A negative resistance oscillator circuit using a Gunn diode.  It consists on a series resonant circuit (L and C) connected across a Gunn diode D.  A DC voltage source Vb biases the diode into its negative resistance region and provides power.  A choke RFC prevents the AC signal current from flowing through the voltage source.  R is the equivalent damping resistance due to losses in the tuned circuit.
Actual Gunn diode oscillators use a parallel resonant circuit; this circuit uses a series resonant circuit because it is easier to analyze mathematically.
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Chetvorno