Professor Mohammed Sobhy

Emeritus Professor of Electronics

About

Analysis and applications of non-linear electronic systems.

Research interests

Microwave engineering, solid state electronics.

Professional

Fellow of the Institution of Electrical Engineers (FIEE)

Publications

Showing 50 of 56 total publications in the Kent Academic Repository. View all publications.

Article

  • Almoteriy, M., Sobhy, M. and Batchelor, J. (2018). Characterization of Wideband Antennas for Point-to-Point Communications. IEEE Transactions on Antennas and Propagation [Online]. Available at: https://doi.org/10.1109/TAP.2018.2851367.
    Antenna frequency response can be characterized in terms of effective aperture and gain. Antennas can also be characterized as a two-port network to ascertain the antenna transfer function (S21). This characterization is important in point-to-point (P2P) communication, as the frequency response can vary due to changes in the radiation pattern in the physical channel. This paper presents a process to investigate the frequency response of a wideband antenna in order to identify the best orientation of the antenna for P2P communication. The process predicts the antenna’s effective aperture and gain for each orientation. An equivalent circuit for the wideband antenna is also derived to obtain the total radiated power. The frequency-variant radiation pattern is ascertained from the S21 phase obtained from the equivalent circuit. For each orientation, the S21 phase is analyzed based on the linear, minimum, and all-pass phase components, which enables the derivation of an equivalent circuit. The variation of group delay for each orientation is also obtained and compared. The measurements between two identical antennas at the two orientations with a free-space channel were then modeled for simulation in a digital system. This simulation predicts the antenna effects for the two orientations used. Finally, this process was validated by using a non-minimum phase monopole ultra-wideband (UWB) antenna.
  • 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.
  • Luo, Q. et al. (2016). Dual Circularly-Polarized Equilateral Triangular Patch Array. IEEE Transactions on Antennas and Propagation [Online] 64:2255-2262. Available at: http://dx.doi.org/10.1109/TAP.2016.2551260.
    Abstract—This paper presents a novel sequentially rotated patch array antenna with dual circular-polarizations (CP). The present design has the advantages of compact size, simple feed networks, low cross-polarization and high isolation. The radiating elements are dual linearly-polarized (LP) equilateral triangular patches with hybrid feeds. The vertical polarization of the patch antenna is obtained by using an aperture-coupled feed and the horizontal polarization is obtained by using a proximity feed. These two feeds are orthogonally positioned and are printed on different PCB layers, which leads to the high isolation between these two ports and facilitates the design of the feed networks. The array antenna consists of six such dual-LP triangular patches sequentially rotated by 60o and fed by separated feed networks. Since linearly polarized antenna elements are used, the design of the feed network is much simplified. Through sequentially varying the feeding phase by ?60o, dual circular-polarizations are obtained. The operation principle of the array antenna is also analytically explained in this paper. To verify the design
    concept, one dual LP equilateral triangular patch and one dual CP equilateral triangular patch array resonating at 10.5 GHz are designed, fabricated and tested. There is a good agreement between the simulation and measurement results, both of which show that the array antenna exhibits high port isolation and good circular polarizations with low cross polarization at different planes. The proposed design technique can be applied to the design of dual CP array antennas operating at other frequency
    bands.
    Index Terms—dual circular polarization, sequential rotation,
    microstrip, hybrid feed, high isolation
  • Luo, Q. et al. (2015). Design and Analysis of a Reflectarray Using Slot Antenna Elements for Ka-band SatCom. IEEE Transactions on Antennas and Propagation [Online] 63:1365-1374. Available at: http://doi.org/10.1109/TAP.2015.2401393.
