Design of a Compact Dual-band Balanced Bandpass Filter With Wideband Common-mode Rejection

In this paper, a slotted square patch resonator (SSPR) is proposed, and a dual-band balanced bandpass filter (BPF) is designed accordingly. Benefiting from the slots in the horizontal and vertical directions, the size of the SSLR becomes more compact and the first two differential mode (DM) resonant frequencies can be individually tuned. The designed balanced filter operates at 3.48 and 5.81 GHz with fractional bandwidths of 0.816% and 1.96%. Additionally, isolation resistors are added within the SSPR to obtain a wide range of common mode (CM) rejection from 0 to 7.2 GHz.