. Airborne radar. Airplanes; Guided missiles. 576 ANTENNAS AND RF COMPONENTS in a rearrangement of atoms among the various energy levels. In this manner, it is possible to invert the populations of pairs of energy levels connected by microwave transitions. The feasibility of such a device has not yet been demonstrated Fig. 10-46 Single Resonant Circuit with Variable Reactance. MAVARS (Modulating Amplification Using Variable React- ance). In a MAVAR amplifier, three resonant circuits are coupled through a common nonlinear reactive element, so that for certain choices of resonan
. Airborne radar. Airplanes; Guided missiles. 576 ANTENNAS AND RF COMPONENTS in a rearrangement of atoms among the various energy levels. In this manner, it is possible to invert the populations of pairs of energy levels connected by microwave transitions. The feasibility of such a device has not yet been demonstrated Fig. 10-46 Single Resonant Circuit with Variable Reactance. MAVARS (Modulating Amplification Using Variable React- ance). In a MAVAR amplifier, three resonant circuits are coupled through a common nonlinear reactive element, so that for certain choices of resonant frequencies for the circuits, power is pumped from a generator in the highest frequency circuit into the lower frequency circuits and amplification of a low power signal at one of these lower frequencies results. Because they depend for their operation upon the variation of a circuit parameter, they are often called parametric amplifiers. The principle of operation can be il- lustrated with the single resonant circuit shown in Fig. 10-46.^^ Sup- pose that this circuit is oscillating at its resonant frequency/s. It is possible to introduce additional energy into this circuit and thus amplify the oscillating signal by separating the ca- pacitor's plates when it is charged and pushing them together again when the voltage across the capacitor is zero. This pumping action is analogous to the manner in which a child pumps a swing. The frequency at which the capacitor is pumped must be exactly twice the resonant frequency of the original circuit/s, since the capacitor value is increased by pushing together its plates every time the voltage across the variable capacitor is zero, or twice each cycle. The periodic variation of the capacitor would not be obtained in practice by physically moving the plates but rather by applying a large voltage of the proper frequency to a nonlinear capacitor whose incremental capaci- tance varied with applied voltage. An external resonant circuit which
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