Search Results (24)

Multi-Beam frequency scanning leaky-wave antennas (FBS-LWAs) offer a viable solution for hardware miniaturization in direction-of-arrival (DOA) estimation systems. However, the presence of multiple spatial harmonics results in responses in multiple directions for a given incident source, introducing estimation ambiguity and significantly challenging accurate DOA estimation. Moreover, due to the nonlinear frequency response of the FBS-LWA, its response matrix does not satisfy the Vandermonde structure, which renders common rank-recovery techniques ineffective for processing coherent signals. As a result, the DOA estimation of coherent sources using multi-beam FBS-LWAs remains an open and challenging problem. To address this issue, this paper proposes a novel DOA estimation method for coherent signals based on multi-beam frequency scanning leaky-wave antennas. First, the received signals are transformed into the frequency domain via fast Fourier transform (FFT) to construct the signal data matrix from which the covariance matrix is computed.Then, conventional beamforming (CBF) is employed to obtain an initial estimate of the angle set, which will be further refined by a smaller grid to form a candidate angle set. Finally, a maximum likelihood algorithm based on the stochastic principle (Sto-ML) is used to suppress the interference of the parasitic directions and select the final DOA estimates from the candidate angle set. Simulation results show that the proposed method effectively mitigates the impact of parasitic directions and achieves an accurate DOA estimation of multiple coherent sources, even under both low and medium-to-high signal-to-noise ratio (SNR) conditions. Full article

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. Full article

A period-reconfigurable leaky-wave antenna (LWA) with circular polarization (CP) and fixed-frequency beam scanning (FFBS) is developed in this article. Operating in the Ka-band, this antenna consists of a low-loss groove gap waveguide (GGW) as the slow-wave transmission structure, a circular split-ring patch array on the top layer for radiation, and a slotted ground between them for energy coupling. Each slot is independently and electrically controlled by a pair of PIN diodes under the coupling slot. Thus, the period length of the patches can be manipulated and an LWA with CP and FFBS is achieved with −1th spatial harmonics radiated. The simulation results show that the bean-scanning range from 61° to 63° can be realized during the observation frequency band, with good circular polarization and a peak gain of 17.1 dBi, which is verified by the measurement. Full article

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. Full article

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. Full article

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. Full article

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${}^{\circ }$ of space (3 dB coverage), from $\theta$ = −64${}^{\circ }$ to +64${}^{\circ }$ at $\varphi$ = 0${}^{\circ }$. 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${}^{\circ }$ ($\theta$ = −89${}^{\circ }$ to +78${}^{\circ }$) at $\varphi$ = 0${}^{\circ }$, and 154${}^{\circ }$ ($\theta$ = −72${}^{\circ }$ to +82${}^{\circ }$) at $\varphi$ = 90${}^{\circ }$. Full article

In order to properly cover different scenarios, radiation patterns of antennas should be accordingly designed. However, most antennas are unable to provide either broadside beams or designable conical beams, which are the typically used radiation patterns for radio coverage, based on one single-structure format through adjusting parameters before fabrication. In this paper, a planar circular polarized (CP) annular leaky-wave antenna (LWA) is proposed, which is realized on an annular substrate-integrated waveguide (SIW). A broadside beam or a conical beam could be easily obtained through fabricating the LWA with different structural parameters. The operating frequency is 5.75 GHz. The LWA allows only the −1st spatial harmonic to radiate, while the fundamental wave and other spatial harmonics are suppressed in slow wave mode. In order to validate the design effectiveness, two examples for broadside beam and conical beam radiation are fabricated and measured. The measurement results show good agreement with the simulation results. The broadside beam LWA shows a gain of 9.75 dBic and the conical beam LWA with a beam angle of 13° has a gain of 7.93 dBic. The proposed LWA presents promising radiation performance and is a good candidate for wireless communication applications. Full article

A fixed-frequency beam-scanning leaky-wave antenna (LWA) array with three switchable dual-polarized beams is proposed and experimentally demonstrated. The proposed LWA array consists of three groups of spoof surface plasmon polaritons (SPPs) LWAs with different modulation period lengths and a control circuit. Each group of SPPs LWAs can independently control the beam steering at a fixed frequency by loading varactor diodes. The proposed antenna can be configured in both multi-beam mode and single-beam mode, where the multi-beam mode with optional two or three dual-polarized beams. The beam width can be flexibly adjusted from narrow to wide by switching between multi-beam and single-beam states. The prototype of the proposed LWA array is fabricated and measured, and both simulation and experimental results show that the antenna can accomplish a fixed frequency beam scanning at an operating frequency of 3.3 to 3.8 GHz with a maximum scanning range of about 35° in multi-beam mode and about 55° in single-beam mode. It could be a promising candidate for application in the space–air–ground integrated network scenario in satellite communication and future 6G communication systems. Full article

