For airborne early warning （AEW） radars with a side looking rectangular plannar phased array

if the elements in each column are combined into a subarray at the microwave level first

the random amplitude and phase errors existing inevitably in the array elements would give rise to much differeme in column subarray patterns in elevation

especially in sidelobearea

and result in the received clutter with nonstationary characteristics.It is highly desirable that the weight vectors of space time adaptive processing （STAP） be able to adapt the nonstationary characteristics in time.For this purpose

a fast recursive algorithm is presented based on an inverse QR decomposition in this paper.The computer simulation results show that the weight vectors obtained by the proposed algorithm allow the space time adaptive processor outperform the Capon adaptive processor for the rejection of the clutter with nonstationary characteristics.