Radar System Engineering

CHAPTER 16
MOVING-TARGET
INDICATION
BY A. G. EMSLIE AND R. A. MCCONNELL
INTRODUCTION
16.1. The Role of Moving-target Indication.—The object of movingtarget
indication (MTI) is to present the signals received by a pulse
radar set in such a way that moving targets show up while stationary
objects give no response. The most advanced method of doing this
allows the moving targets to be presented on a PPI. Figure 16.1 shows
two PPI photographs, one with MT1 in operation and one without,
taken on a ground radar set at Bedford, Mass., using a wavelength of 10.7
cm and a PRF of 300. The removal of the ground clutter is seen to be
complete. The photographs in Fig. 16.2 were taken at Boston, Mass.,
where, because of screening by a ring of low hills, clutter does not extend
appreciably beyond 10 miles. In these photographs, taken on a set
having a wavelength of 10.7 cm and a PRF of 1650, the effectiveness of
MTI in reducing storm echoes is shown.
The problem of MTI is somewhat more difficult and the results less
satisfactory when the radar set is carried on a moving ship or airplane
because the clutter to be eliminated is itself moving relative to the radar
set and the clear-cut distinction between moving and stationary targets is
lost. In spite of this, it is possible to arrange MT1 so that vehicles
moving on the ground can be seen from an airplane. In the case of a
shipborne set it is possible to compensate for the ship’s own motion and
therefore to see other ships and aircraft in the presence of sea-clutter and
storm echoes.
16.2. Basic Principles of MTI.—Two fundamental ideas are involved
in the solution of the MTI problem: first, a method of reception that
responds differently to fixed and to moving targets; second, an arrangement
that takes advantage of this difference by selecting only the moving
targets.
The method of reception always uses the doppler effect in one form
or another. The simplest arrangement is that shown in Fig. 16.3.
Power from the transmit tw is mixed ~vith the c-w echo from the target.
After detection., the beats between the two frequencies f and f’ can be
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