A GPS antenna multipath rejection performance evaluation was conducted at Lincoln Laboratory. Ground reference station antennas and aviation patches were tested for their ability to reject a muitipath signal. Different types of ground plane structures were used such as choke rings, ground planes, and mock sections of fuselage. Frequencies transmitted were L1 (1575 MHz), L2 (1227 MHz), and the median GLONASS frequency (1609 MHz ). Receive amplitude and phase were measured on each antenna. Subsequently, these data were converted to absoIute gain for a right-hand and Ieft- hand circularly polarized signal as a function of satellitte elevation angle. (Not Complete)