Amar Al-Bassam

Circular Polarization of Periodic Leaky-Wave Antennas With Axial Asymmetry: Theoretical Proof and Experimental Demonstration

This paper includes two contributions. First, it proves that the series and shunt radiation components, corresponding to longitudinal and transversal electric fields, respectively, are always in phase quadrature in axially asymmetric periodic leaky-wave antennas (LWAs), so that these antennas are inherently elliptically polarized. This fact is theoretically proven and experimentally illustrated by two case-study examples, a composite right/left-handed (CRLH) LWA and a series-fed patch (SFP) LWA. Second, it shows (for the case of the SFP LWA) that the axial ratio is controlled and minimized by the degree of axial asymmetry.

Radiation Efficiency of Longitudinally Symmetric and Asymmetric Periodic Leaky-Wave Antennas

This letter derives efficiency formulas and establishes fundamental limitations for longitudinally symmetric periodic leaky-wave antennas (LWAs). The proposed approach is based on an equivalent transmission-line model for periodic structures, which is derived from a lattice topology providing a perfect decoupling between the series and shunt immittances and their respective radiation contributions. A central result of this letter is that a 2-D array composed of uniformly excited 1-D LWAs cannot exceed a radiation efficiency of 50%. The presented theory is validated by comparing measured and finite-difference time-domain (FDTD) simulated radiation efficiencies with the ones predicted by the lattice model for several symmetrical and asymmetrical series-fed patch (SFP) array antenna and composite right/left-handed (CRLH) antenna configurations.

Vortex beam generation using circular leaky-wave antenna

Vortex beams, which are electromagnetic beams carrying orbital angular momentum, have a great potential for communication, sensing, imaging and tweezing applications. Unfortunately, the spatial light modulator technology that is used in the optical regime to generate vortex beams is not applicable at radio frequencies and the recently introduced metasurface technology suffers from integration difficulty. To solve these issues, we introduce here the concept of generating vortex beams using a circular leaky-wave antenna (CLWA). In this approach, the spiral-shaped phase fronts of the vortex wave are produced by the interference of circularly twisted phase fronts due to off-broadside radiation in the unfolded antenna, while the beam is obtained from the restricted circular aperture of the CLWA. The paper explains the principle in details and provides an experimental demonstration for the case of unit topological charges. The antenna may support simultaneously different orbital angular momenta so as to provide an unprecedented multiplexing technology.

Transversal Asymmetry in Periodic Leaky-Wave Antennas for Bloch Impedance and Radiation Efficiency Equalization Through Broadside

This paper demonstrates that unit cell asymmetry with respect to the transversal axis -or transversal asymmetry- is an essential design parameter in periodic leaky-wave antennas (P-LWAs). Specifically, it shows that transversal asymmetry can be leveraged to fully and systematically solve the well-known radiation degradation of P-LWAs at broadside, where it provides both open-stopband closure and efficiency equalization. The problem is addressed via a generic equivalent circuit model composed of a series resonator, a shunt resonator and ideal transformers for modeling asymmetry by a single and simple parameter, namely the transformation ratio. Once the series and shunt frequencies have been balanced (frequency-balancing), equalization is ensured by adjusting the degree of asymmetry in the unit cell so to match the at-broadside Bloch impedance to the off-broadside Bloch impedance. This equalization condition is referred to as quality factor balancing ( Q-balancing) and it is related to the Heaviside condition (distortionless propagation) in homogeneous transmission lines. Based on this theory, optimization schemes for employing commercial fullwave eigenmode and drivenmode solvers are proposed to design unit cells with equalized efficiencies. Finally, two examples of P-LWAs are presented, a composite right/left-handed (CRLH) P-LWA and a series-fed coupled patch (SFCP) P-LWA, and verified to fully confirm the predictions of the theory obtained by circuit modeling.

A 60 GHz circularly polarized antenna array for line-of-sight train-to-train communication

In this paper, an antenna module for an ultra-low latency system for line-of-sight train-to-train communication is presented. This module consists of a high-directivity 60 GHz circularly-polarized antenna array, which consists of slot-fed truncated-corner patch antennas. Furthermore, it employs a microstrip-to-stripline via transition and Balun to provide balanced line to be integrated to mm-wave transceiver chip on the RF-frontend. Additionally, a radome has also been designed to protect the antenna against the open environment, since it will be integrated at the mechanical coupler of a train. Finally, measurement results of the antenna module with the radome will be provided, which shows relatively low sidelobe level and 5.1 GHz axial ratio (AR) bandwidth.

Broadside Dual-Channel Orthogonal-Polarization Radiation Using a Double-Asymmetric Periodic Leaky-Wave Antenna

This paper demonstrates that double unit-cell asymmetry in periodic leaky-wave antennas (P-LWAs), i.e., asymmetry with respect to both the longitudinal and transversal axes of the structure—longitudinal asymmetry (LA) and transversal asymmetry (TA)—allows for the simultaneous broadside radiation of two orthogonal modes excited at the two ports of the antenna. This means that the antenna may simultaneously support two orthogonal channels, which represents interesting polarization diversity characteristics for wireless communications. The double asymmetric (DA) unit cell combines a circularly polarized LA unit cell and a coupled mode TA unit cell, where the former provides equal radiation in the series and shunt modes while the latter separates these two modes in terms of their excitation ports. It is also shown that the degree of TA in the DA unit cell controls the cross-polarization discrimination level. The DA P-LWA concept is illustrated by two examples, a series-fed line-connected patch (SF-LCP) P-LWA and a series-fed capacitively coupled patch (SF-CCP) P-LWA, via full-wave simulation and also experiment for the SF-LCP P-LWA case.

Dual-channel radiation using a single double-asymmetric periodic leaky-wave antenna

This paper presents a periodic leaky-wave antenna (P-LWA) that is capable of simultaneously radiating two orthogonal polarizations, i.e. of supporting two independent information channels, using a single antenna structure excited at both ends. The development of this P-LWA is based on previous work that identified fundamental relationships between the longitudinal or transversal asymmetries of the periodic unit cell and the radiation properties of the P-LWA. The proposed P-LWA is a double-asymmetric unit-cell structure that combines the properties of single longitudinal and single transverse asymmetric structures to exhibit the aforementioned unique property. It is demonstrated in the particular design of a series-fed patch (SFP) P-LWA.