Design of Double-Ridge Waveguide Balanced Filter and Filtering Power Divider

In this article, the double-ridge waveguide (WG) is investigated for designing high-performance balanced bandpass filter (BPF) and filtering power divider (FPD). It can be found that the two ridges' surface currents under fundamental mode operation have inherent characteristic of same amplitude and anti-phase. Based on this, an in-line balanced BPF using double-ridge WG resonators is designed while the coupling between the resonators is fulfilled by the evanescent mode of the rectangular WG. The high common-mode (CM) suppression in the frequency range of interest is obtained naturally. On the basis of the filter prototype, a balanced FPD can be easily implemented by proper adding the outputs on the last ridge resonator. For demonstration, both of them have been fabricated and measured. Measured results indicate that the filtering response centers at 3.5 GHz and the 3-dB fractional bandwidth (FBW) is about 13% with an insertion loss (IL) of <tex-math notation="LaTeX">$<$</tex-math> 0.35 dB. Both balanced BPF and FPD have wide and high differential-mode (DM) upper stopband rejection, and the CM suppression is better than 65 dB in the passband.