With recent enhancements in semiconductor technology, the microwave frequency range beyond 50 GHz becomes more attractive for wideband communication applications like 802.11ad, microwave links, or automotive RADAR. Low phase noise is essential for these applications to work properly and its accurate measurement is needed to improve the performance. The test setups are difficult, especially when cross correlation of two receive paths is needed to suppress additional phase noise added by local oscillators or mixer stages. Two external harmonic mixers and a phase noise tester are used to test phase noise analysis of signal sources with frequencies up to 500 GHz.