A Compact Interlaced-Double-Ridge Waveguide Balanced Filter With Wideband CM Suppression

Abstract

In this letter, a novel compact balanced bandpass filter (BPF) based on an interlaced-double-ridge waveguide (IDRWG) resonator is proposed. By modifying the two ridges of the traditional double-ridge waveguide (DRWG) resonator to an interlaced-ridge structure, the IDRWG resonator achieves a lower fundamental frequency ( $f_{r0}$ ), implying that a compact filter can be constructed. Here, the anti-phase property of the two interlaced ridges is maintained. Accordingly, a compact IDRWG balanced filter with low differential-mode (DM) loss can be realized. At the same time, the first harmonic ( $f_{r1}$ ) of the IDRWG resonator acts as a common-mode (CM) resonance. By optimizing the dimensions of the resonator, the ratio of $f_{r1}$ / $f_{r0}$ can be enlarged, leading to wideband CM suppression of the balanced filter. Demonstrated results show good agreement between simulated and measured performance, with the balanced BPF centered at 2.5 GHz exhibiting about 20% bandwidth, insertion loss (IL) of <0.37>60 dB from 0 to 8.2 GHz.