In this paper, a novel design of a diplexer for mobile communication base station is proposed, theoretically investigated and successfully tested. The proposed design of the diplexer is implemented on the base of interdigital filters. Successfully fabricated and tested diplexer operates within frequency bands 2.3–2.4/2.49–2.69 GHz and shows high performances: reflection loss within pass bands is less −20 dB, insertion loss is −0.15 dB, isolation is −30 dB and intermodulation is −124 dBm. Computer-aided design of the diplexer is carried out on the basis of combined technique, which includes filter synthesis using coupling matrices, eigenvalue problem solution for single resonator, interresonator coupling calculation and final full wave simulation and optimization of diplexer. The suggested design is a promising candidate for the implementation of diplexers with narrow, moderate and wide bandwidths for standard mobile communication frequency bands.