Compact Dual Band Branch Line Coupler for Wireless Applications

This work describes the design of a compact size dual band branch line coupler for wireless applications. In this design, open stubs are inserted at the middle of each classical coupler arm to convert it into an equivalent T shape line. ABCD-matrix analysis are used to derive the design formulas necessary for calculating the characteristic impedances and the electrical lengths of the modified coupler arms. To attain compactness in size, stubs are 90-degree bended in the outer and the inner area of the coupler. Rectangular ground slots are added to enhance the coupler performance at the designed frequencies. The designed coupler operates at 2.45 and 5 GHz corresponding to wireless applications. Simulations are done using Ansys HFSS software on RO4003 substrate with a thickness of 0.813 mm and a dielectric constant of 3.55. Values of the simulated S-parameters show that both the isolation coefficient and the return loss are lower than -20 dB at the targeted frequencies.