Wideband directional couplers and power splitters

Abstract

Microwave quadrature couplers and out-of-phase power combiners/dividers are in many aspects crucial devices and are used in many microwave subsystems, such as mixers, modulators, antenna beam forming networks and antenna array feeds to name a few. In modern microwave circuits there is an increasing demand for wideband operation and lower costs (no complex structures), and thus the power couplers/dividers must follow the same requirements. This thesis presents the design and characterisation of four different quadrature hybrid designs based on a Branch Line Coupler (BLC) core structure and a 180 power splitter through a combination of a wideband Wilkinson power divider and a phase shifting network at the output ports. The manufactured quadrature hybrid measured a 60 % fractional bandwidth (6.5 GHz - 12 GHz) with a maximum amplitude and phase imbalance of 0.5 dB and 5.8 respectively. Return loss better than 11 dB and isolation better than 15 dB was achieved over the whole operational bandwidth. Regarding the out-of-phase power divider a 110% fractional bandwidth (4.31 GHz - 14.97 GHz) was achieved with return loss and isolation better than 13.5 dB and 20 dB respectively, accompanied by an amplitude and phase imbalance of 0.5 dB and 13.4. All proposed circuits were constructed on a single commercially available dielectric substrate in a microstrip structure.