This paper describes a 155Mbps self-calibrating direct transmitter for Ka-band satellite communications. It uses an 8-PSK modulation to fit the data rate of 155Mbps into a 72MHz channel bandwidth, and employs an adaptive pre-compensation technique to maximize the LO and image suppressions. An FPGA implements the 8-PSK mapper, the pulse-shaping filters and the pre-compensation, while a DSP adaptively estimates the pre-compensation coefficients. A subharmonic vector modulator brings analog inphase and quadrature signals directly from baseband to the 30GHz carrier. Experimental results show that the adaptive pre-compensation technique can effectively suppress the LO leakage and image