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Subelement A
RADAR Principles
Section 3
Frequency and Wavelength
Frequencies generally used for marine RADAR are in the ___ part of the radio spectrum.
  • UHF
  • EHF
  • Correct Answer
    SHF
  • VHF

The answer is "SHF," which stands for "Super High Frequency." Frequencies in the Super High Frequency range are generally used for marine RADAR systems.

Marine RADAR systems operate using radio waves in the microwave part of the electromagnetic spectrum. The frequency range used for marine RADAR typically falls within the Super High Frequency (SHF) band, which corresponds to frequencies between 3 gigahertz (GHz) and 30 gigahertz (GHz). SHF frequencies are higher than those used for typical communications, making them suitable for RADAR applications due to their shorter wavelengths and better resolution capabilities.

Mnemonic: "SuperHighFrequency"

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Practical RADAR operation requires the use of microwave frequencies so that:
  • Correct Answer
    Stronger target echoes will be produced.
  • Ground clutter interference will be minimized.
  • Interference to other communication systems will be eliminated.
  • Non-directional antennas can be used for both transmitting and receiving.

Practical RADAR operation requires the use of microwave frequencies so that stronger target echoes will be produced.

The choice of microwave frequencies in RADAR systems is based on several factors that contribute to the generation of stronger target echoes:

  1. Antenna Size: The wavelength of microwave frequencies is relatively small compared to lower frequency bands. This allows for the construction of smaller and more efficient antennas, which can provide better directional control and focus the transmitted energy towards the target. This focused energy results in a stronger and more concentrated beam towards the target.

  2. Atmospheric Attenuation: Microwave frequencies are less prone to attenuation or weakening of the signal by the atmosphere compared to higher frequencies. This means that microwave signals can travel longer distances through the atmosphere with reduced signal loss, resulting in stronger echoes when they are reflected back from the target.

  3. Radar Cross Section (RCS): The RCS of a target is a measure of how effectively it reflects radar signals. Certain types of targets, such as aircraft or ships, have larger RCS at microwave frequencies due to their size and shape. This means that they reflect a higher portion of the incident microwave energy, resulting in stronger echoes being received by the RADAR system.

Mnemonic: ""Micro Echo Boost"

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An S-band RADAR operates in which frequency band?
  • 1 - 2 GHz.
  • 4 - 8 GHz.
  • 8 - 12 GHz.
  • Correct Answer
    2 - 4 GHz.

An S-band RADAR operates in the frequency band of 2 to 4 gigahertz.

RADAR systems use different frequency bands for various applications. The S-band is one of the frequency bands commonly used for RADAR applications. It covers the range from 2 to 4 gigahertz (GHz) on the electromagnetic spectrum. S-band RADAR systems are employed in various fields, including weather RADAR, marine RADAR, and air traffic control RADAR, due to their ability to provide a good balance between resolution and atmospheric absorption.

Mnemonic: "Spectrum"

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A RADAR operating at a frequency of 3 GHz has a wavelength of approximately:
  • 1 centimeter.
  • Correct Answer
    10 centimeters.
  • 3 centimeters.
  • 30 centimeters.

To find the wavelength of a RADAR operating at a frequency of 3 GHz, we can use the formula:

Wavelength (in meters) = Speed of light (in meters per second) / Frequency (in Hertz)

Step 1: Convert the frequency to Hertz: 3 GHz = 3 * 10^9 Hertz (since 1 GHz = 10^9 Hertz)

Step 2: Calculate the wavelength in meters: Wavelength (in meters) ≈ 299,792,458 meters per second / 3 * 10^9 Hertz

Wavelength (in meters) ≈ 0.09993 meters

Step 3: Convert the wavelength to centimeters: Wavelength (in centimeters) ≈ 0.09993 meters * 100 centimeters per meter

Wavelength (in centimeters) ≈ 9.993 centimeters

So, the wavelength of a RADAR operating at a frequency of 3 GHz is approximately 9.993 centimeters.

Mnemonic: "GigaHertzWavelength"

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The major advantage of an S-band RADAR over an X-band RADAR is:
  • Correct Answer
    It is less affected by weather conditions.
  • It has greater bearing resolution.
  • It is mechanically less complex.
  • It has greater power output.

The major advantage of an S-band RADAR over an X-band RADAR is that it is less affected by weather conditions.

S-band RADAR operates at lower frequencies, typically between 2 to 4 gigahertz (GHz), while X-band RADAR operates at higher frequencies, usually around 8 to 12 gigahertz (GHz). The choice of frequency affects how RADAR signals interact with atmospheric elements such as rain, snow, and fog.

Mnemonic: "S-Safer"

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An X band RADAR operates in which frequency band?
  • 1 - 2 GHz.
  • 2 - 4 GHz.
  • 4 - 8 GHz.
  • Correct Answer
    8 - 12 GHz.

An X-band RADAR operates in the frequency band of 8 to 12 gigahertz.

X-band RADAR operates at higher frequencies compared to other RADAR bands. The X-band typically covers the frequency range from 8 to 12 gigahertz (GHz) on the electromagnetic spectrum. These higher frequencies provide X-band RADAR with several advantages, such as higher resolution and accuracy, making it suitable for various applications, including weather monitoring, air traffic control, and defense systems.

Mnemonic: "Xtreme"

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