Radar System Engineering

SEC.11.11] DESIGN CONSIDERATIONS FOR THE R-F HEAD 423
Types oj Container.—If the r-f head is not pressurized, the supporting
framework for the parts will be a rectangular affair consonant with the
standard construction practices used on the rest of the radar. The usual
rules of accessibility and convenience will dictate the placement of parts.
If, however, the unit is to be pressurized, further consideration must be
given to the container. It is almost essential to be able to remove the
pressure cover and make tests and adjustments without disconnecting
the r-f transmission line or any power or signal cable. This rules out
methods of mounting the units in which the support brackets attach
Although rectangular containers are most economical of space, they
are difficult to pressurize because of their tendency to become spherical
under pressure, with resultant severe shear strains in the corners. In a
ship set, where only small pressure differentials are expected, a rectangular
cover is feasible. If it is not too large, a rectangular housing cast out of
light metal can be made strong enough to stand the 30 lb/inz test pressure
required for airborne r-f heads. It has been common practice, however,
to use cylindrical housings with domed ends because only tensile strains
are then involved and the housing can be very light.
One example of pressurized airborne container design is illustrated
in Fig. 11.27, and discussed fully in Sec. 11.12.
The heat generated in the magnetron rises as the average power level
is increased, but the generation of heat in the receiver components is
substantially constant from one radar set to another. If the transmitter
power is more than about 50 kw, the thermal load for any pressurized