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In this paper, a ferrite-filled rectangular waveguide as a balanced composite right/left-handed (CRLH) transmission line is considered. Based on the surface current density of dominant mode, a centerline longitudinal slot on the broad wall of this ferrite-filled rectangular waveguide can be radiate to the free space as a leaky-wave antenna (LWA). This proposed LWA has the both capability of the fixed-bias frequency scanning and fixed-frequency bias scanning from negative to positive angles. However, the gain of the centerline slotted ferrite-filled rectangular waveguide antenna is not acceptable. By adding another slot and changing the position of slots on the broad wall, the gain is improved to more than 9 dB in frequency range of 6.59–6.69 GHz. [ABSTRACT FROM AUTHOR]

In the paper, a circularly polarized (CP) frequency beam-scanning antenna based on photonic crystal (PC) is proposed, which possesses the characteristics of eliminating open-stopband (OSB). In the microwave field, the PC is typically constructed by embedding the air or metal column into the material. However, it is difficult for the PC with perfect magnetic conductor walls to accomplish the degeneracy of eigenmodes at the Γ point. Additionally, antennas based on the PC with perfect electric conductor walls exhibit a narrow scanning angle. The proposed unit based on 1D PC possesses perfect electric and magnetic conductor walls. The unit can not only eliminate OSB but also has a wide scanning range. In addition, the unit breaks into the original symmetrical field distributions of 1D PC. Based on the perturbation theory, leaky-wave slots can be designed to generate electromagnetic waves with the CP characteristics. And a CP antenna based on the unit is designed. The antenna can achieve a 70° beam-scanning within the entire operating band (7.6–9.2 GHz), and the variation of the realized gains is below 1.0 dBi around the broadside frequency. Simultaneously, the antenna is fabricated and measured. The measured results are in accordance with the simulation, which validates the success of the design. [ABSTRACT FROM AUTHOR]

A microstrip circularly polarized (CP) leaky-wave antenna (LWA) operating in the X-band, and having the characteristics of a broad axial ratio bandwidth is proposed. The proposed LWA is made up of 13 unit cells in series through microstrip feeding lines. Elliptical and rectangular slots are etched in each unit cell to achieve the radiation of CP waves. The open stopband at the broadside frequency can be suppressed by shifting the feeding line position and etching two circular notches on both sides of each radiation patch. To validate the proposed method, a prototype antenna operating in the X-band is manufactured and measured. The measured result demonstrates that the -10-dB impedance bandwidth of the microstrip CP LWA is 42.2% (7.96-12.22 GHz); the 3-dB axial ratio bandwidth is 26.4% (9.2-12.2 GHz); the gain of the antenna is 16.0 dBic. Besides, the main beam maintains good CP radiation properties while it continues to scan from -22° to +18°. [ABSTRACT FROM AUTHOR]

In this article, a low-profile, microstrip-based, periodic leaky wave antenna has been proposed for vehicle-to-vehicle (V2V) communications. The leaky-wave structure, loaded periodically with stepped impedance resonator stubs operates in the 5.4–6.2 GHz frequency band, which includes the WAVE (Wireless Access in Vehicular Environments) band (5.85–5.925 GHz) required for automated vehicular communications. The S11 obtained in the spectrum is below −12.68 dB. While the majority of the antennas designed for V2V communications produced omnidirectional patterns, the structure proposed in this work yields a directional pattern, preventing unnecessary outages of signals. The periodic structure gives an added advantage of beam scanning, resulting in a wider, yet directive coverage in the desired frequency band. A backward beam scan from −13˚ to −31˚ is obtained in the frequency range of 5.4–6.2 GHz with a gain variation of around ±0.6 dB only. [ABSTRACT FROM AUTHOR]

A novel technique is presented based on a sinusoidal curve‐shaped one‐dimensional periodic leaky‐wave antenna to eliminate open stopband (OSB) and enhance gain. The radiating stub is inspired by a sinusoidal curve showing zero phase constant at a single broadside frequency (9 GHz) and ripple‐free attenuation constant. The technique is first used on a unit cell with half‐cycle sinusoidal‐curved radiating stub to achieve uniform gain and OSB suppression. Subsequently, to further improve the gain, a unit cell with a full‐cycle sinusoidal‐curved radiating stub with an offset introduced at the centerline is applied. Finally, the full‐cycle sinusoidal stub is modified by introducing a pair of inclined "branching" half‐cycle sinusoidal stubs at an angle θ° from the centerline to further enhance the gain. A 4.65 dB gain improvement is observed along with complete OSB elimination for the proposed design. [ABSTRACT FROM AUTHOR]

Two-dimensional leaky-wave antennas (LWAs) are a class of planar, traveling-wave radiators with attractive features of a low profile, ease of feeding, frequency reconfigurability of the radiation pattern, and polarization agility. Their use in conjunction with array feeders has been the subject of various investigations in recent decades, thanks to the additional degrees of freedom provided by the presence of multiple independent sources. Here, we provide a review of some of the most recent and promising array-fed two-dimensional (2-D) LWAs, selecting a couple of the most significant structures in application, namely Fabry–Perot cavity antennas and bull's-eye antennas, and discussing some of their recently proposed advanced features. [ABSTRACT FROM AUTHOR]

