VDP Industrial Series
Datasheet
ANT-8/9-VDP-2000-ccc
Antenna Definitions and Useful Formulas
VSWR - Voltage Standing Wave Ratio. VSWR is a unitless ratio that describes the power reflected from the
antenna back to the radio. A lower VSWR value indicates better antenna performance at a given frequency.
VSWR is easily derived from Return Loss.
10 Return Loss + 1
20
VSWR =
10 Return Loss − 1
20
Return Loss - Return loss represents the loss in power at the antenna due to reflected signals, measured in
decibels. A lower return loss value indicates better antenna performance at a given frequency. Return Loss is
easily derived from VSWR.
VSWR − 1
Return Loss = −20 log10
VSWR + 1
Efficiency (η) - The total power radiated from an antenna divided by the input power at the feed point of the
antenna as a percentage.
Total Radiated Efficiency - (TRE) The total efficiency of an antenna solution comprising the radiation
efficiency of the antenna and the transmitted (forward) efficiency from the transmitter.
2
VSWR − 1
TRE = η 1 −
•
VSWR + 1
Gain - The ratio of an antenna’s efficiency in a given direction (G) to the power produced by a theoretical
lossless (100% efficient) isotropic antenna. The gain of an antenna is almost always expressed in decibels.
( )
G
Gdb = 10 log10
GdBd = GdBi − 2.51dB
Peak Gain - The highest antenna gain across all directions for a given frequency range. A directional antenna
will have a very high peak gain compared to average gain.
Average Gain - The average gain across all directions for a given frequency range.
Maximum Power - The maximum signal power which may be applied to an antenna feed point, typically
measured in watts (W).
Reflected Power - A portion of the forward power reflected back toward the amplifier due to a mismatch at
the antenna port.
2
VSWR − 1
VSWR + 1
decibel (dB) - A logarithmic unit of measure of the power of an electrical signal.
decibel isotropic (dBi) - A comparative measure in decibels between an antenna under test and an isotropic
radiator.
decibel relative to a dipole (dBd) - A comparative measure in decibels between an antenna under test and
an ideal half-wave dipole.
Dipole - An ideal dipole comprises a straight electrical conductor measuring 1/2 wavelength from end to end
connected at the center to a feed point for the radio.
Isotropic Radiator - A theoretical antenna which radiates energy equally in all directions as a perfect sphere.
Omnidirectional - Term describing an antenna radiation pattern that is uniform in all directions. An
isotropic antenna is the theoretical perfect omnidirectional antenna. An ideal dipole antenna has a donut-
shaped radiation pattern and other practical antenna implementations will have less perfect but generally
omnidirectional radiation patterns which are typically plotted on three axes.
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