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Engineering Notes
RF POWER AMPLIFIERS TECHNICAL REFERENCE MATERIAL
VSWR & Return Loss (Impedance)
Impedance = Z = Ei/Ii
50 Ohm or 75 Ohm is normally used as the amplifier interface to other equipment where: Ei and Ii are the incident voltage and current.
VSWR = E max / E min = (1 + |P|) / (1 - |P|)
where P = reflection coefficient = (Z - Z0) / (Z + Z0)
Return Loss in dB = 20 log |P|
| COMMON TRANSFORMATIONS | ||||
| VSWR | RETURN LOSS |
POWER REFLECTED |
POWER TRANSMITTED |
REFLECTION COEFFICIENT |
| 1.0 1.1 1.25 1.5 1.75 2.0 3.0 6.0 - |
- 26.4 dB 19.1 dB 14.0 dB 11.3 dB 9.5 dB 6.0 dB 2.9 dB 0 dB |
0 % 0.2 % 1.2 % 4.0 % 7.4 % 11.1 % 25.0 % 51.0 % 100 % |
100 % 99.8 % 98.8 % 96.0 % 92.6 % 88.9 % 75.0 % 49.0 % 0 % |
0.00 0.05 0.11 0.20 0.27 0.33 0.50 0.71 1.00 |
Notes:
1. A purely capacitive or inductive load has an infinite VSWR.
2. VSWR = ZL / ZO or ZO / ZL for resistive loads only.
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