Investigating phase center variations due to digital beamforming

The “Phase Center” is an essential quantity for characterizing antennas in precise navigation applications such as geodetics or avionics. Signal processing algorithms generally assume the radiated wave-front from the antenna is spherical at the target position. The position of the phase center defines the position of an ideal point source radiator for the purpose of system design. Therefore, accurate determination of the phase center is crucial for system design purposes. In practice, the phase center is an estimate of the true antenna phase front. It generally depends on the angular position of the target, the polarization and the range of solid angles of interest. Because this concept is critical for proper system design, it is essential that an unambiguous self-consistent technique be implemented to determine the phase center. The phase center of complex, highly directional antennas may be very difficult and costly to measure. Other factors such as antenna mounting, feed structure or measurement uncertainty can lead to additional errors. An efficient alternative to measurement is the application of mathematical methods that take advantage of 3D electromagnetic field simulation. These approaches save time and reduce uncertainty when compared with measurement, since the antenna environment may easily be varied and measurement uncertainty is eliminated. The method used to determine the antenna PC position will be presented in this talk. This approach is currently used by the German Aerospace Center (DLR) to investigate phase centre variations (PCV) caused by digital beamforming. The far-field data obtained from HFSS are used to analyze PCV for different incident signal directions of arrival under realistic antenna conditions, accounting for mutual coupling and output impedance mismatch. Several methods for phase center calculation will be presented and their advantages and disadvantages will be discussed.