1-19
The INDICATOR produces a visual indication of the echo pulses in a manner that, at a minimum,
furnishes range and bearing information.
While the physical configurations of radar systems differ, any radar system can be represented by the
functional block diagram in figure 1-16. An actual radar set may have several of these functional
components within one physical unit, or a single one of these functions may require several physical
units. However, the functional block diagram of a basic radar set may be used to analyze the operation of
almost any radar set.
In the following paragraphs, a brief description of the operation of each of the major components is
given.
Synchronizer (Timer)
The synchronizer ensures that all circuits connected with the radar system operate in a definite timed
relationship. It also times the interval between transmitted pulses to ensure that the interval is of the
proper length. Timing pulses are used to ensure synchronous circuit operation and are related to the prf.
The prf can be set by any stable oscillator, such as a sine-wave oscillator, multivibrator, or a blocking
oscillator. That output is then applied to pulse-shaping circuits to produce timing pulses. Associated
components can be timed by the output of the synchronizer or by a timing signal from the transmitter as it
is turned on.
Transmitter
The transmitter generates powerful pulses of electromagnetic energy at precise intervals. The
required power is obtained by using a high-power microwave oscillator, such as a magnetron, or a
microwave amplifier, such as a klystron, that is supplied by a low-power rf source. (The construction and
operation of microwave components can be reviewed in NEETS, Module 11, Microwave Principles.) The
high-power generator, whether an oscillator or amplifier, requires operating power in the form of a
properly-timed, high-amplitude, rectangular pulse. This pulse is supplied by a transmitter unit called the
MODULATOR. When a high-power oscillator is used, the modulator high-voltage pulse switches the
oscillator on and off to supply high-power electromagnetic energy. When a microwave power amplifier is
used, the modulator pulse activates the amplifier just before the arrival of an electromagnetic pulse from a
preceding stage or a frequency-generation source. Normally, because of the extremely high voltage
involved, the modulator pulse is supplied to the cathode of the power tube and the plate is at ground
potential to shield personnel from shock hazards. The modulator pulse may be more than 100,000 volts in
high-power radar transmitters. In any case, radar transmitters produce voltages, currents, and radiation
hazards that are extremely dangerous to personnel. Safety precautions must always be strictly observed
when working in or around a radar transmitter.
Duplexer
A duplexer is essentially an electronic switch that permits a radar system to use a single antenna to
both transmit and receive. The duplexer must connect the antenna to the transmitter and disconnect the
antenna from the receiver for the duration of the transmitted pulse. The receiver must be completely
isolated from the transmitted pulse to avoid damage to the extremely sensitive receiver input circuitry.
After the transmitter pulse has ended, the duplexer must rapidly disconnect the transmitter and connect
the receiver to the antenna. As previously mentioned, the switching time is called receiver recovery time,
and must be very fast if close-in targets are to be detected. Additionally, the duplexer should absorb very
little power during either phase of operation. Low-loss characteristics are particularly important during
the receive period of duplexer operation. This is because the received signals are of extremely low
amplitude.
