Calibration of UWB UAV Radar for the Remote Measurement of Reflection Coefficient

In this work, the possibility of the remote measurement of reflection coefficient in the ultra-wide frequency range from 425 MHz to 1010 MHz from the board of unmanned aerial vehicle (UAV) using ultra-wide band (UWB) radar was investigated. With this in mind, the antenna-feeder path of UAV UWB radar is calibrated. The calibration process consisted in measuring the reflection coefficient from the brass mesh sheet at various UAV hovering heights. Printed log-periodic dipole antenna was used as transmitter-receiver antenna. As a result, the antenna return loss in an empty-room and the complex antenna response function of the antenna-feeder path of the UAV UWB radar were found. It is shown that the amplitude of the reflected wave from a brass mesh sheet can be measured with root-mean square error (RMSE), RMSE=0.017 1/m and a determination coefficient (R
²
) of R
²
= 0.967. Therewith the UAV hovering heights measured by the pulse method and the on-board laser rangefinder correlates with each other with R2=0.999 and with RMSE=3.5cm (distance measurement error of the laser rangefinder is ±1cm, surface irregularities of the brass mesh sheet were no more than 1.5cm). Measured in the frequency range from 500 MHz to 900 MHz, the reflection coefficient from fresh lake water by UAV UWB radar with a relative error of no more than 7.5% (practically does not depend on the height of the UAV hovering, approximately from 2.2 m to 5.2 m) coincides with the calculated one by the Stogryn's formulas.