    This paper presents a folded reflectarray designed for Ka-band satellite communication applications. The array element is a dual-polarized slot antenna with multilayered PCB structure and is designed to operate at 29.5-30.8 GHz band for both transmitting and receiving with single linear polarization. Vias are employed to suppress the surface wave propagation and reduce the mutual coupling between adjacent array elements, for achieving a reflectarray with a wide scan angle range. An equivalent circuit model for the array element is developed and it agrees well with the EM simulation results. Several passive demonstrators consisting of 116 elements spaced by 0.5?30GHz were fabricated and measured. The experimental results show that the presented reflectarray is capable of steering the beam up to ±60° in both Eand H-planes with low cross-polarization level.
  • Gu, C. et al. (2015). Compact Smart Antenna with Electronic Beam-Switching and Reconfigurable Polarizations. IEEE Transactions on Antennas and Propagation [Online]:1-1. Available at: http://doi.org/10.1109/TAP.2015.2490239.
    This paper presents a compact-size, low-cost smart antenna with electronically switchable radiation patterns and reconfigurable polarizations. This antenna can be dynamically switched to realize three different polarizations including two orthogonal linear polarizations and one diagonally linear polarization. By closely placing several electronically reconfigurable parasitic elements around the driven antenna, the beam switching can be achieved in any of the three polarization states. In this design, a polarization reconfigurable square patch antenna with a simple feeding network is used as the driven element. The parasitic element is composed of a printed dipole with a PIN diode. By using different combinations of PIN diode ON/OFF states, the radiation pattern can be switched towards different directions to cover an angle range of 0° to 360° in the azimuth plane. The concept is confirmed by a series of measurements. This smart antenna has the advantages of compact size, low cost, low power consumption, reconfigurable polarizations and beams.
  • Sanz-Izquierdo, B. et al. (2010). Dual-Band Wearable Metallic Button Antennas and Transmission in Body Area Networks. IET Microwaves, Antennas & Propagation [Online] 4:182-190. Available at: http://dx.doi.10.1049/iet-map.2009.0010.
    A dual-band metallic antenna with the appearance of a button on a pair of jeans for use with wearable computer networks, emergency rescue scenarios and future wireless medical applications is presented. The design operates at 2.4 GHz WLAN and the HiperLAN/2 bands and a parametric study is given to aid the design process together with measurement and simulation of the structure on a body. A study of transmission between pairs of on-body antennas is presented to give insight into on-body propagating line of sight and non-line of sight channels. A term 'body gain' is defined to quantify how the body attenuates the channel.
  • Sanz-Izquierdo, B., Batchelor, J. and Sobhy, M. (2010). Button Antenna on Textiles for Wireless Local Area Network On Body Applications. IET Microwaves, Antennas & Propagation [Online] 4:1980-1987. Available at: http://dx.doi.org/10.1049/iet-map.2009.0199.
    A design of a wearable antenna for wireless local area network (WLAN) applications is presented in this study. The antenna consists of a button shape outer cylindrical structure and an internal central via connected to a top disc at one end and the metal ground plane at the other. The overall size and shape achieved are those of a standard metal jeans button which camouflages the antenna for wearable applications. The proposed wearable antenna is designed for 2.4 and 5GHz with monopole-type radiation patterns at each band. This allows for transmission to other worn devices on the body. An investigation into the measured permittivity of cotton denim is presented and a section on the equivalent circuit modelling of the antenna and the fabric is given.
  • Sobhy, M., Sanz-Izquierdo, B. and Batchelor, J. (2007). System and circuit models for microwave antennas. IEEE Transactions on Microwave Theory and Techniques [Online] 55:729-735. Available at: http://dx.doi.org/10.1109/TMTT.2007.893675.
