# Professor Steven Gao

Professor

Professor Steven (Shichang) Gao is Chair of RF and Microwave Engineering, and the Director of Post-gradudate Studies (Research) at School of Engineering and Digital Arts, University of Kent, UK.He is an expert in the fields of space antennas, smart antennas, RF/microwave/millimetre-wave engineering, space-borne radars, electromagnetic field theory and applications. He authored, co-authored and co-edited 3 books including Space Antenna Handbook (Wiley, 2012), Circularly Polarized Antennas (Wiley-IEEE, 2014), and Low-cost Smart Antennas (Wiley, 2019), over 300 papers in international journals and conferences, and 8 patents. He is a Fellow of IEEE, the Royal Aeronautical Society and IET, and was a Distinguished Lecturer of IEEE Antennas and Propagation Society (2014-2016). 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 Scholar at Swiss Federal Institute of Technology (ETH Zurich, Switzerland), a Visiting Fellow at Chiba University (Japan), and a Visiting Scholar 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 has held Visiting Professorships at many universities such as Northwestern Polytechnic University (China), University of Calabria (Italy), Xidian University (China), Shanghai University (China), etc.He is an Associate Editor of several international Journals (IEEE Transactions on Antennas and Propagation; Radio 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 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, Co-Chair of Workshop on "New Technology Development for Space" in 2015 IEEE Microwave Symposium, etc. He is a member of the editorial boards of many Journals such as  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 many international conferences and workshops (IEEE APWC'2017, UCMMT'2017, iWAT’2017, AES'2014, IWAT'2014, SOMIRES'2013, APCAP'2014, etc).He received over 20 research grants funded by EU, EPSRC and industries. Recently he 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), “Low-Profile Ultra-Wideband Wide-Scanning Multi-Function Beam-Steerable Array Antennas” (EPSRC), "Digital Beamforming Synthetic Aperture Radars onboard small satellites constellations "(DIFFERENT, funded by EU FP7 Space Programme), etc.

## Research interests

Smart antennas, space antennas, space-borne radars, phased arrays, MIMO, antenna and radio propagation for 4G/5G/6G mobile communications, mobile terminal antennas, base station antennas, antennas for satellite communications, antennas for small satellites, RF/microwave/millimetre-wave circuits and RF front ends, mobile communication systems, satellite communications, inter-satellite links, wireless power transfer, UWB radars, GNSS reflectometry, synthetic-aperture radars, electromagnetic modelling and small satellites

## Teaching

Antennas and PropagationRF/Microwave EngineeringSatellite and Optical CommunicationCommunication SystemsElectronic and RF Circuits

## Supervision

Prof. Steven Gao is an expert in the fields of antennas, smart antennas, phased arrays, MIMO, mobile communication antennas, radio propagation, 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

Showing 50 of 192 total publications in the Kent Academic Repository. View all publications.

