Compact Microstrip Narrow Bandpass Filter with Good Selectivity and Wide Stopband Rejection for Ku-Band Applications

A new microstrip narrow bandpass filter with good selectivity and wide stopband rejection for Ku-band application is proposed in this letter. The characteristic of the triple-mode stub-loaded resonator has been investigated. The resonance frequencies of the degenerate modes can be adjusted easily to satisfy the bandwidth of the narrow bandpass filter. Two parallel-coupling feed structures with cross-coupling have been used to generate two transmission zeros at the lower and upper stopband, which can improve the filter selectivity. To validate the design theory, a new microstrip Ku-band narrow bandpass filter has been designed, fabricated, and measured. Simulated and experimental results are provided with good agreement.