Characterisation of tunnel diodes at microwave frequencies

Microwave characteristics of coaxial-mounted tunnel diodes are investigated. Measured immittance data are used to deduce the equivalent-circuit parameters of the diode without recourse to d.c. or low-frequency measurements. The results indicate that the series-resistance component is frequency dependent, while the rest of the parameters in the circuit are frequency invariant. The phenomenological cause of this observed variation is attributable to the microwave absorption within the narrow p-n junction. An important consequence is that the true resistive cut-off frequency of a tunnel diode is lower than the value suggested by the low-frequency equivalent-circuit parameters.