The proposed paper presents the design of a leaky‐wave antenna inspired by holographic metasurfaces employing thin film. Leveraging the holographic principle, this metasurface showcases its transformative capacity by converting an omnidirectionally radiating monopole into a highly directional antenna emitting leaky waves. The holographic metasurface is constructed using a thin film of polyimide (PI) (Df = 0.008; Dk = 3.5), measuring 50 μm in thickness. The antenna structure comprises multiple layers, commencing with the top PI layer, succeeded by a 40 μm thick adhesive layer (Df = 0.004; Dk = 6). Subsequent layer includes the Rogers RT/duroid 5880 substrate (Df = 0.0009; Dk = 2.20), grounded at the bottom and has a thickness of 1.6 mm. The meticulously tailored design of the proposed antenna ensures optimal performance at 15 GHz, facilitating directional radiation and precise beam steering at 10 degrees (ϴ = 10°). This innovative design, incorporating the holographic metasurface on thin film, significantly enhances the antenna's performance, increasing gain from 1.5 dBi to 13.8 dBi. [ABSTRACT FROM AUTHOR]

An H-shaped slotted leaky-wave antenna (LWA) is proposed based on balanced composite right/left-handed (CRLH) transmission lines (TLs) to improve the backward scanning bandwidth and achieve constant gain. The proposed antenna consists of a substrate-integrated waveguide (SIW) unit cell array configured by an H-shaped slot cut in the top layer of the SIW and a patch embedded beneath the H-shaped slot. The proposed design improves the backward scanning bandwidth compared to planar SIW LWAs. The measured beam radiation is in the range from −79° to 80° over the frequency range of 7.6–12.5 GHz. Moreover, a constant gain of greater than 10 dB is achieved over the entire X-band frequency range. [ABSTRACT FROM AUTHOR]

A novel contactless excitation method for leaky‐wave antennas (LWAs) is proposed based on near‐field coupling between a physically disconnected input feed section and input ports of LWAs. Periodic slot‐pairs in substrate‐integrated waveguides are used to implement a plurality of planar LWAs in the Ka‐band, where contactless excitation allows switching of the input port along an antenna array without any mechanical disconnection and reconnection of coaxial connectors, thereby opening the path for mechanical switching‐based pattern reconfiguration. To demonstrate the proposed principle of contactless excitation, prototypes are shown with detailed reflection characteristics and radiation pattern measurements. [ABSTRACT FROM AUTHOR]

In a highly integrated analog radio-over-fiber transceiver, seamless integration of the antenna-frontend is crucial as an antenna is generally implemented on a high-κ material, which is set to highly degrade the antenna's performance. This work is concerned with the radiation behavior improvement of a planar leaky-wave antenna with an inductive partially reflecting surface (PRS) on a high-κ substrate for the development of a highly directive antenna. To begin with, we show how a thin and single-mode resonance (SMR) inductive PRS on high-κ materials in a planar leaky-wave antenna is set to provoke two resonance frequencies (i.e., PRS and cavity resonances) to converge, thereby diminishing the antenna's broadside directivity. By applying an equivalent circuit model, we explain how a multi-mode resonance (MMR) PRS can adequately be applied to address the underlying challenges. Subsequently, the leaky-wave radiation behavior of an antenna with a heterogeneous substrate is investigated and analytical equations are derived and verified with a full-wave simulation. The effects of material permittivity and thickness in a heterogeneous-cavity antenna on leaky-wave performance are investigated using these approximate yet accurate-enough equations. To justify the findings, two 9 × 9 planar leaky-wave antennas are prototyped on heterogeneous substrates based on SMR and MMR PRS and the radiation performances are compared. Our investigations reveal that in the proposed scenario, an MMR PRS can significantly enhance the antenna's broadside directivity by over 4 dBi at the resonance frequency (27.5 GHz), which is also set to improve radiation pattern compared to a SMR-based antenna. Finally, a single-fed dual-band aperture-shared antenna with a large frequency ratio (S-band and Ka-band) is developed and fabricated on a high-κ substrate based on the proposed MMR PRS. [ABSTRACT FROM AUTHOR]

Abstract This paper addresses the issue of constructing millimeter band antennas using dielectric waveguide structures. A new type of linear antenna, incorporating metal pins on the side walls of the grooved dielectric waveguide, is proposed for generating polarization perpendicular to the waveguide axis. However, these antennas suffer from the drawback of cross-polarized radiation in directions close to the waveguide axis. To overcome this limitation, a modified antenna design with transverse polarization is introduced, featuring a closed groove waveguide with a longitudinal slot at the top of the wall. The paper provides a comparison between two types of dielectric waveguide antennas: first, waveguide antenna with grooves in the dielectric which results in longitudinal polarization, and second, waveguide antenna with quarter-wavelength pins which results in transverse polarization. Electrodynamic modeling data are provided to demonstrate the effectiveness of the proposed antennas for satellite, 5G antenna, and radar applications. Finally, an antenna of quarter-wavelength pins is proposed with a frequency of 39 GHz, a gain of 19.8 dBi, and a width of the radiation pattern of 3.2 $$^{\circ }$$ ∘ , and a sidelobe level (SLL) of -13.3 dB has been achieved.

