Design of a microstrip diplexer with a novel structure for WiMAX and wireless applications

In this paper, a novel combination of coupled lines, loops, step impedance and low impedance sections are used to design a compact microstrip diplexer. The designing method is based on obtaining transmission matrices and finding the effective parameters in tuning the resonance frequencies. T-shape tapped lines feed structures are added to three terminals of the proposed diplexer to decrease insertion losses at the both passbands without increasing the overall size. The proposed diplexer with a total size of 573.11 mm² operates at 2.6 GHz for IEEE 802.16 and 802.20 WiMAX technology and 6 GHz for wireless applications. The insertion losses at the lower and higher resonance frequencies are 0.6 dB and 0.9 dB, respectively. The proposed structure is simulated, fabricated and measured. The measurement results are in a good agreement with the simulations.