Radar System Engineering

254 RADAR BEACONS [SEC. 85
radar sets, theinterrogator-responsorbecomessonearlyacompleteradar
set that it may as well be made to be one.
In the case of beacons carried by aircraft to extend the range and to
facilitate identification by ground radar sets, i~ is obviously desirable to
have only one type of beacon for all aircraft under the surveillance of a
comprehensive system of like ground radar sets. It is also desirable that
these beacons give signals of the same degree of resolution in azimuth as
that of the radar signals. It seems likely that the radar sets and beacons
will be designed together as parts of a system operating at 3000 31c/sec
or higher. There appears to be little to be gained by trying to have this
system operate at the same frequencies as the beacons for use with airborne
radar sets unless it is required that the same beacons that are to be
interrogated by the ground radar sets also reply to interrogation by
airborne radar sets.
8.5. Independence of Interrogation and Reply .—Although the fundamental
considerations that underlie the design of beacons and beacon
systems are the same as those for radar in general, there are certain consequences
of the almost complete independence of the interrogation and
reply links that need explicit mention.
Range.—The expression for the power received by the beacon is given
by Eq. (2.14). For its maximum value, using a notation defined belo\v,
we get
Subscript i–interrogation leg.
Subscript r–response leg.
Subscript T–transmitting components.
Subscript S-receiving components.
R = distance from interrogator to beacon ~aI,le units,
A = wavelength of the radiation 1 ..
P = power in watts.
Gma,= maximum value of effective gain.
(PS,)~., = maximum value of the available peak po~ver received by
the beacon.
P,, = peak value of the power transmitted by the interrogator
(radar).
(G.,)max = maximum value of the gain of the transmitting antmna
of the interrogator.
(Gs,)max = maximum value of the gain of the receiving antenna of the
beacon.
xi = transmitted
wavelength.
If we let P~i represent the peak value of available recei~-ed power
necessary for triggering the l~eacon and l?! represent the corresponding