Spaced-Antenna Aperture Synthesis Using an X-Band Active Phased-Array

Spaced antenna (SA) radars retrieve wind-fields by tracking resolution volume sized bins of scatterers as they advect between two physically displaced antennas. To date, SA methods have been applied for profiling the ionosphere and precipitation free atmosphere. The primary technological difficulty in applying these methods to probe precipitation at microwave frequencies is the requirement for such a short antenna separation that a significant overlap in apertures is necessary. In this article, we synthesize overlapped apertures by segmenting active phased-arrays into subarrays that are multiplexed in time. Antenna pattern measurements are then employed to evaluate beamforming errors on a family of implementations. Based on measurements and Monte Carlo simulations, we find that highly overlapping apertures are most immune to beam squint errors. This is because element-level phase errors are retained on the synthesized SAs and differential beam squint errors are minimized. Finally, we demonstrate a novel method to measure relative phase center displacement between SAs that obviates the need for near-field antenna measurements.