What happens to system performance when VSWR exceeds 2:1 at a critical junction?
Consequences of High VSWR
A VSWR of 2:1 means the reflection coefficient magnitude is 0.333, and 11.1% of the incident power is reflected back toward the source. While this seems modest, the consequences cascade through the system in multiple ways.
| Parameter | L-Network | Pi/T-Network | Transmission Line |
|---|---|---|---|
| Bandwidth | Narrow (<10%) | Moderate (10-30%) | Broad (>30%) |
| Components | 2 (L, C) | 3 (L, C, C or C, L, C) | Stubs, lines |
| Q Control | Fixed by impedance ratio | Adjustable | Set by line length |
| Frequency Range | DC-6 GHz | DC-6 GHz | 1-100+ GHz |
| Design Complexity | Low | Medium | Medium-high |
Frequently Asked Questions
At what VSWR should I be concerned?
VSWR 1.5:1 to 2:1 is generally acceptable with modest performance impact (< 0.5 dB mismatch loss). VSWR 2:1 to 3:1 causes noticeable degradation and should be investigated. VSWR above 3:1 indicates a serious mismatch, damaged connector, or cable fault that requires attention.
Can high VSWR damage components?
Yes. Power amplifiers can be damaged by reflected power causing excessive voltage swings at the output transistors. Solid-state amplifiers typically have VSWR protection circuits. High VSWR can also cause arcing in high-power waveguide systems where the standing wave voltage exceeds the breakdown threshold.
How does VSWR affect phase?
Impedance mismatch creates a frequency-dependent phase shift that is not linear. This phase ripple can degrade the EVM of wideband modulated signals, particularly for OFDM systems where subcarrier phase coherence is critical.