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Subel. E
6 questions
Subelement E

Antenna Systems

Section 39

Antenna Systems

Slotted waveguide arrays, when fed from one end exhibit:

  • Correct Answer
    Frequency scan.
  • High VSWR.
  • Poor performance in rain.
  • A narrow elevation beam.
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A typical shipboard RADAR antenna is a:

  • Rotary parabolic transducer.
  • Correct Answer
    Slotted waveguide array.
  • Phased planar array.
  • Dipole.

A typical shipboard RADAR antenna is a slotted waveguide array.

A slotted waveguide array is a type of antenna commonly used on shipboard RADAR systems. It consists of multiple waveguide elements arranged in an array and equipped with slots or openings along their length.

The design of a slotted waveguide array allows for efficient radiation and reception of electromagnetic waves. When high-frequency RF signals are fed into the waveguides, the slots act as radiating elements, emitting the electromagnetic waves in a controlled pattern.

The slots in the waveguide array are precisely dimensioned to achieve the desired radiation pattern and beam shape, allowing for beam steering and target tracking capabilities. By controlling the amplitude and phase of the signals fed into each waveguide element, the antenna can electronically steer the beam in both azimuth and elevation, without physically moving the entire antenna structure.

The slotted waveguide array provides the advantages of electronic beam scanning, which allows for fast target acquisition, tracking, and versatility in various operational scenarios encountered on ships.

Mnemonic: "Slotted Efficiency"

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Good bearing resolution largely depends upon:

  • A high transmitter output reading.
  • A high duty cycle.
  • A narrow antenna beam in the vertical plane.
  • Correct Answer
    A narrow antenna beam in the horizontal plane.

Good bearing resolution largely depends upon:

A narrow antenna beam in the horizontal plane.

Bearing resolution in a radar system refers to the ability to accurately determine the direction or angle from which a target is emitting signals or reflecting them back to the radar. A narrow antenna beam in the horizontal plane plays a significant role in achieving good bearing resolution.

When the antenna beam is narrow in the horizontal plane, it provides a finer angular resolution. This means that the radar system can distinguish between two closely spaced targets and accurately determine their azimuth angles or bearings. A narrow beamwidth allows the radar to focus its energy more precisely in the horizontal direction, leading to better discrimination between targets in that plane.

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The center of the transmitted lobe from a slotted waveguide array is:

  • Correct Answer
    Several degrees offset from a line perpendicular to the antenna.
  • Perpendicular to the antenna.
  • Maximum at the right hand end.
  • Maximum at the left hand end.
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How does antenna length affect the horizontal beamwidth of the transmitted signal?

  • The longer the antenna the wider the horizontal beamwidth.
  • Correct Answer
    The longer the antenna the narrower the horizontal beamwidth.
  • The horizontal beamwidth is not affected by the antenna length.
  • None of the above.
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What is the most common type of RADAR antenna used aboard commercial maritime vessels?

  • Parabolic.
  • Truncated parabolic.
  • Correct Answer
    Slotted waveguide array.
  • Multi-element Yagi array.
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