Closed-form design method for broadband parallel-coupled microstrip coupler with tight coupling and practical spacing

A closed-form method to design microstrip couplers that have tight coupling, practical dimensions, simple structure, and broadband performance is presented. The method is based on the quasi-static even-odd mode approach. According to the proposed method, three-lumped capacitor connected at the center of the coupled structure are used to relax the requirement on the gap width between the coupled lines. The simulated and measured results of 3 dB couplers designed using the proposed method confirm its validity. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2790–2794, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26395