LAUSR

In this paper, a bandpass–bandpass two channels diplexer with operating frequencies of 1.7 GHz and 2.1 GHz is designed and fabricated on RT/duroid substrate. A via hole, coupled transmission lines and stepped impedance resonators are used in the proposed structure, to achieve low insertion loss, good suppression band and a compact size. Two microstrip filters are designed separately for first and second channels; then the designed filters are combined to make the proposed diplexer. The measured results show that the obtained insertion losses are better than 0.5 dB and the obtained return losses are better than 20 dB at the operating frequencies of both channels. Also, the achieved isolation is better than 40 dB at operating frequencies, which shows good isolation between two channels. The final size of the proposed circuit is obtained 28.7 mm $$\times$$ 37 mm or 0.22  $$\lambda _{g}$$ $$\times$$ 0.28  $$\lambda _{g}$$ . Finally, the fabricated diplexer is compared with the other related diplexers, which shows good performances, compared to the other works.