ANTENNA Flashcards
A metallic conductor system capable of radiating and capturing electromagnetic energy
Antenna
Couples energy from a transmitter to an antenna or
from antenna to a receiver
Transmission Lines
A special type of transmission line that consists of a
conducting metallic tube through which high-frequency
electromagnetic energy is propagated
Waveguide
Electrical energy that has escaped into free space in the
form of transverse electromagnetic waves
Radio Waves
The plane parallel to the mutually perpendicular lines of
the electric and magnetic fields.
Wavefront
The ratio of radiated to reflected energy
Radiation Efficiency
Antenna wherein two conductors are spread out in a straight line to a total length of one quarter wavelength.
Quarter Wave Antenna
Another name for quarter wave antenna.
Vertical Monopole or Marconi
A half-wave dipole
Hertz Antenna
A special coupling device that can be used to
direct the transmit and receive signals and provide the necessary isolation
Diplexer
A polar diagram or graph representing field strengths or power densities at various angular positions relative to an antenna.
Radiation Pattern
Radiation pattern plotted in terms of electric field
strength or power density
Absolute Radiation Pattern
Radiation pattern plots field strength or power density
with respect to the value at a reference
Relative radiation Pattern
The primary beam of an antenna.
Major Lobe
The major lobes that propagates and receive
the most energy.
Front Lobe
Lobes adjacent to the front lobe.
Side lobes
The secondary beam of an antenna.
Minor Lobes
Lobes in a direction exactly opposite the front lobe
Back Lobe
The ratio of the front lobe power to the back lobe
power.
Front to Back Ratio
The ratio of the front lobe to a side lobe.
Front to Side Ratio
The line bisecting the major lobe; or pointing from
the center of the antenna in the direction of maximum
radiation.
Line of Shoot or Point
of Shoot
Antenna that radiates energy equally in all directions
Omni-directional Antenna
The primary beam of an antenna.
Major Lobes
Radiates power at a constant rate uniformly in all
directions.
Isotropic Radiator
The direction in which an antenna is always pointing.
Maximum Radiation
It is defined as an equivalent transmit power. It stands
for Effective Isotropic Radiated Power.
EIRP
The equivalent power that an isotropic antenna would have to radiate to achieve the same power density in the chosen direction at a given point as another antenna.
Effective Radiated Power (ERP) or (EIRP)
The power density in space and the actual power that a receive antenna produces at its output terminals.
Captured Power Density
It describe the reception properties of an antenna
Capture Area
Another name for capture area
Effective Area
The relationship of captured power to the received
power density and the effective capture area of the
received antenna.
Directly Proportional
It refers to the orientation of the electric field radiated
from the antenna.
Polarization
The angular separation between the two half-power
(-3dB) points on the major lobe of an antenna’s plane
radiation pattern.
Antenna Beamwidth
The frequency range over which antenna operation is satisfactory.
Antenna Bandwidth
Another name for antenna input terminal
Feedpoint
The feedpoint presents an ac load to the transmission
line.
Antenna Input Impedance
The simplest type of antenna. Another names for elementary doublet ? Short Dipole; ? Elementary Dipole ? Hertzian Dipole
Elementary Doublet
Any dipole that is less than one-tenth wavelength
Electrically Short
Hertz antenna is name after him and he was the first
to demonstrate the existence of electromagnetic
waves.
Heinrich Hertz
A single pole antenna one quarter wavelength long; mounted vertically with the lower end either connected directly to ground or grounded through the antenna coupling network.
Marconi Antenna
Main disadvantage of Marconi Antenna.
Must be close
to the Ground
A technique use to increase the electrical length of
an antenna
Loading
A coil added in series with a dipole antenna which
effectively increases antenna’s electrical length.
Loading Coil
A loading coil approximately increases the radiation resistance of the antenna
5 Ohms
An individual radiator; such as a half or quarter wave dipole. Two types of antenna elements ? Driven ? Parasitic Two Elements of a single antenna ? Two Wire ? Folded Dipole
Antenna Element
Its purpose is to increase the directivity and concentrate
the radiated power within a smaller geographic area.
Array
Elements that are directly connected to the transmission
line and receive power from the source.
Driven
Elements are not connected to the transmission line;
they receive energy only through mutual induction with
a driven element.
Parasitic
parasitic element that is shorter that its associated
driven element.
Director
Radiation pattern depends on the relative phase of feeds.
Driven
The simplest type of antenna arrays
Broadside Arrays
A widely used antenna commonly uses a folded dipole
as the driven element and named after two Japanese
scientists.
Yagi Uda
Typical directivity of a yagi-uda antenna.
7 dB and 9 dB
Formed by placing two dipoles at right angles to each other.
Turnstile Antenna
A class of frequency-independent antennas.
Log Periodic
A broadband VHF or UHF antenna that is ideally suited
for applications for which radiating circular rather than
horizontal or vertical polarized electromagnetic waves
are required.
Modes of propagation:
? Normal
? Axial
Helical Antenna
Antennas having half power beamwidths on the order of 1o or less. Three important characteristics: ? Front-to Back Ratio; ? Side-toSide Coupling ? Back-to-Back Coupling
Microwave Antenna
Antenna that provides extremely high gain and
directivity and are very popular for microwave
and satellite communications link.
Two main part
? Parabolic Reflector
? Feed Mechanism
Parabolic Reflector Antenna
The effective area in a receiving parabolic antenna
and is always less than the actual mouth area.
Capture Area
