SWR
Understanding SWR
SWR is one of the most commonly measured parameters in RF systems, particularly for antenna installations. It provides an intuitive measure of impedance match quality. Field technicians typically measure SWR with handheld analyzers to verify antenna installations, cable integrity, and connector quality.
SWR Measurement
- Handheld antenna analyzer: Most common field tool. Measures SWR vs frequency.
- In-line SWR meter: Bird wattmeter or similar directional coupler-based instrument.
- VNA: Measures S11, from which SWR is calculated.
SWR Guidelines
| SWR | Return Loss | Reflected Power | Rating |
|---|---|---|---|
| 1.0 | Infinite | 0% | Perfect |
| 1.2 | 20.8 dB | 0.8% | Excellent |
| 1.5 | 14.0 dB | 4% | Good |
| 2.0 | 9.5 dB | 11% | Acceptable |
| 3.0 | 6.0 dB | 25% | Poor |
| 5.0 | 3.5 dB | 44% | Bad |
Frequently Asked Questions
What is SWR?
SWR measures the impedance match quality of an antenna or component. SWR = 1.0 means perfect match. SWR = 2.0 means 11% of power is reflected. Lower SWR is better. It is the same measurement as VSWR.
What SWR is acceptable?
For most antenna installations, SWR < 2.0 is acceptable. For high-performance systems, SWR < 1.5 is expected. For precision measurement grade, SWR < 1.2. A typical well-matched antenna has SWR < 1.5 across its operating band.
Does high SWR damage the transmitter?
Yes, high SWR reflects power back to the transmitter. Most modern transmitters have SWR protection circuits that reduce output power when SWR exceeds 2-3:1. Without protection, reflected power can damage the PA output transistors through voltage or current stress.