VO2 switch based submillimeter-wave phase shifters

Abstract

A monolithic 3-bit phase shifter has been fabricated and demonstrates broadband and low loss performance from 220 GHz to 240 GHz. The phase shifter utilizes an ultra-low loss vanadium dioxide switch for phase state control. The design uses a low-pass π-filter networks as phase shift elements for 45, 90 and 180 degree bits. This phase shifter's mean insertion loss of 7.6 dB is 3dB lower than any other passive phase shifter we could identify in literature and comparable to the best active vector-sum devices. The RMS phase error is a competitive 6.8 degrees at 230GHz and averages only 8 dB over the band from 220 to 240 GHz. This phase shifter's complete circuit footprint is < 0.1mm2 easily fitting within (λ/2)2 ∼ 0.4 mm2 array spacing. A second topology was also demonstrated that consists of a one-port transmission line reflection phase shifter (TLPS) using a variable length, short-circuit terminated synthetic transmission line. This device demonstrates an average insertion loss of 5.2 dB and RMS phase error of 30 degrees. We can find no passive phase shifter with comparable performance or compactness to either of the devices presented here.