VSWR Graph
VSWR
1.324
Reflected Power
25%
3:1
11%
2:1
0%
1:1
1.3GHz
1.4GHz
1.5GHz
What is VSWR?
The Voltage Standing Wave Ratio (VSWR) is a measurement of how well an antenna is matched to a source
impedance, typically 50-ohms. It is calculated by measuring the voltage wave that is headed toward the load
versus the voltage wave that is reflected back from the load. A perfect match has a VSWR of 1:1. The higher
the first number, the worse the match, and the more inefficient the system. Since a perfect match cannot
ever be obtained, some benchmark for performance needs to be set. In the case of antenna VSWR, this
is usually 2:1. At this point, 88.9% of the energy sent to the antenna by the transmitter is radiated into free
space and 11.1% is either reflected back into the source or lost as heat on the structure of the antenna. In
the other direction, 88.9% of the energy recovered by the antenna is transferred into the receiver. As a side
note, since the “:1” is always implied, many data sheets will remove it and just display the first number.
How to Read a VSWR Graph
VSWR is usually displayed graphically versus frequency. The lowest point on the graph is the antenna’s
operational center frequency. In most cases, this is different than the designed center frequency due to
fabrication tolerances. The VSWR at that point denotes how close to 50-ohms the antenna gets. Linx
specifies the recommended bandwidth as the range where the typical antenna VSWR is less than 2:1.
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– 2 – ANT-1.4-CW-HWR-ccc Data Sheet
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