Abstract:
This paper presents the design of a novel dual-mode dual-band bandpass filter with good selectivity. The resonant structure of the filter consists of two short-circuited stub loaded resonators (SSLRs) connected to the same grounded metal column. Firstly, the resonant frequency of a single SSLR is analyzed by odd-/even-mode analysis method and the variation regulation of single SSLR resonant frequency is obtained. Secondly, in order to realize the miniaturization of the filter, two SSLRs are connected to the same metal column and then the microstrip line is folded, and the change in the passband of the filter is analyzed by adjusting the length of the branch. Thirdly, in the design, double-stub feeders are used to feed the two resonators separately and the source-load coupling is introduced, so that an additional transmission zero can be provided in the upper stopband to increase the stop-band suppression. Finally the transmission zeros of the filter are analyzed and the rules of variation are summarized to improve the selection characteristics of the filter. Based on this analysis, the filter is simulated, processed and tested, and the final physical measurement results are consistent with the software simulation results.