Tunable microwave bandpass filter based on liquid crystal-periodic loaded lines

Jing-Hua Ran^1*, Yuh-Chyi Chang¹, Tien-Lun Ting¹, Tsung-Hsien Lin¹

¹Department of Photonics, National Sun Yat-Sen University, Kaohsiung, Taiwan

* Presenter:Jing-Hua Ran, email:jruan5762@gmail.com

This paper presents a compact, low-voltage tunable microwave bandpass filter that integrates liquid crystal (LC) materials with a periodic loaded line (PLL) structure. The filter, utilizing the voltage-dependent dielectric anisotropy of LC, achieves dynamic frequency tuning from 6.57 GHz to 7.70 GHz. With a 4 μm LC cell gap, the design reduces driving voltage while providing a tuning range of 1.13 GHz (16.1%), an average bandwidth of 0.82 GHz, and low insertion loss (3–5 dB). This architecture is promising for reconfigurable RF modules and adaptive systems.

Keywords: microwave, tunable filter, liquid crystal