What VSWR represents
VSWR is a way of expressing impedance mismatch. A perfect 50-ohm match would have a VSWR of 1:1. Real switches have a higher value because the RF path is not perfectly matched at every frequency.
Relationship to reflection
When impedance differs from the system impedance, part of the incident RF wave is reflected. VSWR, return loss and reflection coefficient are different ways of describing this same mismatch phenomenon.
Why it matters
High reflected power can reduce delivered power, disturb amplifier operation, create standing-wave peaks and increase uncertainty in precision measurements. The acceptable VSWR depends on the surrounding system.
Frequency and switch state
VSWR changes with frequency and can differ by port or switch state. A complete design review therefore considers the worst specified value over all required paths and frequencies.
High-power systems
Mismatch becomes especially important at high RF power because standing waves can create voltage or current peaks greater than those implied by average forward power alone. Power ratings may require derating as load VSWR increases.
Good measurement practice
Use calibrated RF instrumentation, high-quality adapters and proper connector torque. Inspect worn connectors because a damaged interface can make a good switch appear to have poor VSWR.
Key takeaway
VSWR expresses mismatch; evaluate it over frequency, switch state and expected load conditions.