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Section
IV
THEORY OF OPERATION
4.1
Principle
of
Operation
There are
two
radar systems
used
in air
traffic
control. The
first
system, which
is
designated the
primary
radar system opera
tes
on the normal radar principle. i.e.
with
reflected pulses. The second system. designated
the secondary radar system, coded response
pulses
are inîtiated in the aîrcraft
ATC
transponder
equipment
by
interrogation pulses sent by the ground stations. Bath radar systems usually
work
together
to
profit
from
the advantages
of
both.
SSR
ANTENNA
PSR
--
ANTE
NNA
------=--=-----MAIN
PlLSE
---
--·
------
--···
4.1.1
Primary Radar System
JL
MAIN
PULSE
-
REFLE:CTED
INTERROGATION
---PULSES
..
COOED
REPLY
PULSES
}
PRIMARY SURVEILLANCE
RADAR (PSRl
}
SECONDARY SURVEILLANCE
RADAR (SSRI
The primary radar system
is
based
on the pulses radiated
by
a radar antenna being reflected and received
by
the antenna, this thus being referred
to
as
passive
return radiation. Depending on the corresponding
position
of
the antenna, the direction and the
time
the pulse takes between targets and antenna determines
the distance. This
information
is
displayed on the radar screen
of
the
air
traffic
contml.
The main advantage
of
the
primary
radar system
is
its independent mode
of
operation,
since
it
requires
no
support
from the
aircraft
system.
On
the other hand, the effectiveness
of
the
primary
radar system
is
1 i
mited
over 1
ong
distances,
low
ai
re
raft
height
and
under
certain weather conditions.
4-1
The document reference is online, please check the correspondence between the online documentation and the printed version.
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