Dual-band Filter with Adjustable Zero Structure

In this paper, a dual-band filter based on an open-stub loaded open-loop resonators is designed. The second passband of the dual-band filter is obtained by tuning the length and position of the open-stub. In order to improve the out-of-band rejection of the filter, a spurline is embedded in the resonator, and an additional transmission zero is added. The theory has been verified by analyzing and simulating the dual-band filter with HFSS.