Basestation antenna systems in 5G present two significant challenges for antenna measurement: up to 256 antennas and integrated transceiver with antenna, resulting in an elimination of traditional RF port interfaces and large DUTs (device under test). Several transceiver performance metrics are typically measured in far-field type conditions, including Error Vector Magnitude (EVM), Adjacent Channel Leakage Power (ACLR), and Spectral Emissions Mask (SEM). Due to the basestation size in the 5G sub 6GHz frequency bands, this requires a far-field chamber with 10 to 50 meters of range length. This paper proposes a method using a variant of a hardware based Fourier transform located in the near-field of the DUT antenna in order to create far-field conditions-a plane wave converter (PWC). A phased antenna array of 156 elements is placed within 1.5 meters of a high gain basestation antenna of dimensions 60x60 cm. There is excellent agreement between the gain measurement results of the PWC with measurement results from a certified chamber. The measurement system is bidirectional and able to directly measure both traditional antenna metrics of gain as well as transceiver metrics of EVM, ACLR, SEM, and receiver sensitivity.