Beam steered reactively loaded printed microstrip loop antennas

Printed microstrip loop antennas loaded with reactive components are analysed to demonstrate the capability of beam steering by reactance adjustment. The geometry of the printed microstrip loop including reactive element loading is represented as a superquadratic function so that the current distribution, hence radiation pattern for various antenna loop shapes, can be calculated using a unified method of moment formulation. The effects of the loop shapes and dielectric substrates on the beam steering capability and input impedance characteristics are investigated. It is found that continuous beam steering can be achieved and that a compromise has to be made between the maximum beam steering and minimum input VSWR. A 1.0 GHz experimental verification is provided, which demonstrates that beam steering of 24° can be achieved by control of a single reactive element, while low crosspolarisation (∼−20 dB) and VSWR (∼1.7) can be simultaneously maintained.