A Novel Compact $E$-Plane Waveguide Filter With Multiple Transmission Zeroes

This paper presents a novel compact E-plane waveguide filter using multiple resonators, which lead to multiple transmission zeroes. The proposed filter is less than 0.15 λ g in length of a waveguide. The key of the proposed method is to design the locations of transmission zeroes. Four transmission zeroes, of which two are located in the upper stopband, while the other two are in the lower stopband, are produced by four resonators. The couplings between the resonators and locations of the transmission zeroes are carefully analyzed and designed, which enhance the selectivity as well as the out-of-band performance. Theoretical studies and experimental investigations are conducted to demonstrate the proposed design. The good agreement between the simulation results and measurement results is achieved. Moreover, this kind of filter can be implanted well in E-plane structures.