Hairpin bandpass filter with broadband spurious-response suppression

This paper describes a novel but simple technique for suppressing spurious passbands inherent in conventional hairpin-line bandpass filters. The technique proposed comprises loading the hairpin with an open-loop square ring slot in the ground plane located in the proximity of the input and output. The measured performance of the resulting this slotted ground plane exhibits out-of-band rejection of spurious resonance frequencies by -39 dB, -35 dB and -42 dB at 3f₀, 4f₀ and 5f₀, respectively. By adjusting the parameters of the square split-ring slotted ground plane, spurious response suppression of -44 dB is achieved at 2f₀. Results show rejection >; -20 dB is achieved up to 7f₀.