Low insertion loss wideband bandpass filter with six transmission zeros

A modified wideband bandpass filter based on a bandstop filter is realised using half-wavelength and one-wavelength open-circuited resonators. Six transmission zeros are utilised to obtain the sharp rejection characteristics over a broad stopband. The passband bandwidth can be varied by changing the impedance of the configuration. A compact prototype filter with 27% bandwidth is demonstrated. Without coupling gaps between resonators, the new filter shows low insertion loss and is easy for fabrication. To illustrate the concept, a bandpass filter is designed, fabricated and measured. Simulated and measured results are found in good agreement with each other.