A Reconfigurable Feed Network for a Dual Circularly Polarised Antenna Array

A novel miniaturised reconfigurable, switchable feed network for a four elements dual circularly polarised antenna array is proposed. The four feeds are in phase quadrature to give a phase shift of 90 degrees between each neighbouring antenna element, producing a circularly polarised pattern. The feed network consists of three conventional Wilkinson power dividers which can be individually reconfigured in length using PIN diodes switches. By controlling the bias voltages of these PIN diodes, the 90 degrees phase increment can be allocated in either clockwise or counter-clockwise directions. Two orthogonal patterns with left-hand circular polarisation (LHCP) and right-hand circular polarisation (RHCP) are generated. The operating frequency is 2.45GHz, targeting WiFi applications. After miniaturisation and optimisation, the feed network achieves a low return loss, equal power splitting, low insertion loss and accurate phase difference. Fabrication and measurement results closely correlate with those obtained from simulations. The reconfigurable feed network is particularly useful for diversity reception to combat channel fading in indoor wireless LAN applications.