Design of tri-band coupler and wideband phase shifter

Abstract

Branch-line coupler and phase shifter are widely used passive components in RF and microwave communication systems. The designing of circuits operating at multi-band frequencies has the advantage of both compact size and cost. Therefore, it becomes very fascinating to design the RF and microwave circuits with such specifications. This thesis work has been divided into two parts. The first part focuses on the designing of Tri-band coupler with a port matching technique in which architecture of 3-dB tri-band branch line coupler operating at three arbitrary frequencies is presented. It is capable to provide a phase shift of 90º and equal power division at its output ports. To validate the proposed design procedure, a coupler working at 1.8 GHz, 2.4 GHz and 3.5 GHz is prototyped. The second part of the thesis work focuses on designing and validation of wideband phase shifter circuit with stub loaded transmission lines in which a modified architecture of wideband phase shifter having 90º phase shift is presented. A number of design examples capable of multiple phases shift up to 90º for a wide bandwidth are presented to demonstrate the effectiveness of the proposed phase shifter. The designed phase shifters have a bandwidth of operation 190MHz around central frequency. To validate the reported design procedure, a 90º phase shifter working at 1.8 GHz is prototyped. The proposed design is able to provide the 90º phase difference over a bandwidth of 106 % considering only 3º phase ripples. Both designs are prototyped on Rogers5880 substrate with thickness of 1.575 mm and dielectric constant of 2.2. All EM Simulated and results measured with VNA are in good agreement with each other.