Tunable Ka-band waveguide resonators and a small band band-pass filter based on liquid crystals

In this paper we present the design of Liquid Crystal filled waveguide resonators. Waveguide resonators achieve higher Q-factors then planar technologies, and form the basis for filters of smaller bandwidth. Two possible approaches for positioning the Liquid Crystal inside the cavity are discussed. One of this approaches is designed to fulfill the requirements for mechanical and temperature stability for space applications. Measured Q-factors and tuning ranges for both variants are presented, including the verification of electric biasing. Additionally a 3-pole bandpass filter operating at a center frequency of 20 GHz and a relative bandwidth of 1% was constructed and measured. Tunability with magnetic biasing was verified to be greater than 450 MHz.