Full Wave Electromagnetic approach to the Calibration of Polarimetric Phased Array Radars

The Computational Electromagnetics (CEM) is widely used for designing antennas. Yet, the capability of the CEM tools is seldom used in calibration of phased arrays. Determining polarimetric characteristics of an antenna and biases in the variables using these tools are in principle feasible. We have evaluated the capability of one CEM tool to characterize polarimetric biases as function of scanning angle in the principal plane. The antenna differential gain and differential phase bias predictably the differential reflectivity and differential phase respectivly. The calibration of the large phased array radars is a challenging task for CEM due to complexity of radiating structure, as well as its size increases computation time so that calibration at every pointing direction may become impractical. Nevertheless, the path for calibration of the large phased arrays starts with scaled down models and building elements of larger arrays.

The first step in this work evaluates the capability of the CEM tool WIPL-D to simulate the element patterns and subarrays of the antenna used in the Advanced Technology Demonstrator (ATD) and possibly in the future generation of the Multifunction Phased Array Radar (MPAR). Comparisons between measured and modeled results are presented and these demonstrate satisfactory agreement. The beam steering effects are investigated for the ATD subarray. Of special interest are the effects of radome structure on the biases of the polarimetric variables. These biases are present in the measurements on the scaled down version of the ATD, the Ten Panel Demonstrator(TPD).The effects of beam steering on the differential gains and differential phases are quantified for different conditions of the radome. Finally, CEM modeling is exploited to investigate the bias source found in the TPD measurements.