Compact planar dual-band crossover using two-section branch-line coupler

The design of a four-port crossover that can be operated at two arbitrary frequencies by using two branch-line couplers is presented. This design utilises the advantage of the transmission phase characteristic of the branch-line coupler. The proposed circuit also features compact size, a planar structure, widely separated frequency bands, and good inter-band rejection between the two operating frequencies. For verification, both simulation and measured results of a microstrip crossover operating at 900 MHz and 2.45 GHz are given and are consistent with each other.