  We report a broadband microwave frequency converter based on a coherent Kerr
optical micro-comb generated by an integrated micro-ring resonator. The
coherent micro-comb displays features that are consistent with soliton crystal
dynamics with an FSR of 48.9GHz. We use this to demonstrate a high-performance
millimeter-wave local oscillator at 48.9GHz in the Q-band for microwave
frequency conversion. We experimentally verify the microwave performance up to
40 GHz, achieving a ratio of 6.8 dB between output RF power and IF power and a
spurious suppression ratio of > 43.5 dB. The experimental results show good
agreement with theory and verify the effectiveness of microwave frequency
converters based on coherent optical micro-combs, with the ability to achieve
reduced size, complexity, and potential cost.