Recently, the community has seen a rise in interest and development regarding holographic antennas. The planar hologram is made of subwavelength metal patches printed on a grounded dielectric board, constituting flat metasurfaces. When a known reference wave is launched, the hologram produces a pencil beam towards a prescribed direction. Most earlier works on such antennas have considered only a single beam. For the few later ones that studied multiple beams, they were achieved either by having each beam taken care of by a distinct frequency or by partitioning the hologram, thereby depriving each beam of the directivity it could have had it not shared the holographic aperture with other beams. There have been recent studies related to the use of tensor surface impedance concepts for the synthesis of holograms which have attained control over the polarizations and intensities of the beams. However, this approach is complicated, tedious, and time-consuming. In this paper, we present a method for designing a planar holographic leaky-wave multi-beam metasurface antenna, of which each simultaneous beam radiating at the same frequency towards any designated direction has a tailorable amplitude, phase, and polarization, all without hologram partitioning. Most importantly, this antenna is exempted from the need for the cumbersome technique of tensor impedance. Such features of beam configurability are useful in selective multiple-target applications that require differential gain and polarization control among the various beams. Only a single source is needed, which is another benefit. In addition, effective methods to mitigate sidelobes are also proposed here. Designs by simulations according to the method are herein validated with measurements performed on fabricated prototypes. [ABSTRACT FROM AUTHOR]

Here, a wide‐angle phase‐frequency scanning linear array composed of leaky‐wave antennas (LWAs) is proposed. The unit cell of the proposed LWA element consists of microstrip lines and grounded vias. By increasing the scanning rate based on theoretical analysis, wide scanning range with low gain fluctuation of the LWA element is achieved. For gain enhancement, the LWAs are arranged along their length to form a linear array. A method combining theoretical derivation and numerical calculation is used to obtain a high efficiency and low sidelobe level (SLL) of the array. To verify the design method, a 1×4 $1\times 4$ linear LWA array is designed, fabricated and measured. The main beam of the LWA array can scan from −60° $-60^\circ $ to 50° $50^\circ $ in frequency band of 9.3–11.6 GHz with gain fluctuation less than 2 dB and SLL less than −9 $-9$ dB. The measured results are in good agreement with the simulated results. [ABSTRACT FROM AUTHOR]

A low‐cost W‐band leaky‐wave antenna with two‐dimensional scanning capability is presented. By using the low‐loss transversal long‐slot array structure with a single‐layer parabolic reflector, the antenna realizes a passband from 85 to 102.8 GHz with Voltage Standing Wave Ratio <2. This antenna has a backward radiation direction, which changes with frequency in one dimension, and with the feeding wave front direction in the other dimension. The maximum sidelobe is measured to be −14.2 dB, 5 dB lower compared to the previous‐published longitudinal long‐slot array. A low‐cost, low‐loss, low‐profile design is provided for W‐band 2‐D beam scanning, with backward scanning capability, which is easy to fabricate and could be used for high‐solution sensing and point‐to‐point communications. [ABSTRACT FROM AUTHOR]

This paper addresses the issue of constructing millimeter band antennas using dielectric waveguide structures. A new type of linear antenna, incorporating metal pins on the side walls of the grooved dielectric waveguide, is proposed for generating polarization perpendicular to the waveguide axis. However, these antennas suffer from the drawback of cross-polarized radiation in directions close to the waveguide axis. To overcome this limitation, a modified antenna design with transverse polarization is introduced, featuring a closed groove waveguide with a longitudinal slot at the top of the wall. The paper provides a comparison between two types of dielectric waveguide antennas: first, waveguide antenna with grooves in the dielectric which results in longitudinal polarization, and second, waveguide antenna with quarter-wavelength pins which results in transverse polarization. Electrodynamic modeling data are provided to demonstrate the effectiveness of the proposed antennas for satellite, 5G antenna, and radar applications. Finally, an antenna of quarter-wavelength pins is proposed with a frequency of 39 GHz, a gain of 19.8 dBi, and a width of the radiation pattern of 3.2 ∘ , and a sidelobe level (SLL) of -13.3 dB has been achieved. [ABSTRACT FROM AUTHOR]

Wireless systems are facing increasing pressure due to the growing demand for data transmission. One potential solution to this problem is to shift communication frequencies toward the terahertz (THz) spectrum. However, this requires the development of new components that can efficiently process signals at these high frequencies and transmit them via highly directional beams. In this study, a novel approach is proposed to achieving efficient THz signal processing by combining two existing technologies: photonic crystals and leaky‐wave antennas. Incorporating a 2D photonic crystal inside a leaky‐wave waveguide allows to manipulate the wave vector of the guided wave in unique ways, which in turn impacts the far‐field radiation pattern emitted through the leaky‐wave aperture. The device fabrication uses 3D printing of alumina and allows for convenient and scalable manufacturing. Through numerical simulations and experiments, free‐space data transmission at rates of few hundred Mbps at a carrier frequency of 101.2 GHz is demonstrated. The findings illustrate the feasibility of photonic crystal‐based leaky‐wave antennas and lay the groundwork for the development of compact and high‐performance components for THz wireless communication systems. [ABSTRACT FROM AUTHOR]

In this paper, a novel composite right-/left-handed (CRLH) leaky-wave antenna with a simple structure, low cost, high gain, and wide beam-scanning range performance for the millimeter wave (mmWave) band. The proposed antenna comprises a series-fed array of asymmetrically slotted elliptical CRLH unit cells loaded with a short-circuit stub. By optimizing the length of the stub, the condition of the CRLH structure is balanced to enable beam scanning from the backward to the forward direction within the mmWave band. The proposed antenna exhibits a wide beam-scanning angle of 112° (-60° to 52°), coupled with high gain and radiation efficiency at the designated band. Furthermore, it is fabricated on a traditional microwave substrate, Rogers RT/duroid 5880, thus offering a cost-effective approach to streamlining the manufacturing process. The measurement results confirmed a peak realized gain of 16.8 dBi. The excellent performance achieved using a low-cost design makes the proposed antenna attractive for 5G mmWave applications. [ABSTRACT FROM AUTHOR]

