Compact Interference Based Microstrip Single-Pole Double-Throw Utilizing Liquid Crystal Phase Shifter

Abstract

This paper presents an interference based single-pole double-throw (SPDT) in microstrip line topology utilizing microwave liquid crystal (LC). The SPDT consists of a power divider, DC blocks, high performance LC based phase shifters and a 3 dB quadrature branch-line coupler. It is fabricated on two glass substrates in order to include a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$20 \boldsymbol{\mu} \mathbf{m}$</tex> LC layer, using standard photo lithography. The phase shifter takes the advantage of high performance LC GT7-29001, which has high anisotropy and low dissipation factor as well as defected ground structure (DGS), which decreases the dimension and insertion loss (IL). Bias is applied through high impedance lines onto the LC phase shifters. The SPDT works from 26 GHz to 30 GHz where return loss> 15 dB. When switched on, the SPDT has de-embedded IL< 4.5 dB and high isolation> 28 dB in the band. 5V DC bias voltage can enable switching on and off within 2.6 s. The proposed SPDT is promising in analog beam forming networks and high power switching cases. Compared to the previous LC based SPDT, the proposed design show significant improvements in dimensions, switching speed, IL and fabrication complexity.