CH 4: Radar System Components Flashcards
Pulse Radar System definition
Range and Azimuth is determined by…?
Pulse radars use a process of transmitting discrete bursts of RF Energy as the frequency of the radar system.
Pulse radar systems can figure out range and azimuth.
Range is determined by the time that takes a post to go to target and return. Target azimuth is determined by the relative position, or antenna orientation, when the pulse strikes the target.
Transmitter definition and purpose
The Transmitter group of a modern pulse radar normally consists of a pulse generator or waveform generator, modulator, and some kind of power amplifier.
The purpose of the transmitter is to deliver a series of high energy burst of radio frequency energy to the antenna.
Waveform generator definition
The way form generator generates the proper waveform or pulse, normally at a low power level, before delivery to the modulator.
(Part of the transmitter group)
Modulator definition
The modulator is a major portion of the transmitter. The modulator provides an extremely powerful, very short pulse of direct current (DC) voltage to the power amplifier. The modulator has an energy storage device and a switch.
(part of transmitter group)
Power amplifier definition
The power amplifier for a modern radar is normally a klystron, traveling wave tube, cross field amplifier, or solid-state amplifier. No matter what power amplifier is used, the purpose of the transmitter group is to produce a series of pulses at the correct amplitude, at the proper interval, with the exact way form, and at the operating frequency of the radar.
(Part of transmitter group)
Duplexer definition
Isolation definition
A duplexer is required when both the transmitter and receiver use the same antenna.
The duplexer acts as a rapid switch to protect the sensitive receiver from damage when the high power transmitter is on. When the transmitter is off, the duplexer directs the weak target signals to the receiver. The duplexer’s main purpose is to minimize power loss and maximize isolation.
Isolation refers to the amount of transmitter power that ‘bleeds through’ the duplex or to the receiver during transmission.
Receiver group definition
The capabilities of the receiver group are critical to read or performance. The ability of the radar receiver to detect the presence of the target return and extract the required information is limited primarily by noise. Noise can never be completely eliminated.
The most common Pulse radar receiver is the superheterodyne receiver. A superheterodyne receiver consist of an RF amplifier, a mixer and local intermediate frequency (IF) amplifier, a detector, and a video amplifier.
External noise definition
Thermal noise definition
Noise that enters the receiver through the antenna along with the target return.
Noise generated within the receiver.
Receiver Group Process Flow
RF amplifier->Mixer/local oscillator->IF amplifier-> Detector->video amplifier
RF amplifier: boosts the signal received from the antenna and duplexer and filters out as much external noise as possible.
Mixer: converts the boosted RF signal to a lower IF.
Local Oscillator: provides the signal to mix with the RF signal for the mixer to produce an IF that is easier to process.
IF amplifier: increases the IF signal level and includes a matched filter. The matches filter maximizes the signal-to-noise ratio which enhances detection of target return.
Detector: usually a crystal diode, extracts the video modulation from the IF or converts the IF to s video signal.
Master timer/synchronizer definition
The brain of a basic pulse radar- it coordinates the operation of the various parts of the radar. Exact timing within the radar is necessary to get accurate range. The master timer is an oscillator that triggers the transmitter to initiate transmission of a pulse. Simultaneously, the master timer sends a signal to initialize the display to ensure that range and azimuth information is accurately displayed.
Antenna definition/purpose
During transmission
During reception
The function of the antenna during transmission is to concentrate the radar energy from the transmitter into a shaved beam that points in the desired direction.
During reception, or listening time, the function of the antenna is to collect the returning radar energy contained in the echo signals, and deliver the signals to the receiver. Radar antennas are characterized by directive beams that are usually scanned in a recognizable pattern.
Radar display definition/purpose
4 types of radar displays
The purpose of the radar display is to take the information derived from the radar target in the receiver group and present it to the operator in a usable format.
There are four basic types of raider displays: the A scope, B scope, range height indicator (RHI) scope, and plan position indicator (PPI) scope.
A scope display definition
The A scope is used to display target range or velocity. Threat system using A scope displays include air interceptors (AI) with range-only radar, surface to air missiles( SAMs), and radar directed anti-aircraft artillery (AAA) systems.
The A scope displays range or velocity in relation to amplitude. The operator must distinguish the target return from other returns, including ground return and noise.
B scope display definition
The B scope is used to display target range and azimuth. Threat system using the scope displays include AI and SAM systems. The position of the target return to the right or left of the centerline of the screen shows the azimuth of the target. The position of the target return in relation to the bottom of the display, or zero range, shows target range.
RHI (range height indicator) scope display definition
The RHI scope is used to display range and elevation. The RHI scope is used with height finder radars, and a modified RHI scope is used for ground-controlled approach (GCA) radars. The sweep trace of the display produces a fan shaped display with the vertex at the lower left of the scope. The intent of swiped up and down and his synchronized with the display.
