Optimizing the performance of branch-line couplers using open ended stubs

In this paper we use open ended stubs on transmission line to design compact BLC by using planner microstrip technique. We will derive in detail the closed formulas for the BLC design. The effect of changing the number of open ended stubs on the coupler performance is investigated. It has been shown that the number of open ended stubs used for optimum design depends mainly on the center frequency range used. Also it has been shown that at frequency range (1-2 GHz) there are a big difference on the design area of the coupler for both the conventional and open ended stubs. The paper presents a comparative study between the performance of the BLC using both open ended and conventional approach.