Broadband quadrature coupler with slotted ground plane

The design of an edge‐coupled quadrature directional coupler, which has a broadband performance and relaxed coupled‐line spacing, is presented. A slotted ground plane is used underneath the coupled region in order to relax the requirement for a narrow slot between the coupled lines. The simulated and measured results show that the designed coupler exhibits a coupling of 3 ± 1 dB across the band 3.8 GHz to 9.8 GHz, when the spacing between the coupled lines is 0.12 mm. Without the slot in the ground plane, the spacing should be less than 0.001 mm to achieve the same value of coupling across that band. This broadband coupling is accompanied by an isolation and return loss in the order of 13 dB or better across the band 3–10 GHz. The designed device has a compact size with a dimension of 30 mm × 20 mm.