Analysis to two-tone, third-order distortion in cascaded two-ports

The third-order intermodulation distortion (IMD) of a system composed of a number of cascaded two-port networks is considered. The two-tone, third-order intercept point (IP) is highly dependent on the phase angles of the IMD signals, which are usually unknown to the system designer. Consequently, worst-case design strategies are normally used in these situations. General bound formulas are developed for the IP that include the effects of mismatches between component networks. Expressions for the expected value and variance of the IP of two cascaded two-port networks are also obtained. A comparison of these results with measurements indicates that worst-case design strategies are overly conservative in many situations