Implementation of a compact diplexer based on a modified T-shaped step-impedance resonator (MTSIR) for 5G networks

In this paper, a microstrip diplexer with a very compact size is presented for 5G networks. The proposed diplexer operates at 3.5 GHz and 4.2 GHz, which fall within the 5G extended C-band (3.3-4.2 GHz) allocation, showing potential for next generation wireless applications. The design of this diplexer utilizes two similar filters with different sizes. In designing the filters, T-shaped resonators, meandered lines, and coupled lines are used to form a novel structure called the modified T-shaped step-impedance resonator (MTSIR). The proposed diplexer employs two modified T-shaped step-impedance resonators (MTSIRs) to achieve compact size, low insertion loss, and high isolation in the 5G extended C-band, while maintaining a very low frequency ratio of 1.2. The proposed diplexer operates at a frequency of 3.5 GHz with an insertion loss of 0.5 dB. The second channel of the diplexer operates at a frequency of 4.2 GHz with an insertion loss of 0.8 dB. The designed diplexer features a very compact size of 18.2 mm × 10.9 mm, corresponding to a normalized size of 0.16 λg × 0.28 λg.