Cross-coupled dielectric waveguide filter

A cross-coupled dielectric waveguide filter based on blind holes and via holes is proposed in this study. Using a unique all-hole design, a fourth-order cross-coupled dielectric waveguide bandpass filter is realized by drilling via holes or blind holes in a square dielectric waveguide, followed by coating the surface with thin metal. Magnetic coupling is realized using two blind holes located symmetrically above and below each other. Further, electrical coupling is realized using a combination of two blind holes located symmetrically above and below each other and an interconnecting via hole. Both types of coupling are analyzed and designed. Moreover, a circular via hole is provided in the middle of the square cavity to suppress the parasitic response of the filter. Coupling debugging holes, resonant debugging holes, and feed holes are realized using shallow blind holes, thereby alleviating the process of manufacturing and debugging. The structure of the designed filter is discussed, simulated, manufactured, and measured. The results show that the proposed filter has a center frequency of 3.5 GHz, an insertion loss of less than 0.5 dB, a return loss of less than 15 dB, and a relative bandwidth of 5%, exhibiting excellent performance that includes two out-of-band transmission zeros.