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Why all the interest in sub-harmonic mixers (SHM) these days? Because millimeterwave is where all the growth is, and sub-harmonic mixers are often cheaper and more convenient than fundamental mixers.
Sub-harmonic mixers are usually accomplished buy using an anti-parallel Schottky diode pair, either in shunt or in series. The three ports are tapped off using filter structures, the RF and LO could be bandpass, while the IF is usually low-pass.
One characteristic of SHM is that the mixer loss is quite sensitive to drive level. There is an optimum drive level, below or above it the loss increases. If you plot this it looks like an upside down parabola.
Contact us if you want us to work on posting an example to this page, or even better, if you want to contribute one!
More to come!