# Standing-wave ratio (SWR, VWSR, IWSR)

The standing-wave ratio (SWR) is a measure of impedance matching of a load to a transmission line or waveguide. It is a ratio of the maximum amplitude of the standing wave on the line to the minimum amplitude of the standing wave on the line. The SWR is usually expressed as a ratio of two complex numbers, SWR = (Vmax / Vmin), or as a ratio of two power levels, SWR = (Pmax / Pmin). The SWR can also be expressed as a phase angle, SWR = tan (θ), where θ is the phase angle between the maximum and minimum amplitudes.

The SWR is a measure of the efficiency of power transfer from the transmission line to the load. The SWR is unity when the load is matched to the transmission line and there is no reflected power. The SWR is greater than unity when there is reflected power and less than unity when there is absorbed power. The SWR is infinite when the load is an open circuit and there is no power transfer to the load.

The SWR can be used to optimize the match between the transmission line and the load. The SWR can also be used to troubleshoot problems in a transmission line or system.

The SWR is also known as the voltage standing-wave ratio (VSWR), the current standing-wave ratio (CSWR), or the impedance standing-wave ratio (ISWR).

### What is standing wave in VSWR?

In electrical engineering, a standing wave, also called a stationary wave, is a wave whose amplitude remains constant in time. The amplitude of a standing wave varies in space, with the maximum amplitude occurring at the nodes and the minimum amplitude occurring at the antinodes. The standing wave is said to have a wavelength that is twice the length of the medium.

In a transmission line, a standing wave is created when the line is not perfectly matched to the load. The impedance mismatch creates reflections that combine with the incident wave to create a standing wave. The standing wave ratio (SWR) is a measure of the impedance mismatch and is defined as the ratio of the maximum to minimum amplitude of the standing wave. What is a good standing wave ratio? A good standing wave ratio is one where the ratio of the amplitudes of the two waves is close to 1. This indicates that the two waves are in phase and that there is little energy lost in the system.

##### What is the difference between SWR and VSWR?

The short answer is that SWR is a measure of how well matched your antenna is to the impedance of your radio, while VSWR is a measure of how well matched your antenna is to the impedance of free space.

The longer answer is that SWR (Standing Wave Ratio) is a measure of the reflections caused by mismatched impedance between your antenna and your radio. The higher the SWR, the more reflections and the worse your antenna will work. VSWR (Voltage Standing Wave Ratio) is a measure of the reflections caused by mismatched impedance between your antenna and free space. The higher the VSWR, the more reflections and the worse your antenna will work.

In general, you want to have a low SWR and a low VSWR. However, it is possible to have a low SWR and a high VSWR, or a high SWR and a low VSWR. It all depends on the impedance of your antenna and the impedance of your radio.