A fully integrated 4-element phased-array transmitter at 24 GHz with on-chip PAs is implemented in a 0.18 μm CMOS process. It has a beam-forming resolution of 10°, a peak-to-null ratio of 23 dB, and isolation between paths of 28 dB. Each CMOS PA can deliver up to +14 dBm into a 50 Ω load. The transmitter supports a 500 Mb/s QPSK signal and has a bandwidth in excess of 400 MHz. The die size is 6.8×2.1 mm2 and the complete 4-element transmitter, including the 4 on-chip PAs, draws 788 mA from a 2.5 V supply.