We show a simple, convenient, and cost-effective scheme for tunable frequency upconversion at millimeter-wave band without a local oscillator. By launching a 2.5-Gb/s directly modulated baseband signal into a Fabry–Pérot laser diode (FP-LD), the mode of the FP-LD is locked by the high-order sideband of the injected signal. The beating frequency of the injection-locked mode and the injected signal can generate upconversion subcarriers. In our experiment, tunable frequency subcarriers of 28.4, 29.3, and 30.5 GHz are obtained without any radio-frequency local oscillator. The single sideband phase noises of 83.88, 76.36, and 78.54 dBc/Hz @ 10 kHz (at 28.4-, 29.3-, and 30.5-GHz subcarriers, respectively) are shown. The proposed scheme has potential to generate much higher frequency carriers.