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A novel technique to design a phase correcting structure for an electromagnetic band gap resonator antenna (ERA) is presented. The aperture field of a classical ERA has a significantly non-uniform phase distribution, which adversely affects its radiation characteristics. An all-dielectric phase correcting structure 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 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 3dB directivity bandwidth of 8%.

Electromagnetic (EM) metasurfaces are essential in a wide range of EM engineering applications, from incorporated into antenna designs to separate devices like radome. Near-field manipulators are a class of metasurfaces engineered to tailor an EM source’s radiation patterns by manipulating its near-field components. They can be made of all-dielectric, hybrid, or all-metal materials; however, simultaneously delivering a set of desired specifications by an all-metal structure is more challenging due to limitations of a substrate-less configuration. The existing near-field phase manipulators have at least one of the following limitations; expensive dielectric-based prototyping, subject to ray tracing approximation and conditions, narrowband performance, costly manufacturing, and polarization dependence. In contrast, we propose an all-metal wideband phase correcting structure (AWPCS) with none of these limitations and is designed based on the relative phase error extracted by post-processing the actual near-field distributions of any EM sources. Hence, it is applicable to any antennas, including those that cannot be accurately analyzed with ray-tracing, particularly for near-field analysis. To experimentally verify the wideband performance of the AWPCS, a shortened horn antenna with a large apex angle and a non-uniform near-field phase distribution is used as an EM source for the AWPCS. The measured results verify a significant improvement in the antenna’s aperture phase distribution in a large frequency band of 25%.

This paper addresses a critical issue, which has been overlooked, in relation to the design of Phase Correcting Structures (PCSs) for Electromagnetic Bandgap (EBG) Resonator Antennas (ERAs). All previously proposed PCSs for ERAs are made either using several expensive Radio Frequency (RF) dielectric laminates, or thick and heavy dielectric materials, contributing to very high fabrication cost, posing an industrial impediment to the application of ERAs. This paper presents a new industrialfriendly generation of PCS, in which dielectrics, known as the main cause of high manufacturing cost, are removed from the PCS configuration, introducing an All-Metallic PCS (AMPCS). Unlike existing PCSs, a hybrid topology of fully-metallic spatial phase shifters are developed for the AMPCS, resulting in an extremely lower prototyping cost as that of other state-of-theart substrate-based PCSs. The APMCS was fabricated using laser technology and tested with an ERA to verify its predicted performance. Results show that the phase uniformity of the ERA aperture has been remarkably improved, resulting in 8.4 dB improvement in the peak gain of the antenna and improved sidelobe levels (SLLs). The antenna system including APMCS has a peak gain of 19.42 dB with a 1-dB gain bandwidth of around 6%.

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High-directivity antenna systems that provide 2D beam steering by rotating a pair of phase-gradient metasurfaces in the near field of a fixed-beam antenna, hereafter referred to as Near-Field Meta-Steering systems, are efficient, planar, simple, short, require less power to operate and do not require antenna tilting. However, when steering the beam, such systems generate undesirable dominant grating lobes, which substantially limit their applications. Optimizing a pair of these metasurfaces to minimize the grating lobes using standard methods is nearly impossible due to their large electrical size and thousands of small features leading to high computational costs. This paper addresses this challenge as follows. Firstly, it presents a method to efficiently reduce the strength of "offending" grating lobes by optimizing a supercell using Floquet analysis and multi-objective particle swarm optimization. Secondly, it investigates the effects of the transmission phase gradient of PGMs on radiation-pattern quality. It is shown that the number of dominant unwanted lobes in a 2D beam-steering antenna system and their levels can be reduced substantially by increasing the transmission phase gradient of the two PGMs. This knowledge is then extended to 2D beam-steering systems, where we demonstrate how to substantially reduce all grating lobes to a level below −20 dB for all beam directions, without applying any amplitude tapering to the aperture field. When steering the beam of two Meta-Steering systems with peak directivities of 30.5 dBi and 31.4 dBi, within a conical volume with an apex angle of 96 • , the variation in directivity is 2.4 dB and 3.2 dB, respectively. We also demonstrate that beam-steering systems with steeper gradient PGMs can steer the beam in a wider range of directions, require less mechanical rotation of metasurfaces to obtain a given scan range and their beam steering is faster. The gap between the two metasurfaces in a Near-field Meta-Steering system can be reduced to one-eighth of a wavelength with no significant effect on pattern quality.

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