Modified phoenix cell for microstrip reflectarray antennas

This paper presents a modification on the structure of a recently proposed microstrip reflectarray cell, called Phoenix [4]. Phoenix cell was developed to operate in the X-band frequency range for a linearly polarized microstrip reflectarray antenna. Phoenix is designed to overcome the limited antenna bandwidth being a common issue faced by most microstrip reflectarray cells. The design is based on the idea of employing multiresonators to each cell which in turn improves the bandwidth characteristics. Another interesting feature is the phase variation cycle where the dimensions of the element that delivers a phase shift of 0° are identical to the 360° phase shift element, and this is the reason behind the phoenix name. In this paper a modification is proposed on the structure of the phoenix cell where more resonating rings are attached to the surface of the element. These rings have in turn reduced the cell size which used to be larger than λover2, thus no more grating lobes are expected and a higher antenna gain can be achieved. Moreover, the modified phoenix has improved the delivered linear phase characteristics which indicates less phase errors compared to the old phoenix. Simulations are carried out for the phoenix cell before and after modifications. Also two reflectarrays were designed to operate at 9.4 GHz to evaluate the performance of the phoenix cell together with the modified version by comparing measurements. All simulations were carried out using CST-Microwave Studio 2012.