Tunable second-order bandpass filter based on dual ENZ waveguide

A novel tunable filter based on ENZ waveguide technology is presented and discussed. This kind of filter utilizes the possibility of independent tuning of two types of resonances that occur in ENZ waveguides using short slot cuts in the ENZ channels. By forming a dual-channel configuration, a second-order bandpass filter can be obtained using zero-order-resonance (ZOR) from one channel and Fabry-Perot (FP) resonance from the other one (whose frequency is slightly different from ZOR). Both resonances can be simultaneously and equally tuned by changing the respective slots' lengths. The maximum observed passband shift is 900 MHz or 8.3%. During filter tuning, 3 dB-bandwidth varies between 330 MHz (3.4%) and 470 MHz (4.4%) as the length of the tuning slots decreases. Maximum insertion loss observed is 1.8 dB.