Broadband microstrip reflectarray formed by double circular ring elements

A single-layer microstrip reflectarray antenna composed of double-circular rings elements of variable sizes is presented. Compared to single microstrip patches or rings of rectangular or circular shape, the double circular ring elements offer much a larger phase variation range and lower phase slopes and lead to broader operation of a reflectarray. Using these elements, a prime-focus reflectarray operating at 10 GHz is designed and its performance is compared with counterparts employing conventional single resonant microstrip patch or ring elements. The computed results of gain variation with frequency demonstrate a 1-dB gain bandwidth of 51% for a linear reflectarray composed of 13 elements developed on a 6mm foam substrate.