We present a method to generate a frequency-doubled microwave signal by employing a coupling-modulated ring resonator. Critical coupling is achieved when the resonator intrinsic loss is perfectly balanced by the external coupling enabled by a Mach–Zehnder interferometer coupler. The high suppression of the carrier leads to a clean two-tone optical signal with the frequency interval two times larger than that of the input microwave frequency. The beating of the two-tone signal at a photodiode generates the frequency upconverted microwave signal. A theoretical model is established to analyze the modulation process and the microwave signal generation. Experimental results show that the electrical harmonic suppression ratio is around ～20 dB (29 dB) for an input microwave signal with 5 dBm (10 dBm) power.