How do I measure the IP3 of a component using a spectrum analyzer and two signal generators?

Measuring IP3 requires a two-tone test setup with two signal generators, a combiner, and a spectrum analyzer: (1) Setup: Signal Generator 1: set to frequency f1 (e.g., 1000 MHz). Signal Generator 2: set to frequency f2 (e.g., 1001 MHz). Combiner: a resistive (Wilkinson) or reactive combiner connects both generators to the DUT input. The combiner must provide > 20 dB isolation between the two generator ports (to prevent one generator from modulating the other). Device Under Test (DUT): the amplifier, mixer, or other component being measured. Spectrum Analyzer: connected to the DUT output. Set the span to cover f1, f2, 2f1-f2, and 2f2-f1 (e.g., 997 to 1003 MHz). Resolution bandwidth: narrow enough to resolve the tones (typically 10-100 kHz). (2) Measurement procedure: set both generators to equal power (e.g., -20 dBm each at the DUT input). Measure the output power at f1 and f2 (P_fund, should be approximately equal). Measure the output power at 2f1-f2 and 2f2-f1 (P_IM3). Calculate OIP3 = P_fund + (P_fund - P_IM3)/2. IIP3 = OIP3 - Gain. Verify: change the input power by 1 dB. The IM3 should change by 3 dB. If not: the device may be compressing. Repeat the measurement at a lower input level. (3) Important considerations: the signal generators must have low phase noise and low harmonics (the generator IM3 products must be much lower than the DUT IM3). Use isolators between the generators and the combiner (to improve generator-to-generator isolation). The spectrum analyzer noise floor must be at least 10 dB below the IM3 products. The combiner introduces 3 dB loss per generator (for a resistive combiner) or 3 dB loss total (for a Wilkinson). Account for this loss in the power calculation.