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

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.