### Article

• Yang, Q., Gao, S., Wen, L., Ban, Y., Ren, J., Yang, X. and Liu, Y. (2020). Millimetre-Wave Dual-Polarized Differentially-Fed 2D Multibeam Patch Antenna Array. IEEE Transactions on Antennas and Propagation [Online]. Available at: https://dx.doi.org/10.1109/TAP.2020.2992896.
In this paper, a novel millimetre-wave dual-polarized 2D multibeam antenna array incorporating differentially-fed antenna elements is proposed to achieve high cross-polarization discrimination (XPD) when the beams scan to the maximal pointing angles. The antenna element is composed of a SIW cavity with four shorted patches placed inside, and it is differentially excited for dual-polarization by a pair of feeding strips and transverse slots beneath the patches. Differential excitation is realized by a power divider designed on two laminate layers. Two Butler Matrices placed perpendicularly with each other in different laminates are employed to generate four tilted beams with dual-polarization. A 2 × 2 dual-polarized 2D multibeam antenna array working at 28 GHz is designed, fabricated, and measured. The operation bandwidth of the antenna is 26.8 GHz – 29.2 GHz. The improvement in the XPD is experimentally demonstrated by far-field measurement. When the beams scan to 30◦ off the boresight, the measured XPDs are 28 dB at the centre frequency and higher than 25 dB over the operation bandwidth, which confirms that the cross-polarized radiation in the 2D multibeam antenna array is suppressed by using the differential-feeding technique. The measured gain is in the range from 7.6 dBi to 10.5 dBi.
• Gu, C., Gao, S., Fusco, V., Gibbons, G., Sanz-Izquierdo, B., Standaert, A., Reynaert, P., Bösch, W., Gadringer, M., Xu, R. and Yang, X. (2020). A D-band 3D printed antenna. IEEE Transactions on Terahertz Science and Technology [Online]. Available at: http://dx.doi.org/10.1109/TTHZ.2020.2986650.
This paper reports the design and fabrication of a novel all-metal antenna operating in the millimeter-wave band. Based on the resonant cavity antenna (RCA) concept, the principle of antenna operation is explained, and a parametric study of several key design parameters is provided. A novel impedance matching technique is introduced to broaden the antenna return loss bandwidth. Two gain enhancement methods have been employed to achieve a more directive beam with reduced side lobes and back lobes. The D-band antenna prototypes are produced using i) all-metal printing without any post-processing; ii) dielectric printing with copper metallization applied later. Comparisons of the simulated and measured results amongst the antennas fabricated using the two additive manufacturing techniques are made. Measurement results of the two antenna prototypes show that the proposed design can achieve a 14.2% bandwidth with a maximum gain of 15.5 dBi at 135 GHz. The present work is the first D-band resonant cavity antenna fabricated using two different 3D printing methods.
• Xu, R., Gao, S., Izquierdo, B., Gu, C., Reynaert, P., Standaert, A., Gibbons, G., Bosch, W., Gadringer, M. and Li, D. (2020). A Review of Broadband Low-Cost and High-Gain Low-Terahertz Antennas for Wireless Communications Applications. IEEE Access [Online] 8:57615-57629. Available at: https://doi.org/10.1109/ACCESS.2020.2981393.
Low-terahertz (Low-THz, 100 GHz-1.0 THz) technology is expected to provide unprecedented data rates in future generations of wireless system such as the 6th generation (6G) mobile communication system. Increasing the carrier frequencies from millimeter wave to THz is a potential solution to guarantee the transmission rate and channel capacity. Due to the large transmission loss of Low-THz wave in free space, it is particularly urgent to design high-gain antennas to compensate the additional path loss, and to overcome the power limitation of Low-THz source. Recently, with the continuous updating and progress of additive manufacturing (AM) and 3D printing (3DP) technology, antennas with complicated structures can now be easily manufactured with high precision and low cost. In the first part, this paper demonstrates different approaches of recent development on wideband and high gain sub-millimeter-wave and Low-THz antennas as well as their fabrication technologies. In addition, the performances of the state-of-the-art wideband and high-gain antennas are presented. A comparison among these reported antennas is summarized and discussed. In the second part, one case study of a broadband high-gain antenna at 300 GHz is introduced, which is an all-metal model based on the Fabry-Perot cavity (FPC) theory. The proposed FPC antenna is very suitable for manufacturing using AM technology, which provides a low-cost, reliable solution for emerging THz applications.
• Wen, L., Gao, S., Luo, Q., Hu, W. and Yin, Y. (2020). Wideband Dual Circularly Polarized Antenna for Intelligent Transport Systems. IEEE Transactions on Vehicular Technology [Online] 69:5193-5202. Available at: https://doi.org/10.1109/TVT.2020.2980382.
A wideband dual circularly polarized (DCP) antenna is presented for intelligent transport system (ITS) applications, which can be used to improve the receiver sensitivity and communication quality of ITS. The presented DCP antenna is composed of an orthogonal power divider (OPD) with two orthogonal input ports, four phase shifters for quadrature phase output, and four crossed dipoles for DCP radiation. Detailed equivalent circuit analysis shows that the OPD has two orthogonal inputs and four equal magnitude in-phase and out-of-phase outputs. To achieve two sets of orthogonal quadrature output signals for DCP radiation, the lumped element based differential right-hand transmission line unit cell and left-hand transmission line unit cell are elaborately introduced as the ±45° phase shifters, and incorporated into the OPD. Eventually, orthogonal quadrature signals are successfully obtained and fed to the crossed dipoles for DCP radiation. The proposed antenna was then designed, fabricated, and measured for ITS applications. The measured results show that the overlapped impedance bandwidth of both two input ports is 1.07–1.85 GHz (53.4%), and the isolation is higher than 15.2 dB. Moreover, low axial ratio (<1.7 dB) and symmetrical radiation patterns are achieved for unidirectional DCP radiation.
• Wang, J., Zhou, Y., Gao, S. and Luo, Q. (2020). An Efficiency-Improved Tightly Coupled Dipole Reflectarray Antenna Using Variant-Coupling-Capacitance Method. IEEE Access [Online] 8:37314-37320. Available at: https://doi.org/10.1109/ACCESS.2020.2973574.
In this paper, a tightly coupled dipole reflectarray antenna as well as a variant-coupling-capacitance method to improve the antenna aperture efficiency is presented. Tightly coupled elements and true-time-delay lines are employed in the design of a wideband reflectarray. The proposed reflectarray can operate from 2 GHz to 5 GHz with the gain varying from 11.3 dBi to 21 dBi. Moreover, we propose a variant-coupling-capacitance method to improve the reflectarray aperture efficiency at lower frequency. By changing the coupling capacitance between neighboring elements according to their positions in the reflecting surface, a more linear equivalent distance delay line is achieved. Hence, phase error is reduced. According to measurement, the reflectarray gain in 2 GHz using the proposed method is increased by 3 dBi compared with the previous design. Aperture efficiency in 2 GHz is improved by 21.6%.
• Wen, L., Gao, S., Luo, Q., Yang, Q., Hu, W., Yin, Y., Wu, J. and Ren, X. (2019). A Wideband Series-Fed Circularly Polarized Differential Antenna by Using Crossed Open Slot-Pairs. IEEE Transactions on Antennas and Propagation [Online]. Available at: https://dx.doi.org/10.1109/TAP.2019.2951994.
A novel method of designing a wideband series-fed circularly polarized (CP) differential antenna by using crossed open slot-pairs is presented in this paper. The near-field distributions and input impedance analyses show that the closely spaced open slot-pairs can radiate as the crossed dipoles and have stable radiating resistance with a compact radiator size. Besides, a wideband half-power phase shifter by using open slot is proposed and utilized to realize CP radiation. The proposed CP antenna is composed of a wide slot-pair and a narrow slot-pair. In the antenna design, the narrow slot-pair is not only excited as a radiator, but also elaborately loaded to provide wideband half-power output and quadrature phase excitation to the wide slot-pair. Both the proposed half-power phase shifter and CP antenna are illustrated by the corresponding equivalent circuits. Based on these analyses, the proposed antenna is designed, fabricated and measured. Compared to the simulated traditionally designed counterpart, 2.1 times wider axial ratio bandwidth is achieved for the proposed antenna. The measured overlapped bandwidth for axial ratio <3 dB and return loss >10 dB is 1.95-3.45 GHz (55.6%). Also, the antenna gain and radiation patterns are measured, which agree well with the simulated results.
• Yang, Q., Gao, S., Luo, Q., Wen, L., Ren, X., Wu, J., Ban, Y. and Yang, X. (2019). A Low Complexity 16 X 16 Butler Matrix Design Using Eight-Port Hybrids. IEEE Access [Online] 7:177864-177873. Available at: https://doi.org/10.1109/ACCESS.2019.2958739.
