Exam Flashcards
What is the MUR equation?
MUR = cT/2
What is the Beamwidth equation?
BW = kλ/L (K = 65)
Draw basic TX/RX block diagram
Draw MTI Diagram
Draw Doppler Block Diagram
What are primary and secondary radars
Primary radars sends out radar pulse and then detects a reflection back off of target
secondary radar sends out radar pulse and then waits for target transponder to return signal
What is Sub refraction? Use a diagram
What is super refraction? Use a diagram
Super-refraction. Super-refraction is caused by a decrease in refraction with height
and frequently occurs in the tropics where very cold sea currents are predominant, for
example in the Gulf of Aden, Red Sea and the Mediterranean. When super-refraction does
occur, it is not necessarily uniform in its effects on all bearings. This is especially true when
a ship’s radar is operated in the vicinity of large landmasses.
The operational effects are:
a. An increased surface detection range due to a greater bending effect on the radar
wave overcoming the radar horizon.
b. Decreased detection ranges for targets outside of the duct (e.g. loss of low air
cover).
c. Height estimation can be suspect.
Disadvantages of the increased range are:
a. Increased sea and land clutter. In general, sea clutter is stronger and over a
greater range as duct height increases.
b. Multiple trace echoes (target ranges may be ambiguous).
c. Distorted shapes.
What are the benefits of digital plot extraction?
The benefits of digital plot extraction, summarized simply, are:
- Continuous monitoring without distraction
- Faster and more accurate updates
- Handling many targets simultaneously
- Reduced errors
- Detailed and consistent track data.
WTAD Explain Magnetron
Here’s a simpler explanation of how a magnetron works:
- Structure: It has a central cathode and an outer anode with cavities in between.
- Magnetic Field: A magnet creates a magnetic field in the interaction space between the cathode and anode.
- Electron Movement: Electrons emitted from the cathode are pulled towards the anode but are bent by the magnetic field.
- Oscillation: As electrons move past the cavities, they cause the cavities to oscillate, generating microwaves.
- Output: These microwaves are directed into a waveguide and then sent to an antenna.
- Efficiency: The magnetron is efficient but generates heat, which needs to be cooled.
WTAD Explain Klystron
Here’s a simpler explanation of how a klystron amplifier works:
- Electron Gun: It generates a beam of electrons.
- Input Cavity: A small input signal causes electrons to speed up or slow down, creating groups (or bunches) of electrons.
- Drift Space: These bunched electrons travel through a tube where faster electrons catch up with slower ones, enhancing the bunching.
- Output Cavity: The electron bunches pass through an output cavity, transferring their energy to generate a strong microwave signal.
- Collector: Remaining energy in the electron beam is converted to heat, requiring a cooling system.
- Magnets: Magnets focus the electron beam throughout the tube.
WTAD Explain TWT
Here’s a simplified explanation of how a Traveling-Wave Tube (TWT) works:
- Input Signal: A low-power microwave signal is fed into the tube at one end.
- Electron Gun: It emits a beam of electrons that travel down the center of the tube.
- Helix Structure: The microwave signal travels along a helical structure, which slows it down to match the speed of the electron beam.
- Continuous Interaction: The electron beam and the microwave signal interact continuously, amplifying the signal as they travel together.
- Output Signal: The amplified microwave signal is extracted at the other end of the tube and sent to a waveguide.
- Heat Absorption: The remaining energy in the electron beam is absorbed as heat in the collector and requires cooling .
Define Glint and Scintilation
Glint:
- Definition: Glint is the changing position of a radar target on the radar display.
- Cause: It happens because the target’s orientation changes, altering the reflection.
- Effect: This causes the radar to see the target in slightly different places, leading to tracking errors.
Scintillation:
- Definition: Scintillation is the flickering of a radar target’s signal strength.
- Cause: It occurs due to changes in how the target reflects the radar signal or interference from multiple reflections.
- Effect: This makes the target appear to move or change size, causing potential tracking inaccuracies.
Draw and explain multi path with/without freq agility
Without Frequency Agility
- Direct Path: Signal goes straight from the transmitter to the receiver.
- Reflected Path: Signal bounces off surfaces (like buildings) before reaching the receiver.
- Effect: The two paths mix, causing the signal to fluctuate. This can make it hard to accurately track the target.
With Frequency Agility
- Direct Path: Signal still goes straight from the transmitter to the receiver.
- Reflected Path (Frequency Agile): The transmitter changes its frequency, causing the bounced signal to shift.
- Effect: Changing the frequency reduces the fluctuations, leading to a more stable signal and better tracking accuracy.
Diagrams
- Top Diagram (Without Frequency Agility): Shows strong fluctuations in signal due to fixed interference patterns from direct and reflected paths.
- Bottom Diagram (With Frequency Agility): Shows reduced fluctuations because the changing frequency smooths out the interference effects.
How does Mulipath effect VCD? (VCD diagram)
• Multipath causes radar signals to reflect off surfaces and combine with direct signals.
• This leads to areas where signals strengthen or weaken (constructive and destructive interference).
• The result is a pattern of coverage gaps and peaks, affecting radar performance at various heights .
