It may be mounted in its own cabinet or in a standard
19-inch rack.
To increase the channels available, the TACAN set
can be operated in either the X or Y mode. The Y
mode changes the pulse pair spacing and the auxiliary
burst count and spacing, and increases system delay.
ANTENNA GROUP OE-273(V)/URN
Shown in figure 2-8, the Antenna Group OE-
273/URN is a solid-state, high-performance,
electronically-scanned,
all-band TACAN antenna
system, complete with integral monitoring system and
built-in fault isolation capability. The antenna group
develops the coarse and fine bearing modulations
electronically.
Rather than forming the TACAN radiation pattern
by the old mechanical rotation method, the AS-3240
achieves the same effect by digital switching of
parasitic elements arranged in concentric arrays
around the central radiator. Twelve inner elements
provide the 15-Hz modulation (replacing the single-
phase rotating parasitic element in the mechanically
rotated antenna), and 32 outer elements provide the
135-Hz modulation (replacing the nine outer elements
of the rotated antenna).
The 15- and 135-Hz
modulation pattern is provided by electronically
switching the diodes in each of the parasitic elements
in prescribed time sequence, which is repeated once in
each 15-Hz interval.
In effect, the elements are rotated electrically,
rather than mechanically. An advantage this provides
is the elimination of the bandwidth limitations inherent
in the old mechanically-rotated antennas.
In the
electronically-scanned antenna, the appropriate ring
for a given frequency segment is activated by a fast
electronic switch, based on information from the
TACAN frequency synthesizer. This allows
instantaneous band switching and all-band operation.
Figure 2-8.—Antenna Group OE-273(V)/URN.
2-7
