Characterisation of Horizontally Induced Vibrations on Antenna's Channel Response at Millimetre-Wave

This paper characterises the impact of horizontally induced vibration on the antenna's channel response due to fast vehicle manoeuvres or the side push of wind during the overtaking of a large vehicle on a motorway at millimetre wave (mmWave) frequencies. The resultant misalignment perturbs the point of observation, which produces Doppler shifts. A new composite antenna and channel model, including horizontal vibration within the antenna mounting, is developed by measuring the scattering parameters (S21) at discrete intervals of time using a vector network analyser (VNA) that generates a swept tone with a radio frequency (RF) measurement bandwidth of 2GHz centred at 25.5GHz. The S21 over discrete intervals of time represents the channel time-frequency transfer function which is utilised to generate the Doppler variant transfer function and the Doppler power spectrum after post-processing at a vibration frequency below 100Hz. It is proven experimentally that the induced Doppler power is directly proportional to the probability density function (PDF) of the Doppler Shifts. This indicates that Doppler shifts with high probabilities of occurrence have higher Doppler powers. For example, a Doppler shift ≤2000Hz having a PDF = 0.6 or above arrives with a higher power of up to −20dBm as compared to the Doppler shift of ±4000Hz, which has a lower PDF = 0.1 and Doppler powers ≤−25dBm.