Abstract-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.Index Terms-Bloch-Floquet theorem, circular polarization (CP), composite right/left-handed (CRLH) transmission line structures, leaky-wave antenna (LWA), periodic structure, phase quadrature, series-fed patch (SFP).
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 offbroadside 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.
Abstract-The 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 -or 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 an 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 seriesfed capacitively-coupled patch (SF-CCP) P-LWA, via full-wave simulation and also experiment for the SF-LCP P-LWA case.
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