High Isolated and Wide Stopband Switchable Diplexer with Inserted Lowpass Filter

A wide stopband and high isolated diplexer is proposed in this paper. Firstly, a diplexer based on composite resonator with high isolation level of 40dB is designed. Secondly, by inserting a wide stopband lowpass filter (LPF) in the common port of the diplexer, a diplexer with wide stopband is achieved. Thirdly, PIN diodes are loaded to the diplexer, and diplexer with switchable response is realized. Four states switchable diplexer with suppression level of 20dB up to 5.83f
0
is designed. In each state, the suppression level is better than 20dB.