Amir Khurrum Rashid

Bio: Amir Khurrum Rashid is an academic researcher from Southern University of Science and Technology. The author has contributed to research in topics: Antenna (radio) & Terahertz radiation. The author has an hindex of 4, co-authored 18 publications receiving 102 citations. Previous affiliations of Amir Khurrum Rashid include Namal College & University of Science and Technology of China.

A Miniaturized Flexible Frequency Selective Surface for X-Band Applications

Abstract: In this paper, a novel and miniaturized band-stop frequency selective surface (FSS) is presented. This FSS provides effective shielding in X-band, with attenuation of at least 56 dB. The proposed FSS provides 3-dB fractional bandwidth of 48% which is necessary to cover X-band. Moreover, the proposed design is polarization independent as it provides a stable frequency response at normal and oblique angles of incidences for both perpendicular TE and parallel TM wave modes. The copolarized and cross-polarized scattering parameter $S_{21}$ is analyzed at the selected band-stop/notch frequencies. More importantly, the proposed FSS is suitable for conformal applications and hence finds wider employability. A prototype of the proposed FSS is fabricated and tested. The measured results are in good agreement with the simulated results.

45° Linearly Polarized and Circularly Polarized High-Scanning-Rate Leaky-Wave Antennas Based on Slotted Substrate Integrated Waveguide

Abstract: A class of 45° linearly polarized and circular polarized high scanning rate leaky wave antennas are proposed in this paper, which is based on slow-wave substrate integrated waveguide structure. High scanning rate leaky wave antennas have recently become attractive for imaging applications and automotive radar. These applications also require a continuous scanning range without an open stopband, as seen at broadside for ordinary leaky wave antennas. Furthermore, both 45° linearly polarization and circularly polarization are required in practical applications. In this paper, we propose an all-in-one leaky wave antenna design, which features high scanning rate, continuous scanning capability across the broadside, 45° linear polarization or circularly polarization, single-layer configuration, and single-side radiation. Two design examples are provided to illustrate the proposed principle. Both simulation and experimental validation are given.

Design of High-Gain and Small-Aperture Endfire Antenna Using a Phase-Reversal Technique

Abstract: A phase-reversal technique is proposed in this article to overcome the gain-aperture tradeoff of endfire antennas. Such a tradeoff fundamentally forbids simultaneous high gain and small cross-section aperture. The phase-reversal technique breaks this tradeoff and hence allows one to design a high-gain endfire antenna with a small cross-section aperture. To illustrate the proposed phase-reversal technique, a crossover stripline structure is implemented. The antenna radiates into the endfire direction within 9.5–10.5 GHz and it achieves 13 dBi endfire radiation gain with only $0.047\lambda _{0}\,\,\times \,\,0.022\lambda _{0}$ cross-section aperture size. These results successfully validate the proposed phase-reversal technique. Such a high-gain and small-aperture endfire antenna is potentially useful for microwave imaging in lossy medium.

Analysis of Asymmetrically Corrugated Goubau-Line Antenna for Endfire Radiation

Abstract: We systematically analyze and describe a new type of traveling-wave endfire antenna based on an asymmetrically corrugated Goubau line that exhibits high efficiency and has a low profile. By proving that asymmetry is a necessary condition in addition to the Hanson–Woodyard condition for traveling-wave endfire radiation, we study the effect of asymmetric corrugation on the mode guide and coupling. We subsequently show that two different waves are independently guided along the two corrugated edges, whose phase difference leads to a transversally polarized dipole moment radiating in the endfire direction. A closed-form expression for the radiation pattern is derived based on the proposed analysis to approximately predict the antennas’ optimum length. To verify the proposed analysis and design principles, results from an experimental prototype operating at 13–15 GHz are also provided. The experimental results show that the antenna design has an average gain of 9.9 dBi and an average efficiency of 82%. The agreement between the predicted results and the final optimized results validates the proposed analysis.

High Roll-Off Frequency Selective Surface With Quasi-Elliptic Bandpass Response

Abstract: A high roll-off, third-order frequency selective surface (FSS) with quasi-elliptic bandpass response is presented. It is based on substrate integrated waveguide technology. Its unit cell includes three cavities that support at the TE101 mode. Interactions of resonators are dominated by magnetic couplings. The coupling matrix is analyzed and used to design FSS. Guidelines for a coupling-matrix-based FSS design are given. Transmission zeros realized close to the lower and upper narrow passband lead to high roll-off characteristics. In addition, a cross-polarization feature is easily achieved. Finally, a prototype is designed and fabricated to validate the proposed structure. A stable frequency response in passband has been obtained with an oblique incidence of 40° for TE polarization. Good agreement between the simulated and measured results verifies the design concept of bandpass FSS.

Multi-level conversion : high voltage choppers and voltage-source inverters

Abstract: The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<>

A General Review of Multilevel Inverters Based on Main Submodules: Structural Point of View

Abstract: Multilevel inverters (MLIs) are being used in wide range of power electronic applications. These converters have attracted a lot of attention during recent years and exist in different topologies with similar basic concepts. This paper presents five main submodules (SMs) to be used as the basic structures of MLIs. The paper reviews the common MLI topologies from the structural point of view. The topologies are divided into the different SMs to show conventional MLI configurations and future topologies that can be created from the main SMs. A comparative study between different topologies is performed in detail. The MLIs are categorized and investigated with from different perspectives such as the number of components, the ability to create inherent negative voltage, working in regeneration mode and using single dc source.

Frequency Selective Surfaces: A Review

Abstract: The intent of this paper is to provide an overview of basic concepts, types, techniques, and experimental studies of the current state-of-the-art Frequency Selective Surfaces (FSSs). FSS is a periodic surface with identical two-dimensional arrays of elements arranged on a dielectric substrate. An incoming plane wave will either be transmitted (passband) or reflected back (stopband), completely or partially, depending on the nature of array element. This occurs when the frequency of electromagnetic (EM) wave matches with the resonant frequency of the FSS elements. Therefore, an FSS is capable of passing or blocking the EM waves of certain range of frequencies in the free space; consequently, identified as spatial filters. Nowadays, FSSs have been studied comprehensively and huge growth is perceived in the field of its designing and implementation for different practical applications at frequency ranges of microwave to optical. In this review article, we illustrate the recent researches on different categories of FSSs based on structure design, array element used, and applications. We also focus on theoretical breakthroughs with fabrication techniques, experimental verifications of design examples as well as prospects and challenges, especially in the microwave regime. We emphasize their significant performance parameters, particularly focusing on how advancement in this field could facilitate innovation in advanced electromagnetics.