Muhammad U. Afzal

Bio: Muhammad U. Afzal is an academic researcher from University of Technology, Sydney. The author has contributed to research in topics: Directivity & Antenna (radio). The author has an hindex of 17, co-authored 84 publications receiving 874 citations. Previous affiliations of Muhammad U. Afzal include Macquarie University & University of the Sciences.

Steering the Beam of Medium-to-High Gain Antennas Using Near-Field Phase Transformation

Abstract: A method to steer the beam of aperture-type antennas is presented in this paper. Beam steering is achieved by transforming phase of the antenna near field using a pair of totally passive metasurfaces, which are located just above and parallel to the antenna. They are rotated independently or synchronously around the antenna axis. A prototype, with a peak gain of 19.4 dBi, demonstrated experimentally that the beam of a resonant cavity antenna can be steered to any direction within a large conical region (with an apex angle of 102°), with less than 3-dB gain variation, by simply turning the two metasurfaces without moving the antenna at all. Measured gain variation within a 92° cone is only 1.9 dBi. Contrary to conventional mechanical steering methods, such as moving reflector antennas with multiaxis rotary joints, the 3-D volume occupied by this antenna system does not change during beam steering. This advantage, together with its low profile, makes it a strong contender for space-limited applications where beam steering with active devices is not desirable due to cost, nonlinear distortion, limited power handling, sensitivity to temperature variations, radio frequency losses, or associated heating. This beam steering method using near-field phase transformation can also be applied to other aperture-type antennas and arrays with medium-to-high gains.

Multiobjective Particle Swarm Optimization to Design a Time-Delay Equalizer Metasurface for an Electromagnetic Band-Gap Resonator Antenna

Abstract: This letter presents an efficient particle swarm optimization (PSO) algorithm developed to design a near-field time-delay equalizer metasurface (TDEM) for the purpose of improving directivity and radiation patterns of classical electromagnetic band-gap resonator antennas. Triple layers of conductive printed patterns in the metasurface were optimized by the PSO algorithm to systematically design the TDEM. Predicted and measured results show a significant improvement in antenna performance including 9.6 dB enhancement in antenna directivity, lower sidelobes, and higher gain. The measured directivity of the prototype is 21 dBi, and 3-dB bandwidth is 11.8%.

Dielectric Phase-Correcting Structures for Electromagnetic Band Gap Resonator Antennas

Abstract: A novel technique to design a phase-correcting structure (PCS) for an electromagnetic band gap (EBG) resonator antenna (ERA) is presented. The aperture field of a classical ERA has a significantly nonuniform phase distribution, which adversely affects its radiation characteristics. An all-dielectric PCS was designed to transform such a phase distribution to a nearly uniform phase distribution. A prototype designed using proposed technique was fabricated and tested to verify proposed methodology and to validate predicted results. A very good agreement between the predicted and the measured results is noted. Significant increase in antenna performance has been achieved due to this phase correction, including 9-dB improvement in antenna directivity (from 12.3 dBi to 21.6 dBi), lower side lobes, higher gain, and better aperture efficiency. The phase-corrected antenna has a 3-dB directivity bandwidth of 8%.

Single-Dielectric Wideband Partially Reflecting Surface With Variable Reflection Components for Realization of a Compact High-Gain Resonant Cavity Antenna

Abstract: This communication presents a design methodology for a compact low-cost partially reflecting surface (PRS) for a wideband high-gain resonant cavity antenna (RCA) which requires only a single commercial dielectric slab. The PRS has one nonuniform double-sided printed dielectric, which exhibits a negative transverse-reflection magnitude gradient and, at the same time, a progressive reflection phase gradient over frequency. In addition, a partially shielded cavity is proposed as a method to optimize the directivity bandwidth and the peak directivity of RCAs. A prototype of the PRS was fabricated and tested with a partially shielded cavity, showing good agreement between the predicted and measured results. The measured peak directivity of the antenna is 16.2 dBi at 11.4 GHz with a 3 dB bandwidth of 22%. The measured peak gain and 3 dB gain bandwidth are 15.75 dBi and 21.5%, respectively. The PRS has a radius of 29.25 mm ( $1.1\lambda _{0}$ ) with a thickness of 1.52 mm ( $0.12\lambda _{g}$ ), and the overall height of the antenna is $0.6\lambda _{0} $ , where $\lambda _{0}$ and $\lambda _{g}$ are the free-space and guided wavelengths at the center frequency of 11.4 GHz.