A multi-layer beam-scanning leaky wave antenna (LWA) for remote vital sign monitoring (RVSM) at 60 GHz using a single-tone continuous-wave (CW) Doppler radar has been developed in a typical dynamic environment. The antenna’s components are: a partially reflecting surface (PRS), high-impedance surfaces (HISs), and a plain dielectric slab. A dipole antenna works as a source together with these elements to produce a gain of 24 dBi, a frequency beam scanning range of $30°$, and precise remote vital sign monitoring (RVSM) up to 4 m across the operating frequency range (58–66 GHz). The antenna requirements for the DR are summarised in a typical dynamic scenario where a patient is to have continuous monitoring remotely, while sleeping. During the continuous health monitoring process, the patient has the freedom to move up to one meter away from the fixed sensor position.The proposed multi-layer LWA system was placed at a distance of 2 m and 4 m from the test subject to confirm the suitability of the developed antenna for dynamic RVSM applications. A proper setting of the operating frequency range (58 to 66 GHz) enabled the detection of both heart beats and respiration rates of the subject within a $30°$ angular range. Full article

This paper proposes a new design of leaky wave antenna (LWA) based on substrate integrated waveguide (SIW) technology for THz applications. The suggested LWA structure has a combination of longitudinal and transverse slots and makes a 10-element linear array of radiating elements. To address the problem of open-stop-band (OSB), four additional smaller slots were etched on the corners of longitudinal and transversal slots. At the broadside, this LWA provided a gain of 12.33 dBi, and a continuous wide beam scanning range from +78° to −6° via the broadside while exhibiting efficient radiation performance over the operating frequency bands of 105 GHz to 109 GHz with a peak gain of 16.02 dBi. Full article

A novel substrate integrated waveguide (SIW) adopting a leaky-wave antenna (LWA) for continuous beam scanning for tri bands is presented. For continuous beam scanning (CBS), optimization of different parameters associated with the unit cell has been carried out. Apart from this, optimal impedance matching is also obtained with the help of the characteristic impedance of the waveguide. The proposed SIW LWA scans from −58° to + 59° along with 14.50 dBi gain when the frequency changes from 10 GHz to 18.22 GHz and provides a scanning rate of 14.23. The beauty of the suggested antenna is its smaller size and high gain, along with a wider scanning range (117°) capability. This antenna’s final prototype has been fabricated, and the measurement results are matched with the simulation results. Full article

This paper presents a 2D multibeam antenna (2D-MBA) for two-dimensional scanning of space with fully passive elements using the substrate integrated waveguide (SIW) leaky-wave antenna (LWA) and Rotman lens for telecommunication applications. An LWA structure with 19 slot elements based on SIW in the frequency range of 14.5–22.5 GHz was designed to scan theta angles from −60 to +35 degrees, and a wideband Rotman lens was designed with five inputs, five outputs, and eight dummy ports to scan phi angles from −30 to +30 degrees. Finally, for two-dimensional space scanning, a five-element SIW LWA array was combined with a Rotman lens, and the whole structure was simulated and implemented in full-wave CST software. By optimizing the structure, the return losses of the input ports were below −10 dB, and the maximum measured gain was 20.3 dBi. Full article

This paper presents a new layered dielectric leaky-wave antenna (LWA) for the sub-terahertz (THz) frequency range capable of efficient operation at the broadside with a wide beam scanning angle and stable gain. It consists of a conductor-backed alumina dielectric image line (DIL) with two different dielectric layers mounted on top of each other for performance improvement. The upper layer is a high permittivity RO6010 substrate to enhance the directivity as a superstrate and the lower layer is a low-permittivity RT/duroid 5880 substrate stacked on the alumina DIL to prevent the probable excitation of higher-order modes in the DIL channel. A 15-element linear array of radiating overlapped discs is used to mitigate the open stop-band (OSB) problem, fed by the mentioned waveguide, was designed and simulated at frequencies around 170 GHz. The dominant mode of the layered dielectric waveguide is perturbed by the infinite space harmonics generated by two sets of overlapped discs periodically sandwiched between the layers. It exhibited a relatively wide impedance bandwidth of 28.19% (157.5–206 GHz). Its radiation mechanism has been widely studied through simulations. The results revealed that the antenna provides a wide scanning capability through the broadside from −23° to 38°, covering the frequency range between 157.5 GHz and 201.5 GHz. For an array with 15 radiating elements, the simulated peak gain in the band is 15 dBi and the broadside gain is 13.6 dBi at 172 GHz. Full article

Microwave radar sensors have been developed for non-contact monitoring of the health condition and location of targets, which will cause minimal discomfort and eliminate sanitation issues, especially in a pandemic situation. To this end, several radar sensor architectures and algorithms have been proposed to detect multiple targets at different locations. Traditionally, beamforming techniques incorporating phase shifters or mechanical rotors are utilized, which is relatively complex and costly. On the other hand, metamaterial (MTM) leaky wave antennas (LWAs) have a unique property of launching waves of different spectral components in different directions. This feature can be utilized to detect multiple targets at different locations to obtain their healthcare and location information accurately, without complex structure and high cost. To this end, this paper reviews the recent development of MTM LWA-based radar sensor architectures for vital sign detection and location tracking. The experimental results demonstrate the effectiveness of MTM vital sign radar compared with different radar sensor architectures. Full article