A narrow-band two-cavity filter with five transmission zeros

The presented filter has two transmission poles and five transmission zeros. The parallel coupling between two hairpin resonators, the open-circuited stubs result in three transmission zeros in the vicinity of the passband. The two stubs which share a common grounded via-hole contribute two additional transmission zeros in the upper stopband. The novel filter with 4.5% fractional bandwidth (FBW) has been designed and fabricated to verify the validity of the proposed method. Measured results are in good agreement with the electromagnetic simulation. The measured results show five transmission zeros in the stopband, located at 1.72GHz, 2.25GHz, 2.55 GHz, 3.17 GHz, 4.33 GHz, respectively. The circuit size of proposed bandpass filter only occupies 20 ^x 17mm².