EO1-3 Flashcards
RADAR stands for?
Radio Detection and Ranging
Reflection
Change in the direction of a wave when it meets a different media. (The change in direction of a radio wave as it bounces off a target)
Refraction
Change in the direction of a wave due to a change in the transmission medium. (some of the energy will slow down and change direction slightly as it penetrates the targets surface)
Diffraction
A portion of the waves energy hits a target and bends around it.
Absorbtion
When the target takes in some of the EM energy and transforms it into internal energy.
Polarization
Orientation of a radio wave
Noise
Unwanted enegry that interferes with target detection.
Scatter
When a radio wave hits a target and bounces off in many directions at once.
What can a Radar measure?
Range, Angle, and Relative Velocity
Continuous wave Radar
Send out a continuous signal from one antenna, which bounces off the target and returns to a second antenna.
Pulsed radar
Sends a signal from a transmitter through an antenna. Then stops transmitting, so return pulses can come through the same antenna.
A pulsed radar has a monostatic or bistatic configuration?
Monostatic Configuration
Pulsed radars are good at determining what?
Range
CW radars are better at determining what?
velocity
How well a radar can measure angle depends on what?
The precision with which a radar can focus the waves into a beam
Beamwidth
The amount spreading in the main portion of the radars beam. Measured in degrees.
A complete measurement of angle includes what two measurements?
Azimuth and Elevation
What is relative velocity?
The measurement of how fast a target is moving toward or away from the radar.
You measure relative velocity how?
by using the Doppler Effect
What is the doppler effect?
The waves reflecting off a target will be compressed or stretched due to a targets motion.
Periodic wave
Waves that repeat the same basic voltage or current variations, over identical time interval.
Aperiodic wave
Waves that do not repeat.
What is a phase angle?
An expression in degrees or radians of a specific point in time in time with relation to freq.
A sine wave can be described in terms of what?
Amp, freq, and period or phase
What is a period?
The measure of time interval between 2 identical points on 2 adjacent cycles.
When 2 waves have any phase difference they are said to be what?
Out of phase
When 2 waves have 0 phase difference and have the same period they are said to be what?
In phase
When 2 waves are 90? out of phase they are said to be white?
In quadrature
When 2 waves a 180? out of phase they are said to be what?
In opposition
Fundamental Freq
The first sine wave in a series
Fourier analysis
a mathematical procedure for decomposing a complex waveform into a collection of sine waves with various frequencies and amplitudes
Bandwidth
The range of a band of freq, measured between the lowest freq limit and highest freq. limit of the band.
All other harmonics are integer multiples of what?
The Fundamental Frequency (FF)
The FF is equal to what?
The Pulse Repetition Frequency (PRF)
The Fast Fourier Transformation (FFT)
Doppler radars transmit and receive a pulse train and then continuously translate the data from the time domain into the freq domain.
What is spectrum?
Is the distribution of the amplitude and phase of the components of a wave as a function of frequency.
Optimum BW
3rd drop out. (3/PD)
Minimum BW
1st drop out. (1/PD)
Pulse Duration Formula
1/BW min
Signal to Noise ratio (SNR)
The ratio between the received signal and the noise
False Alarm
Noise threshold set too low causes radar to declare a target detection when there is no target present.
Missed Detection
Thresh hold is set too high, low power returns from a target will not register.
What is Range Resolution?
The ability to make the distinction between two ojbects.
What does the compression ratio indicate?
The amount of increase of power within the PD effective as compared to the transmitted PD actual.
What is freq excursion?
The total change in freq over the duration of a pulse.
How can a radar system transmit more engery to the target, using lower power pulses but still maintaining a desired range res?
Made possible by match filter, is intrapusle modulation.
What is intrapulse modulation?
The changing of the phase or freq while transmitting a pulse.
Intrapulse Modulation can be evaluated by what 3 factors?
Compression ratio, peak-to-sidelobe ratio (PSR), and Doppler Tolerance
Most prevalent method of intrapulse modulation?
LFMOP
What is Linear Frequency Modulation on the Pulse (LFMOP)?
Type of intrapulse modulation. is the constant increasing or decreasing of freq during transmission of a pulse. Aka Chirp
What is Non-Linear Modulation on the Pulse (NLFMOP)?
Applies a weighting function to a LFMOP signal. (Less doppler tolerant. Lower PSR.)
What is the strongest LFMOP sidelobe?
-13.2dB down from the main lobe.
T/F High PSR can cause detection problems?
True. can cause problems in low power returns.
What is Doppler Shift?
The change in freq caused by moving targets.
What is Doppler Tolerance?
The range of Doppler frequencies over which a wave form can still detect targets after match filtering.
T/F LFMOP waves are not doppler tolerant
False. LFMOPs naturally extend over a large range of frequencies. while the Doppler Shift will shift the entire range of freq up or down, most of the range will still correlate in the matched filter.
Consequence of Doppler shift in relation to PD?
Larger doppler shifts will correlate less, degrading pulse compression and creating a larger PD.
Consequence of Doppler shift in relation to target detection?
Not all of the signal will correlate, resulting in a lower amp with which to make a target detection.
Phase Shift Keying (PSK)
Digital modulation scheme that conveys data by changing (modulating) the phase of a reference signal (carrier wave).
Bi-Phase Shift Keying
Is an intrapulse modulation technique that encodes a pulse with a binary code using the 180? phase shift.
What is the simplest form of phase shift keying?