    This paper describes how circuit and system models are derived for antennas from measurement of the input reflection coefficient. Circuit models are used to optimize the antenna performance and to calculate the radiated power and the transfer function of the antenna. System models are then derived for transmitting and receiving antennas. The most important contribution of this study is to show how microwave structures can be integrated into the simulation of digital communication systems. This enables system designers to predict the effect of the microwave subsystem on the digital signals and calculate the resulting bit error rate.
  • Sanz-Izquierdo, B. et al. (2006). Single and Double Layer Planar Multiband PIFAs. IEEE Transactions on Antennas and Propagation 54:1416-1422.
    A compact multiband planar inverted-F antenna (PIFA) suitable for distributed radio-over-fiber repeater networks is modified into a planar structure. It is shown that the planar antenna performance is not degraded with respect to the original PIFA and further, a two layer design is demonstrated to offer improved feed matching. The European bands for GSM, DCS-1800, DECT, UMTS, Bluetooth and HiperLAN2 are all covered. A model of the antenna is introduced as a first stage to developing an equivalent circuit.
  • Sobhy, M. et al. (2001). TLM Modelling of Microstrip Patch Antenna on Ferrite Substrate. International Journal of RF and Microwave Computer-Aided Engineering [Online] 11:131-139. Available at: http://dx.doi.org/10.1002/mmce.1014.
    A new TLM modelling method has been developed for patch antennas on magnetized ferrite substrate.The antenna has magnetically controllable resonance frequency and beam direction.The anisotropic permeability tensor of ferrite is modelled by state equations derived from the Polder tensor.Simulation results agree with measurement.
  • Elsehely, E. and Sobhy, M. (2000). Reduction of interference in microwave automotive radars Perkins, T. ed. IEEE MTT-S International Microwave Symposium Digest 1-3:1419-1422.
    A technique is presented to minimise false decisions in automotive microwave radars operating in close proximity. The technique also reduces the requirement on the microwave power of the radar as signals can be detected with very low signal to noise ratios. The signal processing is achieved in real time using a field programmable array.
  • Elsehely, E. and Sobhy, M. (2000). Real time radar target detection under jamming conditions using wavelet transform on FPGA device Syst Soc, S. F. I. T. ed. IEEE International Symposium On Circuits and Systems [Online] 4:545-548. Available at: http://dx.doi.org/10.1109/ISCAS.2000.858809.
    An Architecture and a prototype implementation of radar target detection under jamming condition are presented. This paper presents an implementation of the work presented in [1] on the field programmable gate array (FPGA). The algorithm designed in this paper is based on the multiresolution wavelet analysis, calculation of the wavelet maxima coefficients, integration of the maxima coefficients and identification of the target pulse edges from unwanted coefficients. The implementation occupies about 2500 configurable logic blocks on a Xilinx XC4000XLA family FPGA.
  • Sobhy, M. and Shehata, A. (2000). Secure computer communication using chaotic algorithms. International Journal of Bifurcation and Chaos 10:2831-2839.
    In this paper the application of chaotic algorithms in sending computer messages is described. The communication is achieved through email. Other transmission media can also be used. The algorithm has a degree of security many orders of magnitude higher than systems based on physical electronic circuitry. Both text, image or recorded voice messages can be transmitted. The algorithm can be used for computer communication and for secure databases.
  • Sobhy, M. and Shehata, A. (2000). Secure e-mail and databases using chaotic encryption. Electronics Letters [Online] 36:875-876. Available at: http://dx.doi.org/10.1049/el:20000686.
