Wide-band lumped-element directional coupler with an arbitrary coupling coefficient

A method of synthesising wide-band directional lumped-element couplers with an arbitrary coupling coefficient is presented. The proposed synthesis method can realise a co-directional type lumped-element coupler with a wider operational bandwidth than conventional design methods while maintaining good amplitude and phase relationships of the output ports. Two coupler prototypes with coupling coefficients of 10 and 20 dB are designed and fabricated to verify the design concept. The measurements are very close to the theoretical predictions.