Conventional Leaky-wave Antenna Research Articles

Frequency dependent parametric radiation through a nonlinear fundamentally slow travelling wave structure

AbstractThis article presents a nonlinear leaky wave antenna (LWA) with frequency dependent parametric radiation based on a fundamentally slow‐wave transmission line (TL) structure. Unlike a conventional LWA that radiates at the excitation frequency, the radiation for the proposed travelling wave structure relies on the parametric frequencies based on the injected pump signals. The proposed nonlinear fundamentally slow wave structure utilizes a periodic sharply bend TL loaded by varactor diodes as nonlinear elements. By utilizing the n = −1 spatial harmonic, the fundamentally slow wave structure can enter the leaky wave region at higher frequencies, where the parametric radiation results from the bifurcation of the injected pump signals. Such TL‐based nonlinear LWA reduces the design complexity and fabrication difficulty. The resulting parametric frequency radiation can be used for beam steering, which provides additional degree of design freedom.

Low-Dispersive Leaky-Wave Antennas for mmWave Point-to-Point High-Throughput Communications

In this article, we present two efficient leaky-wave antennas (LWAs) with stable radiation pattern, operating at 60 GHz. Both antennas exhibit attractive properties such as significantly reduced beam-squint, low loss, low sidelobes, high directivity, and simple manufacturing. The beam-squint of conventional LWAs is reduced by refracting the leaked waves in a dispersive lens and the low sidelobe levels are achieved by tapering the leakage rate along the aperture. Since the antennas are implemented in groove gap waveguide technology, the losses are low. The two antennas are different in terms of their asymmetric/symmetric leakage tapering with respect to the broadside direction. Both designs are optimized for low sidelobes, but since symmetry is enforced in one, the resulting performance in terms of sidelobes is suboptimal. However, in the symmetric design, multiple stable beams can be obtained, simultaneously or independently. Twenty percent bandwidth is obtained with less than ±0.5° beam-squint. In this frequency range, the gain is stable at 17 and 15 dBi for the asymmetric and symmetric designs, respectively. The designs are intended for point-to-point links in mmWave communication networks where low losses, directive beams, and low sidelobes are expected to be key features.

An Open Cavity Leaky-Wave Antenna With Vertical-Polarization Endfire Radiation

This communication presents an all-metal high-gain vertical polarization (VP) leaky-wave antenna (LWA) with exact endfire radiation. The antenna is composed of ten periodic-arranged open cavity elements coupling fed by double-sided parallel-strip lines (DSPSLs). Different from the conventional LWA with frequency-scanning performance, the endfire beam of the proposed antenna is fixed due to the nondispersion property of the air-filled TEM LWA. Moreover, the array characteristic of the proposed TEM LWA is investigated to suppress the unwanted grating lobe with a suitable period. In order to validate the performance of the proposed antenna, a prototype was fabricated and tested. Because of the mutual coupling between every radiation element, the electric field distribution along the array is uniform, contributing to a high endfire gain of 13.6 dBi within a short array length of 2.9λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . Furthermore, the extension ability is validated to achieve a higher endfire gain when expanding the array length. Consequently, the proposed LWA is a good candidate for the planar high-gain VP endfire antenna.

Single-Beam Leaky-Wave Antenna With Lateral Continuous Scanning Functionality Based on Spoof Surface Plasmon Transmission Line

A continuous beam scanning leaky-wave antenna (LWA) supporting lateral radiation is proposed in this paper. It is based on a spoof surface plasmon (SSP) transmission line (TL) which is a single-layer conductor structure. The proposed SSP TL is slotted periodically with rectangular holes on the metallic strip conductor. Circular patches are loaded periodically along one side of the SSP TL to achieve an additional momentum for converting the slow-wave mode to a fast-wave mode and then modulate the SSP wave into a spatial wave. The proposed SSP LWA produces a single lateral beam rather than double beams usually existed in conventional SSP LWAs, as highly desired in many applications. As operating frequencies increase from 7 to 15 GHz, the proposed SSP LWA achieves a continuous beam scanning range of 65° from forward to backward with stable high gains. As its primary advantage, this proposed SSP LWA does not lose radiation efficiency even at broadside, which is often suffered by conventional LWAs. Both the transmission characteristics of the SSP TL and the radiation mechanism of the SSP LWA are investigated. Finally, the proposed SSP LWA is designed, fabricated, and measured. The measured results agree well with the simulated ones over a wide operating frequency range, which validates its good performances. The proposed SSP LWAs provide a low-cost solution to planarly integrated communication systems.

