Miniaturized quad-channel microstrip diplexer with low insertion loss and wide stopband for multi-service wireless communication systems

In this paper, a compact four-channel diplexer is designed using a microstrip structure to separate input signals at 2.07/3.94 GHz and 2.37/4.49 GHz and load them on two output ports. The presented diplexer is designed utilizing a novel structure, which can be applied in modern multi-band wireless communication systems and IEEE 802.16 WiMAX that covers 3.17–4.2 GHz. This diplexer is consisting of coupled lines, a spiral cell and U-shape structures that are integrated to obtain a high performance. To create four passbands at two output ports, the proposed structure is miniaturized so that it occupies only a 0.025 λ _g ² circuit size where λ_g is the guided wavelength calculated at 2.07 GHz. Moreover, the low insertion losses are obtained at all channels. Another achievement of this work is obtaining a wide stopband. After the last passband, harmonics are attenuated up to 8 GHz, which is suitable for ultra wideband applications. The introduced diplexer is fabricated to confirm the design process where the measured results are in a good agreement with the simulations.