This article introduces an architecture for a millimeter-wave multi-mode radar transmitter IC, which supports three key radar waveforms: 1) continuous-wave (CW/FMCW); 2) pulse; and 3) phase-modulated continuous-wave (PMCW), all from a single front end. The proposed IC, implemented in a 45-nm CMOS silicon-on-insulator (SOI) process for operation in the 60-GHz band, integrates a broadband frequency tripler, a two-stage pre-amplifier, two power mixers, and mixed-signal baseband waveform generation circuitry. The transmitter radar operation in multiple modes is enabled by configuring the power mixers and the associated waveform baseband circuitry. An important advantage of this approach is that the overall signal bandwidth, a key performance metric in radar, is limited only by the RF output nodes in pulse generation. A novel broadband frequency tripler design technique based on a current-reuse topology is also proposed for LO generation with >59% output fractional bandwidth. On-wafer measurement results for the full TX IC in CW mode show an average output power of 12.8 dBm from 54 to 67 GHz with a peak power of 14.7 dBm and the harmonic rejection ratio >27 dB. The measurement in pulse mode demonstrates programmable pulsewidth from 20 to 140 ps, which translates to >40-GHz radar signal bandwidth. The PMCW mode operation is also demonstrated in this case with 10-Gb/s PRBS modulated radar signal. The IC consumes 0.51 W and occupies 2.3\times 0.85 mm2 of die area excluding pads.