EW300: Final Exam
Radiant Power
*Energy per time* from a source (W)
How does a Track While Scan (TWS) system respond when a target fails to appear in an established tracking gate ?
*Establish a turn gate* around the last known position of the target.
Background Limited
*Lack of contrast* between *target and background*
Irradiance
*Power per unit area* incident on a surface (W/m^2)
Scan Rate
*how fast* the antenna is rotated
*Exam 3* The main purpose of the Magnetic Anomaly Detection (MAD) system is to
*provide a precise location of a submarine* with sufficient accuracy to permit weapons delivery
Smin
*weakest possible signal* that could still yield a valid return
Which statements are true about threshold levels?
-*Decreasing the threshold level* is likely to display *more false returns* -The *power level of a received signal must be greater than the threshold level* in order to be displayed on the RADAR screen. -The threshold level *can be adjusted manually*
If unambiguous RADAR range is dictating maximum detection range for a specific target, which of the following actions could an operator perform to optimize radar performance in detecting that target?
-*Increase the Threshold Level *to filter noise -*Decrease PRF* to Increase Runamb
advantages Electro Optics have over RADAR:
-Covert (passive) -Precision imaging (ID possible)
Which of the following must be true to resolve a single target from a group?
-Cross range resolution (azimuth and elevation) must be less than actual distance between targets at the same range. -Range resolution must be less than distance between actual targets at the same bearing and altitude.
What variables enhance SAR cross range resolution
-Decreased frequency -increased distance travelled by antenna
Which of the following are true regarding Track While Scan (TWS) systems compared to Servo Tracking Systems?
-Has a reduced track update rate compared to Servo Tracking Systems -Creates a track file for individual targets -Some systems employ beam splitting to enhance angular resolution. -The system is able to lead the problem by calculating where the contact will be in the future
What change in variables would result in a decreased cross range resolution for an ISAR system?
-Increase in integration time -Decrease in frequency
Which of the following result in *enhanced cross range resolution*?
-Increasing *antenna size* -Increasing *frequency* -decreasing* range to target*
select advantages of electronically steered arrays
-Instantaneous beam positioning -Less moving parts -Can adjust beamwidth to cater towards search or fire control desires
Which ranges do we attempt to maximize through system design, location, and operation to achieve the greatest distance our RADAR can detect (and correctly display) a target?
-Over the Horizon RADAR Range *Roth* -Unambiguous RADAR Range *Ruanmb* -Simplified Max RADAR Range *Rmax*
Which of the following changes would result in a decrease in maximum radar range (Rmax)?
-Reduced *RADAR cross section* of target -Widening *beamwidth* (azimuth or elevation)
Which of the following can possibly impact maximum detection range for a RADAR system?
-Transmission frequency -Shape of the target -Height of our antenna -pulse width and rest time
What does denial jamming do?
-increase you noise equivalent power; impacts Rmax
Put the following "gates" in the order used by a track-while-scan radar during a normal tracking sequence:
1)*Acquisition* gate 2)Tracking gate 3)Turn gate -----*R before U*
Select all examples of thermal radiators from the list below:
1)Car engine 2)body heat 3)Terrain
Write the steps of the Detect to Engage sequence in order.
1)Detect *DeLoClassTrackSN* 2)Localize 3)Classify 4)Track 5)Selection 6)Neutralize
Select common military applications for LASERS from the following list.
1)IR dazzler 2)Designating targets 3)Directed energy weapons 4)Range approximation
ALL characteristics that apply to LASERs
1)Inefficient 2)Low Divergence (Collimated) 3)Coherent 4)Monochromatic
the two types of antenna polarization
1)Linear 2)Circular
the key components that make up a *basic Pulsed RADAR system*
1)Receiver 2)*SINGLE Antenna* 3)Transmitter 4)*Duplexer*
The radar cross section of a target is dependent upon:
1)Size 2)shape 3)construction *material * 4)*aspect angle* of the target.
Electromagnetic wave energy is attenuated due to
1)Spreading 2)Scattering 3)Absorption
Beamforming can be achieved by which two means?
1)quasi-optical reflectors 2)antenna array
Which of the following are true regarding phased array antennas?
A 2-D array is required to focus a beam in both azimuth and elevation
Thermal Resolution
Ability to detect small variations in temperature differences
Emissivity
Accounts for the difference in *total radiant energy between Blackbody and Graybody* converts ideal exitance into actual material exitance by accounting for differences in blackbody vs graybody properties.
Regarding SAR and ISAR, which of the following is true?
All of the above. -SAR uses the motion of the transmitter/receiver to create the large aperture. -ISAR uses the motion of the target to create a synthetic aperture. -SAR is used to provide a high-resolution image of large non-moving targets. -ISAR is extremely effective in imaging surface contacts.
A linear antenna array consisting of two (2) half-wave dipole antennas, spaced λ/2 apart, and excited by the same signal in phase, would form a/an _______ beam pattern.
Broadside
Wien's Law
Calculates wavelength of maximum radiation
What type of interference occurs when overlapping EM waves have 0 degrees of phase difference between them?
Constructive
(Graph question about contrast exitance)
Contrast exitance: two curves that are drawn it is in between; *below curve helps determine thermal resolution*(energy available to integer?)
Which jamming tactic involves providing the RADAR with a *false target location* (false angles and/or ranges)?
Deception Jamming
Pulse Doppler RADAR
Detects *bearing, range, and relative velocity; ALL 3* of a target using a mixer and 1 antenna.
