The components of the pulse radar and their function in:-
(a) Timer. This unit provides sharp trigger or timing pulses of fixed frequency for transmitter and indicators.
(b) Pulse Modulator. Once trigger pulse is received from the timer the pulse modulator produces sharp rectangular pulses of HT voltage for fixed duration to bring the transmitter(Tx) Oscillator into conduction.
(c) Transmitter. This may is a high power oscillator like magnetrons. This transmitter produces RF energy during the pulse period. The RF energy is fed to antenna via duplexer.
(d) Duplexer. Normally a single antenna is used in radar sets for transmitting and receiving. Duplexer is nothing but a electronic switch, which consists of TR and ATR. During the transmission the TR prevents RF energy entering in to receiver and during reception the ATR switch takes care to see that whole RF energy in the echo pulse is directed into the receiver.
(e) Antenna. It is a mechanical device, which acts as the transducer between free space and trans-receiver equipment. The RF energy is concentrated into a narrow beam by a highly directional antenna. It is rotated 360° for search purpose. The rotation of antenna is synchronised with the rotation of Time base in indicators.
(f) Receiver. A highly sensitive Super Heterodyne receiver is used in the radar sets. The first stage may be a low noise RF amplifier. Generally RF amplifier is avoided. Therefore the first stage of radar receiver is a mixer stage.
(g) IF Amplifier. These may have a centre frequency of 30 M Hz or 60 M Hz and a bandwidth of 1 M Hz. The purpose of this unit is to amplify the received signal at IF and give its output to the next stage i.e., detector.
(h) Indicator. This unit combines information received from three different units of radar sets. They are :-
(i) Timing information received from timer for synchronising start of time base with start of transmission for measuring accurate range.
(ii) Rotation information received from antenna.
(iii) And also the actual video from the detector and video amplifiers.
Study on Pulse Diagram
a – Pulse Width b – Pulse Repetition Period c – Peak Power d – Average Power
Pulse Width (PW). It is the duration “T” for which the radar Tx sends the RF Energy into the space. It is represented in microseconds.
Pulse Repetition Frequency (PRF). The number of pulses transmitted by the transmitter in one second is called PRF or the pulse repetition frequency. It is represented in Hz and it is normally between 200 to 10000 Hz.
Pulse Repetition Period (PRP). It is the time interval between the start of one pulse to the start of next pulse. In other words, it is the inverse of PRF i.e., 1/PRF will give you PRP.
Peak Power (PP). The instantaneous power of the transmitter during the pulse is defined as the peak power.
Average Power (AP). The amount of power transmitted in one second is called average power.
P Av = PP x PW X PRF
= PP x Duty cycle
Duty Cycle. It is the product of PRF and pulse width. It gives the total time the transmitter was on in one second.
Duty Cycle = PW x PRF