Reconfigurable Leaky-wave Antenna Research Articles

Beam-Switching Antennas for 5G Millimeter-Wave Wireless Terminals.

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∘.

A Linearly and Circularly Polarization-Reconfigurable Leaky Wave Antenna Based on SSPPs-HSIW

In this manuscript, a reconfigurable leaky wave antenna is proposed with linearly polarized and circularly polarized properties, which is composed of two layers with feeding waveguide and radiation elements. The bottom layer is a half-mode substrate integrated waveguide etched with a spoof surface plasmon polaritons structure as a high-dispersion feeding waveguide to excite 8 circular patches as radiation elements in the top layer. In a unit element, the horizontal linear polarization (HLP) and right-hand circular polarization (RHCP) radiation are switched using a p-i-n diode crossing a slot of a circular metal patch. HLP performance is achieved as the p-i-n diode is switched off, and RHCP is achieved as the p-i-n diode is switched on. The measured results verify the design theory and the simulated results. Over the working band of 10.4~12.8 GHz, the proposed antenna can radiate scanning beams covering about a 73° region, including the broadside direction with HLP and RHCP.

Reconfigurable leaky wave antenna with low sidelobe based on spoof surface plasmon polariton

A low sidelobe leaky wave antenna (LWA) based on Spoof Surface Plasmon Polariton (SSPP) with switchable right/left-handed circular polarization (CP) and linear polarization (LP) radiation function by controlling the status of two PIN diodes is proposed. Two symmetrical SSPP transmission lines (TLs) are connected through two PIN diodes, and the ON–OFF of diodes constitute three different transmission modes. Two rows of the tapered arranged elliptical patches are loaded periodically around the TL to break the original stable transmission structure for radiation, and suppress the antenna sidelobe levels to less than −10 dB. After experimental verification, the reconfigurable antenna can reach three functionalities: (1) Mode 1: 22°right-handed CP beam scanning from 8.3 to 9.0 GHz; (2) Mode 2: 22°left-handed CP beam scanning from 8.3 to 9.0 GHz; (3) Mode 3: 78°LP beam scanning from 8.3 to 10.3 GHz. In Mode 1 and 2, the axial ratios (ARs) are lower than 3 dB, and the average gain can reach 11.6 dBi, while 13.4 dBi in Mode 3. A leaky wave antenna that can switch the radiation function of linear/circular polarization with favorable performance characteristics, such as wide scanning range, high gain, low sidelobe levels, and high efficiency, makes it an ideal candidate for wireless communication.

A Review of Reconfigurable Leaky-Wave Antennas

A comprehensive survey of the reconfigurable leaky-wave antennas (LWAs) is made in this paper. Beam-steering and unique radiating features of LWA are highlighted particularly. Therefore, the radiation mechanism of different types of LWA, including uniform, quasi-uniform, periodic, and metamaterial LWAs are discussed in detail. The guiding structures for realizing LWAs, namely microstrip, waveguide, substrate integrated waveguide (SIW), and half-mode SIW (HMSIW) are investigated as well. Basic concepts of electronic beam-scanning LWAs are also introduced, and several state-of-the-art reconfigurable LWAs are studied thoroughly. The investigated reconfigurable LWAs are suitable for beam-scanning applications due to their compactness, ease of implementation, reasonably high gain, and relatively wide beam-scanning range, as will be demonstrated through this comprehensive review.

Polarization-Reconfigurable Leaky-Wave Antenna With Continuous Beam Scanning Through Broadside

A simple single-layer reconfigurable leaky-wave antenna (LWA) is presented that has polarization agility and beam-scanning functionality. This LWA system realizes a scanned beam that can be switched between all of its linear polarization (LP) and circular polarization (CP) states using only one dc biasing source. A slot-loaded substrate-integrated waveguide (SIW)-based LWA is first explored to attain CP performance with continuous beam scanning through broadside. This CP LWA realizes a measured CP performance with a 3 dB gain variance within 2.75–3.35 GHz for scan angles ranging from −28.6° to +31.5°. A row of shorted stubs is then incorporated into the CP LWA to obtain similar LP performance. Finally, by introducing p-i-n diodes into this LP LWA configuration to facilitate reconfigurable connections between the main patch and the shorted stubs, the radiated fields can be switched between all of its CP and LP states. The measured results of all three antennas confirm their simulated performance. It is demonstrated that the main beam of the polarization-reconfigurable LWA can be scanned from −31.5° to +17.1° with gain variations between 9.5 and 12.8 dBic in its CP state and from −34.3° to +20° with them between 7.8 and 11.7 dBi in its LP state.

