Radar Flashcards
RADAR stands for ___
Radio Direction and Ranging
It works on the basis that ___ ___ can be reflected off suitable objects, and the time between transmission and reflection can be used to calculate the distance because the speed of transmission is known
microwave pulses
RADAR uses _HF
SHF
RADAR is limited to ___
line of sight
RADAR is best with __ wavelengths
short
A pulse is a short burst of __ energy mixed with long periods of silence
EM
Contiuous wave radar is used in radio __ and __ systems
altimeters, Doppler
RF energy is created with ____
magnetrons
The RF energy is released at intervals, known as the ___, which are determined by the range required.
PRF
The range of a target is determined by measuring the ___
time taken for a pulse of energy to travel there and back.
It takes _ microseconds for a wave to travel 1000m
3
Primary radar has a time interval of _ microseconds for every 1000m slant range
6
___ wavelengths are required to penetrate cloud
long
The strength of an echo received back at a radar set varies with the ___ of the target and its ___.
size, distance
The returning pulse is not reflected, but ___, as the pulse makes valence electrons ripple and release energy
re radiated
Power is ___ proportional to the square of the field strength
directly
Echo power is ___ proportional to the distance of the target
inversely
Every time you double the range of a target, you reduce the power of its echo by 2^_
4
To double the effective range of the primary radar, the power output must be increased by a factor of __
16
The transmitter has to generate __ power at ___ frequencies
high high
The radio frequency energy is produced inside the __ __ by a ___
HF oscillator, magnetron
The transmitter has to be capable of switching on and off rapidly to produce ___, achieved by the ___
pulses, modulator
The transmitter has to send out pulses at regular intervals, via the ___
synchroniser
The pulses travel through a ___ cable, or hollow metal tube called a ___ ___, which prevents excessive power loss at it is tuned to the wavelength.
coaxial, wave guide
The RF energy is injected into the waveguide by a ___
probe
A waveguide is not required for weather radar, as it uses ___ on a flat array
slots
The transmitted signal is very ___, but the received one is very weak.
strong
The receiver circuits must be protected against the ___ energy from the transmitted signals.
high
A duplexer is a routing device that directs outgoing pulses to the ___ and incoming pulses from the ___ to the ___.
antenna, antenna, receiver
Orange peel dishes produce a ___ and __ beam
wide narrow
Parabolic dishes produce a __ beam, spreading more distance
focussed
A phase array has a series of ___ ____, like small dipoles, which are arranged in a line and fed with signals that are in phase with each other.
conducting elements
The interference pattern from a phase array produce a __ beam
pencil
When receiving, a larger dish can receiver ___ signals
weaker
Beam width (degrees) = ___
( 2 x wavelength in cm ) / diameter (ft)
Beam width (degrees) = ___
( 70 x wavelength ) / diameter
The advantages of a narrow beam are ___
- Bearings easier to acquire
- Greater concentration of energy
- More range
- Target definition
A ___ pulse length with a ___ beam will get the best picture
short, narrow
The antenna should be able to produce a ___ beam and receive a __ beam
thin wide
___ antenna can eliminate lateral lobes, and concentrate more energy in the main beam
slotted
The receiver should have a _ overall gain, with ___ random noise in the circuitry
high little
The received signal is sent to the ___ ___ ___
plan position indicator
