7

Datasheet

CW Series Antenna

490 MHz

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.

VSWR =

10

+ 1

Return Loss

20

10

- 1

Return Loss

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

Efficiency

- The total radiated power divided by the input power at the feed point of an antenna.

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.

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

G

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).

Omnidirectional

- Term describing an antenna radiation pattern that is uniform in all directions (spherical).

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.

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.