A Wideband Millimeter-wave Tunable Filter based on Periodic Square Spiral Structure and Liquid Crystal Material

In this paper, a novel wideband band-pass center frequency tunable filter is proposed based on liquid crystals for applications at millimeter-waves, which uses a micro-strip periodical structure with loading square spiral resonators. The tunable range of the proposed filter is about 1.59 GHz while the external bias voltage of the liquid crystal turns from 0V to 30V. The filter center frequency ranges from 39.08 GHz to 40.67 GHz. And the insertion loss of filter is about 3.9dB. The proposed filter has many advantages, such as continuously electrically tunability, miniaturization, low tuning voltage, etc. Therefore, a great potential of such a filter has been shown for use in the next communication system.