Uniform impedance ring 0°/180° couplers with arbitrary ring impedances and power division ratios

Uniform impedance ring 0°/180° couplers have been developed that possess arbitrary values for the ring impedance and the power division ratio. The power division ratio of the proposed coupler can be adjusted to an arbitrary value for any fixed ring impedance. This makes it possible to obtain a very wide range of power division ratios without any restriction to the line impedance in the design of the coupler. The proposed coupler structure has been analysed rigorously for its scattering characteristics. As a result, general solutions for the coupler are derived in a concise form in terms of the ring impedance and the power division ratio, as well as for the optimum solutions needed to minimise the overall coupler size. The relationships between the coupler size, the ring impedance and the power division ratio also have been investigated. Extensive design and circuit simulation experiments have been conducted in order to analyse the impact of the different ring impedances on the coupler performance under varying power division ratios. An optimum ring impedance value is found from this study and is used to design, fabricate and measure two prototype couplers.