    An application of chaotic algorithms in sending computer messages is described. The communication is achieved through an e-mail channel. Other transmission media can also be used. The algorithm has a degree of security many orders of magnitude higher than systems based on physical electronic circuitry. Text, image or recorded voice messages can be transmitted.
  • Sobhy, M. and Burman, S. (2000). The transition from solitons to chaos in the solution of the logistic equation. International Journal of Bifurcation and Chaos 10:2823-2829.
    The discrete logistic map was one of the first equations to be studied for the production of chaos. We shall show that a soliton solution exists for the differential logistic equation when the output is the derivative of the dependent variable rather than the variable itself. Furthermore, when the logistic equation is solved using Euler's forward algorithm a transition from a soliton solution to chaos exists and can be accurately predicted. The results are used directly to design an electronic soliton generator.
  • Ody, M., Common, A. and Sobhy, M. (1999). Continuous symmetries of the discrete nonlinear telegraph equation. European Journal of Applied Mathematics 10:265-284.
    The method of classical Lie symmetries, generalised to differential-difference equations by Quispel, Capel and Sahadevan, is applied to the discrete nonlinear telegraph equation. The symmetry reductions thus obtained are compared with analogous results for the continuous telegraph equation. Some of these 'continuous' reductions are used to provide initial data for a numerical scheme which attempts to solve the corresponding discrete equation.
  • Sobhy, M., Hosny, E. and Nasser, A. (1997). Chaos in microwave systems. European Microwave Conference, 1997. 27th [Online] 2:1301-1308. Available at: http://dx.doi.org/10.1109/EUMA.1997.337977.
    The presentation reviews microwave circuits that exhibit chaotic behaviour and will emphasise the need for microwave designers to examine the possibility of circuits becoming chaotic. The paper gives the basic analysis tools for examining the stability of microwave circuits and several examples reported in the literature will be presented.
  • Hicks, A., Common, A. and Sobhy, M. (1996). Approximations to large amplitude solitary waves on nonlinear electrical lattices. Physica D: Nonlinear Phenomena [Online] 95:167-186. Available at: http://dx.doi.org/10.1016/0167-2789(96)00038-3.
    In this paper we describe an approximate method to characterise solitary wave solutions of nonlinear lattice equations. It is based upon one and two point Pade approximations to a series of the real exponential travelling wave solutions of the underlying dispersive system. The theory is applied to an example of a lattice system which models an experimental nonlinear transmission line and the results obtained are consistent with numerical simulations even for relatively large amplitude solitary waves. The speed-amplitude relation is investigated and compared with that derived using quasi-continuum methods.
  • Said, A., Hosny, E. and Sobhy, M. (1995). A Family of Modular Fully Differential Switched-Capacitor Filters for Stimulating Ladder Filters. International Journal of Circuit Theory and Applications 23:185-216.
    The switched capacitor filters proposed in this paper are based on the simulation of LC ladder filters through the state variable equations. They include all-pole and finite transmission zero, lowpass filters, bandpass and highpass filters. The introduced family of filters has a fully differential structure; consequently it has the advantages of improved power supply and common mode rejection ratios and extended dynamic range. Since the proposed family of filters simulates LC ladder filters, it inherits their low passband sensitivities. One of the main advantages of this family of filters is that it has a modular structure composed of key and auxiliary circuits. This modular structure results in easier design and implementation procedures in VLSI fabrication. The double-sampling concept is applied to the introduced modular blocks, which is essentially needed in high-frequency applications. A comparison with similar published work available in the literature is presented and illustrative examples are given.

