VSWR, return loss and S11 are three views of one defect — reflected power. VSWR 2.0 costs only 0.51 dB of mismatch loss, so the number that really matters is whether the antenna stays matched across the band in your enclosure, not whether it hits 1.5.
| Term | What it is | Direction of "better" |
|---|---|---|
| VSWR | Voltage standing wave ratio on the feed line. 1.0:1 = perfect | Lower is better, 1.0 ideal |
| Return loss (RL) | Reflected power expressed in dB | Higher is better (14 dB > 9.5 dB) |
| S11 | The VNA's measured input reflection coefficient in dB | More negative is better (S11 = −RL) |
| Γ (gamma) | Reflection coefficient, linear 0–1 | Lower is better; Γ² = reflected power fraction |
The conversions are exact:
| VSWR | Γ | Return loss | S11 | Reflected power | Mismatch loss | Power delivered |
|---|---|---|---|---|---|---|
| 1.00 | 0.000 | ∞ | −∞ | 0 % | 0.00 dB | 100 % |
| 1.10 | 0.048 | 26.4 dB | −26.4 | 0.23 % | 0.01 dB | 99.8 % |
| 1.20 | 0.091 | 20.8 dB | −20.8 | 0.83 % | 0.04 dB | 99.2 % |
| 1.30 | 0.130 | 17.7 dB | −17.7 | 1.70 % | 0.07 dB | 98.3 % |
| 1.50 | 0.200 | 14.0 dB | −14.0 | 4.0 % | 0.18 dB | 96.0 % |
| 1.70 | 0.259 | 11.7 dB | −11.7 | 6.7 % | 0.31 dB | 93.3 % |
| 2.00 | 0.333 | 9.5 dB | −9.5 | 11.1 % | 0.51 dB | 88.9 % |
| 2.50 | 0.429 | 7.4 dB | −7.4 | 18.4 % | 0.88 dB | 81.6 % |
| 3.00 | 0.500 | 6.0 dB | −6.0 | 25.0 % | 1.25 dB | 75.0 % |
Two talking points worth keeping straight:
1. The dB cost of VSWR 2.0 is 0.51 dB. A typical sub-GHz IoT link runs with 10–20 dB of margin. Half a dB does not decide whether a meter is read. Requiring VSWR ≤ 1.5 makes buyers reject serviceable parts and makes honest low-cost antennas look bad. 2. What actually hurts is bandwidth and detuning. VSWR 2.0 measured at the band edge usually means something nearby is pulling the antenna — an enclosure, a metal panel, a hand, a battery, a badly sized ground plane. The same mechanism that raised VSWR also skewed the pattern and dropped radiation efficiency, and those costs are far larger than 0.5 dB. A 2.0 at band edge plus a shifted pattern is a real problem; a flat 2.0 across the band is not.
Ask for VSWR versus frequency across the whole operating band, measured in the final enclosure. What you are looking for:
| Curve shape | Reading |
|---|---|
| Low and flat across the band | Healthy; the antenna is intrinsically matched |
| Sharp notch at one frequency | Good match at the design point, narrow bandwidth — risky with component tolerances |
| Rising toward both band edges | Bandwidth limit; expect unit-to-unit spread in production |
| Center frequency shifted up or down | Detuned by enclosure or ground plane — needs a matching change, not a new antenna |
| No clear resonance at all | Usually a broken feed, wrong connector polarity, or a missing ground reference |
A single "VSWR < 2" line item on a datasheet tells you almost nothing about which of these you have.
Contact: Mr.Li
Phone: 0755-33169935
Tel: +86-755-33169935
Email: cs#antennahome.com (change # to @ )
Add: Build-2 201#, ShangXue Industry Park, Bantian, Longgang District, Shenzhen, Guangdong Province, China