Antenna
Glossary
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 multipath 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 multipath 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 elementFront 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).
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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