On the Use of the $Z$ Transform of LTI Systems for the Synthesis of Steered Beams and Nulls in the Radiation Pattern of Leaky-Wave Antenna Arrays

This paper addresses the use of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$Z$</tex-math></inline-formula> transform to synthesize radiation patterns with prescribed nulls from a phased array of electronically reconfigurable leaky-wave antennas (LWAs). This approach provides the relationship between such antennas and linear and time invariant (LTI) systems. Using this signal processing perspective, the proper locations of the poles and zeros of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$Z$</tex-math></inline-formula> transform of the associated LTI system provide a radiation pattern with prescribed specifications (mainly main lobes’ directions and surrounding radiation nulls). Then, these poles and zeros’ positions can be transformed into particular values of the LWA array control coefficients. The effectiveness of the proposed technique is demonstrated with the synthesis of various radiation patterns, with application to reconfigurable smart antennas. A comparison with more conventional uniform linear array architecture is also performed to evaluate the synthesis flexibility and system complexity of the proposed approach.

Radiation Pattern-Reconfigurable Leaky-Wave Antenna for Fixed-Frequency Beam Steering Based on Substrate-Integrated Waveguide

A novel reconfigurable leaky-wave antenna (LWA) with fixed-frequency beam-steering property is presented. The proposed antenna is designed on a substrate-integrated waveguide (SIW) whose effective width can be electronically changed. There are two rows of vias designed on each side of the SIW, and the vias in the outer rows are directly connected to the ground plane and top wall of the waveguide, but the vias in the inner rows are connected to the ground plane and top wall through p-i-n diodes that work as binary switches. By setting the states of the switches in a coding way, the effective width of the SIW can be changed numerically. Then, the propagation constant and the beam direction of the LWA can be altered accordingly. A prototype of the proposed antenna is fabricated and measured to verify the design procedures. The measured results show that the main beam direction can be steered from 46° to 68° in a step of 7° at the operating frequency of 5.2 GHz, which confirms the effectiveness and practicability of this design.

DoA Estimation Using Compact CRLH Leaky-Wave Antennas: Novel Algorithms and Measured Performance

Traditional direction-of-arrival (DoA) estimation algorithms for multielement antenna arrays (AAs) are not directly applicable to reconfigurable antennas due to inherent design and operating differences between AAs and reconfigurable antennas. In this paper, we propose novel modifications to the existing DoA algorithms and show how these can be adapted for real-time DoA estimation using two-port composite right/ left-handed (CRLH) reconfigurable leaky-wave antennas (LWAs). First, we propose a single/two-port multiple signal classification (MUSIC) algorithm and derive the corresponding steering vector for reconfigurable LWAs. We also present a power pattern cross correlation algorithm that is based on finding the maximum correlation between the measured radiation patterns and the received powers. For all algorithms, we show how to simultaneously use both ports of the two-port LWA in order to improve the DoA estimation accuracy and, at the same time, reduce the scanning time for the arriving signals. Moreover, we formulate the Cramer–Rao bound for MUSIC-based DoA estimation with LWAs and present an extensive performance evaluation of MUSIC algorithm based on numerical simulations. In addition, these results are compared to DoA estimation with conventional AAs. Finally, we experimentally evaluate the performance of the proposed algorithms in an indoor multipath wireless environment with both line-of-sight (LoS) and non-LoS components. Our results demonstrate that DoA estimation of the received signal can be successfully performed using the two-port CRLH-LWA, even in the presence of severe multipath.

Experimental Results of Novel DoA Estimation Algorithms for Compact Reconfigurable Antennas

Reconfigurable antenna systems have gained much attention for potential use in the next generation wireless systems. However, conventional direction-of-arrival (DoA) estimation algorithms for antenna arrays cannot be used directly in reconfigurable antennas due to different design of the antennas. In this paper, we present an adjacent pattern power ratio (APPR) algorithm for two-port composite right/left-handed (CRLH) reconfigurable leaky-wave antennas (LWAs). Additionally, we compare the performances of the APPR algorithm and LWA-based MUSIC algorithms. We study how the computational complexity and the performance of the algorithms depend on number of selected radiation patterns. In addition, we evaluate the performance of the APPR and MUSIC algorithms with numerical simulations as well as with real world indoor measurements having both line-of-sight and non-line-of-sight components. Our performance evaluations show that the DoA estimates are in a considerably good agreement with the real DoAs, especially with the APPR algorithm. In summary, the APPR and MUSIC algorithms for DoA estimation along with the planar and compact LWA layout can be a valuable solution to enhance the performance of the wireless communication in the next generation systems.

