In this work, a microstrip diplexer with 0.004 λg2 (10.1 × 23 mm) overall size is designed, analyzed and fabricated. The proposed diplexer has the smallest size compared to the previously reported microstrip diplexers. The proposed diplexer has a simple and novel structure, wide flat channels and very low. An innovative microstrip structure based on thin coupled lines is used to design of the proposed diplexer. Since in a simple structure the possibility of manufacturing errors reduces, having a simple structure is one of its advantages. Another advantage of this diplexer is two low of 0.17 and 0.14 dB at the lower and upper channels. The operational frequencies of our diplexer are tuned to work at 0.9 GHz and 1.8 GHz for GSM application. It has the privileges of very compact size, simple structure, small , two wide fractional bandwidths (FBWs) of 21 and 24.3% and acceptable and isolation. Due to its two wide FBWs, the presented diplexer is suitable for broadband communication systems. We have fabricated and measured the introduced diplexer to verify the design methodology and simulation results. The obtained results of the diplexer measurement confirm the simulation.
