A single-layered balanced filtering crossover with high selectivity based on square patch resonator

A new design of single-layered balanced filtering crossover with high selectivity based on square patch resonator is proposed. Originated from the degenerate modes, that is, TM₁₂ and TM₂₁ on square patch resonators, the feasibility of intrinsic common-mode (CM) suppression and channel isolation is conceived. For demonstration, a first-order balanced crossover prototype is designed. Afterwards, to enhance selectivity, a square patch resonator is subtly divided into two identical parts and then introduced into the prototype. Hence, a balanced filtering crossover with a fifth-order Chebyshev response is formed. Furthermore, stubs are deployed between adjacent patch resonators to introduce mixed couplings. Thus, two controllable transmission zeros are obtained, and better out-of-band suppression is achieved. Ultimately, the proposed crossover is fabricated and measured. High performance in terms of differential-mode filtering response, in-band CM suppression and channel isolation demonstrates the feasibility of the proposed method.