Weapons 6 weeks
Which of the following are true regarding Track While Scan (TWS) systems compared to Servo Tracking Systems? -Can only track 1 contact at a time. -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 confirm target location faster than the RADAR scan rate. -The system is able to lead the problem by calculating where the contact will be in the future. -The system uses Monopulse RADARs to provide fire control resolution.
-The system is able to confirm target location faster than the RADAR scan rate. -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.
Pulse Doppler RADAR
. Detects bearing, range, and relative velocity of a target using a mixer and 1 antenna.
Pulse Repetition Frequency (PRF)
. number of pulses transmitted per second.
Rest Time (RT)
. the non-transmit time or the interval between electromagnetic pulses.
6 Functions of a Weapon System
1. Neutralization 2. Localization 3. Target Detection 4. Classification 5. Tracking 6. Weapon Selection
Attributes of a continuous wave RADAR system; 1. Displays contact relative ___________ 2. Uses the principle of _______________to compare received frequency to transmitted frequency 3. ______________ transmits and receives radio waves
1. velocity 2.Doppler Shift 3.Simultaneously
Relative to mechanically steered arrays, select advantages of electronically steered arrays; A. Instantaneous beam positioning B. Less moving parts C. No loss in efficiency at high angles off of boresight. D. Can adjust beamwidth to cater towards search or fire control desires. D. Lighter, so motor can rotate easily. E. Circular polarization, so better for satellite communication relay.
A, B, D
Which of the following must be true to resolve a single target from a group? A. Range resolution must be less than distance between actual targets at the same bearing and altitude. B. Cross range resolution must be smaller than the size of the target. C. Cross range resolution (azimuth and elevation) must be less than actual distance between targets at the same range. D. Cross range resolution (azimuth and elevation) must be greater than actual distance between targets at the same range. E. Range resolution must be geater than basic RADAR range.
A, C
Which of the following are true regarding threshold level ? A. Threshold level can be altered/optimized by an operator B. Threshold level is only useful to filter away false contacts C. Increasing the threshold level often increases the number of targets displayed on a PPI D. Threshold level can only be set to a greater power level than minimum signal for detection
A, D
Put the following "gates" in the order used by a track-while-scan radar during a normal tracking sequence; Tracking gate Acquisition gate Turn gate
Acquisition, Tracking, Turn
Beamforming can be achieved by which two means? Antenna array Quasi-optical reflectors Increasing power Decreasing range to target Shifting wavelength
Antenna array Quasi-optical reflectors
Which of the following are true regarding phased array antennas? A. All elements in an array apply the same phase shift to uniformly steer the array. B. Broadside arrays are designed to create constructive inteference along the boresight C. A 2-D array is required to focus a beam in both azimuth and elevation D. Endfire arrays are designed to create destructive interference along the antenna wire (out the ends).
B, C
Which of the following changes would result in a decrease in maximum radar range (Rmax)? A. Increase in RADAR transmitting power B. Reduced RADAR cross section of target C. Widening beamwidth (azimuth or elevation) D. Reducing minimum signal for detection
B, C
Which of the following result in enhanced cross range resolution? A. Increasing range to target B. Increasing antenna size C. Increasing frequency D. Decreasing frequency E. decreasing range to target F. Decreasing antenna size
B, C, E
What type of interference occurs when EM waves interact with one another and the resultant wave increases in amplitude? A. Neutral B. Constructive C. Destructive D. Impressive
B. Constructive
steps to determining detectable ranges for a RADAR system;
Calculate maximum RADAR range Calculate over-the-horizon RADAR range Calculate unambiguous RADAR range Calculate minimum RADAR range Detectable ranges are from minimum RADAR range to the smallest value of maximum, unambiguous, and over-the-horizon RADAR range
what type of interference occurs when the maxima of two waves add together (the two waves are in phase), so that the amplitude of the resulting wave is equal to the sum of the individual amplitudes
Constructive
Electromagnetic wave energy is attenuated due to __________, __________, and __________ A. Interference B. Gain C. Diffraction D. Spreading E. Scattering F. Absorption
D. Spreading E. Scattering F. Absorption
2 waves that are exactly 180 degrees out of phase will achieve ___________ interference
Destructive
Basic Pulse RADAR
Detects bearing and range to target using a single antenna
Basic Contiunuous Wave RADAR
Detects bearing and relative velocity of target using 2 antennas.
Frequency Modulated Continuous Wave RADAR
Determines target bearing, relative velocity, and range with 2 anttenas and changing frequency over a given time period.
