Electrically tunable liquid crystal phase shifter with excellent phase shift capability per wavelength based on opposed coplanar waveguide

Abstract

A tunable liquid crystal phase shifter based on opposed coplanar waveguide (OCPW) with excellent phase shift capability per wavelength is proposed. The proposed OCPW not only has good transmission characteristics and a quasi-TEM operating mode similar to the CPW, but also avoids the metalized via and complicated bias circuit in designing the phase shifter. Consequently, the phase shifter is easy to fabricate and miniaturize. The main structure of the phase shifter includes two functional components. One is the transition section, in which the flaring grounds and gradient stubs are utilized to realize the impedance and wave-number matching to the OCPW phase shift part; the other is a tunable phase shift section, which is composed of the OCPW centerline and ground with staggered periodic stubs stretching out. To realize tunable phase shifting by applying different DC bias voltages, a DC bias network capable of blocking RF signal is elaborately designed. An equivalent circuit model of the phase shift part is established and represented using the ABCD matrix, so that the relation between the related parameters and the phase shift per wavelength can be easily obtained to guide the design. The measurement results demonstrate that the proposed phase shifter achieves a total of 300° phase shifting, as high as 289°/λ0 phase shift per wavelength, and a good figure-of-merit of 59°/dB at 14.5 GHz. The phase shifter features the reflection coefficient less than −10 dB and the transmission coefficient bigger than −6 dB from 9.3 to 15 GHz.