Beamforming networks such as Butler Matrices are important for multibeam array antenna applications. The challenge for Butler Matrix design is that their complexity increases with the number of ports. In this paper, a novel approach of designing a 16 X 16 Butler Matrix with significant structure simplification is presented. The eight-port hybrids with no crossovers are used to simplify the network. To ensure the network has the same magnitude and phase responses as the standard one, the location and phase shifting value of each fixed phase shifter are derived from the $S$ -matrix of each hybrid. A $16\times 16$ Butler Matrix network operating from 9 GHz–11 GHz is designed to validate this concept. The compensated microstrip 3-dB/90° directional coupler, the phase shifter with a shunt open-and-short stub and the crossover with a resonating patch are used to reduce the transmission loss and enable broadband operation.
• Hu, W., Liu, X., Gao, S., Wen, L., Qian, L., Feng, T., Xu, R., Fei, P. and Liu, Y. (2019). Dual-Band Ten-Element MIMO Array Based on Dual-Mode IFAs for 5G Terminal Applications. IEEE Access [Online] 7:178476-178485. Available at: https://doi.org/10.1109/ACCESS.2019.2958745.
A dual-band ten-element MIMO array based on dual-mode inverted-F antennas (IFAs) for 5G terminal applications is presented in this paper. The proposed dual-mode IFA is composed of two radiators, which are etched on the outer and inner surfaces of the side-edge frame. The outer part of the antenna generates the low-order mode at 3.5 GHz, while the inner part radiates another one-quarter-wavelength mode at 4.9 GHz. In this way, the IFA can achieve dual-band operation within a compact size of 10.6 × 5.3 × 0.8 mm 3 . Based on the proposed antenna, a dual-band ten-element multiple-input and multiple-output (MIMO) array is developed for 5G terminal applications. By combining neutralization line structures with decoupling branches, the isolations between the elements are improved. To validate the design concept, a prototype of the ten-element MIMO array is designed, fabricated, and measured. The experimental results show that the proposed antenna can cover the 3.3-3.6 GHz and 4.8-5.0 GHz bands with good isolation and high efficiency. Furthermore, the envelope correlation coefficient (ECC), and channel capacity are also calculated to verify the MIMO performances for 5G sub-6GHz applications.
• Yang, Q., Gao, S., Luo, Q., Wen, L., Ban, Y., Yang, X., Ren, X. and Wu, J. (2019). Dual-Polarized Crossed Slot Array Antenna Designed on a Single Laminate for Millimeter-Wave Applications. IEEE Transactions on Antennas and Propagation [Online]. Available at: http://dx.doi.org/10.1109/TAP.2019.2952244.
A novel dual-polarized crossed slot planar array antenna is presented in this paper. The proposed design integrates the antenna array with the feeding networks on a single laminate. The antenna element is developed by using a TE210 and TE120 mode cavity, which is constructed by inserting a number of metalized posts around the crossed region of two perpendicular
substrate integrated waveguides (SIWs). The crossed slot is etched over the cavity and is excited from two orthogonal directions to realize dual-polarization. Owing to the orthogonality
between the TE210 and TE120 mode, high isolation and low crosspolarization are achieved. A prototype of the designed antenna array operating at 25 GHz is fabricated and measured. The
measured results confirm that the presented array antenna has high port isolation (> 41 dB), high cross-polarization discrimination (XPD) (>26 dB) and high aperture efficiency (40%). With
advantages of simple configuration, good radiation performance and easy fabrication, this proposed array antenna is a good candidate for millimeter-wave wireless systems.
• Hu, W., Qian, L., Gao, S., Wen, L., Luo, Q., Xu, H., Liu, X., Liu, Y. and Wang, W. (2019). Dual-Band Eight-Element MIMO Array Using Multi-Slot Decoupling Technique for 5G Terminals. IEEE Access [Online] 7:153910-153920. Available at: https://doi.org/10.1109/ACCESS.2019.2948639.
This paper presents a dual-band eight-element multiple-input multiple-output (MIMO) array using a multi-slot decoupling technique for the fifth generation (5G) mobile communication. By employing a compact dual-loop antenna element, the proposed array obtains two broad bandwidths of 12.2% and 15.4% for sub-6GHz operation. To reduce the mutual coupling between antenna elements, a novel dual-band decoupling method is proposed by employing a multi-slot structure. The proposed MIMO array achieves 15.5-dB and 19.0-dB isolations across the two operating bands. Furthermore, three decoupling modes generated by different bent slots can be independently tuned. Zero ground clearance is also realized by the coplanar arrangement of the antenna elements and decoupling structures. The proposed MIMO array was simulated, fabricated, and measured. Experimental results agree well with the simulations, showing that the dual-band MIMO array has good impedance matching, high isolation, and high efficiency. In addition, the envelope correlation coefficient and channel capacity are calculated and analyzed to validate the MIMO performance of the 5G terminal array. Such a dual-band high-isolation eight-element MIMO array with zero ground clearance is a promising candidate for 5G or future mobile applications.
• Zhu, G., Du, J., Yang, X., Zhou, Y. and Gao, S. (2019). Dual-Polarized Communication Rectenna Array for Simultaneous Wireless Information and Power Transmission. IEEE Access [Online] 7:141978-141986. Available at: https://doi.org/10.1109/ACCESS.2019.2943611.
A dual-polarized communication rectenna array with high isolation and low cross polarization for simultaneous wireless information and power transmission (SWIPT) is presented. It consists of a 2 × 2 element receiving antenna array and a high efficiency rectifier based on voltage doubler topology. The receiving element is corner-fed to achieve high isolation of more than 20 dB between the dual-polarized ports, which guarantees low mutual interference between the communication and the rectifying ports. To receive enough electromagnetic (EM) wave for rectifying and meanwhile meet the communication sensitivity, this 2 × 2 array uses its 2 × 2 vertical polarization ports and 1 × 2 horizontal polarization ports for power rectifying, and the rest 1 × 2 horizontal polarization ports for communication. For the communication port, the measured gain is 10.9 dBi and the cross polarization is less than -20 dB. The performance of the whole communication rectenna array has been measured, where a 2 × 4 circularly-polarized array with a gain of 17.5 dBi, settled 1 meter away is used as the transmitter. Measured results show that the system achieves a peak microwave - direct circuit (mw-dc) conversion efficiency of 74.9 % for the CW signal, and 67 % for the QPSK signal with 10 MHz channel bandwidth on the load of 345 Ω at 2.58 GHz operating frequency.
• He, W., Zhang, L., He, Y., Wong, S., Mao, C., Chu, P., Ge, L. and Gao, S. (2019). An Ultra-Wideband Circularly Polarized Asymmetric-S Antenna With Enhanced Bandwidth and Beamwidth Performance. IEEE Access [Online] 7:134895-134902. Available at: https://doi.org/10.1109/ACCESS.2019.2941551.
This paper introduces an ultra-wideband circularly polarized (CP) asymmetric-S antenna with wide axial ratio beamwidth (ARBW) for C-band applications. The proposed antenna is realized by bending a linearly polarized dipole into asymmetric-S shape with variable trace width, which achieves CP radiation. Unlike the reported symmetric-S antenna, the proposed antenna is constituted with two unequal curved arms to enhance the bandwidth and beamwidth performances. Compared with the symmetric-S antenna, the proposed antenna demonstrates much wider AR bandwidth and wider ARBW over broader frequency range. A prototype is fabricated to verify the design principle. The measured and simulated results are very consistent and both indicate that the proposed antenna has a wide impedance bandwidth (VSWR <; 2) of 70.2% (3.58 to 7.46 GHz), and a wide 3-dB AR bandwidth of 84.8% (2.75 to 6.8 GHz). Moreover, maximum ARBW of 153° is achieved, and a 3-dB ARBW of more than 100° is maintained within a wide operation bandwidth of 46.3% (3.65-5.85 GHz).
• Yin, Z., Yang, X., Yu, F. and Gao, S. (2019). A Novel Miniaturized Antipodal Vivaldi Antenna with High Gain. Microwave and Optical Technology Letters [Online]. Available at: https://doi.org/10.1002/mop.32029.
A novel antipodal Vivaldi antenna operating at an ultra‐wideband of 5.2 to 40 GHz with high gain and miniaturized size is presented in this article. By introducing a pair of radiation arms with maple‐leaf edge shape, the antenna gain is increased by 1 to 3 dB over the upper operation band (10‐40 GHz) compared to the normal antipodal Vivaldi antenna (AVA). To remain the beamwidth while increasing the gain, two rows of specialized symmetrical metallized vias are loaded on the two inside edges of the exponentially slot. By loading the resistors between the top and the bottom planes, the side lobe level at E‐plane is reduced by 3 dB. This proposed maple‐leaf antipodal Vivaldi antenna (MAVA) has the miniaturization size of 0.66λg × 0.68λg × 0.003λg. According to the simulated results, the relative bandwidth of the reflection coefficient less than −10 dB is 154%, and the gain is higher than 10 dBi over the 22 to 40 GHz band with the maximum value of 14.3 dBi. The antenna design is validated by the measurements
• Zhang, Z., Cheng, Z., Liu, G., Ke, H., Sun, H. and Gao, S. (2019). Efficiency‐enhanced Doherty power amplifier using Chireix‐like compensation technology. International Journal of RF and Microwave Computer-Aided Engineering [Online] 29:e21949. Available at: https://doi.org/10.1002/mmce.21949.
