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Antenna directivity
This is the relative gain of the main beam of an antenna pattern to a
reference antenna, usually an isotropic or standard dipole.
Attenuation
A decrease in signal magnitude between two points. These points may be
along a radio path, transmission line or other device.
Beam width (minus 3dB beam width)
The amount of angle (either azimuth or zenith) covered by the antennas
maximum gain (in decibels) until the signal drops of 3dB in each direction.
Bandwidth
Usable frequency range of the antenna, measured in MHz (1x106 cycles per
second, Mega-Hertz) or GHz (1x109 cycles per second, Giga-Hertz)
Cross Sectional Area
The amount of area that a body projects onto one plane. Used as a rough
estimate of the amount of a body that will experience wind drag
dB
DeciBels A technique for expressing voltage, power, gain, loss, or frequency
in logarithmic form against a reference. Typical references include volts,
watts or Hz. DeciBels are calculated using the expression: dB = 10*log(x/y)
dBc
DeciBel Referenced to the carrier
A technique for expressing a power measurement in logarithmic form using
the carrier power as a reference
dBi
Decibels isotropic, a relative gain measurement with respect to an isotropic
radiator in free space (uniform emitter in free space, a theoretical situation).
Normally used to describe gain for antennas operating at 1GHz or above.
dBd
Decibels over dipole, a relative gain measurement with respect to a half
wave dipole (0 dBd = 2.14 dBi) using a standard dipole antenna as a reference.
DC Continuity
The ability of a system to return a DC current. Some antennas are a DC
open (any monopole type antenna), some DC short (any folded dipole antenna).
Please note that DC continuity does not directly relate to RF continuity.
DC Ground
A low impedance conductor, capable of carrying away unwanted RF interference/static/noise.
Delay spread
A type of distortion due to multi-path resulting in the spreading out
or “smearing” of the received signal. It occurs when identical
signals arrive via different paths and have different time delays
Diffraction
A type of distortion due to multi-path resulting in the spreading out
or “smearing” of the received signal. It occurs when identical
signals arrive via different paths and have different time delays.
A propagation phenomenon that allows radio waves to propagate beyond
obstructions via secondary waves created by the obstruction. Classic types
of diffractions are smooth earth and knife-edge.
Dipole
A monopole with a ground balance (mirror image).
Dipole Array
A group of dipoles use to transmit/receive together as one.
Feed Element
A dipole arrangement that can be inserted into a larger array of elements
(a grid array for example) which increase the performance of the feed
element Front to Back Ratio (FTB)
The difference (logarithmic subtraction) between the antenna's maximum
gain (normally in the direction the antenna is pointed) and the gain in
the opposite direction (i.e. 10dBd - (-12dBd) gives a FTB of 22dB). It
does not matter if you use dBi or dBd as long as they are consistent)
Gain
A logarithmic measure of how well an antenna radiates or receives when
compared to a reference antenna (a perfect point source dBi or a half
wave dipole dBd), this can be highly directive with the intensity varying
greatly over small angles.
Grid Array
A group of elements (in a straight line or parabola for example) used
to increase performance of a feed element (a yagi antenna is one particular
style of grid array)
Hertz
Hz - A radio frequency measurement (one hertz = one cycle per second).
Monopole
A single exposed radiator, usually requiring a ground plane to provide
directivity (gain).
Off-Set Dipole
A vertically aligned dipole off-set (normally a 1/4 wave of 1/2 wavelength
of the operating frequency) from a large vertical element (the mast).
Omni Directional
Omni antennas radiate their RF energy in all directions, essentially outwards
in a three-dimensional spherical pattern.
Polarization
The plane in which the radio waves propagate. Vertically polarized waves
travel up and down while traveling forward. Horizontally polarized waves
travel left and right while traveling forward.
Propagation
The process an electromagnetic wave undergoes as it is radiated from the
antenna and spreads out across the physical terrain. See also propagation
channel.
Propagation Channel
The physical medium electromagnetic wave propagation between the transmit
and receive antennas, and includes everything that influences the propagation
between the two antennas.
RF Continuity
The ability of a system to provide a closed circuit for the RF current
to provide RF radiation.
Reflection
A process that occurs when a propagating electromagnetic wave impinges
upon a obstruction whose dimensions are very large when compared to the
wavelength. Reflections from the surface of the earth, and from buildings
or walls produce reflected waves which may interfere, constructively of
destructively at the receiver.
RF
Radio Frequency - Electromagnetic waves in the frequency range of 30 kHz
to 300 GHz.
Reciprocity
For practical purposes (although not universally the case) antennas transmit
and receive signals with the same directivity pattern (gain).
Voltage Standing Wave Ratio (VSWR)
A comparison of the power transmitted to the power received back from
the system with respect to a 50 Ohm line impedance. A VSWR of 1.0 is a
100% efficient antenna, a VSWR of 1.5 is 97%, a VSWR of 2.0 is 89%.
Wavelength
The physical distance that a radio wave travels during one complete cycle,
the length is determined by the speed of light divided by the frequency
of the wave.
Yagi
An array of straight elements in line with a dipole to form a parasitic
array in which the feed point of the dipole "sees" an increase
in gain/directivity.
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