layers are employed, leading to high flexibility in choosing desired frequencies for each band. The beam scanning capability of this proposed antenna is also investigated, where a beam scanning angle range of ±15o is achieved in two orthogonal polarizations. To verify this design concept, three passive antenna prototypes were designed, fabricated and measured. One prototype has broadside radiation patterns whilst the other two prototypes have frozen beam scanned to +15o. The measured results agree well with the simulated ones, showing that high gain, high port isolation, and low cross cross-polarization levels are obtained in both bands. Compared to the conventional high gain dual-band dual-polarized SAR antennas, the proposed antenna has achieved a significant reduction in the complexity, mass, size, loss and cost of the feed network.
  • Zhang, L. et al. (2016). Planar Ultra-Thin Small Beam-Switching Antenna. IEEE Transactions on Antennas and Propagation [Online]. Available at: http://doi.org/10.1109/TAP.2016.2620490.
    A novel planar ultrathin electronically steerable parasitic array radiator (ESPAR) is presented in this paper. Through theoretical analysis of the electric fields of orthogonally crossed dipoles in phase quadrature, it is found that the crossed dipoles radiate linearly polarized wave with a rotational electric field in the azimuth plane. This characteristic is then utilized to design a planar crossed dipole ESPAR, termed as “CD-ESPAR.” Furthermore, a simple but effective impedance matching method is also proposed and analyzed. To verify these concepts, a prototype with compact size and very low profile (0.42 λ0 × 0.42 λ0 ×0.006 λ0) resonating at 2.3 GHz is designed, fabricated, and measured. The measured results indicate that the proposed antenna achieves more than 17.8% impedance bandwidth and can produce four directional beams, covering the whole azimuth plane. Owing to its planar ultrathin structure, compact size, electronically beam-switching ability, low power, and low cost characteristics, it is promising for applications in wireless communications
  • Mao, C. et al. (2016). Compact Highly Integrated Planar Duplex-Antenna for Wireless Communications. IEEE Transactions on Microwave Theory and Techniques [Online] 64:2006-2013. Available at: http://dx.doi.org/10.1109/TMTT.2016.2574338.
    This paper proposes a novel concept of an integrated duplex antenna for realizing a compact multifunction RF front end by integrating a duplexer and a dual-band patch antenna. First, an all-resonator-based duplexer is designed. It is composed of two sets of split-ring resonators as channel filters, which are joined by a dual-mode stub-loaded resonator as the junction resonator. Then, a novel dual-band patch antenna is achieved by coupling a patch with a hairpin resonator through a slot in the ground. Uniform radiation characteristics have been achieved across the two bands. Finally, the duplexer is integrated with the dual-band patch antenna to form a highly integrated duplex antenna by coupling the hairpin resonator to the junction resonator of the duplexer directly. In this process, the 50-Omega interface and matching network between them are removed, contributing to a compact footprint. The details of codesign approach have been discussed in this paper. Compared with the traditional cascaded duplexer and antennas, this paper is much more compact and integrated but with an improved frequency response. A prototype of an integrated duplex antenna at S-band is fabricated and measured, showing two operation channels of 2.52-2.65 GHz for transmitting and 2.82-2.94 GHz for receiving with an isolation of over 32 dB. The measured results agree well with the simulation results.
  • Zhang, M. et al. (2016). Design of Novel Reconfigurable Reflectarrays with Single-bit Phase Resolution for Ku-Band Satellite Antenna Applications. IEEE Transactions on Antennas and Propagation [Online] 64:1634 -1641. Available at: http://doi.org/10.1109/TAP.2016.2535166.
    Reconfigurable reflectarray antennas operating in Ku-band are presented in this paper. First, a novel multilayer unit-cell based on polarization turning concept is proposed to achieve the single-bit phase shift required for reconfigurable reflectarray applications. The principle of the unit-cell is discussed using the current model and the space match condition, along with simulations to corroborate the design and performance criteria. Then, an offset-fed configuration is developed to verify performance of the unit-cell in antenna application, and its polarization transformation property is elaborated. Finally, an offset-fed reflectarray with 10×10 elements is developed and fabricated. The dual-polarized antenna utilizes the control code matrices to accomplish a wide angle beam-scanning. A full wave analysis is applied to the reflectarray, and detailed results are presented and discussed. This electronically steerable reflectarray antenna has significant potential for satellite applications, due to its wide operating band, simple control and beam-scanning capability.
  • Mao, C. et al. (2016). A Novel Multiband Directional Antenna for Wireless Communications. IEEE Antennas and Wireless Propagation Letters [Online] 16:1217-1220. Available at: https://doi.org/10.1109/LAWP.2016.2628715.
    A novel multiband patch antenna with unidirectional radiation is proposed by integrating resonators in the design. The multiple frequency bands are achieved based on a coupled resonators network. The topology and design methodology are detailed. The patch not only works as the last-order resonator of the network, but also as the radiating element. Using this approach, multiple bands can be achieved without changing the shape of the radiation element. In addition, the operation bands can be adjusted by adjusting the coupling between the resonators. In this work, the four bands are designed at 4.6, 5.05, 5.8, and 6.3 GHz as a proof-of-concept. The prototype is fabricated and tested, and measured results agree very well with the simulations, showing an excellent performance in terms of impedance matching, radiation patterns, gains, and cross-polarization discrimination.

Conference or workshop item

  • Gu, C., Gao, S. and Sanz-Izquierdo, B. (2017). Low-cost wideband low-THz antennas for wireless communications and sensing. in: 10th UK-Europe-China Workshop on Millimetre Waves and Terahertz Technologies (UCMMT), 2017. IEEE. Available at: https://doi.org/10.1109/UCMMT.2017.8068470.
    Terahertz technology is expected to provide a significant improvement in wireless system performance. A common assumption is that traditional microwave devices can be scaled down to operate at higher frequency bands. However, it can be a challenge to directly transfer the design methodology from microwave to THz band as the size of the devices becomes a few millimeter large. The reduced antenna size at the THz band limits the suitable fabrication processes. This paper reviews a wide range of THz antennas and their fabrication methodology. Then based on the resonant cavity antenna concept, an all-metal 300 GHz wideband high-gain antenna is designed and simulated. The presented metallic antenna is suitable to be fabricated using 3D printing techniques, which can lead to a low-cost, reliable solution for the emerging THz applications.
  • Gu, C., Gao, S. and Sanz-Izquierdo, B. (2017). Wideband low-THz antennas for high-speed wireless communications. in: Electromagnetics in Advanced Applications (ICEAA), 2017 International Conference on. IEEE, pp. 141-145. Available at: https://doi.org/10.1109/APWC.2017.8062263.
    This paper presents a brief review of low THz antennas and discusses their corresponding manufacturing techniques. In addition, a new antenna is introduced for the 300 GHz frequency band. The design is an all-metal structure with interesting features such as compactness, high gain, and wide operational bandwidth. These characteristics make it a promising solution for future high-speed THz communication systems.