Terahertz radars based on leaky-wave antennas are promising for the realization of radar systems with high resolution over short ranges. This type of radar relies on spatial frequency mapping to realize a wide field of view without mechanical actuation or electrical beam steering. Previously, integrated leaky-wave antennas based on metallic wave confinement have been implemented, but the high ohmic losses limit the realized antenna gain, which is essential for extending the range of such a system when limited power is available. Here, we demonstrate an all-dielectric leaky-wave antenna fabricated monolithically from silicon and then apply leaky-wave radar techniques to realize a terahertz radar system capable of real-time data acquisition. Through this all-dielectric approach, we can avoid metallic losses, achieving an experimentally measured maximum realized gain of 25 dBi and a 34.3° 3-dB field-of-view while utilizing established and scalable fabrication techniques essential for the wide-spread adoption of terahertz technologies. We foresee this technique being applied to a variety of real-time radar applications, and here we demonstrate two potential use-cases: multi-object tracking and differentiation of liquids. [ABSTRACT FROM AUTHOR]

Planar metasurface lens structures based on microstrip technology, optimized to control the propagation of surface waves (SWs), are presented. Two different lenses are studied, i.e., a converging or plane-wave-like lens and a diverging lens. Near-field simulations and measurements are reported to demonstrate the guiding features of the designed lenses, which have also been proposed as a feeding system for planar leaky-wave antennas (LWAs). Far-field results show improvements in terms of reduced cross polarization and sidelobe level as well as increased realized gain when compared without these SW lenses. The proposed structures are also simple to manufacture and are employed herein to control SW fields generated by a TM0 surface-wave launcher (SWL) integrated in the ground plane of the developed prototype demonstrators. Some applications include high-gain radar and remote sensing satellite antennas as well as microwave and millimeter-wave communication systems.

The efficient series connection of planar leaky-wave antennas (LWA) to obtain directive frequency beam scanning, is proposed in this paper. Conditions for the proper performance are here derived, showing that the distance between antennas must be minimized while optimizing the phase shift introduced by the interconnection. Consequently, the methodology to design the transition is presented by an example using SMA connectors and a meander coaxial cable. Such series arrangement is useful to overcome the restricted directivity of planar LWAs in the UHF band due to limited PCB standard manufacturing sizes, while optimizing the radiation efficiency. The presented theory is validated with practical design examples of microstrip LWA arrays operating in the 900 MHz UHF band. Also, the frequency-beam scanning behaviour of the series-fed LWA array is analysed, demonstrating good performance when the proposed design conditions are satisfied, compared to a non-optimized design which can lead to destructive interference in the desired scanning directions.

Resonant cavity antennas (RCAs) produce reasonably high gains (15-20 dBi) with thin form factors, and find strong applications in wireless communication. A recently proposed RCA achieves a broad 3dB bandwidth of over ${20\%}$ using a spherically modified ground (SMG), but its curved metallic surface is very costly to manufacture at high frequencies. In this paper, we planarize this broadband RCA by replacing the SMG with a true-time-delay metasurface (TTD-MS) which mimics the both reflection phase shift and time-delay of the SMG over antenna’s entire operation bandwidth. We verify our proposed method through full-wave simulations and experimental measurements. Our measurements demonstrate an impedance bandwidth $({\rm S_{11}\le -10\:{\mathrm{ dB}}})$ of ${32\%}$ and a 3dB-gain bandwidth of ${21.3\%}$ (from 11.95 GHz to 14.8 GHz), with a peak gain of 17.5 dBi. This performance is comparable to the RCA with the SMG, but we have planarized the structure, leading to dramatic simplification in fabrication. The height of the cavity is also reduced by ${20\%}$ . The proposed TTD-MS RCA exhibits high gain, stable impedance matching, reduced cavity height and simple configuration, and elucidates a new path to RCA design for microwave and mm-wave frequencies.

Fixed frequency beam-scanning leaky-wave antennas have been a focus of attention for many scholars in recent years, and numerous related results have been obtained. However, these antennas suffer from several issues such as small beam-scanning range, low gain, and unsatisfactory impedance matching. To address these problems, this paper proposes a microstrip line (ML) antenna unit based on liquid crystal (LC) materials etched Complementary Split Ring Resonator (CSRR). In a first-of-its-kind approach, the substrate integrated waveguide (SIW) structure and the ML transmission structure are combined to present the SIW-ML transmission structure. The antenna operates in the Ka-band with excellent resonance characteristics at 34.7 GHz, and the S11 parameters are below − 13 dB in the frequency range of 30–40 GHz, indicating outstanding impedance matching. By arranging 56 antenna units, a periodic leaky-wave antenna is created, enabling fixed-frequency beam-scanning at 34.7 GHz. Experimental results show that the antenna can achieve scanning of angles between − 53° and + 60° with a gain of up to 12.63 dB. Once single-beam scanning is achieved, a method combining LC and discrete amplitude weighting technique, as well as multi-beam theory, is proposed for multi-beam study. Experimental results reveal that the designed 56-unit beam-scanning antenna can effectively realize beam scanning in two directions. [ABSTRACT FROM AUTHOR]

A segmented periodic slot array leaky‐wave antenna (LWA) is proposed for beamforming applications. The LWA consists of N $N$ segments, each with a unique propagation constant achieved through varying periodicity and slot size. By using segments with different propagation constants, the proposed LWA can achieve beamforming such as flat‐top beams and side‐lobe level (SLL) reduction. The LWA is based on a substrate‐integrated waveguide with periodic double transverse slots in the broad wall of the waveguide. The double slots allow for reflection‐canceling to suppress the broadside stopband and hence can achieve beamforming capabilities in the backward, broadside, and forward directions. Full‐wave simulations are used to demonstrate the proposed concept for flat‐top beamforming in the mm‐wave band at 30 GHz. Experimental demonstration is conducted using two prototypes for flat‐top beams and SLL reduction, with good agreement with full‐wave simulations. [ABSTRACT FROM AUTHOR]

