Both 1dB compression and 3rd order intercept points are used as performance measure of RF amplifier, RF mixer etc. It provides the limit of linear region and point from where device will move to saturation or nonlinear region.

Power output of RF device should vary according to the input power linearly. The point from when power output does not vary linearly with the input device that point is referred as saturation or compression point. At this place 2 dB changes in the input power results in only 1dB change in the output power.

Let us understand 3rd order intercept point with example of two frequency signals f1 and f2 fed as input to the RF amplifier within the bandwidth limit of amplifier. Normally it should produce amplified f1 and f2 signals but due to distortion in an amplifier it produces harmonics at other frequencies. The second order products include f1-f2 and f1+f2. The third order products include 2f1 +/- f2 and 2f2 +/- f1. The most troublesome components are 2f1-f2 and 2f2-f1, which falls within the amplifier bandwidth and level of which is referred as 3rd order intercept point.

3rd order intercept point (TOI) is usually 10dB higher than the 1dB compression point.