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A compact metasurface-based circularly polarized (CP) dielectric resonator antenna (DRA) is proposed with wideband characteristics. The antenna forms a very simple structure, composed of a rectangular DR, a single coaxial probe, and plus-shaped unit cells-based metasurface. The metasurface is realized on a grounded FR-4 substrate. Next, a rectangular DR is loaded centrally over the metasurface. The DR is fed with a perturbed probe feed at an appropriate angle of ( $\theta $ =29°), along the diagonal line. Thus, a novel hybrid technique involving the angle of feed location from the center of DR, and the N $\times $ N unit cells-based metasurface is utilized for generating a wideband CP radiation. The resonance from the rectangular DR and surface waves along the $7\times $ 7 plus-shaped unit cells-based metasurface is exploited to achieve a wide 3-dB axial ratio (AR) and impedance matching bandwidth. The fabricated antenna prototype used for the validation of predicted results confirms the successful implementation of the proposed technique. Measured results demonstrate a wide impedance bandwidth of 32% (3.6 GHz - 7.0 GHz) and an overlapping 3-dB AR bandwidth of 20.4% (4.2 GHz - 5.2 GHz). Moreover, the antenna adopts a left-hand circular polarization (LHCP) with 6–7 dBic measured gain within the operational frequency range. Overall, the proposed antenna offers low-profile, simplicity, ease of design, and high performance.

Energy harvesting (EH) or scavenging is recognized as harvesting energy from ambient energy sources in the surrounding environment. This paper reports a literature review on radio frequency (RF) EH using different metasurface/metamaterial structures based on split-ring resonators (SRRs), electric inductive-capacitive (ELC) resonators, square-patch unit cells, square-ring unit cells, etc. The essential parameters in rectifying antenna (rectenna) design are included, such as receiving antenna efficiency, conversion efficiency, dimensions, supporting substrate properties, frequency band, and overall performance, etc. It is noted that rectenna design using conventional antennas such as microstrip antennas, monopole antennas, slot antennas, dielectric resonator antennas, etc. suffers from low power conversion efficiency with larger size. To overcome the above-mentioned constraints and enhance the conversion efficiency with smaller size, metasurface/metamaterial structures are used as EH collectors. An introduction to EH is discussed, followed by an overview of energy sources in the ambient environment. Several hypothetical and experimental studies on metasurface-based EH systems are summarized.

In this article, a low profile circularly polarized (CP) antenna with wide 3-dB axial ratio beamwidth (ARBW) is presented. Two-pair of parallel slots are etched on a circular patch and manifested as magnetic dipoles (MDs). These narrow slots are arranged symmetrically about the axes, and one pair is orthogonal to another pair of slots. The philosophy of CP radiation across a wide angular range strongly depends on the spacing between the paired-dipoles, for example spacing of $0.22\lambda _{0}$ , two-orthogonal far-field radiated components become equal across a wide-angle. Moreover, this particular spacing between the paired-dipoles provides a symmetrical electric field distribution along the periphery of the patch, which ensures the broadside LHCP radiation with wide 3-dB ARBW of 228° and 214° at the plane of $\varphi = 0^{\circ }$ and $\varphi = 90^{\circ }$ , respectively. The measured results from the fabricated prototype exhibit good agreement with the simulated results. The antenna has impedance bandwidth (IBW) and CP bandwidth (CPBW) of 2.6% (64 MHz), and 0.9% (22 MHz), respectively. The broadside radiation holds antenna gain higher than 5 dBic across the entire CPBW.

A miniaturized four-element antenna of 20 mm × 20 mm with edge-to-edge distance of 4.9 mm between the array antennas operating from 4.6–8.6 GHz is investigated in this article. The antenna consists of 4 × integrated dipole driven elements, and complementary split ring resonator (CSRR) metacells are loaded on the both sides of each dipole arms. The loaded meta-couplers magnetically couple to dipole drivers, and the induced resonance effect improves the 10-dB impedance bandwidth (IBW) to 60.6%. To improvise the isolation between antenna elements, metallic vias are implemented that trap electromagnetic (EM)-surface waves to condense into the ground. So, the meta-couplers induce electromagnetic (EM)-propagation as surface wave trapments for radiation and decouple near-field condensed currents, acting as couplers/decouplers. The maximum isolation achieved is >−22.5 dB without any external decoupling network. The diversity parameters indicate good attributes in isotropic, indoor, and outdoor channel environments with an envelope correlation coefficient (ECC) < 0.165 and realized gain of 5.5 dBi with average radiation efficiency of 80–90% in the desired operating bands. An equivalent circuit model using lumped components is designed for the proposed four-element antenna. For validation, a prototype antenna is fabricated and measured to be implemented in 5G applications, which shows good correlation with the full-wave simulated results.