how to measure ip3

Maybe two tone test method ?

Hi, attached please find a presentation file from Agilent (you can also find it at the agilent web site). Using an isolator before the power combiner is important because some power from one of the signal generators may be coupled to the other signal generator and may cause inaccuracies. Of course, you have to calibrate your measurement setup first. Especially the losses at the output of your DUT is critical. I don't know what kind of an amplifier you measure, but ip3 makes sense for low noise amplifiers. As IP3 is obtained from an extrapolation, your input power should be small enough.

GSM Receiver Intermodulation characteristics:
The reference sensitivity performance shall be met when the following signals are simultaneously input to the receiver:
- a useful signal at frequency fo, 3 dB above the reference sensitivity level (-99dBm)
- a continuous (CW), static sine wave signal at frequency f1 and a level of -43 dBm
- a pseudo-random sequence, at frequency f2, with level -43 dBm
such that f0 = 2f1 - f2 and |f2-f1 | = 800 kHz.

The IIP3 limits for a GSM LNA you can find using this formula:
IIP3(dBm) = Interf_lev(-43dBm) + (Interf_lev(-43dBm) – RX_lev(-99dBm) + S/N(dB) ) / 2