Abstract :
Four microwave mechanisms found in Gunn diodes are discussed. Firstly, growing space-charge waves give a frequency dependent negative resistance which can be used to obtain amplification as well as to make oscillators. When any region or domain of high electric field is formed in a Gunn diode, three other microwave mechanisms are found: a current or voltage generator is created by the collapse of the domain if it drifts out of the diode at the anode contact; a negative resistance is sustained by the presence of the domain; finally, d.c. can be converted into r.f. by parametric mechanisms. This last effect is caused by the modulation of the circuit reactance due to the insertion and removal of the capacitance associated with the high-field domain. An equivalent circuit is discussed and is used to explain how these effects contribute to the various modes of oscillation exhibited by Gunn diodes.
