Analysis and Design of a Planar Crossover for Dual-Frequency Applications

This work demonstrates the design of a planar microstrip dual-frequency crossover. A two section branch-line structure with a symmetrical H-shaped inner transmission line is used to realize the dual-frequency operation in crossover to function at two arbitrarily chosen frequencies. Even-odd mode analysis is employed to derive the closed form design equations. The proposed microstrip crossover is found to be realizable for a large range of frequency ratios from 2.08 to 4.1, which covers most of the practical dual-band applications. The presented theoretical analysis is supported by fabricating a dual-band crossover for WLAN (IEEE 802.11/n) application operating at 2.4 GHz and 5.0 GHz. The measured results indicate more than 20 dB return loss and less than 1 dB insertion loss at the design frequencies. The two channels are well isolated from each other by more than 30 dB. The measured results are found to be well matching with the simulated results.