Dual-band planar crossover with two-section branch-line structure

A dual-band planar crossover with simple structure is proposed. This crossover is derived from the conventional single-band two-section branch-line crossover by doubly extending the length of its vertical transmission lines, which realizes the dual-band operation. Closed-form equations for design parameters are derived, which simplifies design procedure of the proposed crossover and shows that the available bandwidth of the passband increases with the increasing frequency ratio. By adding one short-circuited stub and one open-circuited stub to the originally proposed dual-band crossover, two types of modified dual-band crossovers and their closed-form design equations are proposed for smaller and larger frequency ratios applications. For verification, four different dual-band crossovers are designed and simulated, of which two microstrip crossovers operating at 1/1.8 and 1/2.3 GHz are fabricated and measured. The measured results are in good agreement with the simulated ones.