Published on 10/13/2026
A datasheet lists a cable assembly as "VSWR 1.3 max, insertion loss 0.8 dB max at 6 GHz." Another says "return loss 17.7 dB min." A buyer wonders whether the second cable is worse. It is the same quality: VSWR 1.3 is a return loss of 17.7 dB.
Insertion loss, return loss and VSWR are the three numbers that describe how well an RF cable moves a signal. Insertion loss is how much signal you lose passing through. Return loss and VSWR are two ways of expressing how much signal reflects back. Once you know the conversion, you can read any datasheet.
This guide defines each number, gives the formulas and a conversion table, shows the mismatch loss that reflections cause, and gives typical limits. For how these numbers appear in a test report see our cable assembly test report article, and for scattering parameters on a VNA see our VNA bench guide.
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Insertion loss is the power lost between input and output, in dB. A VNA measures it as the magnitude of S21. It combines conductor loss, dielectric loss, and connector loss, and it grows with frequency and length.
Cable loss scales roughly with the square root of frequency for conductor loss, so a cable that loses 3.0 dB at 5.5 GHz loses roughly 3.4 dB at 7.0 GHz.
Some of the signal reflects from every mismatch, such as a connector, a bend or a crimp. The reflection coefficient, written gamma, is the ratio of reflected to incident voltage.
| VSWR | Return loss (dB) | Reflected power | Mismatch loss (dB) | Quality |
|---|---|---|---|---|
| 1.05 | 32.3 | 0.1% | 0.003 | Excellent |
| 1.10 | 26.4 | 0.2% | 0.010 | Very good |
| 1.20 | 20.8 | 0.8% | 0.036 | Good |
| 1.25 | 19.1 | 1.2% | 0.054 | Good |
| 1.30 | 17.7 | 1.7% | 0.075 | Typical limit for cable assemblies |
| 1.50 | 14.0 | 4.0% | 0.177 | Acceptable at high frequency |
| 2.00 | 9.5 | 11.1% | 0.512 | Poor |
| 3.00 | 6.0 | 25.0% | 1.249 | Very poor |
Specifying VSWR and insertion loss?
Share limits and frequencies and we will confirm the build.
Talk to an EngineerThe reflections cost only 0.075 dB at VSWR 1.3, so the insertion loss dominates here. Mismatch matters most when it is combined with other reflections, causing ripple in the system response.
| Parameter | Typical good value for cable assembly | Common cause when bad |
|---|---|---|
| VSWR (to 6 GHz) | 1.30 max or better | Poor connector, bad crimp, kink |
| VSWR (to 18 GHz) | 1.50 max or better | Connector mismatch, damaged pin |
| Return loss | 17 dB or higher at 6 GHz | Same as above |
| Insertion loss | Within cable datasheet plus connector loss | Wrong cable, long length, damaged cable |
Mistakes to avoid
Check that your limits are stated at the right frequencies. SigmaRF sweeps every assembly on a VNA for VSWR and insertion loss from 100 MHz to 40 GHz.
A cable can have low insertion loss and poor return loss (short cable, bad connector) or high insertion loss and good return loss (long thin cable, good connectors). Specify both: insertion loss for the loss budget, and VSWR or return loss for reflection.
S21 insertion lossS11 return lossVSWRMismatch lossReflection coefficientdB
What is the difference between insertion loss and return loss?
Insertion loss is signal lost passing through the cable, measured as S21. Return loss is how much signal reflects back at the input, measured as S11.
How do you convert VSWR to return loss?
Compute gamma = (VSWR - 1) / (VSWR + 1), then return loss = -20 x log10(gamma). For VSWR 1.5 the return loss is 14.0 dB.
What is a good VSWR for a cable assembly?
1.3:1 or better to 6 GHz is typical for good assemblies, with limits rising at higher frequencies depending on the connectors.
What return loss equals VSWR 2:1?
9.5 dB. About 11 percent of the power reflects.
Is higher or lower return loss better?
Higher. A return loss of 20 dB reflects 1 percent of the power, while 10 dB reflects 10 percent.
What is mismatch loss?
The power lost to reflections. At VSWR 1.5 it is 0.18 dB and at VSWR 2.0 it is 0.51 dB.
What is S21 and S11?
S21 is transmission through the cable (insertion loss). S11 is reflection at the input port (return loss).
Does low VSWR mean low insertion loss?
No. They are separate: a long cable can have a good VSWR and a high insertion loss.
Insertion loss tells you what you lose, return loss and VSWR tell you what reflects. Learn one conversion (VSWR 1.3 is 17.7 dB) and the rest of the table follows. Always state both limits at specific frequencies.
SigmaRF assemblies are VNA-swept for VSWR and insertion loss before shipment, 100 MHz to 40 GHz, at our India (Vadodara) and USA (Cleveland area) facilities, with lead times as short as 2 days.
Need assemblies with verified VSWR and loss?
Send your frequency and limits for a quote.
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