Reconfigurable Leaky-Wave Antenna Based on Periodic Water Grating

A reconfigurable leaky-wave antenna using periodic water grating on the top of a grounded glass slab is presented in this letter. A probe-fed unidirectional surface-wave launcher is designed to feed the antenna. Two prototypes of the proposed antenna are fabricated and tested to demonstrate its radiation performance and tuning capability. Measured results of the first static antenna show that a maximum gain of 16 dB, a wide impedance bandwidth (|S11|<;-10 dB) from 4.1 to 6.6 GHz (46.7%), and a large beam-scanning range over the impedance band from the back-fire to nearly broadside direction are obtained. Measured results of the second dynamic antenna show that the beam-pointing angle can be tuned from -32° to 18 ° at 5.5 GHz, while the return loss maintains better than 10 dB.

Electronically Steerable 1-D Fabry-Perot Leaky-Wave Antenna Employing a Tunable High Impedance Surface

A novel fixed-frequency electronically-steerable one-dimensional (1-D) leaky-wave antenna is presented. The antenna is based on a parallel-plate waveguide loaded with a planar partially reflective surface and a tunable high impedance surface (HIS), which creates a 1-D Fabry-Perot leaky-waveguide. The tunable HIS consists of printed patches loaded with varactor diodes that allow the electronic tuning of the cavity resonance condition. Using a simple Transverse Equivalent Network, it is theoretically shown how the variation of the varactors' junction capacitance allows the scanning of the antenna pointing angle from broadside towards the endfire direction at a fixed frequency. Experimental results of an antenna prototype operating at 5.6 GHz are reported, demonstrating that the new reconfigurable leaky-wave antenna can provide electronic beam scanning in an angular range from 9 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}$</tex></formula> to 30 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$^{\circ}$</tex></formula>

Microwave MEMS devices designed for process robustness and operational reliability

This paper presents an overview on novel microwave micro-electromechanical systems (MEMS) device concepts developed in our research group during the last 5 years, which are specifically designed for addressing some fundamental problems for reliable device operation and robustness to process parameter variation. In contrast to conventional solutions, the presented device concepts are targeted at eliminating their respective failure modes rather than reducing or controlling them. Novel concepts of MEMS phase shifters, tunable microwave surfaces, reconfigurable leaky-wave antennas, multi-stable switches, and tunable capacitors are presented, featuring the following innovative design elements: dielectric-less actuators to overcome dielectric charging; reversing active/passive functions in MEMS switch actuators to improve recovery from contact stiction; symmetrical anti-parallel metallization for full stress-control and temperature compensation of composite dielectric/metal layers for free-standing structures; monocrystalline silicon as structural material for superior mechanical performance; and eliminating thin metallic bridges for high–power handling. This paper summarizes the design, fabrication, and measurement of devices featuring these concepts, enhanced by new characterization data, and discusses them in the context of the conventional MEMS device design.

Low-Loss Ku-Band Artificial Transmission Line With MEMS Tuning Capability

An artificial transmission line unit cell is presented based on the so-called composite right/left handed transmission line. It is implemented on a microelectromechanical system process on glass, and is suitable for applications such as reconfigurable leaky-wave antennas and series feed networks. The device presents state-of-the-art performance in terms of differential phase shift over losses (38deg/dB at 14 GHz) and quasi-zero drive power consumption. It is monolithic and has a total footprint of 4 mm2.

Performance Improvement of a Wideband MIMO System by Using Two-Port RLWA

In this letter, we demonstrate the performance achievable with a highly reconfigurable leaky-wave antenna (RLWA) when used as a building block of a wideband multiple-input-multiple-output (MIMO) communication system. The antenna design consists of a periodic structure, composed of cascaded composite right/left-hand (CRLH) microstrip unit cells with tunable electrical characteristics, that is capable of steering its radiation beam over a wide angular range. Field measurements collected in an indoor environment employing an array of dipoles at the transmitter and the RLWA and an array of dipoles at the receiver are used to measure the RLWA achievable gains. We show that the proposed antenna is capable of providing significant gains, with respect to a traditional array of dipoles, while reducing the space occupied by the antenna on the communication device.

Pattern reconfigurable leaky-wave antenna design by FDTD method and Floquet's Theorem

A pattern reconfigurable millimeter-wave coplanar waveguide leaky-wave antenna is designed by using the finite-difference time-domain (FDTD) method combined with Floquet's theorem and the simple linear interpolation technique. The concept of equivalent period is presented for mixed-periodic structures. The novel design process results in a reduction in the design time compared with that of the traditional FDTD method.

A Novel Reconfiguration CPW Leaky-Wave Antenna for Millimeter-Wave Application

A novel reconfigurable millimeter-wave leaky-wave antenna is proposed according to the radiation characteristics of periodically loaded coplanar waveguide and simulated by the finite-difference time-domain method. The simulated results demonstrate that the single main beam of this antenna operating at 35.0GHz can scan with small steps in the E-plane from −90° to 90° except the angle around 0°. The main beam scanning is obtained by the antenna structure reconfiguration with nine discrete states controlled by embedded switches and two feed ports. The antenna is useful for millimeter-wave applications.