Book section

  • Sanz-Izquierdo, B. et al. (2008). Study of Single and Dual Band Wearable Metallic Button Antennas for Personal Area Networks (PANs). in: Russer, P. and Siart, U. eds. Time Domain Methods in Electrodynamics: A Tribute to Wolfgang J. R. Hoefer. Berlin: Springer Verlag, pp. 173-187.
    A small WLAN/Bluetooth antenna with the appearance of a metallic button is reported for use with wearable computer systems and covert communications. A single band version is discussed in addition to a dual band design that also covers the HiperLAN/2 band. No external matching circuits are required when the antenna is fed with a 50 Omega coaxial line. A lumped element equivalent circuit is presented for the dual band design together with parametric data curves to inform the design process. A 3 layer human body is included in the simulation and measurements are given to demonstrate the on-body performance. The antenna is disguised as a small metallic button, having the appearance of the waist button used in denim jeans.

Conference or workshop item

  • Almoteriy, M., Sobhy, M. and Batchelor, J. (2018). Antenna Modeling Technique for Digital Communication Systems. in: 15th International Conference on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design (SMACD). IEEE. Available at: https://doi.org/10.1109/SMACD.2018.8434852.
    This paper demonstrates the characterization and
    modeling of an antenna to predict its effect when used in a digital
    communication system. The technique was applied to a
    commercial dual-band antenna. An equivalent circuit model was
    derived to characterize the antenna behavior in the frequency
    domain. A time domain system model was also derived to enable
    the estimation of the antenna effects in a digital system. The results
    show that the antenna caused symbol scattering and contributed
    to the error vector magnitude.
  • Batchelor, J. et al. (2018). RFID monitoring for Assistive Technologies beyond the Clinic. in: 12th European Conference on Antennas and Propagation. IET. Available at: http://dx.doi.org/10.1049/cp.2018.0979.
    A UHF RFID tilt angle and location sensing system is described for tracking users of assistive or rehabilitative technologies in their homes. Results show 3-axis accelerometer angles can be read at 10 Hz, and location within a room can be determined within 0.5 m resolution. A skinmounted microstrip patch antenna is proposed for the RFID communications and power harvesting.
  • Alshammari, A., Sobhy, M. and Lee, P. (2017). Digital Communication System with High Security and High Noise Immunity: Security Analysis and Simulation. in: Barolli, L., Xhafa, F. and Conesa, J. eds. 12th International Conference on Broad-Band Wireless Computing, Communication and Applications (BWCCA-2017). Springer, pp. 469-481. Available at: https://doi.org/10.1007/978-3-319-69811-3_43.
    In this paper, our approach is to provide a cryptosystem that can be compared to a One-Time Pad. A new cryptosystem approach based on Lorenz chaotic systems is presented for secure data transmission. The system uses a stream cipher, in which the encryption key varies continuously. Furthermore one or more of the parameters of the Lorenz generator is controlled by an auxiliary chaotic generator for increased security. The CDMA system for four users has been tested using MATLAB-SIMULINK. The system has achieved a good performance in presence of noise compared to other communication systems.
  • Sobhy, M., Batchelor, J. and Howells, G. (2016). Identification of Transmitting Antennas in Secure Internet of Things Networks. in: Loughborough Antennas and Propagation Conference LAPC16. Loughborough, pp. 1-3.
    Bluetooth and WIFI channels are open to public users and have few security procedures. One security aspect is for a receiver to be able to verify the identity of the transmitter. This paper describes methods of identifying transmitters by the properties of their antennas.
  • Shastri, A. et al. (2016). Evaluation of a low-cost inkjet printed slot antenna for energy harvesting applications. in: Loughborough Antennas & Propagation Conference (LAPC), 2016. Institute of Electrical and Electronics Engineers (IEEE), pp. 1-5. Available at: https://doi.org/10.1109/LAPC.2016.7807593.
