Letter | Published:

A New Microwave Mixer


THE Hall effect in semi-conductors has been used at microwave frequencies for the measurement of power. It has recently been demonstrated that a simple modification to the power-measuring equipment leads to a mixer. The principle of operation of this mixer is straightforward. A local oscillator is used for establishing a field in a resonant cavity and a small piece of semi-conductor is placed at a point in this cavity where there is maximum magnetic field and no electric field. The semi-conductor is coupled to a second wave-guide carrying a microwave signal, the coupling being effected by a probe which causes a current to flow in the semi-conductor; the direction of the current is selected to be at right angles to the local oscillator magnetic field. Since the signal is coupled to the semi-conductor by electric field, whereas the local oscillator field at the semi-conductor is magnetic, there is no interaction between the local oscillator and signal channels. A Hall electromotive force is established, the instantaneous value of which is proportional to the product of the local oscillator magnetic field and the signal current. This electromotive force has therefore components of frequencies equal to the sum of the local oscillator and signal frequencies and to their difference. The latter signal can be amplified as in a normal mixer.

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