Novel low-loss microstrip triplexer using coupled lines and step impedance cells for 4G and WiMAX applications

In this paper, a new microstrip triplexer with flexible resonance frequencies is designed based on the propertiesof coupled lines, steps, and spiral cells. It operates at 2.67 GHz for 4G LTE and at 3.1 GHz and 3.43 GHz for IEEE802.16 WiMAX. The close resonance frequencies make it suitable for frequency division duplex applications. In order toimprove insertion loss, the LC equivalent circuit of the proposed resonator is analyzed. Moreover, careful alignment ofthe coupled lines and step impedance structures is performed to improve the insertion and return losses so that they are0.72/0.63/0.81 dB and 24.5/24/24.7 dB, respectively. The frequency response shows good selectivity for each channel.Meanwhile, there are several transmission zeros above the first channel and below the last one that improve the stopbandproperties. The proposed triplexer is fabricated and measured. The simulation and measurement results are in goodagreement, which validates the introduced methodology.

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