Explain how the elementary dipole antenna transmits electromagnetic waves. Explain how the elementary dipole antenna transmits electromagnetic waves


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Explain how the elementary dipole antenna transmits electromagnetic waves.

  • Explain how the elementary dipole antenna transmits electromagnetic waves.

  • Calculate optimum antenna height for a given frequency both grounded and ungrounded.

  • Identify the two types of antenna polarization.

  • Interpret the beam power distribution pattern for a single dipole antenna and a linear antenna array (broadside and end fire) and identify sidelobes.

  • Describe how quasi-optical systems increase antenna directivity.



A time varying electric field (E) (from an alternating source - oscillator) will generate a time-varying magnetic field (B).

  • A time varying electric field (E) (from an alternating source - oscillator) will generate a time-varying magnetic field (B).

  • A magnetic field will generate an electric field.

  • So, an E-field will produce a B-field that produces an E-field that produces ….

  • The E-field / B-field interaction produces a propagating electromagnetic wave perpendicular to E & B fields.

  • There exists a continuous transfer of energy between fields.











Linear Polarization (horizontal or vertical)

  • Linear Polarization (horizontal or vertical)

  • Circular Polarization (for 3D maneuvering)

  • Antenna Polarized in direction of Electric Field

    • Transmit and receive antennas should have same polarization in order to receive optimum energy




High sensitivity/High Directivity increases radar detection range and exploits weak signals

  • High sensitivity/High Directivity increases radar detection range and exploits weak signals

  • Radars separated by ½ wavelength to utilize constructive/destructive interference



Ability to focus energy in a specific direction (azimuth and elevation)

  • Ability to focus energy in a specific direction (azimuth and elevation)

    • Power Density of beam not uniform
    • Beamwidth measured at 3 dB down point in az/elev
    • Search Radar - larger beamwidth for detection and tracking
    • Fire Control Radar – smaller beamwidth for accurate targeting solution






By inducing phase shift between elements, can electronically focus beam and steer it

  • By inducing phase shift between elements, can electronically focus beam and steer it

  • No mechanical breakdown, physical restrictions, and can use same system for multiple roles (Search, Tracking, Fire Control) simultaneously





Parasitic Elements - used to concentrate the beam in one direction only .

  • Parasitic Elements - used to concentrate the beam in one direction only .

    • A current is induced in the element to cause destructive interference in specific direction.
  • Reflectors

    • Reflective material placed near radiating antennas.
      • Parabolic shapes (dishes) used to concentrate energy into a narrow beam (i.e. radar reflectors).




Explain how the elementary dipole antenna transmits electromagnetic waves.

  • Explain how the elementary dipole antenna transmits electromagnetic waves.

  • Calculate optimum antenna height for a given frequency both grounded and ungrounded.

  • Identify the two types of antenna polarization.

  • Interpret the beam power distribution pattern for a single dipole antenna and a linear antenna array (broadside and end fire) and identify sidelobes.

  • Describe how quasi-optical systems increase antenna directivity.




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