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In this paper, a leaky-wave antenna based on substrate integrated waveguide is introduced with continuous beam scanning from backward-to-forward through broadside. A new two-part unit cell has been used to achieve the continuous beam without drop of gain in the broadside. This suppresses the open stop-band, the broadside radiation gain would be without a drop, and the side lobe level is kept low. The wide operating bandwidth is obtained, which covers from 11.7 to 19.6 GHz. It is observed that S 11 is below − 10 dB from 11.5 to 20 GHz, and the average S 21 is − 8.5 dB from 11.5 to 20 GHz. Scanning of this antenna is continuous and covers all angles between − 61° to + 34°. The gain in the direction of the broadside beam is equal to 14.2 dB and without a drop. The gain changes are low in the operating frequency and the average gain is 14.1 dB in this antenna, also the average side lobe level is − 12 dB. The average radiation efficiency of this proposed antenna is 73%.

The paper presents a feasibility study on the design of a new metamaterial leaky-wave antenna (MTM-LWA) used in the construction of a 1 × 2 array which is implemented using substrate-integrated waveguide (SIW) technology for millimetre-wave beamforming applications. The proposed 1 × 2 array antenna consists of two LWAs with metamaterial unit-cells etched on the top surface of the SIW. The metamaterial unit-cell, which is an E-shaped transverse slot, causes leakage loss and interrupts current flow over SIW to enhance the array’s performance. The dimensions of the LWA are 40 × 10 × 0.75 mm3. Mutual-coupling between the array elements is suppressed by incorporating a metamaterial shield (MTM-shield) between the two antennas in the array. The LWA operates over a frequency range of 55–65 GHz, which is corresponding to 16.66% fractional bandwidth. The array is shown to exhibit beam-scanning of ±30° over its operating frequency range. Radiation gain in the backward (−30°), broadside (0°), and forward (+30°) directions are 8.5 dBi, 10.1 dBi, and 9.5 dBi, respectively. The decoupling slab is shown to have minimal effect on the array’s performance in terms of impedance bandwidth and radiation specifications. The MTM-shield is shown to suppress the mutual coupling by ~25 dB and to improve the radiation gain and efficiency by ~1 dBi and ~13% on average, respectively.

For this article, we approximated the field of a leaky-wave antenna (LWA) with the field produced by a uniform linear array (ULA). This article aims to provide an initial framework for applications where the generation of an inhomogeneous wave is wished, but, at the same time, a flexibility is required that is difficult to meet with the conventional LWA design. In particular, two different configurations were considered, one with a simple Menzel antenna operating at 12 GHz, and one, relevant for practical applications, with an antenna operating at 2.4 GHz. This study aimed, in both cases, to highlight the distance at which the field produced by the phased array with the chosen sampling method can approximate effectively the one produced by a leaky-wave antenna and to verify whether this could cause issues for the targeted application.

In this work, we show how to modify radiation amplitude with a leaky wave antenna to improve the quality of sound radiation. The designed gradient amplitude leaky wave antenna consists of a straight pipe with periodically loaded membranes, open channels and Helmholtz resonators. An equivalent acoustic composite right/left-hand transmission line that considers the effects of viscous-thermal and viscous-elastic losses is utilized to steer the radiation angle continually from backward to forward as a function of the incident frequency. The numerical results show that by appropriately selecting the structural parameters of the channel and Helmholtz resonator cavity, the quality of the directional radiation is improved based on the gradient distribution of the radiation amplitude and the near unitary phase. Compared with traditional antennas, the proposed gradient amplitude antenna incorporates a frequency scanning capability with gradient amplitude, which improves the directivity quality of the acoustic waves among the operated frequency band, and provides a new design method for acoustic leaky wave antennas.

This paper presents a review of metasurface-based antennas conducted at the Microwave Communication Laboratory (MCL) of Ajou University in the Republic of Korea. In this paper, profile miniaturization, bandwidth enhancement, multiband operation, and radiation pattern control of metasurface-based antennas are considered. The paper first presents metasurface-based antennas implemented by placing various radiators on top of the metasurface. It then presents antennas implemented by placing the radiators below the metasurface with and without the ground plane. Metasurface-based antennas are not only able to achieve high efficiency with a low profile but they are also able to generate extra resonances from the metasurface structures, which significantly enhances the overall performance of the antennas. These additional resonances were utilized in multiband and/or wideband operations. In addition, the design of a planar compact wide-gain-bandwidth metasurface-based antenna and its radiation characteristics are presented at a terahertz (THz) frequency range. The THz antennas were designed with metasurfaces and a planar leaky-wave feeding structure. Finally, the outlook on future research at the MCL for antenna-related work and their applications using metasurfaces is provided.

