Frequency and Transmission Zeros Tunable Filter with Constant Bandwidth

Based on the double-folded 1/4 mode substrate integrated waveguide (DFQMSIW) resonator, a two-order parallel cascade DFQMSIW filter is designed in this paper. The center frequency can be adjusted in the range of 1.1GHz-1.89GHz. The range of transmission zeros at the central frequency of 1.1GHz, 1.5GHz, 1.79GHz is 1.59GHz-1.72GHz, 1.96GHz-2.07GHz, 2.21GHz-2.33GHz, respectively. The absolute bandwidth is kept about 300MHz, the return loss is less than -15dB and the insertion loss is 0.13dB-0.39dB.