This paper introduces a beam‐scanning holographic antenna composed of a substrate‐integrated waveguide (SIW) feeding structure and a rectangular microstrip array. The antenna innovatively combines holographic theory with liquid crystal electrical tunability to realize single‐frequency large‐angle beam scanning function which can effectively solve the problem of beamforming reconfiguration in traditional array antenna systems. In this paper, the variation of dielectric constant of liquid crystal under different bias voltages is quantitatively analyzed. Additionally, the beam forming technology is analyzed under hologram amplitude weighting theory. The relevant theories are verified by manufacturing and testing. The prototype antenna achieves the ultra‐wide beam scanning angle of −63° to 63° at 36 GHz. [ABSTRACT FROM AUTHOR]

A 1-bit phase reconfigurable fixed-frequency beam steering leaky-wave antenna (FBSLWA) with wide-angle steering is proposed in this paper. By controlling two p–i–n diodes on the branches of the element, a stable 180° phase difference is realized. Moreover, the open stop-band effect at the broadside radiation is suppressed by reducing the reflection coefficients of the element. The proposed FBSLWA can achieve wide-angle steering within a frequency bandwidth of 10.4 GHz–11.8 GHz. As for the measured results, they show that the achievable beam steering ranges of the FBSLWA at 10.4 GHz, 11.0 GHz, and 11.8 GHz are −61° to +59°, −64° to +71°, and −62° to +58° respectively, with measured peak gains of 12.1 dBi, 13.9 dBi, and 11.7 dBi. [ABSTRACT FROM AUTHOR]

A novel frequency beam-scanning circularly-polarized leaky-wave antenna with the axial ratio (AR) of less than 3 dB in all the half-power beamwidth ranges based on an H-shaped slow-wave transmission line is proposed for X-band applications. The proposed circularly-polarized leaky-wave antenna is composed of a novel slow-wave transmission line and two rows of elliptical patch structures, leading to wide AR bandwidth, backward-to-forward beam scanning, and stable gain. To verify the proposed antenna, one prototype with a center frequency of 10 GHz is designed and fabricated. Measured results indicate that the main beam scans from -25 to +28 within the operating frequency variation from 8.7 to 11.5 GHz. The 3-dB AR bandwidth and maximum gain are 27.7% and 10.28 dBic, respectively. [ABSTRACT FROM AUTHOR]

This article presents a wide-angle-scanning leaky-wave antenna (LWA) based on a composite right/left-handed (CRLH) transmission line. In contrast to traditional semiconductor elements, thin-film ferroelectric capacitors were implemented in the CRLH unit cells to enable electric beam scanning. The proposed CRLH LWA has a single-layer design without metalized vias and is compatible with PCB and thin-film technologies. To fabricate the CRLH LWA prototype, dielectric material substrates and thin-film ferroelectric capacitors were manufactured, and their characteristics were investigated. Double-sided metalized fluoroplast-4 reinforced with fiberglass with a permittivity of 2.5 was used as a substrate for CRLH LWA prototyping. A solid solution of barium strontium titanate (Ba x Sr 1 − x TiO 3 ) with a composition of x = 0.3 was used as a ferroelectric material in electrically tunable capacitors. The characteristics of the manufactured ferroelectric thin-film capacitors were measured at a frequency of 1 GHz using the resonance method. The capacitors have a tunability of about two and a quality factor of about 50. The antenna prototype consists of ten units with a total length of 1.25 wavelengths at the operating frequency of close to 2.4 GHz. The experimental results demonstrate that the main beam can be shifted within the range of −40 to 16 degrees and has a gain of up to 3.2 dB. The simple design, low cost, and excellent wide-angle scanning make the proposed CRLH LWA viable in wireless communication systems. [ABSTRACT FROM AUTHOR]

Background and Objectives: In this paper, a closed-form mathematical formula has been presented using of the proposed periodic structure E-field distribution, that helps designers to calculate the width of the slots in Quasi Non-Uniform Leaky Wave Antenna (QNULWA). Method: This method is based on two steps. In the first step, some important parameters for the proposed antenna design will be extracted using simulation. In the second step, by solving a discrete differential equation, a general relation will be obtained for these types of antennas. This method has been investigated in the case of slot LWA families. Results: A Leaky wave antenna has been synthesized in the 15.5-18 GHz frequency range for Gaussian radiation pattern. The results of simulation and antenna design will be very close to each other in 2.5 GHz Bandwidth (15.5 - 18 GHz), which shows the accuracy of this formula. Also, By changing the frequency range 2-5 GHz, the main lobe direction of the antenna will scan the space approximately 10 degrees (from 63 to 73 degree). The antenna has an SLL value of about -25 dB and 13 dB Gain at whole band 15.5-18 GHz. Conclusion: The obtained formula helps the antenna designers to calculate the dimensions this type of antenna for any pattern distribution. [ABSTRACT FROM AUTHOR]

In the pioneering work, the radiation diagrams of leaky wave antenna arrays can achieve attenuation nulls and gains at specific angles by manually placing the zeros and the poles in the Z domain of the corresponding discrete linear time‐invariant (LTI) system. This handcrafted design procedure does not allow radiation diagrams with wide beams since the interaction between poles involved in the wide beam and their corresponding leaky modes cannot be easily handled. To overcome this limitation, this paper describes a novel method for designing radiation diagrams of leaky‐wave antenna arrays based on the theory of IIR discrete filters. The proposed method relies on the design of discrete filters with the prototypes of analog low‐pass filters defined by Butterworth and Chebyshev type I polynomials, whose roots along with the bilinear transformation provide the location of the poles and the zeros of the discrete LTI system and, therefore, the parameters of the leaky‐wave antenna array. Results with different designs and a comparison with other approaches show the utility and effectiveness of this novel method to design wide‐beam leaky‐wave antenna arrays. [ABSTRACT FROM AUTHOR]

