15.1 INTRODUCTION TO MTI RADAR

The purpose of moving-target indication (MTI) radar is to reject signals from fixed or slow-moving unwanted targets, such as buildings, hills, trees, sea, and rain, and retain for detection or display signals from moving targets such as aircraft. Figure 15.1 shows a pair of photographs of a PPI (plan position indicator) which illustrate the effectiveness of a properly working MTI system. The distance from the center to the edge of the PPI is 40 nmi. The range marks are at 10-nmi intervals. The picture on the left is the normal video display, showing the fixed-target returns. The picture on the right shows the MTI clutter rejection. The camera shutter was left open for three scans of the antenna; thus aircraft show up as a succession of three returns.

Figure 15.1: ( a) Normal video. ( b) MTI video. These PPI photographs show how effective an MTI system can be. Aircraft appear as three consecutive blips in the right-hand picture because the camera shutter was open for three revolutions of the antenna. The PPI range is 40 nmi.

MTI radar utilizes the doppler shift imparted on the reflected signal by a moving target to distinguish moving targets from fixed targets. In a pulse radar system this doppler shift appears as a change of phase of received signals between consecutive radar pulses. Consider a radar which transmits a pulse of RF energy that is reflected by...