Reconfigurability Mechanisms With Scanning Rate Control for Omega-Bianisotropic Huygens’ Metasurface Leaky-Wave Antennas

In this paper, different reconfigurability mechanisms are proposed to scan the pointing direction at a fixed frequency of recently-proposed leaky-wave antennas based on omega-bianisotropic Huygens' metasurfaces. The tunability of both the waveguide height and the dielectric permittivity of the substrate filling the waveguide are studied, extracting theoretical expressions to predict the dependence of the beam pointing direction with the design parameters. It is shown that it is possible to control the scanning rate, a challenging task for conventional leaky-wave antennas, leading to different performances: high scanning, radiation pattern stability and backward-to-forward scanning. Additionally, the control of the scanning rate is exploited to reduce the beam squinting when varying the frequency. Simulation results of several designs with both impedance sheets and physical realization to implement the metasurfaces demonstrate the validity of the theoretical predictions and the reconfigurability potential of such a structure.

Wide-Angle Beam Scanning Leaky-Wave Antenna Using Spoof Surface Plasmon Polaritons Structure

This paper proposes a wide-angle beam scanning leaky-wave antenna (LWA) fed by a novel spoof surface plasmon polaritons (SSPP) transmission line (TL). In the proposed LWA, circular metallic patches are periodically loaded on both sides of the SSPP TL alternately, and convert guided waves into radiating waves. The transmission characteristics of the proposed SSPP TL are analyzed, and the transmission characteristics and radiation patterns of the proposed LWA are simulated and measured. The simulated and measured results show that the proposed LWA provides approximately 12.5 dBi of radiation gain within a frequency range of 8–24 GHz, and a beam scanning range of 90° from forward to backward continuously by increasing the feeding frequency. The proposed LWA, based on a novel SSPP TL, has advantages of single-layer conductor, continuous wide-angle beam scanning, and high gain especially at the broadside direction, which are difficult realize using conventional LWAs.

A 5 GHz narrow‐beam leaky‐wave antenna using binomially distributed slot based substrate integrated waveguide

AbstractThis article presents a planar substrate integrated waveguide based leaky wave antenna (LWA) with narrow beamwidth, high directivity, and low side lobe levels (SLL). Through first‐time use of binomially distributed slots, a significant decrease in SLL along with a small form factor is achieved. Designed on a Rogers 5880 substrate, the proposed design occupies 250 × 45 mm2 exhibiting a beamwidth of 11.3° and sidelobe level less than −10 dB at 5.6 GHz. In comparison with conventional LWA with uniform slots, a 63% size reduction is also achieved.

Low-Dispersive Leaky-Wave Antenna Integrated in Groove Gap Waveguide Technology

In this paper, the use of a dispersive prism with a triangular shape is proposed to reduce the dispersive radiation nature of a leaky-wave antenna (LWA) in groove-gap waveguide technology. The operation of gap waveguide technology is based on the use of metallic pins that act as an artificial magnetic conductor, so the electromagnetic fields are confined and guided in the desired directions. To control a leaky-wave radiation of these confined fields is possible by tailoring the height of the pins, its periodicity, and the waveguide width. This radiation, as in any conventional LWA, is dispersive, leading to beam squint as the frequency is varied. Here, we mitigate this beam squint by using a prism made of dispersive pins and choosing appropriately their periodicity and height. With this prism, the leaky-wave radiation is focused into one single direction in a wide frequency band. This concept is demonstrated with a prototype designed to radiate at $\varphi =41^\circ $ with a central frequency of 12 GHz and the high gain of 16.5 dBi. A 22% frequency bandwidth for the 3 dB realized gain at $\varphi =41^\circ $ is achieved, and the main radiating direction, with half-power beamwidth of 5°, steers only ±0.5° from 11.4 to 13.4 GHz.

