EW300 Final Review
What parts of the Rmax equation account for spreading?
(4pi)^2 and the fourth root
List the advantages and disadvantages of RADAR versus visual detection systems
Advantages: longer ranges, day/night, sees through clouds Disadvantages: lower resolution, not covert (RADAR gives off energy)
Pulse Doppler is an advanced version of which kind of basic radar principle?
Basic pulsed RADAR
What is meant by ambiguous range?
Beyond a certain range, the radar cannot determine which pulse is being returned, thus throwing off range calculation
A linear antenna array consisting of several half-wave dipole antennas, spaced λ/2 apart and excited by the same signal in phase, would form a/an _______ beam pattern.
Broadside
Match each tracking RADAR with the most appropriate definition:
Conical Scanning RADAR uses a circularly-rotating single beam to track the movement of a target Dual Beam RADAR uses the overlap of two beams to improve accuracy sufficient enough for weapons delivery Monopulse RADAR uses the overlap of four beams to improve accuracy for fire control tracking
Wou assume watch and notice lights of several vessels on the horizon however you observe that no targets are displayed on the surface search PPI. What can your RADAR operator do to correctly display the contacts?
Decrease threshold, increase display range, increase gain
What wave propagation property allows radio waves to "bend" over the horizon?
Diffraction/refraction
T/F - 7. A dipole antenna radiates its energy in all directions perpendicular to its axis, resulting in an electromagnetic field that resembles a sphere.
False
T/F - A Phased Array Radar uses actuators to mechanically move the antenna to steer the beam.
False
T/F - A changing electic field produces a changing gravity field.
False
T/F - A changing magnetic field produces a changing gravity field.
False
T/F - One of the fundamental differences between Continuous Wave (CW) and Basic Pulsed RADAR is that Basic Pulsed has a longer Duty Cycle (DC)?
False
T/F - One of the fundamental differences between Continuous Wave (CW) and Basic Pulsed RADAR is that CW has a shorter Duty Cycle (DC)?
False
T/F - Smin must be greater than the received signal power at the antenna in order for detection.
False
T/F - The simplest form of an electromagnetic antenna is the phased array antenna.
False
Match the proper wave propagation path with the its respective characteristics.
Ground waves: Ducting; Low Frequency; Long Range (Waves can act as if trapped in a duct) Sky Waves: Bent due to Refraction; Medium Frequency; Long Range (note low and medium frequency, very long range propagation is possible) Space Waves: Straight-LOS; High Frequency; Short Ranges (note almost all HF band operate exclusively as this wave.
Select all the thermal radiators (that is, not a selective radiator) from the list below:
Heated Tank Gear (Friction) Heated Ship Stack
What can an ISAR operator do to improve the ISAR return image?
Increase integration time (T)
Which of the below actions will increase the Max RADAR Range?
Increasing Antenna Size (Ae) Increasing Receiver Sensitivity (smaller Smin)
How does increasing the radio frequency affect the power density/shape of the main lobe?
Increasing the frequency decreases the beam width which increases the power density
Servo-controlled tracking systems require an error signal as feedback to adjust the radar position. Because of this, servo trackers will always:
Lags the target
Select all the selective radiators from the list below
Laser Jet Engine Exhast
List selective radiators pertinent to weapon systems:
Laser (laser target designator) Flares (as counter measure for heat seeking missile) Infrared strobe (for NVG target designation) IR Glow stick (for NVG target designation)
A low level light vision system requires:
Light reflected off the object
Select the two types of antenna polarization:
Linear (Vertical and Horizontal) and Circular
In general, do longer or shorter wavelengths "bend" more?
Longer bend more
This system measures changes in the phase of a returned signal (via a phase comparator) in order to determine the motion of the target:
MTI
RADAR cross section is dependent on which factors?
Material, aspect angle, size, and shape (MASS)
Briefly explain how a basic pulsed RADAR set determines range.
Measures time for EM pulse to go out, strike object, and return
What unit of measure is most commonly used to describe the Electro-Optical Spectrum:
Micron
Select all characteristics of a laser:
Monochromatic Coherent Collimated Inefficient
Which of the following three types of propagation loss are accounted for by the equation concerning the simplified maximum RADAR range?
Only spreading
Explain what the target needs to do in order for Inverse Synthetic Aperture RADAR (ISAR) to provide improved target resolution.
Oscillate
Why must the target oscillate in order for ISAR to occur?
Oscillations induce a doppler shift in the return pulse, which gets processed into an image
A Moving Target Indicator (MTI) radar system measures changes in _____ of the returned signals to eliminate stationary targets.:
Phase
A differences in starting point between two EM waves is a difference in:
Phase angle
Consider the following environmental factors on sound speed in water (v): Temperature (T), Pressure (P), and Salinity (S). In the surface layer, which factor causes the greatest variability in v? Why?
