Novel Hybrid Electric/Magnetic Bias Concept for Tunable Liquid Crystal Based Filter

Abstract

This paper presents a novel hybrid bias concept for liquid crystal (LC) filter by using simultaneously electric and magnetic bias fields. It enables continuous tuning with a simplified electrode design, decreased number of electrodes and reduced bias voltage. Furthermore, the tuning efficiency is increased, since the homogeneous bias fields enable a full exploitation of the LC's anisotropy. To demonstrate this concept, a novel reconfigurable gap waveguide two-pole bandpass filter with tunable center frequency and coupling elements is designed at 30 GHz. Liquid crystal technology is applied as tunable material, whereby tunability of the center frequency and coupling elements is obtained by controlling the LC's effective permittivity. The presented filter's center frequency can be tuned from 28.88 GHz to 29.88 GHz with a maximum bias voltage of 100 V, with a return loss of 20 dB and low insertion loss of only 1.65 to 1.95 dB.INDEX TERMS K-band, liquid crystals, microwave filter, millimeter wave communication, tunable circuits and devices.

Liquid Crystal-Filled 60 GHz Coaxially Structured Phase Shifter Design and Simulation with Enhanced Figure of Merit by Novel Permittivity-Dependent Impedance Matching

“…However, for the proof-of-concept standalone device physics characterization stage of LC-based low-power-consuming (e.g., bias voltage up to 20 V [11,24,41]) transmission lines (instead of the power-consuming waveguides [43][44][45][46][47]), the LF-mmW decoupling network is not necessarily needed for the modern generation of vector network analyzers (VNA), wherein a port bias is normally embedded in the VNA for the input of an amplified LF bias signal limited up to 30 V. As such, the complicated decoupling network is not encompassed within our computational modeling frameworks in this work. Nevertheless, for follow-up developments of a real-world phased array feeding system, suitable connector mounting and LF-mmW decoupling network implementation (e.g., by embedding bias tees [48][49][50], introducing additional biasing networks [51][52][53][54], or relying on novel structural mechanisms [55,56]) should be conducted as per the application specifications to address the limitations of the current work's analytical and numerical evaluations. More specifically, the perturbations in the achievable differential phase shift, return loss, and insertion loss due to the addition of the decoupling network (e.g., bias tees as depicted in Figure 2) will be experimentally quantified as ongoing optimization endeavors.…”

Development of non-conventional microwave devices based on substrate-integrated technology for advanced applications

“…When a magnetic field is applied, the phase of the resonators is altered, resulting in a change in the resonance frequency of the filter. The same principle was combined with pin diodes in [61] to enhance the reconfiguration range of the device, further extending its tunability capabilities.…”

“…The inverted microstrip has proved to be very convenient for liquid crystal applications due to its planar geometry, although other guiding technologies also show promise. For instance, in [61], small volumes of liquid crystal were included in the centre of rectangular resonators implemented on a groove gap waveguide, resulting in a tunable filter design.…”