SEVENTH ANNUAL
ASAP '99 WORKSHOP

Brian Freburger
Naval Air Warfare Center

Abstract This paper investigates the use of Space-Time Adaptive Processing (STAP) with circular/cylindrical arrays for the airborne early warning radar mission. Traditionally, STAP has been applied to uniform linear arrays. Due to their inherent redundancy and geometric properties (contours of constant Doppler and cone angle from the array are approximately coincident) uniform linear arrays are well suited to the STAP application. However, when considering the overall radar system, an electronically scanned circular/cylindrical array has advantages: namely, a better combination of even and continual angular and temporal coverage and mechanical simplicity because it does not need to rotate. One such array is being fabricated by Raytheon as part of the Office of Naval Research's UHF Electronically Scanned Array (UESA) program. The analysis in this paper assumes that approximately one third of the array elements are active on receive during a single coherent processing interval.

The results in this paper show that circular arrays are indeed STAP compatible, although there is a performance loss when compared to a uniform linear array. With some care in the choice and implementation of typical STAP algorithms, the loss in performance can be minimized. The majority of the degradation occurs near the clutter ridge at close ranges, where the target returns are relatively strong anyway. At long ranges the performance is barely affected. Furthermore, PRI-staggered post-Doppler STAP fares better than pre-Doppler STAP because of the latter running out of adaptive degrees of freedom. Small performance gains can be realized through focusing techniques, although these require a significant amount of extra computation.

Presentation (pdf format)