Major constraint in leaky wave antenna (LWA) is open stop band. In this paper study of different techniques used by researchers to remove the open stop band problem has been done. Different characteristics of leaky wave antenna with the design of substrate integrated waveguide is also discussed. This paper explain theory and design of the unit cell and array of leaky wav antenna in different frequency range i.e. X-band, Kuband and higher frequency range. Study of various techniques to achieve high beam scanning and higher gain has been done. [ABSTRACT FROM AUTHOR]

Two-dimensional leaky-wave antennas (LWAs) are a class of planar, traveling-wave radiators with attractive features of a low profile, ease of feeding, frequency reconfigurability of the radiation pattern, and polarization agility. Their use in conjunction with array feeders has been the subject of various investigations in recent decades, thanks to the additional degrees of freedom provided by the presence of multiple independent sources. Here, we provide a review of some of the most recent and promising array-fed two-dimensional (2-D) LWAs, selecting a couple of the most significant structures in application, namely Fabry–Perot cavity antennas and bull’s-eye antennas, and discussing some of their recently proposed advanced features.

The emerging field of topological photonics has extended our capability to control and manipulate electromagnetic waves. Thus far, however, research has focused on realizing defect-immune waveguides for on-chip communication. Making similar advancement for antennas, which are an integral component and crucial to the performance of wireless devices, could lead to a parallel impact on wireless communication. In particular, the requirement for impedance matching that is fundamental to current antenna technology constitutes a major limitation to transmitting and receiving free-space signals in terms of bandwidth and power efficiency. Here, we show how reciprocal photonic topological insulator (PTI) metasurfaces can be designed to enable a unique radiation mechanism needless of impedance matching. This relies on the fact that counter-propagating spin states are decoupled from each other; hence, this self-matching characteristic spans the entire bandwidth of the PTI's bandgap. Specifically, we present two strategies for out-coupling spin-polarized edge modes: (1) in the form of an end-fire antenna at the abrupt termination of the PTI with free space and (2) in the form of a leaky-wave antenna by engineering the dispersion of the edge mode to lie above the light line. In the first approach, we compare our results to conventional rectangular waveguide apertures and planar Vivaldi antennas, which either have a large profile or flared ends to obtain gradual impedance matching. In the second approach, we demonstrate how our structure can emit orbital angular momentum (OAM) beams with various orbital charge numbers by simply varying the length of the PTI interface when made into a circular loop. The reduced device area and complexity due to removing the need for any matching network and the ability to easily multiplex OAMs of any charge, in addition to the wideband and high efficiency performance, make the proposed topological antennas highly attractive for many applications. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

With the change in lifestyles, emerging stress and physical parameters of the environment, health-related issues have affected many people worldwide. An important indicator of serious illness is the abnormality in respiration rate. This abnormality leads to asthma, obstructive sleep apnea (OSA) and heart-related diseases. This leads to having more accurate and robust healthcare monitoring and diagnosis facilities. The respiration rate and vital signs are detected through electromagnetic (EM) waves using different antennas. Different types of previous antennas (parabolic, horn, yagi-uda, helical and patch) used for respiration monitoring are studied and compared with the proposed antenna. The limitations of currently used antennas include the bulky size of setup and less directional beam, which may interfere with other devices leading to errors. Substrate integrated waveguide (SIW)-based leaky-wave antenna (LWA) is proposed with better results than current antennas available for respiration monitoring. Experimental work is carried out for the validation of simulated results. The proposed antenna has a gain of 9.72 dB with angular width or approximately HPBW 37.5°. The simulated s11 of the antenna is −16 dB, and the measured s11 is −22.97 dB. VSWR shows antenna radiation efficiency is approx 97%. An experimental setup using VNA is used to detect respiration monitoring in real-time; the system could detect the respiratory activity of the subject with a confidence interval accuracy of 93% and an average error of 7%. [ABSTRACT FROM AUTHOR]

This paper presents a multi-layered composite right-left-handed (CRLH) slow-wave substrate integrated waveguide (SW-SIW) circularly polarized (CP) leaky-wave antenna (LWA) having wide impedance bandwidth (measured: 14.6–18.25 GHz). The CRLH unit cell consists of three radiating slots on top metallic layer, arranged in a crown-shaped fashion, to achieve wideband circular polarization.The bottom ground plane of the standard SIW is connected to the SW structure of the LWA that consists of internal metalized blind vias. Due to the SW effect, a 33% reduction in lateral dimension is achieved, compared to a conventional SIW having the same cut-off frequency. At the same time, the phase velocity is also reduced leading to a reduction in longitudinal dimensions. The dimensions of the antenna are relatively small, with a size of 3.2 × 0.4x.07 λ3. The operating mechanism of the LWA having symmetrical and continuous backward-to-forward scanning range from −64 ° to 64 ° (128 °) is explained by an equivalent circuit model. The measured CP bandwidth (14.6–18.43 GHz) of the LWA completely overlaps the 10-dB return loss bandwidth. The compact dimension, wide symmetric beam scanning, completely overlapped CP, and return loss bandwidths are the major advantages of the proposed antenna.The LWA exhibits stable gain with a peak value of 11.3 dBic (gain variation: from 9.7 to 11.3 dB). The radiation efficiency of the LWA is above 85% within the impedance bandwidth. [ABSTRACT FROM AUTHOR]

The article focuses on terahertz beamforming antennas for various applications. Topics discussed include a proposed pixelated liquid crystal electrically controlled terahertz (THz) metasurface with a crossbar structure and its potential for high-resolution beam steering, active beam deflection, and applications in pencil beamforming, high-speed information processing, and optical computing.

