New Miniature Narrow Band Microstrip Diplexer for Recent Wireless Communications

Using Kappa substrate material, a compact microstrip diplexer is developed in this research with two separate channels based on the coupled junction and two bandpass filters functioning in independent frequency bands. Each filter comprises an input/output feed line and a number of resonators with different impedances. The diplexer's frequency response was modeled and optimized using the Sonnet EM solver. At 2.84 and 4.08 GHz for TX/RX channels, the insertion loss is better than 1 dB for both channels, while the return loss values are 21.2 and 17 dB for transmit and receive filters, respectively. The microstrip diplexer has miniature dimensions of 24 mm x 18 mm with highly narrow bands and band isolation of more than 35 dB. The simulated scattering parameters are in agreement with the measured ones.