Microstrip coupled-line directional coupler with enhanced coupling based on EBG concept

A novel microstrip coupled-line directional coupler with enhanced coupling factor is proposed. It is based on the introduction of an electromagnetic bandgap (EBG) structure on the coupled lines to strongly enhance the designed backward coupling. Accurate analytical expressions are obtained for the main design parameters of the coupler. A 3 dB EBG coupler has been designed, simulated and measured, demonstrating 6.4 dB improvement in the coupling level when compared to a classical coupled-line directional coupler.