Abstract
This paper presents a theoretical design strategy for an ultra-small diplexer optimized for fifth-generation (5G) communication systems. The diplexer design includes a dual-band band-pass filter comprising coupled lines, transmission lines (TLs), and two proposed resonators. These resonator configurations are analyzed for enhanced optimization and structural clarity. Even and odd mode analysis, along with the examination of the LC equivalent circuit, is used to determine the TL parameters. The proposed diplexer operates effectively across four 5G mid-range frequency bands, enabled by the proposed band-pass filter. It functions at 1.08, 1.17, 2, and 2.18 GHz, achieving S(21) values of -1.18, -1.24, -1.24, and - 1.37 dB, respectively, at these frequencies. The final power amplifier circuit benefits from the described diplexer due to its compact size (8.1 mm × 19.4 mm). The proposed power amplifier demonstrates operation at these frequencies of 1.08, 1.17, 2, and 2.18 GHz with a power-added efficiency (PAE) of approximately 63% and a drain efficiency (DE) of about 64%. These results show the proper performance of the proposed diplexer and power amplifier for mid-band 5G applications.