In this work, a comb‐line leaky‐wave antenna with a pair of wide stubs is proposed with enhanced gain and reduced cross‐polarization. To ensure broadside scanning, three sections of transmission lines are used in the stub with the longitudinal offset. The stubs are placed half‐wavelength apart on both sides of the delay line to achieve high gain and a low‐cross polarization level. The antenna provides 46.8% impedance bandwidth with |S11| below −10 dB. The maximum measured gain and total efficiency are 18.5 dBi and 85%, respectively. The optimized broadside frequency of the leaky‐wave antenna is 10.2 GHz. [ABSTRACT FROM AUTHOR]

A high-gain, low-profile, and compact-size single-port leaky-wave antenna powered by spoof surface plasmon polaritons (SSPPs) based line is proposed. The proposed leaky-wave antenna is implemented using a variable-width strip dipole on either side of the spoof surface plasmon polaritons line. The designed antenna consists of a coplanar waveguide (CPW), a transition section, and a strip dipole-loaded SSPPs line. To validate the simulation results, a prototype of the single-port leaky-wave antenna is fabricated and measured. The simulation and measured results are in unison. The designed antenna covers the frequency range of 6.18 - 11.40 GHz. The single-port antenna provides the beam-scanning span of 55 ∘ (- 32 ∘ to + 23 ∘) with a significant gain in the broadside direction. The average realized gain in the scanning range is 11.05 dBi, while the peak realized gain and radiation efficiency are 13.8 dBi and 95%, respectively. The designed antenna is intended to be used as a low-profile antenna for radar and wireless communications. [ABSTRACT FROM AUTHOR]

Controlling objects with body language is an extremely interesting ability for human beings. Recognizing different gestures is an effective way to collect valuable information, which is used to switch the radiation characteristic of beam scanning antennas. However, most existing beam scanning antennas are wire-connected and manually controlled by users. Thereby, a novel framework of gesture-controlled antennas is proposed in this paper. Rather than DC voltages supplied by powers or AC voltages supplied by signal generators, the beam scanning antenna can be effectively controlled by different gesture commands collected in real time from the user. On this basis, considering the advantages of the low cost and wide frequency band of liquid crystal (LC) materials, a LC-based fixed-frequency beam scanning leaky wave antenna (LWA) with gesture-controlled systems is demonstrated as one example. Different gestures can be recognised as controlled information to supply corresponding output signals by field programmable gate arrays (FPGAs) for the LC-based LWA. Based on the proposed framework, a verification system is tested, which demonstrates that the radiation characteristic can be effectively controlled by the user's gesture. This work supplies a novel way for intelligent beam scanning antennas with potential applications in the internet of things (IoT), satellite and 5 G/6 G communications. [ABSTRACT FROM AUTHOR]

Acoustic imaging in water traditionally relies on phased arrays of active electro-acoustic transducers to steer acoustic energy in specific directions. One potential alternative approach to steer acoustic beams is to use a single transducer attached to a dispersive antenna that radiates or receives acoustic energy from different directions as the frequency of operation changes. This is known as a leaky wave antenna (LWA). While LWAs have been proven effective in beam steering for electromagnetic and air-borne acoustic waves, the design of an analog device in water presents a unique challenge due to the low contrast in acoustic impedance between elastic solids and water, which necessitates the consideration of fluid-elastic coupling in the design of the elastic LWA. This work presents an approach to design an elastic metamaterial waveguide coupled to an external fluid domain as one means to create an acoustic LWA for underwater operation. Forward-to-backward radiation is achieved through the design of mass-in-cavity structures that produce simultaneous negative effective mass and modulus by considering fluid-elastic coupling. The design is presented through finite element analysis of individual unit cells and a water-loaded elastic LWA. A design example is presented that steers through backfire to endfire as a function of input frequency. [ABSTRACT FROM AUTHOR]

Recently, the community has seen a rise in interest and development regarding holographic antennas. The planar hologram is made of subwavelength metal patches printed on a grounded dielectric board, constituting flat metasurfaces. When a known reference wave is launched, the hologram produces a pencil beam towards a prescribed direction. Most earlier works on such antennas have considered only a single beam. For the few later ones that studied multiple beams, they were achieved either by having each beam taken care of by a distinct frequency or by partitioning the hologram, thereby depriving each beam of the directivity it could have had it not shared the holographic aperture with other beams. There have been recent studies related to the use of tensor surface impedance concepts for the synthesis of holograms which have attained control over the polarizations and intensities of the beams. However, this approach is complicated, tedious, and time-consuming. In this paper, we present a method for designing a planar holographic leaky-wave multi-beam metasurface antenna, of which each simultaneous beam radiating at the same frequency towards any designated direction has a tailorable amplitude, phase, and polarization, all without hologram partitioning. Most importantly, this antenna is exempted from the need for the cumbersome technique of tensor impedance. Such features of beam configurability are useful in selective multiple-target applications that require differential gain and polarization control among the various beams. Only a single source is needed, which is another benefit. In addition, effective methods to mitigate sidelobes are also proposed here. Designs by simulations according to the method are herein validated with measurements performed on fabricated prototypes.

