This paper presents a diplexer operating at 3.8 GHz and 4.5 GHz with fractional bandwidths of 5.27% and 2.2%, respectively. The proposed diplexer is designed by proposing a new symmetric microstrip structure. Here, unlike many previous works, we do not optimize the previously proposed structures. Instead, we propose a new basic structure. It is made of only complex-coupled lines without any stubs. It exhibits high selectivity, low insertion losses (0.35 dB and 0.57 dB), and good return losses (43 dB and 44 dB), making it efficient for simultaneous signal routing and energy harvesting. The design features satisfactory group delays within the channels. Meanwhile, it suppresses the harmonics, where the maximum frequency of the suppressed harmonics reaches 9 GHz. A comparative analysis of the even/odd modes is performed to understand the resonator behavior and facilitate the optimization. Finally, the proposed diplexer is fabricated and measured to verify the design method.
