Differentially Fed Dual-Circularly Polarized Antenna With Slow Wave Delay Lines

Abstract

A differentially fed dual-circularly polarized (CP) antenna using slow wave delay lines (SWDLs) is investigated in this communication. The antenna consists of two pairs of dipoles, one of which is fed by slow wave feedlines and the other is fed by coplanar striplines (CPSs). Based on the slow wave effect, a 90° phase difference can be realized between the two pairs of dipoles. To achieve dual-CP operation, two orthogonally placed differentially fed baluns are used to drive the feedlines. Subsequently, four parasitic loops are introduced, aiming to obtain high isolation over a wide operation band. Meanwhile, a metal reflector is loaded for unidirectional radiation. Finally, a prototype of the proposed antenna is fabricated and tested. The measurements indicate that the dual-CP antenna realized a port isolation of 38.4% (1.43–2.11 GHz) for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{\mathrm {dd21}}\vert &lt; -15$ </tex-math></inline-formula> dB. Further, the measured −10 dB reflection coefficient bandwidth for the two ports is 1.36–2.40 GHz. Moreover, the dual-CP 3 dB axial ratio (AR) bandwidth is approximately 50.0% from 1.41 to 2.35 GHz. Owing to differential excitation, stable radiation patterns are obtained.