This article presents a novel efficiency‐enhanced Doherty power amplifier (DPA) by using a Chireix‐like compensation technique. This technique introduces a compensation circuit structure at the combiner to offset the phase difference effect of a DPA for enhancing drain efficiency. A DPA based on the proposed structure is fabricated with two 10 W GaN high electron mobility transistor (HEMT) transistors. The fabricated DPA with such proposed compensation structure manifests a measured saturated output power of 43.5 dBm and drain efficiency of 68% to 71% in the frequency range of 3.2 to 3.7 GHz. Forty‐five percent of drain efficiency can be achieved at 6 dB power back‐off. And the adjacent channel leakage ratio (ACLR) is better than −48.6 dBc with digital predistortion.
• Wen, L., Gao, S., Luo, Q., Hu, W., Qingling, Y., Yingzeng, Y., Xiaofei, R. and Jian, W. (2019). A Wideband Differentially Driven Dual-Polarized Antenna by Using Integrated Six-Port Power Divider. IEEE Transactions on Antennas and Propagation [Online] 67:7252-7260. Available at: http://dx.doi.org/10.1109/TAP.2019.2930205.
A new method to design wideband differentially driven dual-polarized antenna with high common mode suppression and high port isolation is presented. The presented antenna can be equivalent as a combination of a six-port power divider and four crossed folded dipoles. The six-port power divider is composed of two orthogonal input ports and four equal magnitude output ports. The detailed analysis illustrates that the six-port power divider can have wide bandwidth and high isolation under odd mode excitation and high common mode suppression under even mode excitation. Therefore, based on the wideband and high even mode suppressed six-port power divider, a wideband differentially driven dual-polarized antenna is developed with high common mode suppression. To validate the design concept, the proposed antenna was designed, fabricated, and measured. The measured results prove that the antenna has a wide impedance bandwidth of 1.64-3.0 GHz (58.6%) for the return loss higher than 15 dB and isolation higher than 35.4 dB. In addition, very high common mode suppression is achieved for the measured common mode reflection coefficient higher than -0.87 dB over the entire bandwidth. With stable antenna gain and half power beamwidth, the develop antenna is suitable for base station applications.
• Kurniawan, F., Sri Sumantyo, J., Ito, K., Gao, S., Panggabean, G. and Prabowo, G. (2019). Circularly Polarized Array Antenna Using the Sequential Rotation Network Feeding for X-Band Communication. Progress In Electromagnetics Research C [Online] 94:203-217. Available at: https://doi.org/10.2528/PIERC19051703.
This paper presents a novel Circularly Polarized (CP) microstrip array antenna with circular shape and slotted by an elliptical ring for X-band communication. This array antenna consists of 4 paths. Each patch is designed with a unique model, and the purposed antenna is mainly circular-shaped. An elliptical ring slot is set at the center of the circular-shaped patch. And a pair of triangle shapes employed as truncation factor is placed at the edge of the circular-shaped antenna. This microstrip array antenna is developed by 2 × 2 patches in a sequential rotation mode with relative phases 0˚, 90˚, 180˚ and 270˚. Total dimension of this array antenna is 60.92 mm × 60.92 mm. The simulated result shows a good agreement with minimum requirement. The center frequency of the antenna design is 8.2 GHz with low-frequency at 8 GHz and high frequency at 8.4 GHz. The proposed antenna produced under -10 dB S11 of 21.9%, maximum gain of 12.47 dBic at the center frequency, and axial ratio bandwidth obtained 12.2%. Simulated result has been validated by fabrication and measurement, then the structure of the antenna design is fabricated on NPC-H22A with a thickness of 1.6 mm and dielectric constant of 2.17. Complete investigation and experimentation are presented in the next sections.
• Xu, H., Gao, S., Wang, H. and Yujian, C. (2019). A Highly Integrated MIMO Antenna UnitA Highly Integrated MIMO Antenna Unit A: Differential/Common Mode Design. IEEE Transactions on Antennas and Propagation [Online]. Available at: http://dx.doi.org/10.1109/TAP.2019.2922763.
Abstract—A novel concept of antenna design, termed as differential/common mode (DM/CM) design, is proposed to achieve highly integrated multi-input multi-output (MIMO) antenna unit in mobile terminals. The inspiration comes from a dipole fed by a differential line which can be considered as a differential mode (DM) feed. What will happen if the DM feed is transformed into a common mode (CM) feed? Some interesting features are found in this research. By symmetrically placing one DM antenna and one CM antenna together, a DM/CM antenna can be achieved. Benefitting from the coupling cancellation of anti-phase currents and the different distributions of the radiation currents, a DM/CM antenna can obtain high isolation and complementary patterns, even if the radiators of the DM and CM antennas are overlapped. Therefore, good MIMO performance can be realized in a very compact volume. To validate the concept, a miniaturized DM/CM antenna unit is designed for mobile phones. 24.2 dB isolation and complementary patterns are achieved in the dimension of 0.330λ0×0.058λ0×0.019λ0 at 3.5 GHz. One 8×8 MIMO antenna array is constructed by using four DM/CM antenna units and shows good overall performance. The proposed concept of DM/CM design may also be promising for other applications that need high isolation between closely-packed antenna elements and wide-angle pattern coverage.
• Hu, W., Liu, X., Gao, S., Wen, L., Luo, Q., Fei, P., Yin, Y. and Liu, Y. (2019). Compact Wideband Folded Dipole Antenna With Multi-Resonant Modes. IEEE Transactions on Antennas and Propagation [Online]. Available at: http://dx.doi.org/10.1109/TAP.2019.2925188.
A compact and wideband folded dipole antenna with multi-resonant modes is presented in this paper. Three resonant modes are obtained by using a modified planar folded dipole and its coupled feeding structure. Incorporating with the shorting pins and parasitic patches, multiple resonant modes in the antenna are manipulated, shifted, and then combined for increasing the impedance bandwidth. Using this concept, a prototype of multi-mode folded dipole is designed, fabricated, and measured. The experimental results show that the proposed antenna achieves a bandwidth of 80% from 1.57 GHz to 3.68 GHz, while occupying a compact size of 0.3λ0×0.15λ0×0.05λ0 (λ0 is the wavelength in free space at the lowest operating frequency). Furthermore, a simple and effective design to achieve good omnidirectional radiation performance is developed by placing two proposed folded dipoles back to back. The antenna exhibits a flat gain variation of less than 1.27 dB over a broad bandwidth (82%) in the horizontal plane. Such a compact, wideband, planar antenna is a promising candidate for indoor signal coverage, wireless access points, and micro base stations in 2G/3G/4G/5G and WLAN/WiMAX wireless comminution systems.
• Wen, L., Gao, S., Luo, Q., Yang, Q., Hu, W., Yin, Y. and Ren, X. (2019). A Wideband Differentially Fed Dual-Polarized Antenna With Wideband Harmonic Suppression. IEEE Transactions on Antennas and Propagation [Online]. Available at: http://dx.doi.org/10.1109/TAP.2019.2920230.
A wideband differentially fed dual-polarized antenna with wideband harmonic suppression is presented. The radiating structure is composed of open slots, stair-shaped strips, and a square patch. To realize symmetrical radiation and low cross-polarization for orthogonal polarizations, eight open slots are etched on the four corners of the square patch. Stair-shaped strips are not only used to excite the open slots, but also introduce the monopole resonance. In addition, patch resonance is excited on the center square patch. To match these different resonances, shorted microstrip lines are utilized to achieve the wide impedance bandwidth. Moreover, compact stepped impedance resonators are elaborately introduced on the top of the patch to achieve wideband harmonic suppression without any increase of the antenna footprint. To verify the design method, the proposed antenna is designed, fabricated, and measured. Measured results demonstrate that the proposed antenna has the impedance bandwidth of 1.70-2.81 GHz for Sdd11 < -15 dB with high isolation of 39 dB. Moreover, wideband harmonic suppression is measured from 3 GHz to 9 GHz with the Sdd11 higher than -2.2 dB and the corresponding harmonic gain lower than -5.3 dBi. In addition, stable gain of 7.2-7.9 dBi and beamwidth of 63-71º are achieved for base station applications.
• Wen, L., Gao, S., Luo, Q., Yang, Q., Hu, W., Yin, Y. and Ren, X. (2019). A Compact Windband Duel-Poloarized Antenna With Enhanced Upper Out-of-Band Suppression. IEEE Transactions on Antennas and Propagation.
• Wen, L., Gao, S., Luo, Q., Yang, Q., Hu, W., Yin, Y., Ren, X. and Wu, J. (2019). A Compact Wideband Dual-Polarized Antenna With Enhanced Upper Out-of-Band Suppression. IEEE Transactions on Antennas and Propagation [Online]:1-1. Available at: https://doi.org/10.1109/TAP.2019.2911412.
A compact wideband dual-polarized antenna with enhanced upper out-of-band suppression is presented in this paper. The proposed antenna is equivalent as two electric dipoles and two magnetic dipoles by using the crossed shunt loops. The incorporation of the electric and magnetic dipoles makes the antenna achieve wide impedance bandwidth and compact radiator size. In addition, four parasitic strips are inserted near the inner edge of the four loops to enhance the antenna upper out-of-band suppression at 3.5 GHz with improved impedance bandwidth. The antenna is fed by the crossed coaxial baluns with high isolation. A shorting sheet is introduced into the baluns to further enhance the upper out-of-band suppression and create another rejection at 4.9 GHz. To demonstrate the design method, the proposed antenna prototype was fabricated and measured. Measured results show that the proposed antenna has a wide impedance bandwidth of 1.625-3.05 GHz (61%) for S_11<-14 dB with the isolation better than 38.3 dB. The upper out-of-band suppression of the antenna is also largely enhanced with measured S_11>-2 dB from 3.35 GHz to 5.25 GHz. In addition, stable antenna gain and radiation patterns are achieved for base station applications.