Refraction
EM wave passes into a medium with a different speed of propagation and the wave bends.
A SAR antenna needs the antenna to be stationary and the target to be moving
F
In order to have less ghost contacts, it is desired to have as small RADAR unambiguous range as possible.
F
Smin must be greater than the received signal power at the antenna in order for detection.
F
T/F; Cross Range Resolution is used in comparision with distance of contacts at depth (along same bearing and altitude) in order to determine whether they will be seen as separate contacts on a RADAR PPI display based on the RADAR's PW and PCR.
False
Fast Time Constant
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.
SAR/ISAR is extremely effective in imaging surface contacts.
ISAR
SAR/ISAR uses the motion of the target to create a synthetic aperture.
ISAR
Which of the following RADAR characterstics extend the range at which ghost images may result on a RADAR screen (PPI)? -Increase in PRT -Increase PRF -Elect to change wave speed -Increase in target height
Increase in PRT
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 Minimum Signal for Detection to filter noise -Increase the Threshold Level to filter noise -Decrease PRF to Increase Runamb -Elevate RADAR Height to increase detection range
Increase the Threshold Level to filter noise Decrease PRF to Increase Runamb
What variables enhance SAR cross range resolution; -Increased frequency -Changing antenna shape from circular to linear -Increased flight altitude of SAR antenna -increased distance travelled by antenna
Increased frequency, increased distance travelled by antenna
RADAR cross section is dependent on which factors? Material Shape Acceleration Mass Range Aspect Angle Frequency Size
Material Shape Aspect Angle Size
Moving Target Indicator (MTI)
Measures changes in return signal phase to filter out stationary targets.
Does a continuous wave RADAR system calculates and displays range to target?
No
The three key limiting ranges are:
RMAX, ROTH, and Runamb
SAR/ISAR is used to provide a high-resolution image of large non-moving targets.
SAR
SAR/ISAR uses the motion of the transmitter/receiver to create the large aperture.
SAR
T/F; A smaller Smin means the RADAR is more sensitive and therefore has increased detection ability and range.
T
Basic Continuous Wave (CW) doesn't displays the contact's range but Basic Pulsed RADAR does
TRUE
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.
Diffraction
The tendency of EM waves to spread out, or bend around objects.
Which of the following can possibly impact maximum detection range for a RADAR system? -Target velocity -Visual line of sight -Transmission frequency -Shape of the target -pulse width and rest time -Height of our antenna
Transmission frequency Shape of the target pulse width and rest time Height of our antenna
Select the key components that make up a basic Continous Wave (CW) RADAR system.
Transmitter Receiver Mixer Two Antennas
Two objects closing will create a positive doppler shift.
True
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? Unambiguous RADAR Range RADAR Range Resolution Cross Range Resolution Simplified Max RADAR Range Over the Horizon RADAR Range Minimum RADAR Range
Unambiguous RADAR Range Simplified Max RADAR Range Over the Horizon RADAR Range
Bandpass filter
Used by Doppler RADARs to filter contacts based on speed.
Reflection
When an EM wave strikes a surface and bounces off it
Can Threshold level be used to filter away false contacts?
Yes
Duty Cycle
a ratio that represents the time that the transmitter is on to one complete cycle of operation.
Select the two types of antenna polarization: a. Linear (Verticle & Horizontal) b. Circular c. Orthogonal d. Spherical
a. Linear (Verticle & Horizontal) b. Circular
Directive Gain
antenna's ability to concentrate energy in the beam
Threshold Level
chosen signal level above which a contact is displayed
________ Cross Range Resolution = _______ precise localization of contact = _________accuracy
decrease, increase, increase
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
Scan Rate
how fast the antenna is rotated
In the radio wave portion of the Electromagnetic spectrum, absorption generally _____________ as frequency ________
increases; increases
____________ RADAR unambiguous will ___________ ghost contacts
increasing, decrease
Servo-controlled tracking systems require an error signal as feedback to adjust the radar position. Because of this, servo trackers will always: mislead, lead, or lag the target?
lag the target
A difference in starting point between two EM waves is a difference in; phase angle frequency wavelength period
phase angle
what type of Resolution is used in comparision with distance of contacts at depth (along same bearing and altitude) in order to determine whether they will be seen as separate contacts on a RADAR PPI display based on the RADAR's PW and PCR.
range resolution
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.
Average Power
the mean power transmitted over the entire cycle.
Cross Range Resolution
the minimum angular separation between two targets at the same range that the RADAR system is able to distinguish as two separate 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.
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.
Smin
weakest possible signal that could still yield a valid return
