Design of Single-/Dual-Band Balanced Filters with High Common-Mode Rejection on Patch Resonators

In this paper, a method for designing single or dual-band balanced filters is presented with inherent common-mode suppression based on the 2-D rectangular patch resonators. The electric field distribution of the involved operating modes in a patch cavity is analyzed in detail. At the beginning, a single-band balanced filter operating at 2.02 GHz is designed based on the fundamental TM10 mode. It is composed of two patch resonators, which is coupled to each other through the slot on the common ground plane. Afterwards, another four coupling apertures are introduced in the ground plane to generate electric coupling between the two patches, thus the second passband can be formed by the excited TM11 mode. Moreover, the center frequency of the second passband can be flexibly adjusted without any influence of the first one by changing the side length of the patch. Finally, two balanced filters are designed and simulated. The single-band one is working at 2.02 GHz and the dual-band one is operating at 2.02 GHz and 3.62 GHz. Both balanced filters are designed with good differential-mode (DM) filtering responses and high in-band common-mode (CM) suppression.