Four-port Coupling Network Design for a Two-Element Biomimetic Antenna Array

Two-element arrays with closely-spaced antennas receive a small phase difference that depends on the angle of arrival (AOA) of a narrowband source in the far-field. Recently several electrical coupling networks have been investigated to amplify the phase difference in the measurements. We present closed-form design equations for a four-port Pi coupling network that delivers maximum power in the measurements and phase difference amplification arising from the mutual coupling between the antennas. The designs are indexed by a real-valued free parameter that provides flexibility in the capacitor and inductor values, and we validate the approach with a numerical example.