A new technique for RF signal frequency measurement is presented. It is based on introducing a frequency dependent phase shift to two RF signal modulation sidebands and sweeping the phase of an optical carrier. The frequency of an incoming RF signal can be determined from the optical carrier phase that results in the cancellation of the system output RF signal. The carrier phase sweeping based frequency measurement system has a very simple single-laser, single-modulator and single-photodetector structure. It is also free of electrical components. Experimental results are presented that demonstrate RF signal frequency measurement over a 2 to 20 GHz frequency range with a 0.1 GHz resolution. Frequency measurement errors of less than ±0.1 GHz for different input RF signal powers and frequencies over the entire 2 to 20 GHz frequency range are also demonstrated.