A Low-Profile Printed Planar Phase Correcting Surface to Improve Directive Radiation Characteristics of Electromagnetic Band Gap Resonator Antennas

Abstract: This communication presents a method to enhance the radiation performance of conventional electromagnetic band gap resonator antennas (ERAs) by improving their aperture phase distributions. A low-profile printed planar phase correcting surface (PCS) was designed and fabricated to demonstrate performance enhancement. Measurements of a prototype demonstrated that the PCS significantly enhances the directive radiation properties of ERAs. This includes an 8 dB increase in peak directivity, 60% reduction in 3 dB beamwidth (from 35° to 14°), and a considerable reduction in side lobe levels.

Wireless Networks With RF Energy Harvesting: A Contemporary Survey

Abstract: Radio frequency (RF) energy transfer and harvesting techniques have recently become alternative methods to power the next-generation wireless networks As this emerging technology enables proactive energy replenishment of wireless devices, it is advantageous in supporting applications with quality-of-service requirements In this paper, we present a comprehensive literature review on the research progresses in wireless networks with RF energy harvesting capability, which is referred to as RF energy harvesting networks (RF-EHNs) First, we present an overview of the RF-EHNs including system architecture, RF energy harvesting techniques, and existing applications Then, we present the background in circuit design as well as the state-of-the-art circuitry implementations and review the communication protocols specially designed for RF-EHNs We also explore various key design issues in the development of RF-EHNs according to the network types, ie, single-hop networks, multiantenna networks, relay networks, and cognitive radio networks Finally, we envision some open research directions

Gain enhancement methods for printed circuit antennas

Abstract: Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.

Phased array theory and technology

Abstract: This review of array antennas highlights those elements of theory and hardware that are a part of the present rapid technological growth. The growth and change in array antennas include increased emphasis on "special-purpose" array techniques such as conformal and printed circuit arrays, wide angle scanning arrays, techniques for limited sector coverage, and antennas with dramatically increased pattern control features such as low sidelobe, adaptively controlled patterns. These new topics have substantially replaced large radar arrays in the literature and constitute a major change in the technology. The paper presents a tutorial review of theoretical developments emphasizing techniques appropriate to finite arrays, but indicating parallel developments in infinite array theory, which has become the useful tool for analysis of large arrays. A brief review of the theory of ideal arrays is followed by a generalized formulation of array theory including mutual coupling effects, and is appropriate to finite or infinite arrays of arbitrary wire elements or apertures in the presence of a conducting ground screen. Some results of array tolerance theory are summarized from the literature and retained as reference throughout discussions of array component requirements and device tolerance for low sidelobe arrays. Examples from present technology include conformal and hemispherical coverage arrays, lightweight printed circuit arrays, systems for use with reflectors and lenses in limited sector coverage applications, and wide-band array techniques.

Steering the Beam of Medium-to-High Gain Antennas Using Near-Field Phase Transformation

Abstract: A method to steer the beam of aperture-type antennas is presented in this paper. Beam steering is achieved by transforming phase of the antenna near field using a pair of totally passive metasurfaces, which are located just above and parallel to the antenna. They are rotated independently or synchronously around the antenna axis. A prototype, with a peak gain of 19.4 dBi, demonstrated experimentally that the beam of a resonant cavity antenna can be steered to any direction within a large conical region (with an apex angle of 102°), with less than 3-dB gain variation, by simply turning the two metasurfaces without moving the antenna at all. Measured gain variation within a 92° cone is only 1.9 dBi. Contrary to conventional mechanical steering methods, such as moving reflector antennas with multiaxis rotary joints, the 3-D volume occupied by this antenna system does not change during beam steering. This advantage, together with its low profile, makes it a strong contender for space-limited applications where beam steering with active devices is not desirable due to cost, nonlinear distortion, limited power handling, sensitivity to temperature variations, radio frequency losses, or associated heating. This beam steering method using near-field phase transformation can also be applied to other aperture-type antennas and arrays with medium-to-high gains.