1-20
Antenna System
The antenna system routes the pulse from the transmitter, radiates it in a directional beam, picks up
the returning echo, and passes it to the receiver with a minimum of loss. The antenna system includes the
antenna, transmission lines and waveguide from the transmitter to the antenna, and the transmission line
and waveguide from the antenna to the receiver. In some publications the duplexer is included as a
component of the antenna system.
Receiver
The receiver accepts the weak echo signals from the antenna system, amplifies them, detects the
pulse envelope, amplifies the pulses, and then routes them to the indicator. One of the primary functions
of the radar receiver is to convert the frequency of the received echo signal to a lower frequency that is
easier to amplify. This is because radar frequencies are very high and difficult to amplify. This lower
frequency is called the INTERMEDIATE FREQUENCY (IF). The type of receiver that uses this
frequency conversion technique is the SUPER HETERODYNE RECEIVER. Superheterodyne receivers
used in radar systems must have good stability and extreme sensitivity. Stability is ensured by careful
design and the overall sensitivity is greatly increased by the use of many IF stages.
Indicator
The indicator uses the received signals routed from the radar receiver to produce a visual indication
of target information. The cathode-ray oscilloscope is an ideal instrument for the presentation of radar
data. This is because it not only shows a variation of a single quantity, such as voltage, but also gives an
indication of the relative values of two or more quantities. The sweep frequency of the radar indicator is
determined by the pulse-repetition frequency of the radar system. Sweep duration is determined by the
setting of the range-selector switch. Since the indicator is so similar to an oscilloscope, the term RADAR
SCOPE is commonly used when referring to radar indicators.
Q17. What radar subsystem supplies timing signals to coordinate the operation of the complete
system?
Q18. When a transmitter uses a high-power oscillator to produce the output pulse, what switches the
oscillator on and off?
Q19. What radar component permits the use of a single antenna for both transmitting and receiving?
SCANNING
Radar systems are often identified by the type of SCANNING the system uses. Scanning is the
systematic movement of a radar beam in a definite pattern while searching for or tracking a target. The
type and method of scanning used depends on the purpose and type of radar and on the antenna size and
design. In some cases, the type of scan will change with the particular system mode of operation. For
example, in a particular radar system, the search mode scan may be quite different from that of the track
mode scan.
Stationary-Lobe Scanning
A SINGLE STATIONARY-LOBE SCANNING SYSTEM is the simplest type of scanning. This
method produces a single beam that is stationary in relation to the antenna. The antenna is then
mechanically rotated continuously to obtain complete 360-degree azimuth coverage. A stationary lobe,
however, cannot satisfactorily track a moving object because it does not provide enough information
about the object’s movement to operate automatic tracking circuits, such as those in fire-control tracking
