A four-port network compensation approach for directional couplers

A novel approach for compensating the phase velocity difference in coupled line structures is presented. It utilizes twofold symmetric four-port networks. Analytical design equations are derived. The method is shown to be superior to other lumped element compensation techniques. The advantages are the simple and straightforward design procedure and the inherently broadband compensation. A realized microstrip coupler exhibits good measured performance, thus confirming the approach.