Radar System Engineering

156 C-W RADAR SYSTEMS [SEC. 5.11
in addition to those at O and 1000 cps. Naturally, these latter filters
were not nearly so critical as the one at 1000 cps.
This concludes the discussion of the design and the leading difficulties
of a system of this type.
Performance was much as expected. In particular, the strong ground
clutter mentioned above was completely eliminated, targets being
tracked regardless of range or position. All other known systems that
have been developed to the field-trial stage were tried at this same site;
none of them eliminated the ground clutter.
The only deficiency of this system, as has been pointed out, is its
inability to function properly when there are a number of targets in the
beam. When this is the case, the range indicated is that of the strongest
target. Thk difficulty may be reduced as desired by reducing the length
of the transmitted puJse, by correspondingly increasing the number of
filter bands, and so increasing the complexity.
Since the general objects of this system are much the same as those
of the MTI system described in Chap. 16, some comparison is in order,
even though this comparison is difficult and possibly dependent on
personal viewpoint.
First, the two systems regarded from an abstract point of view work
on similar principles. Both have, therefore, much the same fundamental
limitations. Practically, however, the two systems use entirely different
apparatus, and consequently when, as is usually the case, apparatus
limitations dominate, the systems may be expected to be entirely different.
Furthermore, because of this apparatus difference, one may expect
future developments to improve the two in different ways and by different
amounts.
Second, the two systems differ in their ability to handle a multiplicity
of targets. As actually constructed, MTI syst~ms use 1- or 2-~sec
pulses and so are capable of handling targets a thousand feet or so apart
in range. On the other hand, the system described in this section works
on only one target, and although a moderate number of additional filters
might be considered as possible whenever anyone wishes to deal with
multiple targets there is certainly a practical limit to their number.
Possibly dividing the total range into 10 pieces would be reasonable.
For traffic control around a busy airport, however, the c-w system would
be almost useless whereas the MTI system would be very good. For
long-range detection of aircraft, an ability to handle 10 targets might
well suffice and the c-w system therefore be adequate.
When, on the other hand, one considers severe ground clutter the
system described above has the advantage over the MTI systems. MTI
systems at present reduce the clutter by perhaps 30 db-which in many
locations is adequate. But mountainous terrain that does not appear