Below is a diagram for a circuit that can be used to operate GaAs diode mixers with self bias.
                The inclusion of a general purpose power rectifier diode (either 1N4001, 1N4002 or 1N4003) in the bias circuit
               allows for self bias operation over a relatively wide range of LO power settings.  Conversion loss can be optimized
                by adjusting LO power applied to the mixer