Bias Tees Integrated Liquid Crystals Inverted Microstrip Phase Shifter for Phased Array Feeds

Microwave phase shifters based on tunable dielectrics such as nematic liquid crystals (NLC) have attracted considerable research attention in the last two decades. To electronically drive the permittivity variations based on the NLC's molecular anisotropy, conventional device configuration is based on externally wiring three-port bias tees as diplexers for frequency-domain multiplexing, i.e. isolating the RF port from the low-frequency high-amplitude bias field. The multi-stage bulky solution significantly impedes its applicability for phased array feeds. To the best of the author's knowledge, limited research has attempted the integration of compact bias tees into the phase shifter. To this end, this work demonstrates a bias-tees-embedded standalone phase shifter integrated on a double-sided RO4003 substrate using advanced fabrication and assembly techniques (photolithography, surface mounting, reflow soldering). The measured differential phase shift reports 391.75 degrees at 10 GHz with the insertion loss up to -5.66 dB (including bias tees) for an optimised design. A figure-of-merit of 69 degrees/dB is achieved, which even outperforms recent advances in NLC-based planar phase shifters without bias tees.