Slot antenna (cont) Slot antenna (cont) Slot antenna (cont) Slot antenna (cont) - The end of the waveguide is terminated in a pyramid terminator to avoid line reflections.
- The radiating field pattern depends on the spacing of the slots (phase relationship) and their orientation with reference to the waveguide.
- A slot cut in the wall of the waveguide, transverse to the direction of the interior boundary currents ( due to the interior em wave) will couple the em energy from inside the wave guide to a radiant free-space wave.
- The length of slot is cut to be a resonant one-half (ʎ/2) wavelength.
TWO TYPES OF DIPOLE ANTENNAS: - Half-wave (ʎ/2) dipole antenna (or Hertz antenna)
- Quarter-wave (ʎ /4) vertical antenna (or Marconi antenna)
- Maxwell equations, the strength of the radiated field is ;
Є = 60 π dl I cosӨ cos w ( t – r/Vc) λr D) DIPOLE ANTENNAS Cont. - A for a free space short-dipole and the radiation pattern (polar diagram) in the vertical plane and a circular in a horizontal plane.
- The electric field, Є is directional in the vertical plane but is omnidirectional on the horizontal plane.
D) DIPOLE ANTENNAS Cont. - Dipole antenna consists of 2 wires (ʎ/4 for its length) , the two wires are separated by a gap and their terminals are connected to the transmitter or the receiver.
This type of dipoles is called half wave length dipole as the total length is ʎ / 2 D) DIPOLE ANTENNAS Cont. D) DIPOLE ANTENNAS Cont. RADIATION PATTERN - The dipole is an electric field antenna, means that the magnetic field is zero at the near field.
- The radiation pattern is like a donut cake with the maximum perpendicular to the dipole, and a null along it.
- The polarization is along the dipole.
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