Design of Branch Line Coupler based on Ridge Gap Waveguide Technology for X-band Application

This paper describes a branch line coupler designed based on the Ridge Gap Waveguide for X-band application. Ridge Gap Waveguide (RGW) technology has been recently noticed as an alternative to hollow waveguides, particularly for high frequencies such as millimeter waves. This new type of gap waveguide is formed between two parallel metal plates which are separated by an air gap less than a quarter wavelength. One of the plates is a perfect magnetic conductor (PMC) to create a high impedance surface and the other a perfect electric conductor (PEC) on top of it. There is no need for electrical contact between them what makes the construction simpler. These new waveguides are completely enclosed by periodic pins structure without the presence of cavity modes and have lower losses than microstrip lines. The prototype 3dB coupler has been simulated and fabricated to operate at 11 GHz. Measurement results confirm simulations and demonstrate about 13% of bandwidth (|S-11| < -10 dB) covering the frequency range of 10.36-11.77 GHz.