Reflectarray element based on variable line length for millimeter-wave radar applications

This paper presents a novel structure of reflectarray element for millimeter-wave reflectarray antennas. The proposed reflectarray element is based on a cut ring patch coupled through an annular slot to a circular patch connected with a variable-length line. The reflectarray element is designed for working at 76 GHz. A progressive phase range covering 460 degrees has been achieved by varying the length of microstrip line. The linearity of the reflection phase versus line-length is also reported and improved by modifying parameters of the patches.