A Compact Multimode Bandpass Filter with Extended Stopband Bandwidth

A compact multimode bandpass filter with low insertion loss, high stopband rejection and wide stopband bandwidth is introduced by using cascaded multimode resonators and compact loading cells in combination. The measured minimum insertion loss is of 1.7dB including the connector loss in the input and output ports in the passband of 5.7~8 GHz. Through the use of cascaded multimode resonators, steep skirt selectivity and wide stopband up to 18 GHz can be achieved. When incorporated with the lowpass loading cells, which have elliptical low-pass response by using the source-load coupling, the stopband of the proposed filter can be further extended up to 40 GHz, with only negligible influence on the passband performance.