High Selectivity and Wide Stopband Limiting Filter With Dual‐Path Resonators and Quasi‐Lumped Topology

In this paper, a high selectivity and wide stopband limiting filter with dual‐path resonators and quasi‐lumped topology is presented. Dual‐path resonators (DPRs) are employed to realize a bandpass cell with multiple transmission zeros (TZs) on both sides of the passband for skirt selectivity enhancement, which is further improved by stepped‐impedance open stubs (SIOSs). To achieve a wide upper stopband without increasing the circuit size, a quasi‐lumped topology incorporating limiting diodes is designed to introduce additional TZs in the upper stopband for controllable spurious‐response suppression. A prototype of the proposed limiting filter is fabricated with a center frequency f 0 of 3.55 GHz. Measurement results show that the stopband is extended up to 5.27 f 0 with a minimum rejection level of 21.4 dB. The selectivity factor, defined as the ratio of the 15‐dB bandwidth (BW) to the 3‐dB bandwidth, is 1.44. Good agreement between simulated and measured results is observed.