Radar System Engineering

614 EXAMPLES OF RADAR SYSTEM DESIGN [SEC. 15.13
perature of 50”C, and must withstand an hour’s operation at 71”C. At
the same time, because of the low temperatures at high altitude, the set
must work satisfactorily at – 55”C.
Severe vibration and shock are encountered in aircraft, and some of
the weight of an airborne radar must be spent on adequate shockisolating
mountings.
Not only must the rectifier-filter power supplies for the radar circuits
operate at any frequency from 400 to 2400 cps; they must also tolerate
poor voltage regulation and poor waveform in the primary power supply.
The presence in the same aircraft of high-power radio transmitters,
sensitive radio receivers, and a high-voltage ignition system makes it
necessary to shield and filter the radar set adequately to prevent it from
interfering with other equipment, and to protect it from interference
arising in other equipment.
Limitations Imposed by Personnel.—A radar for navigational use in
all sorts of aircraft must be manufactured in great quantity with ease
and economy, must be so simple to use and understand that only a short
period of training is necessary to operate it adequately, and must be so
easy to maintain that it can be kept in satisfactory condition with little
maintenance effort. Whereas, in principle, the operators of such a
specialized radar as a blind-bombing device could be highly trained
(though, in point of fact, few were, in the war), the operators of this
navigational set were not primarily concerned wit h learning to operate
it properly. Its own simplicity had to be great enough so that its
operation was no more difficult to master than that, for example, of the
radio compass.
15.13. General Design of the AN/APS-10.—In the framework of
these performance requirements and design limitations, the design of the
AN/APS-10 was attempted. The most important decision concerned
the wavelength to be used. At the outset, experiments were made with a
simple PPI radar based on the 10-cm lighthouse-tube transmitterreceiver
unit used in the AX/APG-15 (Sec. 6.14), using an antenna of
20-in. diameter. It was found that the range “performance was marginal.
Worse, the resolution of the set was so low that excessive skill in interpretation
was needed to navigate with the set in the absence of well-defined
geographical features. Since the larger antenna required to improve
both the range and the resolution of this set could not be housed in
aircraft without creating excessive drag, it seemed clear that a shorter
wavelength would have to be used for general navigation.
The other bands at which components had been developed were
around 3.2 cm and 1.25 cm. The l-cm art was in a very early
state, and equipment was still cumbersome and of poor performance.
For this reason, 3.2 cm was chosen. This was a fortunate choice; for