    A circularly polarized patch antenna fabricated using commercially available, low-cost, printers is described. Two additive processes are combined for the fabrication: stereolithography (SLA) and inkjet printing of silver inks. A widely available SLA 3D printer is employed to fabricate the substrate of the antenna. Inkjet printing is used to deposit the metallic layers of the radiating element on the substrate. The two machines employed are very low-cost in comparison to those used in previously reported work. Good adhesion of the metallic patterns to the substrates is observed. Furthermore, the resistance of the added metallic patch is relatively low. The aim is to demonstrate the use of alternative, inexpensive machines, for the prototyping and manufacturing of antennas on 3D printed substrates. In this work, the antenna operates at the 1.575GHz GPS frequency band. Finite-difference-time-domain simulations compare well with the practical experiments.
  • Miller, J. et al. (2008). Modelling of Wearable Antennas and Channels for Transmission through the Human Body. in: IEEE MTT-S International Mini-Symposium on Electromagnetics and Network Theory and their Microwave Technology Applications.
    As personal communications develop further, there is need to develop wearable antennas that can communicate with wireless LANS, Blue Tooth and other digital systems. Since these antennas will be close to the human body, the properties of the channels they are communicating through must be evaluated together with the enteraction between the channel and the antennas and between the antennas themselves. In order to include this information in the simulation of entire digital communications systems, system models for the antennas and the human body channel must be developed. The paper gives results of measurements on a single antenna and two antennas when placed simultaneously on the human body. Methods of developing system models for the antennas and the channel are explained.
  • Sanz-Izquierdo, B., Batchelor, J. and Sobhy, M. (2007). Compact UWB Wearable Antenna. in: Loughborough Antennas and Propagation Conference 2007. pp. 121-124.
  • Sobhy, M., Sanz-Izquierdo, B. and Batchelor, J. (2007). Deriving system and circuit models from results of electromagnetic simulators. in: 2007 Time Domain Methods in Modern Engineering Electrodynamics, Munich.
  • Sobhy, M., Sanz-Izquierdo, B. and Batchelor, J. (2006). Modelling of Microwave Antennas. in: European Conference on Antennas and Propagation EuCAP06.
  • Sanz-Izquierdo, B. et al. (2006). Compact Antenna for WLAN On-Body Applications. in: 35th European Microwave Conference. IEEE, pp. 819-822. Available at: http://dx.doi.org/10.1109/EUMC.2006.281044.
    A novel wearable antenna for WLAN applications is presented in this paper. The antenna is made up of a button shape cylindrical structure and a central metal disc connected to the metal ground plane. The structure and dimensions achieved are those of a standard metal button with greater deal of camouflage and rigidness than previous wearable antenna developments [1], [2]. The proposed wearable antenna is designed for 2.4 GHz and 5 GHz with the onmidirectional pattern required for transmission with other wearable devices located across the body.
  • Sobhy, M., Sanz-Izquierdo, B. and Batchelor, J. (2006). System and Circuit Models for Microwave Antennas. in: Wireless Technology, 2006. The 9th European Conference. IEEE, pp. 277-280. Available at: http://dx.doi.org/10.1109/ECWT.2006.280490.
    Computer aided procedures have been developed to derive system and circuit models to match measured responses of the reflection coefficient of microwave antennas. System models are used to study the effect of the antenna on digital signals in digital communication systems. Circuit models are used as an aid to designing the antenna and relating the antenna performance to its physical structure
  • Sanz-Izquierdo, B., Sobhy, M. and Batchelor, J. (2006). UWB Wearable Button Antenna. in: European Conference on Antennas and Propagation EuCAP06. pp. 1-4. Available at: http://dx.doi.org/10.1109/EUCAP.2006.4584652.
    This paper reports a novel UWB antenna suitable for wireless on body applications. The antenna is based on previous studies of wearable button antennas and uses the circular metal nail employed in some buttons to create the radiating element of the antenna. The visible part of the antenna was fabricated using PTFE, although other dielectric or plastic material could be used. The novel antenna is intended for textile jackets where the button structure can be easily camouflaged and disregarded as a plastic button. The antenna is fed by a microstrip line and denim was used as the substrate as well as the superstrate that hides the feeding. The antenna achieves the 3.1GHz to 10.6GHz bandwidth required for the ultra-wide-band technology. The radiation patterns are those of a planar circular monopole antenna with no significant deleterious effect of the dielectric structure on the far-field patterns.
