An Ultra-Compact Microstrip Crossover Inspired by Contra-Directional Even and Odd Mode Propagation

A compact microstrip crossover network that occupies an area of 0.027λ×0.027λ at 1 GHz is presented. The network is fully planar and is implemented using printed and surface mount elements. The design is inspired by the idea of a network whose even and odd modes propagate as forward and backward waves, respectively. The resulting circuit is more compact and has fewer elements than any other published planar crossover. At the operating frequency, the proposed crossover was measured in experiment to have 25 dB isolation (ISO), 25 dB return loss (RL), and 0.51 dB insertion loss (IL). The bandwidth (BW) over which the return loss and isolation remained above 15 dB was 5.7% (9.6% in simulation).