Electronically Reconfigurable Monopulse Reflectarray Antenna with Liquid Crystal Substrate

A printed patch reflectarray antenna which is constructed on a tunable liquid crystal substrate is shown to generate reconfigurable sum and difference radiation patterns suitable for monopulse tracking applications. A 12x12 element breadboard antenna was designed to generate a focussed (sum) beam at 10 GHz by adjusting the size of the patches on the two halves of the aperture and applying a bias voltage to one of the halves which contains 6 columns of 12 elements. When the bias voltage is reversed, the change in the two permittivity values of the 500 mum thick liquid crystal substrate is shown to produce a difference radiation pattern. By combining both active and passive design techniques it is only necessary to use 45% of the maximum dynamic phase range which is available from the liquid crystal reflectarray cells. The material characterisation methodology is described and the simulated radiation patterns for the two switching states are shown to be in reasonably good agreement with the measured results.