DC to 40-GHz Compact Single-Layer Crossover

In this letter, a compact, wideband, and fully planar microstrip crossover structure is proposed. This design is based on a compact microstrip to coplanar waveguide transition, which has a measured bandwidth extending from dc to 40 GHz. At 20 GHz, the measured insertion loss, return loss, and isolation are better than 0.35, 21, and 19 dB, respectively. This circuit is ultracompact with the core size of 3 mm × 3 mm, which is 0.2λ × 0.2λ at 20 GHz.