High two tone measurements require excellent isolation between the two signal sources to prevent unintentional crosstalk and intermodulation products generated in the synthesizers.  Previous state of the art test equipment was unable to accurately measure third order intermodulation input intercept points above ~35 dBm due to poor isolation between the synthesizers.  To address this problem in our record high IIP3 T3 mixer family, Marki Microwave has developed a directional bridge capable of isolation as high as 50 dB, with 40 dB typical from 10 MHz to 12 GHz.  For wideband or high IIP3 two tone test systems the PBR-0003, PBR-0006, and PBR-0012 set a new standard for performance.  For more information on how to perform accurate high two tone measurement please feel free to consult one of our design engineers.