In this work, a new basic microstrip structure is proposed and analyzed to obtain a lowpass-bandpass triplexer without any extra matching networks. This is despite the fact that the number of literature on lowpass-bandpass triplexers that have been introduced so far is very low. The lowpass channel cut-off frequency is tuned at 1.85 GHz which makes it appropriate for mid-band 5G and GSM applications. The bandpass channels work at 3.25 GHz and 6.65 GHz for S-band, 5G, WiMAX and C-band applications. The designed triplexer occupies a compact area of 0.021 λg2. In comparison with the previously reported triplexers, the presented triplexer has three low insertion losses of 0.54 dB, 0.16 dB and 0.55 dB. Also, all its channels are flat with three low group delays of 0.79 ns, 0.98 ns and 0.85 ns. For verifying the designing technique and simulation results, we fabricated and measured our triplexer, where all the obtained results are close to each other.