In this paper, we exploit the enhanced penetration reachable through inhomogeneous waves to induce hyperthermia in biological tissues. We will present a leaky-wave antenna inspired by the Menzel antenna which has been shortened through opportune design and optimizations and that has been designed to optimize the penetration at the interface with the skin, allowing penetration in the skin layer at a constant temperature, and enhanced penetration in the overall structure considered. Past papers both numerically and analytically demonstrated the possibility of reducing the attenuation that the electromagnetic waves are subject to when travelling inside a lossy medium by using inhomogeneous waves. In those papers, a structure (the leaky-wave antenna) is shown to allow the effect, but such a radiator suffers from low efficiency. Also, at the frequencies that are most used for hyperthermia application, a classical leaky-wave antenna would be too long; here is where the idea of the shortened leaky-wave arises. To numerically analyze the penetration in biological tissues, this paper considers a numerical prototype of a sample of flesh, composed of superficial skin layers, followed by fat and an undefined layer of muscles.

Anisotropic Self-Complementary Metasurfaces (SC-MTSs) are structures constituted by an alternation of complementary inductive and capacitive strips, which are “self-dual” according to Babinet’s duality principle. They support the propagation of two orthogonally polarized surface-wave modes with the same phase velocity along the principal directions (i.e., along the strips and normal to them). The isofrequency dispersion curves of these modes are hyperbolas, and therefore, these MTSs fall in the category of hyperbolic MTSs. It is shown here that the hyperbolic dispersion curves may degenerate in same cases into almost straight lines, which implies that the velocity of energy transport is constantly directed along the same direction for any possible phasing orthogonal to the strips. In this circumstance, the SC-MTS can be conveniently used to design dual-polarized leaky-wave antennas by modulating the impedances of the complementary strips.

Unmanned aerial vehicles (UAVs) need high data rate connectivity, which is achievable through mm-waves and sub-THz bands. The proposed two-port leaky wave MIMO antenna, employing a coplanar proximity technique that combines capacitive and inductive loading, addresses this need. Featuring mesh-like slots and a vertical slot to mitigate open-stopband (OSB) issues, the antenna radiates broadside and bidirectionally. H-shaped slots on a strip enhance port isolation, and a coffee bean metasurface (MTS) boosts radiation efficiency and gain. Simulations and experiments considering various realistic scenarios, each at varying vertical and horizontal distances, show steered beam patterns, circular polarization (CP), and high-gain properties, with a maximum gain of 13.8 dBi, an axial ratio (AR) <2.9, a diversity gain (DG) >9.98 dB, and an envelope correlation coefficient (ECC) <0.003. This design supports drones-to-ground (D2G), drone-to-drone (D2D), and drone-to-satellite (D2S) communications.

Two-dimensional (2D) leaky-wave antennas (LWAs) are commonly designed to radiate pencil beams at broadside and/or scanned conical beams. Recently, the possibility to radiate narrow null patterns at broadside has also been preliminarily explored. In this work, we first review the design rules to obtain a pencil beam from an infinite 2D LWA and then show how they change for having a beam with a narrow null at broadside. The effects of antenna truncation are also accounted for in both cases, and numerical results show how the optimum conditions are in turn affected. Finally, full-wave validations of practical structures excited with either horizontal or vertical dipoles validate the analysis.

This paper introduces a comparative study on the effect of using different feeding structures on the radiation characteristics of graphene strips leaky wave antenna (GS-LWA) at 2 THz. The effect of different plane wave launchers on the radiation characteristics of GS-LWA is investigated. A planar substrate integrated waveguide (SIW) horn antenna is investigated. It provides a peak gain of 18.2 dBi with a bandwidth of 21.95% and a SLL of 10.6 dB. End-fire radiation from parabolic reflector is employed to launch plane-wave in the GS-LWA. A matching BW of 0.82 THz is achieved with peak gain of 18 dBi. A coplanar fed Yagi-Uda like structure element is studied using a single element and two elements array. The two elements provided the highest matching of -40 dB over BW of 6% and gain of 16.5 dBi. Finally, tapered microstrip line is investigated, it introduces the lowest SLL − 16.1 dB with a gain of 17.5 dBi and BW of 39.57% (1.5–2.24 THz). The selection of proper feeding structure depends on the matching BW, peak radiated gain, and the lowest SLL. A full analysis of the GS-LWA from different feeding methods is presented.