Broadband microwave crossover using parallel-coupled microstrip lines and short-ended stubs

A broadband microwave crossover with planar structure and compact size is proposed. It is composed of four pairs of parallel-coupled microstrip lines terminated with short-ended stubs. The utilised structure is analysed using a second-order even/odd-mode method, which shows that the centre frequency and bandwidth of the passband are defined by the length and coupling factor of the coupled lines, respectively. The proposed design is verified using both full-wave simulations as well as experiments on two prototypes. The achieved results of the two designs indicate fractional bandwidths of 12.5 and 25% with less than 0.8 dB of insertion loss, more than 17 dB of return loss, more than 18 and 12 dB of isolation and a flat group delay with less than 0.4 ns of deviation.