A circular substrate-integrated waveguide bandpass filter with controllable transmission zeros

Herein, a substrate integrated waveguide (SIW) bandpass filter with three transmission zeros is proposed. The filter comprises two semicircular SIW cavities and a circular SIW cavity. This design enabling the propagation modes in different resonant cavities to be cross-coupled to generate transmission zeros and can be flexibly designed within a certain range. Based on this, a bandpass filter with a center frequency of 7.7 GHz was fabricated. The measured data of the vector network analyzer showed that the 3-dB bandwidth of the filter was 205 MHz, the return loss in the passband was less than 20 dB, the out-of-band rejection effect was good, and there were three transmission zeros on both sides of the passband (6.7, 9.6 and 11.6 GHz). The feasibility of the design was verified.