Novel dielectric waveguide filter using isosceles right-angled triangular resonators

A novel dielectric waveguide filter based on isosceles right-angled triangular (RAT) resonators is presented in this letter. By connecting the vertices of four isosceles RAT waveguide cavities, a square fourth-order cross-coupled waveguide bandpass filter is formed. The presented filter uses the partition wall and shallow blind hole to realize positive coupling and the deep blind hole to realize negative coupling. Moreover, the filter facilitates debugging and testing by setting the debugging blind hole on one side of the waveguide and setting the feed blind hole on the opposite side. The design, analysis, and simulation of the physical model of the filter are discussed. The fabricated filter has a center frequency of 3.5 GHz, relative bandwidth of 5%, insertion loss of less than 1 dB, in-band return loss of more than 15 dB, and two out-of-band transmission zeros at 3.27 and 3.65 GHz.