Spiral microstrip patch element for reflectarrays

Reflectarrays offer a competitive alternative to reflectors in many narrow-band, pencil-beam and shaped-beam antenna applications. The basic advantage of reflectarrays is their reduced cost when compared to reflectors-their patch elements can be produced using photolithography. A spiral microstrip patch element geometry with reduced sensitivity to etching errors is proposed and analyzed. The analysis, which is based on a full-wave moment method solution of an infinite array with equal elements, is validated with free-space reflection measurements on an array of equal spiral elements. Using this theoretical tool, the sensitivities of the proposed and square patch elements to etching errors are compared to demonstrate the advantage of the former element.