Basic Contiunuous Wave RADAR
Detects bearing and *relative velocity* of target using *2 antennas*. -Receiver -*Two Antennas* -*Mixer* -Transmitter
Basic Pulse RADAR
Detects bearing and range to target using a *single antenna*
Frequency Modulated Continuous Wave RADAR (FMCW)
Determines target bearing, relative velocity, and range with 2 anttenas *and changing frequency* over a given time period.
Planck's Law
Dictates the *shape of the spectral radiant emittance vs. wavelength curve as a function of temperature and wavelength*
255 is a reasonable value of bandwidth factor.
False
A SAR antenna needs the antenna to be stationary and the target to be moving.
False
Graybodies with the same temperature will always have the same radiant exitance.
False
One of the fundamental differences between Basic Continuous Wave (CW) and Basic Pulsed RADAR is that Basic Pulsed calculates contact's relative motion.
False
Smin must be greater than the received signal power at the antenna in order for detection.
False
The temperature of the environment is vital information needed to solve for bandwidth factor.
False
Fast Time Constant (FTC)
Filters away *atmospheric noise* based on rate of change of return signals.
Sensitivity Time Control (STC)
Filters away *surface-based* environmental noise near the RADAR system.
Transmittance
Fraction of energy that *remains after absorption and scattering*
Bandwidth Factor
Fraction of radiation from the target that is within the sensitive band of the detector.
Stefan-Boltzmann's Law
Gives us the *area under the curve, or exitance*
Beer-Lambert Law
Gives us the *transmittance as a function of wavelength*, environmental attenuation factors, and range to target.
Spatial Resolution
Imaging system's ability to distinguish *separate objects*
Thermal Resolution
In electro-optics, the ability to resolve multiple targets based on their temperature differences is called what?
Spot Jamming
Jamming in which all the power output of the jammer is *concentrated in a very narrow bandwidth*
Swept Spot Jamming
Jamming in which all the power output of the jammer is concentrated in a very narrow bandwidth but *periodically changed to sweep a large bandwidth*
Barrage Jamming
Jamming in which the power is *spread over a large bandwidth* at the same time
Deception Jamming
Jamming where a synthesized RADAR signature is sent to *"spoof" the enemies system*
A low level light vision system requires ______ for object detection.
Light reflected off the object
Moving Target Indicator (MTI)
Measures changes in return signal phase to *filter out stationary targets.*
Radiant Exitance
Power per unit area *emitted* from a source (W/m^2)
Irradiance
Radiant *power per unit area* that incident on a surface, regardless of direction of arrival
Noise Limited
Sensor's internal heat masks signature of target
Blackbody radiator
Substance that absorbs all incident energy and emits all absorbed energy
Which of the following is NOT an advantage of thermal detection?
Suffers little atmospheric attenuation
Pulse integration
The process of *summing successive pulses *along the same bearing in order to detect a target.
Interference
The property by which EM waves *superimpose and their energies* combine when overlapping.
In Electromagnetic warfare, Burn-through occurs when:
The range at which the power of the RADAR return becomes stronger than the Electronic Attack (EA) signal.
Diffraction
The tendency of EM waves to *spread out, or bend *around objects.
*Exam 2* Periods of the day where *target and environment contrast exitance is not present* defines what phenomena?
Thermal crossover
Exitance
Total radiant energy emitted by a body at a temperature.
Bandpass filter
Used by Doppler RADARs to* filter contacts based on speed.*
Refraction
When an EM wave passes into a *medium with a different SPEED of propagation*, and the EM wave bends towards/into the *medium of SLOWER* wave propagation.
Reflection
When an EM wave strikes a conductive surface and *bounces off* it at an angle equal to the incident angle.
Directive Gain
antenna's *ability to concentrate energy* in the beam
Threshold Level
chosen *signal level* above which a contact is displayed
PRF
determines *max unambiguous range*
Pulse Width
determines *range resolution and min range*
Antenna Aperture
effective *area of RADAR's transmitter/receiver* of energy
Noise
generated *internally and externally*, creating *false returns*
Beamwidth
half power (and greater) width of antenna beam
In the radio wave portion of the Electromagnetic spectrum, *absorption generally _____________ as frequency* ________?
increases; increases
Pulse Compression
is a *signal processing technique* in which the receiver is able to resolve two or more targets with overlapping returns down the same bearing but differ in range by varying the carrier frequency.
Servo-controlled tracking systems require an error signal as feedback to adjust the radar position. Because of this, servo trackers will always:
lag the target
What unit of measure is most commonly used to describe the Electro-Optical Spectrum:
micrometer or "microns"
Pulse Repetition Frequency (PRF)
number of *pulses transmitted per second*
A difference in starting point between two EM waves is a difference in:
phase angle
RADAR Cross Section
target's effective area that reflects RADAR energy
Pulse Width (PW)
the *active transmit time* or duration of the electromagnetic pulse
Peak Power (PPK)
the *maximum power* transmitted by a RADAR
Cross Range Resolution (RCROSS)
the *minimum angular resolution* between two targets of the same range which the RADAR system is able to distinguish as two targets
Range Resolution (RRES)
the *minimum range between two targets on the same bearing* that the RADAR system is able to distinguish as two separate targets
Rest time (RT)
the *non-transmit time* or interval between electromagnetic pulses
Duty Cycle (DC)
the *ratio of transmit time to the total time*of one transmission cycle
Pulse Repetition Time (PRT)
the total time for *one transmission cycle*
A Synthetic Aperture Radar (SAR) achieves a large effective aperture by:
using motion of the transmitter/receiver.
