Investigations Into Phase Characteristics of a Single-Layer Reflectarray Employing Patch or Ring Elements of Variable Size

The paper reports on investigations into phase characteristic of a unit cell of a single-layer microstrip reflectarray, which includes patch or ring elements of variable size. The aim is to have a smaller gradient (slower slope) of the reflected wave phase as a function of the elements' size to achieve a wider operational bandwidth and smaller susceptibility to manufacturing errors. The results obtained for single resonance elements demonstrate that a slower slope can be achieved using thicker substrates at the expense of an inadequate phase range of less than 300 degrees. This inadequate phase range leads to the reflectarray elements phase errors, which reduce its directivity. To overcome this problem the use of multiresonance multiring elements is postulated. It is shown that square and circular shaped multiple rings printed on a thick substrate can offer a slower phase slope and the phase range exceeding 360 degrees. The achieved slopes and ranges of double rings are comparable with those of double stacked patches printed on the equivalent low permittivity dielectric substrate. Choosing suitable dimensions of double-ring elements, the phase characteristic can be made approximately a linear function of their size.