Slot-coupled directional couplers between double-sided cylindrical microstrip lines

Slot-coupled directional couplers between double-sided substrate microstrip lines have found applications in the design of many important circuits. To analyze the characteristics of such slot-coupled directional couplers on a curved surface, we present the study of slot-coupled double-sided cylindrical microstrip lines. The inside and outside cylindrical microstrip lines are coupled through a rectangular coupling slot in the common cylindrical ground plane. To solve the problem a full-wave approach incorporating a Galerkin's moment-method calculation is applied. The S parameters of such a directional coupler are calculated and compared with experiment.