RDR - 1 Flashcards
What does RADAR stand for
RADIO DETECTION AND RANGING
Describe the function of common Radar devices: Magnetron
- The purpose of a magnetron is to convert a high
energy DC pulse into an extremely high frequency pulse. - It was commonly used in airborne RADAR due to its light weight, high efficiency, and small size.
– P3C APS-115 used a magnetron transmitter.
Describe the function of common Radar devices: Travelling Wave Tube (TWT)
- The TWT is a broadband, low noise amplifier.
- Its advantage over a magnetron is its low noise factor.
– P-8 APY-10 use a TWT transmitter.
Describe the function of common Radar devices: Waveguides
- Waveguides are hollow, generally rectangular tubes that guide electromagnetic (EM) energy by reflecting energy off the inside surfaces of the waveguide.
- Because the cross sectional dimensions of a waveguide must be of the same order as those of a wavelength, use at frequencies below 1 GHz is not normally considered.
- Waveguide dimensions decrease as the frequency increases.
Describe the function of common Radar devices: Antenna
- An antenna is a device used for radiating radio waves into free space or receiving radio waves from free space.
- The size and design of antennas vary in accordance with the frequency (or wavelength) used.
- The length of the antenna must be matched as closely as possible to the wavelength of the carrier waves.
Describe the function of common Radar devices: Antenna Couplers
- An antenna coupler is a device which makes it possible for one or two antennas to do the electrical work of
many, as opposed to using a separate antenna for each individual wavelength.
Describe the following terms and state their units of measurement: Frequency
- Frequency is the cycles per second of a transmitted signal.
- Unit of measure – Hertz, (Hz) Mega Hertz (MHz) or Giga Hertz (GHz).
1 Hz = 1 Cycle Per Second
two types
- pulsed RF (Nav Radar)
- Continuous wave (Radio station)
Describe the following terms and state their units of measurement: Pulse Width
- Duration of the transmitted pulse measured from the leading edge to the trailing edge of the pulse.
- Unit of Measure - Microseconds (µsecs).
Describe the following terms and state their units of measurement: Pulse Repetition Interval (PRI)
- Time period from the leading edge of one pulse to the next leading edge.
- Unit of measure – micro seconds (µsecs).
Describe the following terms and state their units of measurement: Pulse Repetition Frequency
- Number of pulses transmitted per second.
- Unit of measure - Hertz (Hz).
Describe the following terms and state their units of measurement: Duty Cycle
- Ratio of Transmitter (Tx) ON time over the total pulse period.
- Pulse period is measured from the leading edge of the first pulse to the leading edge of the next pulse.
- No unit of measure – expressed as a percentage.
Duty cycle = Pulse width/Pulse Repetition Interval
Describe the following terms and state their units of measurement: Peak Power
- The amplitude of the transmitted pulse.
- Unit of measure - Kilo Watts (KW) or Mega Watts (MW).
Describe the following terms and state their units of measurement: Average Power
- Output power of a transmitter as measured from the start of one pulse to the start of the next pulse.
- Unit of measure - Watts (W).
Describe the following terms and state their units of measurement: Antenna (AE) Scan Rates
- The speed at which the antenna rotates through 360 degrees.
- Unit of measure – Seconds Per Rotation (SPR).
Explain how RADAR range is derived.
- Range is determined by measuring the time taken for the pulse to leave the RADAR antenna, reflect off a target, and then be received back at the RADAR antenna.
Explain how RADAR bearing is derived.
- Bearing is determined by the direction that the antenna is pointing at the time of reception
What are the two RADAR Principles?
- A high energy pulse is transmitted.
- When it strikes an object, a portion of that pulse may be reflected back to the RADAR.
Describe Exciter
- Exciter – The purpose of an exciter is to generate a
continuous, highly stable, low power signal at the
desired frequency (which is fully selectable) and phase
for output to the transmitter. A reference signal is also
sent to the receiver for phase comparison of the
received pulse.
Describe Transmitter
- Transmitter –The purpose of a transmitter is to
produce the required Radio Frequency (RF) at
sufficient power levels. Transmitters include
magnetrons, klystrons and travelling wave tubes
(TWTs).
Describe Duplexer
- Duplexer - The purpose of the Duplexer is to permit the alternate use of the same antenna for both transmission and reception.
Describe Antenna
- Antenna - The purpose of the antenna, in a basic pulsed
RADAR system, is to provide a coupling between free
space and the transmitter / receiver. The antenna is used
to transmit RF energy into space, concentrating that
energy into a narrow beam. The antenna is also used to
receive energy returned from RADAR targets.
Describe Antenna Couplers
- Antenna Couplers - An antenna coupler is a device
which makes it possible for one or two antennas to do the
electrical work of many, as opposed to using a separate
antenna for each individual wavelength.
Describe Signal Processor
- Signal Processor - Digitised signals from the receiver
are fed to the Signal Processor and sorted by range
and doppler frequency (using a bank of Doppler Filters).
The Signal Processor filters out ground clutter, and
automatically detects target echoes. Echo locations are
stored in a digital memory, then continuously scanned
for display. - Main goal is = Improve the signal to interference ratio
Describe Receiver
- Receiver – The purpose of a receiver is to receive the
weak echo from a target, amplify and present that echo
to the signal processor in a suitable format for
processing.
Describe RADAR Data Processor (RDP)
- RADAR Data Processor (RDP) - The purpose of the RDP is
for:
– Control and performance of routine computations for all RADAR units.
– System timing.
– Scheduling operating mode selection e.g. long range
search, tracking and imaging modes (SAR / ISAR).
– Antenna stabilisation and control, using aircraft Inertial
Navigation Unit (INU) inputs.
– Track acquisition and target tracking.
Describe Display
- Display – Provides the operator with a visual representation
of target echoes.