  • Sobhy, M. et al. (2001). TLM Modelling of Patch Antenna on Ferrites. in: Abstracts of the Millenium Conference on Antenna and Propagation,. p. .
  • Sobhy, M. and Shehata, A. (2000). Chaotic radar systems. in: Perkins, T. ed. IEEE MTT-S International Microwave Symposium (IMS2000). Ieee, pp. 1701-1704.
    The paper describes a radar system based on a chaotic microwave generator [1] and an inverse system to reconstruct the radar pulse signal. Chaotic microwave communication systems offer the possibility of adopting spread spectrum techniques at microwave frequencies with greater noise immunity. Synchronised chaotic systems offer high security. The microwave generator used is based on a frequency multiplier chain and be designed to give any required frequency.
  • Sobhy, M. et al. (2000). TLM Simulation of Patch Antenna on Magnetized Ferrite Substrate. in: 16th Annual Review of Progress in Applied Computational Electromagnetics. pp. 562-569.
    Patch antennas on magnetized ferrite substrate have useful properties like steerable beam direction, tunable resonance frequency and circular polarization. Conventional TLM (SCN) algorithm using open and short circuit stubs are not sufficient to model the magnetized ferrite substrate. A new TLM (SCN) algorithm has therefore been developed. General state equations are used to model the anisotropic and dispersive permeability of the magnetized ferrite substrate. Equivalent circuit for the magnetized ferrite substrate are first derived from the Polder permeability tensor and then transformed to state equations. The new TLM (SCN) algorithm is applied to compute the reflection coefficient S11 and the radiation pattern of a sample patch antenna on magnetized ferrite substrate. The algorithm is numerically stable and computed results agree with measurement.
  • Mostafa, K. and Sobhy, M. (1999). Lumped/distributed single-pulse matched filter for radar applications based on wave digital filters. in: 1999 IEEE International Symposium on Circuits and Systems (ISCAS 99). New York, USA: IEEE, pp. 311-314.
    Based on the theory of wave digital filters (WDFs), two new models are derived to represent single pulse matched filters for radar applications, derived from lumped/distributed ladder networks. The first model contains lumped elements and commensurate transmission lines and the second contains lumped elements and non-commensurate transmission lines.
  • Elsehely, E. and Sobhy, M. (1999). Detection of radar target pulse in the presence of noise and jamming signal using the multiscale wavelet transform. in: 1999 IEEE International Symposium on Circuits and Systems (ISCAS 99). Ieee, pp. 536-539. Available at: http://dx.doi.org/10.1109/ISCAS.1999.778901.
    This paper presents an efficient method to identify the received target pulse in the presence of the noise and received false jamming signal. The multiresolution property of the wavelet transform is well suited for analyzing such multiscale signals. Local maxima of the wavelet transform enable us to detect the location of the target pulse edges. The algorithm introduced in this paper is based on the correction and integration of the local maxima of the wavelet coefficients. This gives a good method to discriminate the true reflected target pulse from the false ones.
  • Sobhy, M. et al. (1999). TLM analysis of microstrip patch antenna on ferrite substrate. in: Matloubian, M. and Ponti, E. eds. 1999 IEEE MTT-S International Microwave Symposium on the Magic Touch of Microwaves. IEEE, pp. 1297-1300.
    A new TLM(SCN) algorithm has been developed for the simulation of microstrip antenna on magnetized ferrite substrate. The anisotropic permeability tensor of ferrite is modelled by state equations-derived from the Polder tensor. Simulation results agree with measurement.
  • Sobhy, M. et al. (1998). TLM Simulation of Ferrite Media. in: Microwave Conference, 1998. 28th European. pp. 244-249. Available at: http://dx.doi.org/10.1109/EUMA.1998.338158.
  • El-Shafei, A. and Sobhy, M. (1998). A time-multiplexing simulator for cellular neural network (CNN). in: Tavsanoglu, V. ed. 5th IEEE International Workshop on Cellular Neural Networks and Their Applications. Piscataway NJ: Ieee, pp. 224-229. Available at: http://bookshop.blackwell.co.uk/jsp/id/International_Workshop_on_Cellular_Neural_Networks_and_Their_App/9780780320703.
