A compact lowpass - dual bandpass diplexer with high output ports isolation

In this paper a compact lowpass-dual bandpass microstrip diplexer is designed, simulated and measured. The presented diplexer consists of a low pass filter (LPF) and a dual-band, band pass filters (BPFs). The main contribution of this work is that a new structure for diplexer is proposed by using T-shaped resonator, ring resonator and meandered lines, which resulted in superior performance in terms of compact size, simple structure, low insertion loss, and high output ports isolation, compared with the previous approaches. The applied proposed LPF has 2.3 GHz cut off frequency and provides a sharp response in transmission band with 537.5 dB/GHz roll of rate. The applied proposed BPF has two pass bands at 3 GHz and 6.2 GHz, with low insertion losses in the two bands. The insertion loss at 3 GHz is only 0.8 dB and at 6.2 GHz is 1.2 dB. The return loss (RL) of the proposed diplexer is better than 20 dB. The designed diplexer has more than 20 dB output ports isolation. The fabricated diplexer has a miniaturized size, which only occupies 33.9 mm x 24.9 mm (0.26 lambda g x 0.35 lambda g).

Automated summary

A compact lowpass-dual bandpass microstrip diplexer was designed in this paper, utilizing T-shaped resonator, ring resonator, and meandered lines for superior performance in terms of compact size, simple structure, low insertion loss, and high output ports isolation. The diplexer included a low pass filter with 2.3 GHz cutoff frequency and a dual-band, band pass filters with pass bands at 3 GHz and 6.2 GHz, showing low insertion losses in both bands. The fabricated diplexer demonstrated more than 20 dB output ports isolation with miniaturized dimensions.