BPSK
What is minimum bit?
Phase shift occurring at integar values of a minimum time increment.
How do you find minimum bit?
Measuring the smallest amount of time between two phase shifts.
PD effective for BPSK is always equal to what?
The duration of the minimum bit.
For BPSK the compression ratio will always be the same as what?
The number of bits.
BPSK: How to find PSR when auto correlating?
Take the peak correlation, biggest number. And comparing it to the highest side lobe.
What is a Barker code?
Is a finite binary sequence with the ideal auto correlation property, such that the off-peak auto correlation coefficients are as small as possible.
Advantages of Unmodulated Intrapulse waveform?
No time/Range Side lobes.
Disadvantages of Unmodulated Intrapulse waveform?
No pulse compression
Advantages of LFMOP?
Good Pulse Compression
Disadvantages of LFMOP?
High PSR (-13.2dB)
Advantages of NLFMOP?
Good Compression (less than LFMOP)
Advantages of BPSK?
Good Pulse Compression (min bit)
Disadvantages of BPSK
Not Doppler Tolerant
Quadriphase PSK
4 points on constellation diagram. 4 phases, shifts 90° when phase shifting. or multiples of 90°.
Polytime Modulation
Changes the time spent on a phase
Blind ranges/main bang eclipsing occur when?
When a target is at a distance from the radar such that the target echo returns to the radar during the time in which another pulse is being transmitted. The radar is then blind to all returns while it is transmitting a pulse. Cant see the target.
What are range ambiguities?
When the target echo from one pulse doesnt make it back to the radar until another pulse has been transmitted.
MUR Formula
C×PRI/2
Interpulse modulation involves changing what?
Changing the time intervals between pulses.
Pulse constant
uses only 1 PRI value
What 3 things do you need for a stagger?
Element, position, firing order
Stagger helps what?
Reduce blind speeds and ranges
Freq excursion is the inverse of what?
PD effective
Dwell and switch
dwells on a PRI for a number of pulses, then switches to a new PRI.
Jitter
Transmits a pulse train using randomly selected PRI values between fixed lower and upper limits. No pattern.
Continous Jitter
PRI values can be anything at all in between the limits.
Discrete Jitter
Only specific PRI values will be used.
What is a special kind of jitter?
Pulse freq modulation
What is a shift register generator (SRG)?
A means of generating random numbers for electronic protection.
Linear recursive sequence (LRS)
number list generated by SRG.
What is MLS ?
Maximum length sequence. 2^n-1
What is Signals Intelligence (SIGINT)?
Intelligence gathering by the interception of signals such as; Communications Intelligence Signals (COMINT), Non-communicative Electronic Intelligence Signals (ELINT), and Foreign Instrumentation Intelligence (FISINT).
ELINT is divided into what 2 major branches?
Technical ELINT (TechELINT) and Operational ELINT (OpELINT)
What is Technical ELINT?
The fine-grain measurement and analysis of signal parameters that describes the signal structure, emission characteristics, modes of operation, emitter functions, and weapons systems associations of such emitters as radars, beacons, jammers, and navigational signals.
A main purpose of TechELINT is
to obtain signal parameters which can define the capabilities and the role that the emitter plays in the larger system, such as a ground radar locating aircraft, and thus lead to the design of radar detection, countermeasure, or counterweapons equipment.
The overall process, including operation of the countermeasures, is…
part of Electronic Warfare (EW).
What is Operational ELINT (OpELINT)?
which concentrates on locating specific ELINT targets and determining the operational patterns of the systems.
OpELINT results are commonly called
Electronic Order of Battle (EOB).
OpELINT also provides threat assessments, often referred to as
tactical ELINT.
OpELINT intelligence products support…
military operational planners and tactical military commanders on the battlefield
Decibel (dB)
a unit used to measure the intensity of a sound or the power level of an electrical signal by comparing it with a given level on a logarithmic scale.
RADAR- Bistatic Configuration:
the transmit and receive antennas are at different locations as viewed from the target (e.g., ground transmitter and airborne receiver).
RADAR- Monostatic Configuration:
the transmitter and receiver are co-located as viewed from the target (i.e., the same antenna is used to transmit and receive).
RADAR- Quasi-monostatic Configuration:
the transmit and receive antennas are slightly separated but still appear to be at the same location as viewed from the target (e.g., separate transmit and receive antennas on the same aircraft).
Normal radar functions:
- range (from pulse delay), 2. velocity (from Doppler frequency shift), 3. angular direction (from antenna pointing)
Signature analysis and inverse scattering includes:
target size (from magnitude of return), target shape and components (return as a function of direction), moving parts (modulation of the return), material composition
The complexity (cost & size) of the radar increases…
with the extent of the functions that the radar performs.
Radiowaves
A category of EM waves at the low end of the RM spectrum, with frequencies ranging from 3kHz to 300GHz.
Scatter is also referred to as…
Diffuse Reflection
Types of Scatter include:
Forward Scatter, Backscatter
How are the PRF and the PRI related?
They are the inverse of each other.
Gain
is the radiation intensity relative to a lossless Isotropic reference.
Modulation
can be defined as the process of impressing information from a modulating signal onto another signal called the carrier.
Amplitude modulation (AM)
is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave.
Angle modulation
is a class of carrier modulation that is used in telecommunications transmission systems. The class comprises frequency modulation (FM) and phase modulation (PM), and is based on altering the frequency or the phase, respectively, of a carrier signal to encode the message signal.
