Reference plane shift considerations for microstrip branch-line couplers

A design method for microstrip branch-line couplers is investigated. The predominant design goal is to create a couple whose direct coupling and isolation response are centered about the correct frequency. Two separate designs are considered. One design considers the reference plane calculation at each tee junction in the device while another is based on a much less tedious design technique. Accurate measurements for each design are included. These indicate a very good agreement between measured data and theory