The constructive and destructive interference gives rise to a phenomenon known as small-scale fading, where the strength of a received signal can fluctuate up to tens of dBs over the small-scale distance of just wavelengths. NIST is one of the three organizations worldwide – to our knowledge – that has taken high-precision measurements for fading at mmWave frequencies. Our measurements indeed show that the fading is weaker, as evidenced by the longer correlation distance – the distance over which the channel can be considered stationary. In addition, we have been able to demonstrate the dependence of correlation distance on beamwidth.
Our comprehensive evaluation of the impact of beamwidth on correlation distance can be found in the reference below:
 A. Hughes, S. Y. Jun, C. Gentile, D. Caudill, J. Chuang, J. Senic, and D. G. Michelson, “Measuring the Impact of Beamwidth on the Correlation Distance of 60 GHz Indoor and Outdoor Channels,” IEEE Open Journal of Vehicular Technology, vol. 2, pp. 180-193, March 2021. https://ieeexplore.ieee.org/document/9382846