A Ku-band reflectarray using variable rings and slots on the ground plane

A unit cell composed of a microstrip ring and a slot on the ground plane is presented. The phase response range of the unit cell at 18 GHz is over 440° with a smooth phase variation. A Ku band reflectarray is designed and measured at 18 GHz to verify its performance. The maximum gain and half-power beam width is 31.7 dB and 4.7°, respectively. The reflectarray gives a high gain despite of some leakage wave to back side.