The impact of TACCAR on STAP algorithm convergence

In an airborne radar, clutter returns from stationary objects undergo a phase shift due to the relative motion of the airborne platform. For a low PRF radar, this phase shift can place the main beam clutter return at virtually any frequency within the clutter Doppler spectrum. Typically, a phase shift or frequency shift is applied to these returns in order to place them in the 0 Hz Doppler filter within the radar signal processor. This phase or frequency shift can be applied either on transmit or receive, and is commonly called the TACCAR shift. The term TACCAR is an acronym for time averaged clutter coherent airborne radar, and the implication of this term is that an average of pulse-to-pulse clutter phase in a coherent radar results in a measure of the main lobe Doppler frequency. In a PRI staggered STAP radar, this TACCAR shift may no longer be necessary, since the STAP solution places the null in the Doppler passband as appropriate to optimize clutter cancellation. However, given that an airborne radar usually has size and weight constraints that can result in limited on-board processing resources, a TACCAR shift may result in fewer processing operations needed to converge on a STAP solution. If this potential processing savings applies, then a TACCAR shift would still be desirable.