A novel cross‐coupled filter with triangular resonators

In this article, a novel isosceles right triangle resonators filter is presented based on cross‐coupling technology. The whole filter is a square structure and it consists of four isosceles right triangle resonators. By introducing negative cross‐coupling between two resonators, a fourth‐order cross‐coupling dielectric waveguide filter with two out‐of‐band transmission zeros (TZs) is implemented. By changing the sign of the coupling coefficient, the TZ can be changed around the passband. Positive coupling is achieved through a coupling partition and shallow coupling blind holes, and negative coupling is achieved through symmetrical upper and lower blind holes. The new resonator structure is introduced and the design, simulation, and physical measurement of the filter are discussed. The results show that the center frequency of the filter is 3.5 GHz and the relative bandwidth is 5.7%. The passband return loss is more than 14 dB, the insertion loss is less than 0.1 dB.