Suspended stripline low-loss bandpass filter with four transmission zeros

A novel fifth-order suspended stripline (SSL) low-loss bandpass filter with four transmission zeros is proposed. The technique of utilising only one cross-coupling structure introduces four transmission zeros to provide high selectivity. By adjusting the parameters of the coupling open loop, the performance of out-of-band of the filter can be changed. A detailed discussion of this effect of the coupling open loop is given. The highest out-of-band rejection of the filter is more than 70 dB. An SSL bandpass filter is designed, fabricated and measured. The measured results are in good agreement with the simulated results.