A novel high-performance microstrip diplexer is proposed and designed in this work. The design is based on patch and thin cells to operate at 0.78 GHz and 1.85 GHz for GSM applications. Owing to the symmetrical structure of the proposed resonator, the odd and even modes analyses are performed to get information about the resonator behavior. This information is useful to optimize the performance and miniaturization, simultaneously. The introduced diplexer has several advantages in terms of low insertion losses, low return losses, high isolation and compact size. It is well miniaturized and optimized with low insertion losses of better than 0.30 dB at the both channels. Meanwhile, the isolation between the channels is better than 42 dB. Our designed diplexer is able to attenuate 1st up to 5th harmonics. To validate the simulation results, we have fabricated the presented diplexer. The results show a good agreement between the measurement and simulation results.
