Electrically controlled tunable bandpass filter based on inner-rotary complementary split-ring resonator

A tunable bandpass filter is developed by utilizing the electrically controlled liquid crystal material. It consists of a half-mode substrate integrated waveguide (HMSIW) with liquid crystal material embedded into the substrate and a modified complementary split-ring resonator (CSRR). The modified CSRR is constituted by a conventional CSRR and two inner-rotary-shape slots. Compared with the conventional CSRR of same size, operation frequency of the proposed inner-rotary CSRR (IRCSRR) can operate at much lower frequency, which is conducive to the realization of circuitry miniaturization. In addition, owing to the load of the metal strip embedded in the substrate, the biasing voltage can be impressed to the liquid crystal more effectively. Numerical results show that by tuning the biasing voltage differently, center frequency of the proposed filter can be shifted from 0.86 GHz to 0.99 GHz, with an insertion loss in passband of 1.71 dB, a return loss better than 15 dB, and stopband suppression better than 40 dB.