Absolute Group Delay Characterization of GNSS Antennas for Reference Receiver Chains

Abstract

Traditionally, group delay characterizations of GNSS antennas have been performed either inside of a portable anechoic chambers or by real measurements of GNSS signals and a short baseline setup. For the results presented in this paper, the characterization of antennas inside anechoic chambers will be investigated. The antenna under test, in our case a Leica AR20 antenna, is calibrated inside the anechoic chamber present at ESTEC laboratories, using a standard gain horn as a transmitting antenna. The standard gain horn antennas have relatively high gain, and thus represent a good transmitting antenna for the calibration as they minimize the illumination of the side walls of the anechoic chamber. The calibration of the group delay of the transmitting antenna is done by means of two identical antennas using transmission method. An accurate measurement of the distance between the antenna reference points is also done, in order to remove the delay introduced by the free space propagation. The final value of group delay is referenced to the antenna reference point (physical point defined by manufacturer), but can be easily transformed to antenna phase center (mathematical point), if the offset of such a point is known. Finally, the variations in group delay versus azimuth and elevation are estimated, as well as the uncertainty budget. Considerations and remarks observed during the testing phase are highlighted throughout the paper.