    A CNN simulator and a Time-Multiplexing algorithm implementation are described. The model for the CNN cell is simulated by SIMULINK(R) but the multiplexing algorithm could be used with any other implementation. The CNN cell model was tested using several templates and the test results, using Connected Components Detection templates ( CCD) are given. This simulator provides a simple and user friendly environment for studying and analyzing CNN dynamics. The, Time-Multiplexing algorithm is tested using the edge detection and CCD templates and the results are attached.
  • El-Shafei, A. and Sobhy, M. (1998). A time-multiplexing simulator for cellular neural network (CNN) using SIMULINK (R). in: IEEE International Symposium on Circuits and Systems (ISCAS 98). Piscataway NJ: Ieee, pp. B167-B170. Available at: http://bookshop.blackwell.co.uk/jsp/id/International_Symposium_on_Circuits_and_Systems/9780780319158.
    A CNN simulator and a Time-Multiplexing algorithm implementation based on a SIMULINK(R) model for CNN are presented in this paper. The CNN cell model was tested using several templates and the test results, using edge detection template are given. This simulator provides a simple and user friendly environment for studying and analyzing CNN dynamics. The Time-Multiplexing algorithm is tested using the edge detection template and the results are attached.
  • Sobhy, M. and Makkey, M. (1998). A new look at analogue computing using switched capacitor circuits. in: IEEE International Symposium on Circuits and Systems (ISCAS 98). New York: IEEE, 345 E 47th St, New York, NY 10017 USA, pp. 484-487. Available at: http://dx.doi.org/10.1109/ISCAS.1998.704508.
    The main objective of this work is to develop an analogue computer base on switched capacitor circuits. The system is suitable for solving nonlinear differential equations in real time. This has considerable advantages in solving systems of equations that cannot be solved analytically and of optimising nonlinear systems. The method has been used to solve nonlinear systems for the generation of Solitons and the results have been compared to measurements.
  • Langley, R. et al. (1997). Using TLM to Simulate Non-Linear and Dispersive Media. in: 2nd IEEE Workshop on Transmission Line Matrix Modelling Theory and Applications. pp. 246-255.
  • Sobhy, M. et al. (1996). Nonlinear system and subsystem modeling in time domain. in: 40th Successive Annual IEEE MTT-S International Microwave Symposium/Exhibition - Bridging the Spectrum. Ieee-Inst Electrical Electronics Engineers Inc, pp. 2571-2579. Available at: http://dx.doi.org/10.1109/22.554605.
    Nonlinear models of microwave subsystems are identified from time domain measurements, Scattering functions in the form of nonlinear time domain functions are used to derive a system identification model instead of an equivalent circuit. The advantage being the simplicity of the measurement and the developed models and the speed and accuracy of the simulation of the entire system.
  • Sobhy, M. et al. (1996). Non-linear system and subsystem modelling in the time domain. in: Ranson, R. G. and Pollard, R. D. eds. 1996 IEEE MTT-S International Microwave Symposium. IEEE, pp. 1755-1758.
  • El-Azeem, M., Sobhy, M. and Hosny, E. (1996). Calculating the impedance of patch antennas using TLM. in: 13th National Radio Science Conference (NRSC 96). I E E E, pp. 135-140.
    The 3-D transmission line matrix (TLM) method is used to calculate the input impedance of patch antennas. The feed line to the antenna is simulated using a TEM line consisting of two electric and two magnetic walls. This simulation has the advantages of matching to the input microstrip and of having a known reference impedance. These two advantages makes accurate calculation of the input impedance possible. The results were compared to previously published measured data
  • Sobhy, M. et al. (1996). Time domain modelling of microwave systems and subsystems. in: 13th National Radio Science Conference (NRSC 96). IEEE, pp. 339-344. Available at: http://dx.doi.org/10.1109/NRSC.1996.551125.
  • Sobhy, M., El-Azeem, M. and Royer, K. (1996). A new multi-grid 3-D TLM algorithm for simulation of microwave FSS. in: Ranson, R. G. and Pollard, R. D. eds. 1996 IEEE MTT-S International Microwave Symposium. IEEE, pp. 439-442.
  • Hosny, E., Nasser, A. and Sobhy, M. (1995). Analysis of Chaotic Behavour in Lumped-Distributed Circuits Applied to DF Practical Microwave Osillators. in: Kirby, L. ed. 1995 IEEE MTT-S International Microwave Symposium. I E E E, pp. 1569-1572.

Forthcoming

  • Luo, Q. et al. (2019). Multibeam Dual-Circularly Polarized Reflectarray for Connected and Autonomous Vehicles. IEEE Transactions on Vehicular Technology.
    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.
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