An EM-Coupled Triangular Open-Loop Filter With Transmission Zeros Very Close to Passband

This letter presents a novel EM mixed coupled triangular resonator filter with a backed aperture. Strong and controllable electric and magnetic coupling is constructed to realize transmission zeros very close to passband. Simulation and measurement results show good performances of the proposed filter such as low insertion loss, high rejection levels, as well as asymmetric characteristics. The fabricated three-pole inline filter can implement a bandwidth exceeding 6% while a very close-to-band transmission zero is simultaneously produced by the EM mixed coupling between the first and second resonators.