This letter proposes a novel single-layer fourth-order balanced bandpass filter based on two coupled dual-mode loop resonators. Two pairs of balanced input/output (IO) feeding lines with unequal arms are employed to excite the outside dual-mode loop resonator, and the inside dual-mode loop resonator with meander lines is coupled to the outside one. Under differential-mode (DM) operation, three finite transmission zeros (FTZs) can be produced and controlled. Under common mode (CM) operation, the rejection level can be controlled by the length of IO feeding arms. For the demonstration, a balanced dual-mode loop filter with the center frequency of 5.2 GHz is designed, fabricated, and measured. The proposed balanced filter has the advantages of compact size, high selectivity, wide stopband of DM response, and good CM suppression.
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