Wideband directional coupler based on zigzag coupling and wedge structure for isolation enhancement

Abstract

This paper presents the design of wideband directional coupler with enhanced isolation performance. Studies show that introducing the zigzag coupling releases the phase-velocity difference between the even- and odd-mode in the coupling region, thus improving the directivity. To further improve the performance, wedge structure is proposed, and therefore, a wideband coupled-line directional coupler is developed with enhanced isolation responses. The presented coupler characterizes simple architecture, planar layout, symmetric topology, symmetric coupling and isolation responses that are the basic difference among many reported works, wide operation bandwidth and more importantly, the wedge structure can be independently loaded and designed, and features a great advantage in this contribution. To validate this study, a prototype coupler that works from less than 7 GHz to over 13 GHz is optimally designed, fabricated and examined experimentally. The developed prototype has a size of 11.1 × 5.4 mm2 (corresponding to 0.69 × 0.34λg2 at the center operation frequency of 10 GHz) on a microwave substrate with a relative permittivity of εr = 3.5 and a thickness of h = 0.508 mm. The measurement and simulation results are in good agreement, thus confirming the design methodology.