• Wang, W., Zheng, Z., Fang, X., Zhang, H., Jin, M., Lu, J., Luo, Q. and Gao, S. (2019). A Waveguide Slot Filtering Antenna With an Embedded Metamaterial Structure. IEEE Transactions on Antennas and Propagation [Online] 67:2953-2960. Available at: https://doi.org/10.1109/TAP.2019.2898989.
A novel waveguide slot filtering antenna with an embedded metamaterial is presented. This filtering antenna consists of a common waveguide slot antenna with longitudinal slots cut on the top broad wall of its rectangular waveguide and a metamaterial surface embedded in the bottom broad wall. The metasurface replaces the conventional metal plane in the form of a bed of nails. In the operating frequency band, the metasurface works as a perfect electric conductor, so the antenna radiates as the traditional waveguide slot antennas. While in the stopband, the metasurface performs as a perfect magnetic conductor to suppress the propagation of electromagnetic wave in the waveguide cavity, so the interference signal is rejected and a filter function is achieved. To show the design process and verify its feasibility, a filtering antenna prototype working in the C-band and having a stopband in the X-band is designed, fabricated, and tested. A good agreement between simulation and measurement is obtained, demonstrating efficient radiations in the working band and a strong suppression of more than 35 dB in the stopband.
• Lou, T., Yang, X., Qiu, H., Yin, Z. and Gao, S. (2019). Compact Dual-Polarized Continuous Transverse Stub Array With 2-D Beam Scanning. IEEE Transactions on Antennas and Propagation [Online] 67:3000-3010. Available at: https://doi.org/10.1109/TAP.2019.2896554.
A dual-polarized (DP) flat antenna array with passive 2-D beam-scanning capability is presented in this paper. The array consists of a DP continuous transverse stub (CTS) array, a flat Risley prism (FRP), and a line source generator. Two sets of CTSs, being constituted by the substrate-integrated waveguide (SIW), share a common aperture and are arranged orthogonally for the DP operation. A novel compact long line source is proposed for exciting this DP-CTS array. The FRP is realized by two linear phase progression phase-shifting surfaces (LPP-PSSs) and is placed above the DP-CTS array. The beam-scanning capability in the azimuth and in the elevation can be realized by rotating simultaneously the two LPP-PSSs in the same and in the opposite directions, respectively. A six-element array prototype is simulated and fabricated. According to the measured results, beam-scanning ranges of 40° in the elevation and 360° in the azimuth are achieved with the maximum gain of 17.8 dBi. The novel contributions from this paper include: 1) a novel compact long line source and 2) the first passive DP 2-D beam-scanning flat antenna array. This array can be extended easily to a higher gain or a circular polarization application.
• Sitompul, P., Sri Sumantyo, J., Kurniawan, F., Edi Santosa, C., Manik, T., Hattori, K., Gao, S. and Liu, J. (2019). A Circularly Polarized Circularly-Slotted-Patch Antenna with Two Asymmetrical Rectangular Truncations for Nanosatellite Antenna. Progress In Electromagnetics Research C [Online] 90:225-236. Available at: https://doi.org/10.2528/PIERC18120503.
In this paper, a circularly polarized slot-patch antenna for nanosatellite is presented. The
novel design of the circularly polarized wave conducted by two asymmetrical rectangular-truncation
techniques implemented on a circularly-slotted-patch on the front side and a deformed-shifted-feedline
on the back side of the substrate. The antenna is printed on substrates with the dielectric constant of
2.17 and thickness of 1.6 mm. The resonant frequency of the proposed antenna is set at 2.2 GHz with
the minimum requirement of the axial ratio bandwidth (ARBW) of 300 MHz. The proposed antenna
produces under 10 dB impedance bandwidth (IBW) 1.2765 GHz or equal to 58% (1.7235–3 GHz) with
Left-Handed Circular Polarization (LHCP). The average antenna gain reaches 4.5 dBic at 2.2 GHz and
the ARBW 327.5 MHz or about 14.88% (2.0275–2.355 GHz). This paper includes the description and
presentation of the completed discussion.
• Arnieri, E., Boccia, L., Amendola, G., Glisic, S., Mao, C., Gao, S., Rommel, T., Penkala, P., Krstic, M., Yodprasit, U., Ho, A., Schrape, O. and Younis, M. (2019). An Integrated Radar Tile for Digital Beamforming X-/Ka-Band Synthetic Aperture Radar Instruments. IEEE Transactions on Microwave Theory and Techniques [Online] 67:1197-1206. Available at: https://doi.org/10.1109/TMTT.2018.2889038.
This paper presents the first experimental assessment of a highly integrated dual-band dual-polarized antenna tile designed for synthetic aperture radar (SAR) digital beamforming (DBF) satellite applications. The demonstrator described in this paper is the first comprehensive experimental validation of an RF module providing the X-band and Ka-band (9.6- and 35.75-GHz) operation with custom downconversion stages. All the antennas, transitions, and downconversion chips are integrated in the same antenna tile fabricated using a customized 15-layer high density interconnect process. The designed tile goes to the limits of the proposed technology and for the high trace density and for the size of the vertical transitions. The proposed results represent the state of the art in terms of compactness for a DBF SAR RF module even though the demonstrator was manufactured with a standard low-cost technology. The experimental assessment proves the validity of the proposed manufacturing and integration approaches showing a substantial agreement between the performance of the individual blocks and of the integrated system.
• Luo, Q., Gao, S., Li, W., Sobhy, M., Bakaimi, I., de Groot, C., Hayden, B., Reaney, I. and Yang, X. (2019). Multibeam Dual-Circularly Polarized Reflectarray for Connected and Autonomous Vehicles. IEEE Transactions on Vehicular Technology [Online] 68:3574-3585. Available at: http://dx.doi.org/10.1109/TVT.2019.2897218.
This paper presents a multibeam dual-circularly polarized (CP) reflectarray for connected and autonomous vehicles.
The developed reflectarray uses one aperture to realize dualband and multibeam operation. At each frequency band, there
are two simultaneously shaped beams with different circular
polarizations. Totally four beams are obtained with a single feed
and each of the beams can be independently controlled. A simple
but effective polarization suppression technique is introduced to
suppress cross polarizations at large scan angles so the CP beam
of the reflectarray can be configured to point at large angles.
Thus, the present reflectarray is suitable to be applied to vehicles
for reliable high data-rate satellite communications. To validate
the design concept, an X-band prototype was designed, fabricated
and measured. The design concept is flexible and can be applied
to the design of dual-band, dual-CP reflectarray with different
frequencies ratios. Moreover, the present design can also be
extended to a continuous beam-steering design by incorporating
phase shifters.
• Wen, L., Gao, S., Luo, Q., Yang, Q., Hu, W. and Yin, Y. (2019). A Low-Cost Differentially Driven Dual-Polarized Patch Antenna by Using Open Loop Resonators. IEEE Transactions on Antennas and Propagation [Online] 67:2745-2750. Available at: http://dx.doi.org/10.1109/TAP.2019.2896491.
A novel differentially driven dual-polarized patch antenna is presented in this communication. The proposed antenna is a low-cost design with a simple configuration, which avoids using the conventional high cost multi-layer PCB technology. The antenna is composed of two intersected open loop resonators, which are connected to each other at the center. By using the electric coupling from the intersected resonators, two orthogonal radiating modes are excited from the top radiating patch. With the even and odd mode current distributions on the intersected resonators, high port isolation and low cross-polarization level are obtained. The external quality factor of the resonator is illustrated by using the analytical model of a double loaded resonator. To demonstrate the design method, the proposed antenna and array are designed, fabricated, and measured. Compared to the traditionally designed capacitively coupled antenna, two times wider impedance bandwidth is obtained for the proposed antenna with high isolation (>38.5 dB) and low cross-polarization level (<-33 dB). The antenna array is designed for 5G base stations, which features the compact size and low reflection coefficient (<-15 dB). In addition, beam scanning performance of the antenna array is also investigated for base station applications.
• Hu, C., Zeng, S., Jiang, Y., Sun, J., Sun, Y. and Gao, S. (2019). A Robust Technique without Additional Computational Cost in Evolutionary Antenna Optimization. IEEE Transactions on Antennas and Propagation [Online]. Available at: https://doi.org/10.1109/TAP.2019.2891661.
A robustness-enhancing technique without additional computational cost in antenna optimization design is presented. The robustness is implemented by minimizing the variances of the gains, axial ratios and VSWRs over the required frequency band. It is demonstrated that the new technique has two obvious advantages. One is that it can ensure the antenna robustness without the extra computational overhead. The other one is that it is possible to broaden the bandwidth of the antenna. We apply this technique to design a microstrip antenna at 2.4GHz. Experimental results show that, by adopting this new technique, the evolved antenna is more robust than by using two other techniques.
