Design and Development of a Compact Rat-Race Coupler

In this paper, design and development of compact Rat-Race coupler is presented. The device is designed with commercial available semi rigid coaxial cable. The semi rigid coaxial is modified for desired impedance required for design of Rat-race hybrid coupler. The physical structure of the coupler is in rectangular form instead of the conventional ring form. With this structure all the ports are available in line on the same side. This eases the integration of the device with other modules or devices in the system. The total area occupied the coupler is reduced drastically by meandering the transmission line. The shielded transmission line provides lesser undesired coupling to other ports and has less line radiation loss. Design, implementation and measured results are presented.