Towards Performant Nematic Liquid Crystal Enabled Tunable Band-stop Filters with Reconfigurable Notch at 60 GHz for beyond-5G Applications: A Comprehensive Design Study

This paper presents the design, analysis, and optimisation of a continuously tunable millimetre-wave (mmW) band-stop filter by harnessing the voltage-dependent permittivity of nematic liquid crystals (LCs). The proposed filter employs an inverted microstrip line (IMSL) topology to house the LC material, enabling electronic reconfiguration of the filter's centre frequency through a low-voltage (<10 V), low-frequency (<1 kHz) bias. This approach overcomes the inherent limitation of discrete tuning in conventional switch-based methods. Through full-wave electromagnetic simulation and systematic geometry parameterisation, we demonstrate a continuous notch-frequency tuning range of 5.8 GHz departing from 60 GHz. The design achieves a high rejection level (>39 dB) and a quality factor (Q) of up to 1.83. Furthermore, this work provides, for the first time, a constitutive loss quantification of the power-dissipation mechanisms in an LC-based tunable filter, offering critical insight into the trade-offs between insertion loss and geometry. The results establish a foundational framework for developing agile, low-power, and fully planar tunable components essential for next-generation mmW communication systems, such as beyond-5G (B5G) and WiGig.