Pressure, Temperature and salinity are constant due to mixing
Consider the following environmental factors on sound speed in water (v): Temperature (T), Pressure (P), and Salinity (S). In the deep isothermal layer, which factor causes the greatest variability in v? Why?
Pressure, temperature and salinity constant at these depths
Concerning transmission loss calculations via the Transmission Loss Equation or a propagation loss curve: Which is the more accurate measure of signal loss? Why is it more accurate?
Propagation loss curve, it is taken from data if the actual region
_____ is a signal processing technique in which the receiver is able to separate two or more targets with overlapping returns on the basis of the frequency. This method combines the high energy of a long pulse width with the high resolution of a short pulse width resulting in a more accurate range resolution.
Pulse Compression
Match the correct RADAR term with the most appropriate definition.
Pulse Width: the active transmit time or duration of the electromagnetic pulse. Rest Time the non-transmit time or the interval between electromagnetic pulses. Pulse Repetition Time (PRT) the total time for one transmission cycle. Pulse Repetition Frequency (PRF) number of pulses transmitted per second. Average Power (Pavg) the mean power dissipated over the entire cycle. Peak Power (Ppk) the maximum power transmitted by a RADAR. Duty Cycle (DC) a ratio that represents the time that the transmitter is on to one complete cylce of operation Range Resolution (Rres) the ability of a radar system to distinguish between two or more targets on the same bearing but at different ranges. Cross Range Resolution or Angular Resolution (Rcross) the minimum angular separation at which two equal targets can be separated when at the same range
When dealing with a Basic Pulse RADAR, the Duty Cycle (DC) is equal to which of the following:
Pulse width divided by the Pulse Repetition Time Pulse Width Multiplied by the pulse Repetition Frequency Average Power Divided by the Peak Power
What variables impact RADAR range resolution?
Pulse width, pulse compression ratio
This type of RADAR routes the calculated Doppler shift through a series of frequency-filters (bandpass filters), which results in the ability to distinguish between targets of different velocities.
Pulse-Doppler RADAR
Beamforming can be achieved by which two means?
Quasi-optical reflectors and antenna arrays
Match the following radar performance factors to the descriptions listed:
RADAR cross section: Effective area that reflects radar energy Noise: is generated internally and externally Threshold Level: set signal level above which receiver recognizes return Smin: weakest signal that receiver detects target Antenna Aperture: radars collector of energy received Beam width: width of antenna beam Antenna Gain: antenna's ability to concentrate energy PRF: determines max unambiguous range
Which kind of resolution is easier to manipulate and why?
Radar resolution, only depends on pulse width
Match the term to its definition.
Radiant Energy: Total energy from a source (J) Radiant Flux: Energy per time from a source (W) Radiant Exitance: Power per unit area leaving a surface (W/m^2) Irradiance: Power per unit area entering a surface (W/m^2) Intensity: Flux emitted per solid angle from a point source (W/sr) Radiance: Power radiated from an extended source, or Intensity per unit area (W/sr m^2)
What does the acronym RADAR stand for?
Radio Detection and Ranging
Continuous wave RADAR cannot measure _____
Range
Frequency Modulated Continuous Wave RADAR is used to derive _____ information from transmitted frequency at the time the reflected signal is received.
Range
Distinguish between the following terms: reflection, refraction, diffraction, & interference.
Reflection: When an EM wave strikes a conductive surface and bounces off it at an angle equal to the incident angle Refraction: When an EM wave passes into a medium with a different speed of propagation and the EM wave resultantly changes direction. Diffraction: The tendency of EM waves to spread out, or bend around objects. Interference: The property by which EM waves signals cumulatively add together when overlapping
Which of the following statements is NOT true for proper operation of an IR detector
Requires active transmission of a signal by the detector to the target for resolution
Post-detection pulse compression improves:
Rres
The Beer-Lambert Law accounts for which type(s) of attenuation?
Scattering Absorption
For selective and thermal radiators, explain how each creates the energy it radiates:
Selective: discrete packets of energy (photons) are emitted as the material electron configuration undergoes a change from an excited state to its ground state. Thermal: internal vibrations of charged particles in the material act like tiny oscillators and generate energy in the form of EM waves over a broad spectrum of frequencies.
The purpose of Electronic Combat is:
Sense the enemy's use of the EM Spectrum and reduce or deprive them of that use
Which of the following sources of noise is NOT a contributing factor to self noise when calculating transmission loss?
Shipping noise (this is ambient noise BOSH)
What types of targets typically osciallte?
Ships
Which ranges are calculated and compared to determine the greatest distance our RADAR can detect a target.
Simplified Max RADAR Range, Unambiguous Range, RADAR Line of Sight Range
Select the key components that make up a basic Pulsed RADAR system.
Single Antenna, Transmitter, Receiver, Duplexer
What RF wavelengths and mode of RF communication would you expect to travel essentially in a Line-of-Sight (LOS)?