• Mao, C., Khalily, M., Xiao, P., Brown, T. and Gao, S. (2019). Planar Sub-Millimeter-Wave Array Antenna with Enhanced Gain and Reduced Sidelobes for 5G Broadcast Applications. IEEE Transactions on Antennas and Propagation [Online] 67:160-168. 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.
• Cai, Y., Li, W., Li, K., Gao, S., Yin, Y., Zhao, L. and Hu, W. (2019). A Novel Ultrawideband Transmitarray Design Using Tightly Coupled Dipole Elements. IEEE Transactions on Antennas and Propagation [Online] 67:242-250. Available at: https://doi.org/10.1109/TAP.2018.2878079.
One of the key challenges in transmitarray (TA) designs is its narrow bandwidth. To overcome this limitation, this paper proposes a novel design of ultrawideband TA antenna based on tightly coupled dipole arrays (TCDAs). The array consists of 20 × 10 unit cells, and each unit cell is composed of a pair of short dipoles connected with a section of meandered transmission line. The size of each unit cell is 20 mm × 10 mm, which is about 0.2λ × 0.1λ, where λ is the wavelength in free space at the lowest working frequency of the TA. By utilizing the strong coupling between adjacent units of the TA, the bandwidth of the TA is improved significantly. To verify the design concept, one prototype of the proposed TA is fabricated and measured. The prototype demonstrates good performance over a bandwidth of 104%, i.e., from 3.0 to 9.5 GHz, which is significantly wider than that of other TAs reported in the literature. Within the working band of the TA antenna, the radiation pattern is stable and no distortion or splitting of the main beam of the antenna is observed. This is the first time that the TA based on TCDA is reported.
• Lou, T., Yang, X., Qiu, H., Luo, Q. and Gao, S. (2019). Low-Cost Electrical Beam-Scanning Leaky-Wave Antenna Based on Bent Corrugated Substrate Integrated Waveguide. IEEE Antennas and Wireless Propagation Letters [Online] 18:353-357. Available at: https://doi.org/10.1109/LAWP.2019.2890995.
This letter presents a novel low-cost leaky-wave antenna (LWA) with the fixed-frequency beam-scanning capability. An improved half-mode corrugated substrate integrated waveguide structure is proposed as the guiding wave structure to reduce the transverse size of the antenna. A novel electronic phase-shifting structure, composed of fan-shaped open stubs with different sizes and PIN diodes, is proposed for beam scanning. This LWA uses interdigital slots as radiating elements, and the phase-shifting structure is placed between the adjacent radiating elements. By changing the switching states of these PIN diodes, the phase difference between the adjacent radiating elements can be controlled. To verify the concept, one prototype of the 2 × 6 array antenna at C -band is designed, simulated, fabricated, and measured. The antenna demonstrates a beam-scanning range of 25° (34°–59°) at fixed frequency, a peak gain of 12.4 dBi with the gain variation less than 2.3 dB. The antenna has low cost and can be easily fabricated using standard printed circuit board process.
• Li, L., Yang, X., Zhu, G., Luo, Q. and Gao, S. (2019). Compact high efficiency circularly polarized rectenna based on artificial magnetic conductor. International Journal of Microwave and Wireless Technologies [Online]. Available at: https://doi.org/10.1017/S1759078719000448.
A compact circularly polarized (CP) rectenna with low profile and high efficiency based on the artificial magnetic conductor (AMC) is proposed in this paper. The receiving CP antenna is a coplanar stripline fed dual rhombic loop with an AMC reflector. The proposed AMC reflector not only improves the antenna gain to 9.8 dBi but also decreases the profile to 0.1 λ0. The AMC reflector also makes the antenna have a harmonic suppression function so the low pass filter between the rectifying circuit and the antenna could be omitted and the rectenna has a compact structure. According to the measured results, the rectenna has the highest conversion efficiency of 76% on the load of 240 Ω with the received power of 117.5 mW. When the linearly polarized transmitting antenna is rotated, the conversion efficiency of the CP rectenna maintains a constant high conversion efficiency of 74%. The compact structure and CP operation of the rectenna made it a good candidate of the wireless battery for some electronic devices and far-distance microwave power transmission.
• Aly, M., Mao, C., Gao, S. and Wang, Y. (2019). A Ku-Band Filtering Duplex Antenna for Satellite Communications. Progress In Electromagnetics Research M [Online] 85:1-10. Available at: https://doi.org/10.2528/PIERM19071506.
In this paper, a dual-polarisation shared-aperture duplex antenna is presented for satellite communications at the standard microwave Ku-band, based on the integrated filtering-antenna concept and co-design approach. The design relies on the use of resonators coupled to the radiating dual-band dual-polarisation antenna. The resonant patch antenna forms one pole of each channel filter, resulting in a third-order filter in the Rx channel and a second-order filter in the Tx channel. The Rx and Tx ports of the antenna take in horizontal and vertical linear polarisations, respectively. The integrated duplexer helps to increase the isolation between the ports and the selectivity of each channel. The integration between the filter and the antenna is achieved by electromagnetic coupling, without the need of external matching circuits. Thus it attains a compact footprint. The operation frequencies of the demonstrated duplexantenna are from 11 to 12.5 GHz (12.8%) for the downlink to the Rx port, and from 13 to 14.4 GHz (10.2%) for the uplink at the Tx port. High port-to-port isolation of over 40 dB is realized to reduce channel interference. Flat in-band average gains are achieved to be 8.3 and 8.6 dBi, for the low- and high-bands, respectively.
• Wen, L., Gao, S., Luo, Q., Tang, Z., Hu, W., Yin, Y., Geng, Y. and Cheng, Z. (2018). A Balanced Feed Filtering Antenna With Novel Coupling Structure for Low-Sidelobe Radar Applications. IEEE Access [Online] 6:77169-77178. Available at: https://doi.org/10.1109/ACCESS.2018.2878793.
A fourth-order filtering patch antenna with a novel coupling structure is presented in this paper. Using the proposed coupling structure, both the balanced coupling feed and cross-coupling are realized. Two identical slots etched on the ground plane are utilized to excite the radiating patch with the reduced cross-polarization level. A short slot etched on the ground plane is employed for cross-coupling, which introduces two controllable radiation nulls with a steep roll-off rate. In addition, owing to the split-ring resonators and hairpin resonators, the improved impedance bandwidth is achieved with the fourth-order filtering response. To demonstrate the proposed design techniques, both the filtering antenna element and the low-sidelobe array are designed, fabricated, and measured. The measured results show that the proposed antenna has the impedance bandwidth of 12% (4.78–5.39 GHz) with the total height of 0.06?0 , the cross-polarization level lower than ?31 dB, and two radiation nulls with the suppression higher than 31 dB. For the low-sidelobe antenna array, wide impedance bandwidth is also obtained with the sidelobe level below ?28.7 dB, the cross-polarization level below ?34 dB, and the out-of-band suppression better than 25 dB.
• Dong, Y., Gao, S., Luo, Q., Wen, L., Mao, C., Dong, S., Li, X., Wei, G., Wen, G., Geng, Y. and Cheng, Z. (2018). Broadband Circularly Polarized Filtering Antennas. IEEE Access [Online] 6:76302-76312. Available at: https://doi.org/10.1109/ACCESS.2018.2883494.
This paper consists of two parts. The first part presents a review of the recent development in broadband circularly polarized filtering antennas. The second part presents a novel design of broadband integrated filtering antenna based on eighth-mode SIW (EMSIW) resonators for rectenna applications. This work has three main novel contributions. First, by adjusting the external quality factors and coupling coefficients of the resonators in this filtering antenna, optimum input impedance with a complex value can be realized within the filtering antenna. Thus there is no need for an external impedance matching network, which is usually required between the antenna and the rectifying circuits; Second, compared with traditional microstrip resonators, high-Q EMSIW cavities are used to increase antenna gain; third, the coupling gap between the EMSIW resonators also acts as the feeding structure of the radiator. So the feeding structures are all on the middle layer. The ground plane on the back side is a complete structure without any defects. This novel structure design improves front-to-back ratio to enhance the antenna receiving efficiency. To validate this method, two C-band circularly polarized integrated filtering antennas with an input impedance of 50 $\Omega$ and complex impedance are designed, simulated, and fabricated. The measured results show that the operating frequency bandwidth of the proposed antennas is more than 14.5% at C-band with the gain above 8 dBi. The 3-dB axial ratio bandwidth is larger than 8.5% and the front-to-back ratio is higher than 18 dB. Moreover, the proposed antenna with complex impedance is conjugate matched with the input impedance of a specific rectifying circuit at 5.8 GHz and harmonics suppression at the second-harmonic frequency is achieved.

