Size reduction and wide bandwidth rat-race coupler with shunt capacitors and composite Right/Left-Handed Transmission Line

This paper introduces a rat-race coupler, with size reduction and bandwidth enhancement, using shunt capacitors, high impedance lines and Composite Right/Left-Handed Transmission Lines (CRLH-TLs). The reduced method of line length is used to combine a short length high impedance line and two shunt capacitors. Also, there is combined CRLH meta-material, using nonlinear phase characteristic of CRLH-TL that consists of series capacitors and shunt inductors, so as to obtain wide bandwidth. The implemented rat-race coupler shows a novel design with compact size that is smaller by 10% and a bandwidth that is larger by 60% than that of a conventional rat-race coupler.

I. Introduction

Next mobile communication systems or Beyond 4G services recommend to support the multi-mode mobile services instead of the single mode. Also, the high data rate transmissions of MIMO (Multi-Input Multi-Output) and smart systems demand a multi-band, multi-access and multi-path of RF system. In addition, these systems require a compact planar design, which is highly desirable in many developing commercial applications. Integration of RF components and compact size can meet the requirement of Next mobile communication systems and provide low costs and low transmission power losses.