DESIGN AND IMPLEMENTATION OF L BAND MICROSTRIP COUPLER WITH IMPROVED COUPLING AND HIGH DIRECTIVITY

Abstract

The couplers are passive devices used in the field of radio technology. They couple a defined amount of the electromagnetic power in a transmission line to a port enabling the signal to be used in another circuit. Directional couplers are most frequently constructed from two coupled transmission lines set close enough together such that energy passing through one is coupled to the other. In this thesis work, a new symmetrical coupled-line circuit structure without any patterned ground plane is proposed to design tight-coupling high-directivity couplers for L Band, which would be found in numerous applications in a microstrip RF front end because of its simple structure and inherent excellent compatibility. Based on a traditional even- and odd-mode technique, closed-form mathematical equations for both circuit electrical parameters and scattering parameters are obtained. Due to the use of two coupled-line sections placed in the vertical direction, the directivity of this novel coupler without any other compensation techniques can be enhanced while maintaining tight-coupling. This microstrip coupled-line coupler can be used for the designs of various balanced power amplifiers, mixers, modulators, measurement systems, circularly polarized antennas, beam-forming array antennas, etc. Advanced Design System (ADS) tool was used for design and simulation. The simulated results show good return loss, quadrature phase characteristics, high directivity, and strong coupling performances of the coupler.