Engineering Notes

RF POWER AMPLIFIERS TECHNICAL REFERENCE MATERIAL

Gain

Normaly expressed in decibels, dB
Power Gain (dB) = 10 Log ₁₀ (RF Output Power / RF Input Power)

Gain is defined as the ratio of the output power to the input power in dB. Assume that the input power is 10 mW (+10 dBm) and the output power is 1 W (1000 mW, +30 dBm). The ratio will be 1000/10 = 100, and the gain will be 10 * log 100 = 20 dB.

It is much easier to calculate gain by converting the power to dBm first, so the gain of the above amplifier will be 30-10 = 20 dB. A simple reduction will reveal the gain. In tradition, all power is read in dBm and the gain is in dB.

Example:

A low noise amp (30 dB gain) cascades with a driver amp (20 dB gain) and a power amp (10 dB gain). The total gain will be 30+20+10 = 60 dB.