### Book section

• Wen, L., Gao, S., Yang, Q., Luo, Q., Ren, X. and Wu, J. (2019). A Compact Dual-Polarized Patch Antenna Loaded With Metamaterial Unit Cell for Broadband Wireless Communication. In: 2019 IEEE MTT-S International Wireless Symposium (IWS). New York, USA: IEEE, pp. 1-3. Available at: https://doi.org/10.1109/IEEE-IWS.2019.8804152.
A compact dual-polarized patch antenna loaded with metamaterial unit cell is presented in this paper for broadband wireless communication systems. The unit cell is composed of two crossed open loop resonators, which are printed on the crossed substrates. Thanks to the loading of the unit cell, a compact patch antenna is realized with two reflection zeroes. The antenna is driven by the differential ports to obtain high isolation and low cross-polarization. The proposed antenna was fabricated and measured for verification. Measured results show that the proposed antenna has the impedance bandwidth of 17 % for S 11 <; -10 dB with the cross polarization lower than -33 dB. Both the simulated and measured results prove that the proposed antenna can be a good candidate for the wireless communication.
• Luo, Q., Gao, S., Li, W., Yang, X. and Wen, G. (2019). Ultra-wideband and Multiband Reflectarrays for Intelligent Multi-functional Platforms. In: 2019 13th European Conference on Antennas and Propagation (EuCAP). New York, USA: IEEE.
This paper includes two parts. In the first part, a review of techniques for designing wideband or multiband reflectarrays is presented. In the second part, two case studies including the designs of one ultra-wideband (UWB) reflectarray and one multi-band reflectarray are presented. The UWB reflectarray is a novel tightly coupled dipole reflectarray (TCDR) whose unit cell is composed of a tightly coupled dipole and a delay line. The minimum distance between adjacent cells is about 1/10 wavelength at the lowest operating frequency. The TCDR operates from 3.4 to 10.6 GHz with stable radiation patterns and aperture efficiency. The multiband reflectarray is a novel dual-band, dual circularly polarized (CP) reflectarray. The dual-band operation of the reflectarray is obtained by using the interleaved circularly polarized triangular patches as the radiating elements. Within each frequency band, two simultaneous shaped beams with different circular polarization and independent control are realized. Both reflectarrays are fabricated and measurement results are presented.
• Sumantvo, J., Chua, M., Santosa, C., Pariguabean, G., Taushima, K., Watanabe, T., Sasmita, K., Mardiyanto, A., Sumantyo, F., Rahardjo, E., Wibisono, G., Supartono, E., Gao, S., Parulian, S., Nasucha, M., Kurniawan, F., Awaludin, A., Purbantoro, B., Ji, Y. and Imura, N. (2019). Hinotori-C: A Full Polarimetric C Band Airborne Circularly Polarized Synthetic Aperture Radar for Disaster Monitoring. In: 2018 Progress in Electromagnetics Research Symposium (PIERS-Toyama). New York, USA: IEEE, pp. 1466-1473. Available at: https://doi.org/10.23919/PIERS.2018.8597722.
This paper aims to present the design and development work of a full polarimetric Circularly Polarized Synthetic Aperture Radar (CP-SAR) system. The CP-SAR sensor is operating in C band with center frequency of 5.3 GHz, operational bandwidth ranged from 100 MHz to 400 MHz, and transmitting peak power of 280 watt. Four circularly polarized antennas (2 units with left handed circularly polarized and 2 units with right handed circularly polarized) were designed and developed with approximately 22 dBic of gain, and beamwidth of 13° and 6° in range and azimuth direction, respectively. This paper also presents the results from the laboratory test and ground test of the CP-SAR sensor, as well as, the flight test results obtained from the maiden flight of the CP-SAR system using CASA/IPTN CN235-MPA aircraft.

