Prediction of Mixer Intermodulation Levels as Function of Local Oscillator Power

During intermodulation testing with diode mixers an increase of intermodulation interference was observed due to an increase of LO power incident to the mixer. This phenomenon conflicted with the theory that increase of LO power reduces intermodulation output of the diode mixer. In these tests the intermodulation decreased as expected when the LO power was further increased. Results of a theoretical and experimental study of how the level of incident LO power affects the intermodulation output levels emanating from the mixer are presented. The predicted results lead to the following experimentally verified conclusions. 1) A drop in power at some intermodulation frequencies occurs for an increase of LO power, depending on LO operating point and order of intermodulation. 2) Power at each intermodulation frequency will repeatedly increase, reach a maximum, and then decrease as power in LO signal increases, where the number of repetitions follows the orders of intermodulation. 3) The maximum intermodulation power at low-order intermodulation frequencies occurs for higher LO power than higher order intermodulation frequencies. LO power operating point is shown to be a significant factor in mixer intermodulation consideration. Application of these results to receiver intermodulation improvement is discussed.