This document is a guest editorial from the journal "Electronics Letters" that discusses the importance of wideband/multiband millimeter-wave antennas for 5G/6G and radar applications. It highlights the increasing demand for higher data rates and system capacity in wireless systems. The editorial presents 16 research papers accepted for publication in a special issue, covering topics such as millimeter-wave antennas for 5G/6G and radar applications, microwave antennas for 5G/6G and radar applications, measurement methods for millimeter-wave antennas, and decoupling methods and other millimeter-wave components. The papers explore innovative designs and technologies to meet the requirements of these applications. The authors of the papers are researchers and professors from various universities and research institutions. [Extracted from the article]

This paper presents a novel periodic grounded coplanar waveguide (GCPW) leaky-wave antenna implemented in an Indium Phosphide (InP) process. The antenna is designed to operate in the 220 GHz–325 GHz frequency range, with the goal of integrating it with an InP uni-traveling-carrier photodiode to realize a wireless transmitter module. Future wireless communication systems must deliver a high data rate to multiple users in different locations. Therefore, wireless transmitters need to have a broadband nature, high gain, and beam-steering capability. Leaky-wave antennas offer a simple and cost-effective way to achieve beam-steering by sweeping frequency in the THz range. In this paper, the first periodic GCPW leaky-wave antenna in the 220 GHz–325 GHz frequency range is demonstrated. The antenna design is based on a novel GCPW leaky-wave unit cell (UC) that incorporates mirrored L-slots in the lateral ground planes. These mirrored L-slots effectively mitigate the open stopband phenomenon of a periodic leaky-wave antenna. The leakage rate, phase constant, and Bloch impedance of the novel GCPW leaky-wave UC are analyzed using Floquet's theory. After optimizing the UC, a periodic GCPW leaky-wave antenna is constructed by cascading 16 UCs. Electromagnetic simulation results of the leaky-wave antenna are compared with an ideal model derived from a single UC. The two design approaches show excellent agreement in terms of their reflection coefficient and beam-steering range. Therefore, the ideal model presented in this paper demonstrates, for the first time, a rapid method for developing periodic leaky-wave antennas. To validate the simulation results, probe-based antenna measurements are conducted, showing close agreement in terms of the reflection coefficient, peak antenna gain, beam-steering angle, and far-field radiation patterns. The periodic GCPW leaky-wave antenna presented in this paper exhibits a high gain of up to 13.5 dBi and a wide beam-steering range from − 60 ° to 35 ° over the 220 GHz–325 GHz frequency range. [ABSTRACT FROM AUTHOR]

The emergence of new technological needs in 5 G/6 G networking and broadband satellite internet access amplifies the demand for innovative wireless communication hardware, including high-performance low-profile transceivers. In this context, antennas based on metasurfaces – artificial surfaces engineered to manipulate electromagnetic waves at will – represent highly promising solutions. In this article, we introduce leaky-wave metasurface antennas operating at micro/millimeter-wave frequencies that are designed using the principles of quasi-bound states in the continuum, exploiting judiciously tailored spatial symmetries that enable fully customized radiation. Specifically, we unveil additional degrees of control over leaky-wave radiation by demonstrating pointwise control of the amplitude, phase and polarization state of the metasurface aperture fields by carefully breaking relevant symmetries with tailored perturbations. We design and experimentally demonstrate metasurface antenna prototypes showcasing a variety of functionalities advancing capabilities in wireless communications, including single-input multi-output and multi-input multi-output near-field focusing, as well as far-field beam shaping. Leak-wave metasurface antennas tailor non-local resonances leveraging judiciously broken spatial symmetries in their design to generate arbitrarily shaped near-field and far-field patterns. [ABSTRACT FROM AUTHOR]

Beam-switching is one of the paramount focuses of 28 GHz millimeter-wave 5G devices. In this paper, a one-dimensional (1D) pattern reconfigurable leaky-wave antenna (LWA) was investigated and developed for wireless terminals. In order to provide a cost-effective solution, a uniform half-width LWA was used. The 1D beam-switching LWA was designed using three feed points at three different positions; by selecting the feeds, the direction of the beam can be switched. The antenna can switch the beam in three different directions along the antenna axis, such as backward, broadside, and forward. The 1D beam-switching antenna was fabricated, and because of the wide beamwidth, the measured radiation patterns can fill 128 ∘ of space (3 dB coverage), from θ = −64 ∘ to +64 ∘ at ϕ = 0 ∘ . Following this, two of these antennas were placed at right angles to each other to achieve two-directional (2D) beam switching. The 2D beam-switching antenna pair was also prototyped and tested after integrating them into the ground plane of a wireless device. The antenna is able to point the beam in five different directions; moreover, its beam covers 167 ∘ (θ = −89 ∘ to +78 ∘ ) at ϕ = 0 ∘ , and 154 ∘ (θ = −72 ∘ to +82 ∘ ) at ϕ = 90 ∘ . [ABSTRACT FROM AUTHOR]

Conformal antennas have been widely used in many fields due to their advantages of low air resistance and better visual appearance. In this paper, an arced conformal leaky-wave antenna (LWA) for a designable directional beam is proposed. The antenna is achieved based on a substrate-integrated waveguide (SIW). On the upper surface, a series of non-uniform transverse slots are etched. In order to guide the design of the antenna, as another key contribution of this work, a theoretical model for the traveling-wave structure is established. Using the model, the radiation property of the LWA is analyzed. In addition, by inputting the desired beam direction, the structural parameters of the LWA can be generated through the model. To verify the performance of the antenna and the model, an LWA prototype working at 28 GHz was fabricated and tested in a microwave anechoic chamber. The experimental results are in good agreement with the simulation results. The antenna achieved a gain of 9.96 dBi with cambered surface area of 1.89 λ02. The proposed method may be a promising candidate for conformal wireless communication applications. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]