### Conference or workshop item

• Yang, Q., Gao, S., Wen, L. and Luo, Q. (2020). A Compact Broadband 16×16 Butler Matrix for Multibeam Antenna Array Applications. In: International Symposium on Antennas and Propagation (ISAP). IEEE. Available at: https://ieeexplore.ieee.org/abstract/document/8963139.
This paper presents a compact 16×16 Butler Matrix operated from 9 GHz - 11 GHz. Compared with the traditional structure, the presented network is much simpler and can be easily designed. The number of needed components in the design is only sixty, where the number of crossovers is four. In addition, the designed network can be fully realized in a single layer laminate with the size of 165 mm × 165 mm (5.5λ 0 × 5.5λ 0 ). It is shown that the maximum simulated output phase error at 10 GHz is only ±8° and the transmission coefficients are in the range of -14.5 ± 1.5dB over the bandwidth. The measured and simulated results agree well. The designed network can be a potential candidate for the one or two dimensional multibeam array antennas.
• Luo, Q., Gao, S., Sanz Izquierdo, B., Yang, X., Ren, X. and Wu, J. (2020). Low-Cost Smart Antenna Using Active Frequency Selective Surfaces. In: International Symposium on Antennas and Propagation (ISAP). IEEE. Available at: https://ieeexplore.ieee.org/abstract/document/8962974.
Smart antenna is a key technology for advanced wireless systems and one of the most important features of smart antenna is electronically beam scanning or switching. It is highly desirable to reduce the mass, power consumption and cost of smart antennas, as the traditional phased array is always associated with high cost due to the use of many T/R modules and complicated beamforming network (BFN). This paper presents the University of Kent's recent research progress in the field of low-cost smart antenna design using active frequency selective surfaces (AFSS). Firstly, this paper presents a brief review of AFSS based beam-reconfigurable antenna including several recent designs reported by the authors' group. Then, a new high-gain AFSS antenna design with some preliminary results will be presented. This is design achieves higher gain than the reported AFSS antennas. A detailed list of references is given at the end of this paper.
• Wen, L., Gao, S., Yang, Q., Luo, Q., Yin, Y., Ren, X. and Wu, J. (2020). A Compact Monopole Antenna With Filtering Response for WLAN Applications. In: International Symposium on Antennas and Propagation (ISAP). IEEE. Available at: https://ieeexplore.ieee.org/abstract/document/8963440.
A novel compact monopole antenna with filtering response for WLAN applications is presented in this paper. The antenna is composed of a capacity-loaded matching patch, two resonators, and two end-coupled monopoles. The resonators consist of wide rectangular patches and narrow shorted lines to form the resonance, and the resonators are printed on the different layers to increase the design flexibility. Two meandering monopoles are located at the edges of the top layer with capacitive coupling at each other's end. The mutual couplings between the meander monopoles are utilized to produce two radiation nulls at the two band-edges. Based on the design method, the prototype of the proposed antenna was designed, fabricated and measured. The measured results show that the antenna has a broad bandwidth of 16% for S 11 <; -10 dB. Also, ideal omnidirectional radiation patterns, and steep band-edge selectivity with two radiation nulls are achieved for the proposed antenna.
• Luo, Q., Gao, S., Yang, X., Tetuko, J. and Sumantyo, S. (2020). Thin Transmitarray Panel with full 360-degree Phase Shift Range. In: International Symposium on Antennas and Propagation (ISAP). IEEE. Available at: https://ieeexplore.ieee.org/abstract/document/8963290.
This paper presents a new design technique to reduce the thickness of the transmitarray (TA) panel while maintaining 360 o phase shift range. Two types of unit cells, the receive-transmit unit cell and the frequency selective surface (FSS) unit cell, are placed in the same aperture. Comparing to the existing ultra-thin TA designs of similar panel thickness, the presented TAs do not suffer from the phase quantization loss and achieve better aperture efficiency. This study proves that it is viable to mix different types of TA unit cells to design a TA. The developed TA shows better gain than a homogeneous TA using the same elements and improved the overall efficiency by 60%. To verify the design concept, one TA with central frequency at 13.3 GHz was designed, fabricated and measured. The measured gain is 21.3 dBi and the calculated aperture efficiency of the TA is 37.9%.
• Wang, Y., Zhu, F. and Gao, S. (2019). 24-GHz Circularly Polarized Substrate Integrated Waveguide-Fed Patch Antenna. In: International Applied Computational Electromagnetics Society Symposium. IEEE, pp. 1-2. Available at: https://doi.org/10.23919/ACESS.2018.8669193.
This paper has presented the design of a 24-GHz patch antenna with characteristics of good circular polarization, simple structure and easy fabrication. The printed antenna consists of two layers of substrates with the lower one for achieving a short-ended substrate integrated waveguide (SIW) and the upper one for supporting the rectangular radiating patch. The left-handed circularly polarized wave has been obtained by etching a 450 rotated cross-shaped slot on the broad wall of the SIW. The obtained results can confirm that the proposed antenna has achieved an impedance bandwidth (|S 11 | ≤-10 dB) of 23.1-25.3GHz and the 3-dB axial ratio bandwidth of 23.2-24.7GHz.
• Wang, Y., Zhu, F. and Gao, S. (2019). Design of a low-profile wideband patch antenna with L-shaped feeding mechanism. In: International Applied Computational Electromagnetics Society Symposium. IEEE. Available at: https://doi.org/10.23919/ACESS.2018.8669243.
This paper has presented the design of a novel low-profile wideband patch antenna. The antenna structure is formed of three layers of substrates with the radiating patches on the top, the grounded patches in the middle and the feeding portion at the bottom. The large operating frequency bandwidth has been obtained due to the L-shaped feeding technique. Moreover, the low cross-polarization level can also be achieved as the feeding structure can be regarded as the preferred differential feeding. The obtained results can confirm that the proposed antenna has achieved a wide impedance bandwidth (VSWR ≤ 2) of about 60% (3-5.5 GHz) and the whole height of the antenna is 6 mm (around 0.06λ l at the lowest operating frequency). The obtained cross-polarization level is less than-30dB compared with co-polarization.
• Qingling, Y., Gao, S., Wen, L. and Qi, L. (2019). Antenna Array Antenna Array Driven by Broadband Integrated Multibeam Network With Flat Amplitudes and Phases. In: The Loughborough Antennas & Propagation Conference (LAPC 2018). IEEE, p. 36. Available at: https://doi.org/10.1049/cp.2018.1457.
This paper presents a broadband integrated Butler Matrix beamforming network (BFN). This proposed Butler Matrix BFN operates between the bandwidth of 28 GHz to 32 GHz and is implemented with subtrate integrated waveguides (SIWs). To facilitate the design and enhance the output amplitude and phase response, the phase shifters are incorporated into the design of directional couplers. Thus, the design of phase shifters doe not take the phase of crossover as a reference. The compensating SIW phase shifter is introduced into the design of −45° phase shifter, which helps to enhance the phase response over the operating bandwidth. The simulated phase dispersions of the designed Butler Matrix BFN are with peak to peak errors of only 13°, and the amplitude response over the bandwidth is −6 3 ± 1.2 dB. The designed Butler Matrix BFN would be a potential candidate in future 5G communications and other wireless communication systems.
• Lehu, W., Gao, S., Qi, L., Qingling, Y. and Yingzeng, Y. (2019). A Compact and Wideband Dual-Polarized Antenna Using Folded Loops. In: The Loughborough Antennas & Propagation Conference (LAPC 2018). New York, USA: IEEE / IET, pp. 21 -21. Available at: https://doi.org/10.1049/cp.2018.1442.
A novel dual-polarized antenna using folded loops is presented in this paper. The proposed dual-polarized antenna is composed of four triangle loops, which is developed from a single polarized antenna with two triangle loops. By using folded method, a linear polarized loop antenna is elaborately transformed into a dual-polarized antenna with the only increase of feed port for another polarization. Design method of the proposed dual-polarized antenna is discussed and illustrated in this paper. By virtue of the folded design method, the proposed antenna shows a compact size compared to the referenced designs. In addition, wide impedance bandwidth is also achieved with simple configuration. To demonstrate the design method, the proposed antenna is implemented and measured. The measured results prove that the antenna has a wideband impedance bandwidth for base stations with VSWR<1.5 and isolation >35 dB from 1.7 GHz to 2.7 GHz. Furthermore, stable gain and HPBW are also obtained for base station applications.
• Zhang, J., Liu, W., Gu, C., Gao, S. and Luo, Q. (2019). Two-Beam Multiplexing with Inter-Subarray Coding for Arbitrary Directions Based on Interleaved Subarray Architectures. In: 2019 IEEE 30th Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC). IEEE. Available at: https://doi.org/10.1109/PIMRC.2019.8904386.
A new method is proposed to achieve millimeter-wave two-beam multiplexing with arbitrary directions based on the interleaved subarray architecture. Beam interference can be mitigated and beam gain augmented by multiplexing multiple beams. Previous techniques can only multiplex two beams whose directions satisfy a specific relationship. By the proposed design and the associated inter-coding technique, two-beam multiplexing for arbitrary directions to serve two users is achieved. Design examples are provided to demonstrate the effectiveness of the proposed method.
• Zhu, F., Zhang, J., Zhou, Z. and Gao, S. (2018). Design of a Low-Profile 3:1 Bandwidth Wide-Scan Tightly Coupled Phased Array Antenna. In: 2018 International Conference on Microwave and Millimeter Wave Technology (ICMMT). IEEE. Available at: https://doi.org/10.1109/ICMMT.2018.8563283.
A low-profile tightly coupled phased array antenna with the characteristics of 3:1 bandwidth and ±45 ° scan has been proposed in this paper. The array element consists of three layers of Duroid 5880 substrates and a couple of dipole arms. The novelty of the design is the loaded cross-shaped patch which is employed to avoid the common-mode resonance when unbalanced feeding the balanced dipoles. The obtained results confirm that, the array with 7mm spacing can operate from 7 to 21 GHz with VSWR ? 2.5 for 45°scan in both E-and H-planes. The absolute gain of embedded central element pattern is less than 0.6dB compared with the ideal gain, indicating low loss and good efficiency. It is also worth mentioning that, the whole thickness of the antenna is around 4.5mm, which means it is suitable for conformal platforms.
• Wang, Y., Zhu, F. and Gao, S. (2018). Planar Microstrip-Fed Broadband Circularly Polarized Antenna. In: 2018 International Conference on Microwave and Millimeter Wave Technology (ICMMT). IEEE, pp. 1-3. Available at: https://doi.org/10.1109/ICMMT.2018.8563456.
The design of a printed microstrip-fed patch antenna featuring characteristics of wideband and circular polarization has been proposed. The planar antenna is evolved from a typical monopole consisting of a rectangular radiating patch and a rectangular ground plane. The circular polarization has been obtained by shifting offset the radiating patch in correspondence with the ground. Moreover, a tapered-shaped feeding line has been employed to improve the impedance matching across a wide frequency band and two stubs have been integrated with the antenna to enhance the axial ratio bandwidth. The obtained results have confirmed that, the bandwidths of the proposed antenna with VSWR ? 2 and axial ratio ? 3 are 140% and 75%, respectively. In addition, the peak realized gain ranges from 1.25 to 3.2 dBi across the operating frequency range.

### Forthcoming

• Yang, Q., Gao, S., Wen, L., Ban, Y., Yang, X., Ren, X. and Wu, J. (2020). Cavity-Backed Slot-Coupled Patch Antenna Array With Dual Slant Polarization for Millimeter-Wave Base Station Applications. IEEE Transactions on Antennas and Propagation.
This paper presents a novel dual slant polarized antenna for millimeter-wave (mmWave) base stations. Compared with the traditional slant polarized mmWave antennas, the proposed antenna offers the advantages of high cross-polarization discrimination (XPD), good aperture efficiency, simple structure, and low profile. The corner-fed substrate integrated waveguide (SIW) cavity is adopted to improve the port isolation and XPD of this slot-coupled antenna. Four corner-truncated patches connected by a thin cross strip are placed over the SIW cavity to increase the operation bandwidth. Then, a 2×8 antenna array is designed to exemplify the antenna element performance. To improve impedance matching, a shorted patch is introduced in designing the series feeding network and the power divider. The experimental results show that the 2-dB-down gain bandwidth of the proposed antenna array reaches 6.0% and the port isolation is better than 20 dB. The gain and XPD of the antenna array measure 16.7 dBi and 25 dB at the center frequency, respectively
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