Novel Topology and Design for Wideband Bandpass Filter With Frequency- and Attenuation-Reconfigurable In-Band Notch

A novel topology and the design method are proposed for a wideband bandpass filter (BPF) with frequency- and attenuation-reconfigurable in-band notch by engineering the complex frequencies of transmission zeros. The proposed topology consists of a fifth-order wideband BPF and two coupled notch resonators. With the two coupled notch resonators, a pair of complex in-band transmission zeros are formed. By controlling the frequency difference between the two notch resonators, a frequency- and attenuation-reconfigurable notch can be obtained in the passband of the wideband BPF. A matrix analysis method is presented to characterize the frequency- and attenuation-tunable in-band notch precisely. The relationship between complex transmission zeros and in-band attenuation is also investigated. To demonstrate the proposed techniques, a prototype using microstrip and evanescent mode resonators is designed and fabricated. The proposed wideband BPF exhibits a reconfigurable in-band notch with frequency tuning from 1.494 to 2.004 GHz and attenuation tuning from 2 to 79 dB. The simulated and measured results are in good agreement with each other, validating the proposed design and method.