A Miniaturized Reconfigurable CRLH Leaky-Wave Antenna Using Complementary Split-Ring Resonators

Composite Right-/Left-Handed (CRLH) Leaky-Wave Antennas (LWAs) are a class of radiating elements characterized by an electronically steerable radiation pattern. The design is comprised of a cascade of CRLH unit cells populated with varactor diodes. By varying the voltage across the varactor diodes, the antenna can steer its directional beam from broadside to backward and forward end-fire directions. In this paper, we discuss the design and experimental analysis of a miniaturized CRLH Leaky-Wave Antenna for the 2.4 GHz WiFi band. The miniaturization is achieved by etching Complementary Split-Ring Resonator (CSRR) underneath each CRLH unit cell. As opposed to the conventional LWA designs, we take advantage of a LWA layout that does not require thin interdigital capacitors; thus we significantly reduce the PCB manufacturing constraints required to achieve size reduction. The experimental results were compared with a nonminiaturized prototype in order to evaluate the differences in impedance and radiation characteristics. The proposed antenna is a significant achievement because it will enable CRLH LWAs to be a viable technology not only for wireless access points, but also potentially for mobile devices.

Tapered composite right/left-handed leaky-wave antenna for wideband broadside radiation

A leaky-wave antenna (LWA) based on tapered composite right/left-handed unit cell sections is proposed for wideband broadside radiation. The substrate-integrated-waveguide metamaterial based antenna consists of three sections with varying slot lengths for unit cells. The measured broadside gain of the proposed tapered antenna prototype is higher than 9.0 dBi over a bandwidth of 4.7% (8.825–9.250 GHz). The bandwidth of the proposed tapered LWA for 1-dB gain variation doubles that of the conventional LWA with non-tapered unit cells. In addition, the proposed antenna is able to scan the beam from −72° to +75° over a frequency range of 8.0–13.0 GHz with the gain greater than 9.0 dBi. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:624–629, 2015

A Compact Wideband Leaky-Wave Antenna With Etched Slot Elements and Tapered Structure

A compact wideband leaky-wave antenna (LWA) with etched slot elements and tapered structure is studied. The proposed antenna is composed of an asymmetric-fed multi-section tapered short leaky-wave antenna with two embedded slots and a ground plane with etched slot elements. Base on the concept of LWA, the asymmetric-fed is utilized to excite the first higher order mode. By etching slot elements on the ground plane, the current distribution of this antenna can be influenced to compact the width of conventional LWA. In order to achieve the impedance matching, this multi-section tapered short leaky-wave antenna is embedded with two rectangular slots. This technique not only improves the impedance matching but also suppresses the back lobe. According to the measured results, the impedance bandwidth achieves about 1.30 GHz for 7-dB return loss, which covers the range from 3.30 to 4.60 GHz, and the scanning angle of the measured main beam is about 36°, which covers the range from 17° to 53°. This short LWA is only about 1.14 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> at 3.4 GHz, and the back lobe can be suppressed by 7.5 dB at 4.3 GHz. Due to the etched slot elements on the ground plane, the frequency of the radiation angle is shifted to lower frequency by 750 MHz, which can compact the width of LWA by more than 20%.

Numerical Simulations of Backward-to-Forward Leaky-Wave Antenna with Composite Right/Left-Handed Coplanar Waveguide

A composite right / left-handed (CRLH) coplanar waveguide (CPW) structure and its leaky-wave antenna (LWA) with continuous backward-to-forward scanning applications are proposed. The structure of the CRLH transmission line (TL) is composed of split-ring resonators (SRRs) for left-handed (LH) series capacitance and short-circuited stubs connected between the CPW central signal line and the ground for LH shunt inductance, while the unavoidable right-handed (RH) parasitic effects series inductance and shunt capacitance are generated by wave propagation through the host transmission line. The dispersion relations are calculated and compared with the equivalent circuit model method and 3D full-wave simulations, which can be used to determine the physical dimensions of the CRLH-CPW, such as in the balanced CRLH-TL case. As a main example, a CRLH-CPW-LWA operating from 1.67 GHz to 1.80 GHz with the dispersion characteristics of the balanced CRLH-TL case shows continuous leakage frequency band (fast wave region) from LH (phase constant β < 0, 1.67 < f < 1.74 GHz) to BH (β > 0, 1.74 < f < 1.80 GHz) state through the transition frequency point (β = 0, f = 1.74 GHz), whereas conventional LWAs operated in RH state only provide forward scanning capabilities (β > 0).

Resonant type leaky-wave antenna using image NRDguide

A novel leaky-wave antenna constructed from an image non-radiating dielectric waveguide (INRDG) is presented. Unlike conventional leaky-wave antennas, the broadside radiation is realised by utilising the resonant characteristic of the leaky INRDG waveguide mode. Experimental results measured at Ku band confirm the effective performance of the antenna.