The 1 dB gain compression point describes amplifier saturation.

An amplifier maintains a constant gain for low-level input signals. However, at higher input levels, the amplifier saturates and its gain decreases. The 1 dB gain compression point (P1 dB) indicates the power level that causes the gain to drop by 1 dB from its small signal value.

The 1 dB gain compression point is derived from the gain relationship between output power and input power. Output power is plotted against input power in the following figure.

Figure 5. 1 dB Gain Compression Point


The straight line on this graph is an extrapolation of the small signal gain of the unit under test (UUT). The input 1 dB compression point is the input power that causes the UUT gain to drop by 1 dB from this small signal value. In this figure, the gain drop occurs at approximately -12 dBm.