Space waves (don't bend)
Match the most correct example with the appropriate term:
Spot Jamming: Jamming where all the power output of the jammer is concentrated in a very narrow bandwidth is known as: Barrage Hamming: Jamming power spread over a large bandwidth at the same time is known as: Sweep Jamming: Jamming where all the power output of the jammer is concentrated in a very narrow bandwidth but periodically changed to sweep a large bandwidth is known as: Deception Jamming: Jamming where a synthesized RADAR signature is sent to "spoof" the enemies system is known as:
Losses associated with optical frequencies (LASERs) include:
Spreading, absorption, and scattering
List and describe the three main energy "losses" in an electromagnetic signal as it propagates over distance:
Spreading: spherically spreads as 1/4pir^2 Scattering: energy bounces off particles/molecules in random directions Absorption: energy absorbed by the medium
Two types of infrared sensor systems are:
Staring and scanning
Select all the functions of a weapon system: detect to engage sequence
Target detection, resolution or localization, classification, tracking, weapon selection, and neutralization
Consider the following environmental factors on sound speed in water (v): Temperature (T), Pressure (P), and Salinity (S). In the thermocline, which causes the greatest variability in v? Why?
Temperature, area of greatest T change
Which of the following statements about Light Amplification (LLL) systems is true?
The can become saturated if too much light is present
Consider an antenna with two radiating elements. The relative phase between the energy received from the two elements at an arbitrary point P is determined by:
The phase difference at which the elements are driven. The distance the energy travels from each element to point P
a. Why does the Transmission Loss estimate formula change at 1000 meters (Explain both the change in general and why it is at 1000m specifically)?
The spreading pattern goes from spherical to cylindrical at that range because we assume an origin of 1000m depth in a 2000m water column.
Which statements are true about threshold levels?
The threshold level can be adjusted manually or automatically. It is the level in which a signal must be greater than in order to be displayed Decreasing the threshold level will result in more contacts
You assume watch and notice lights of several vessels on the horizon however you observe that no targets are displayed on the surface search PPI. Assuming the RADAR is functional, what are some potential reasons for this apparent discrepancy?
Threshold set too high, RADAR display range too low, target has small radar cross section
What does it mean to be able to "resolve" two targets?
To be able to break out two distinct radar returns on radar display
A positive sound speed gradient indicates the sound will refract:
Toward the surface
Select the key components that make up a Continuous Wave (CW) RADAR system
Transmitter, Receiver, Two Antennas, Mixer
T/F - A changing electric field produces a changing magnetic field.
True
T/F - A changing magnetic field produces a changing electric field.
True
T/F - A dipole antenna radiates its energy in all directions perpendicular to its axis, resulting in an electromagnetic field that resembles a doughnut.
True
T/F - An electro-magnetic wave propagates through space due to a changing electric field that produces a changing magnetic field that in turn produces a changing electric field, and so on.
True
T/F - In comparison to the radio spectrum, the electro-optic spectrum consists of higher frequencies and shorter wavelengths
True
T/F - One of the fundamental differences between Continuous Wave (CW) and Basic Pulsed RADAR is that CW has a longer Duty Cycle (DC)?
True
T/F - One of the fundamental differences between Continuous Wave (CW) and Basic Pulsed RADAR is that Basic Pulsed has a shorter Duty Cycle (DC)?
True
T/F - Phased Array Radar uses the change in phase between antenna elements to steer the beam.
True
T/F - The received signal power at the antenna must equal to or greater than Smin in order for detection..
True
T/F - The simplest form of an electromagnetic antenna is the dipole antenna.
True
A Synthetic Aperture Radar (SAR) achieves a large effective aperture by:
Using motion of the transmitter/receiver
Frequency is equal to:
Velocity of propagation in medium divided by wavelength
Continuous wave RADAR calculates _____ from _____
Vlos from Doppler Shit
Wavelength is equal to:
Wave propagation velocity divided by frequency
Wave propagation velocity is equal to:
Wavelength multiplied by frequency
What variables impact RADAR angular (or cross range) resolution?
Wavelength, antenna height/width, range to target
An Inverse Synthetic Aperture Radar (ISAR) attains high resolution by using:
Yaw angle or some rotation of the target to generate a large antenna aperature
Can you affect your RADAR's unamb? How and why or why not?
Yes, change PRF/PRT
Select all statements that are true about Blackbodies.
absorptivity=emissivity absorptivity=1 emissivity=1
Select all statements that are true about Graybodies:
absorptivity=emissivity reflectivity>0 emissivity + reflectivity=1
Effective Antenna Aperature (Ae) is:
area of the antenna times the reflective efficiency
As receiver sensitivity degrades, MDS _____ and Rmax _____
increases and decreases
Burn-through is:
the range at which the strength of the radar echo becomes equal to or greater than the Electronic Attack (EA) signal.
