Reconfigurable Groove Gap Microwave Filter Based on Liquid Crystal Technology with One Transmission Zero

This paper presents a fully reconfigurable third-order microwave filter based on liquid crystal technology. A hybrid bias concept is used to simultaneously apply external magnetic and electric fields to change the orientation of the liquid crystal molecules, thereby changing the permittivity. Additional detuned resonators are used to adjust the inter-resonator coupling and the external quality factor and therefore maintain a constant bandwidth over the center frequency tuning range. To create a steeper passband slope, a singlet cavity with the TE301 mode is used to create a transmission zero near the passband while maintaining an inline configuration. This paper presents, for the first time, a tunable liquid crystal bandpass filter with a transmission zero.