Varactor-Based Phase Shifters Operating in Differential Pairs for Beam-Steerable Antennas

Abstract

A concept of varactor-based phase shifter operating in differential pair for beam-steerable antennas is presented in this article. The basic phase-tuning unit consists of a microstrip transmission line and several shorted-stub-terminated varactors loaded on its edge. A pair of these phase-tuning units working in differential mode can achieve a full 360° phase shift, which allows a low loss and simple structure. An accurate equivalent circuit model for this phase shifter is developed for fast calculation allowing the design and optimization of the structure with a genetic algorithm (GA). A pair of phase-tuning units, each including three stub-loaded varactors, is identified as a practical solution to produce a continuously tunable phase difference nearly covering 0°–360°, with two symmetrical 11°-wide blind zones and a maximum insertion loss of 2.04 dB. A 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times4$ </tex-math></inline-formula> beam-steerable dielectric resonator antenna (DRA) array is then designed, fabricated, and tested to demonstrate the practicality of the proposed phase shifter. The measured results illustrate that the array is able to continuously scan from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 45^\circ $ </tex-math></inline-formula> to 45°, with a tunable operating frequency band from 4.75 to 5.25 GHz. All these findings suggest that the proposed phase shifter concept is promising and practical to realize beam-scanning antennas.