Branch Line Coupler Based on Substrate Integrated Waveguide Technology

This paper presents a 3-dB Quadrature Branch Line Coupler (BLC) using substrate integrated waveguide (SIW) technology. The proposed design is a combination of equal width SIW lines. The structure is having fixed-width lines therefore, can be incorporated into the SIW based microwave circuits. The proposed coupler is designed using derived design equations and simulated at 15 GHz, simulation results show that the reflection coefficients of all the ports are better than 28 dB around the operating frequency, and a good isolation characteristic is achieved which is below 25 dB between the two input ports. At the operating band, two output signals have a phase difference value of $90^{\circ}\pm 1.5^{\circ}$. The insertion loss at centre frequency is 0.84 dB. The proposed structure can be used in butler matrix, mono-pulse comparator circuits, and antenna feeding networks.