Recent advances in air traffic control radars
This paper describes recent improvements in microwave radars used for air traffic control. These improvements have been designed to increase the target-to-clutter ratio so that adaptive thresholding can be used to give a very low false alarm rate and high probability of detection even when the aircraft target is in the presence of strong clutter. Studies show that detection suffers when three types of clutter returns are strong; namely, ground clutter, weather clutter or angels. Angels have been almost universally identified as bird flocks. Under certain terrain and propagation conditions, second-time-around clutter can also be a problem. Here ground returns from the second to last transmitted pulse are received from targets beyond the nonambiguous range. These may be from mountains or from the ground when anomalous propagation conditions occur. Meaningful improvements in this class of radar can be conveniently grouped as shown in Table I. We will briefly discuss each of the three classes listed.