SynopsisWhen used as a frequency-mixing element, the tunnel diode has a performance which is superior in certain respects to that of existing mixer diodes at both u.h.f. and higher frequencies. The paper gives a brief outline of mixer theory and considers its application to the tunnel diode. The results of the analysis are compared with those of other authors, and the experimental results so far achieved are reviewed. List d e E c P F P E Fn fc fr fs S\ Si % G L G 2 G n G n0 M, = n k U of principal symbols = junction capacitance of diode = energy band overlap = electronic charge = conduction band edge on/? side of junction = conduction band edge on n side of junction = valence band edge on p side of junction = valence band edge on n side of junction = Fermi level = Fermi level on p side of junction = Fermi level on n side of junction = resistive cut-off frequency = self-resonant frequency = signal frequency = local-oscillator frequency = image frequency = bandwidth = angular frequency of local-oscillator signal = average value of diode dynamic conductance = fundamental component of diode dynamic conductance = 2nd harmonic of diode dynamic conductance = source conductance = input-circuit shunt conductance = load conductance = output-circuit shunt conductance = equivalent shot-effect conductance of diode = average value of diode equivalent shot-effect conductance = fundamental component of diode equivalentshot-effect conductance = Esaki current = Zener current = diode direct current = diode shot-effect current = equivalent shot-effect current of diode = Boltzmann's constant = series inductance of diode = series inductance of biasing circuit M g -conversion gain of mixer ff 1 = conversion loss of mixer N o -overall noise factor of a receiver N m -noise factor of mixer Nj = noise factor of intermediate-frequency amplifier -R d = negative resistance of diode R s = series resistance of diode R' -series resistance of biasing circuit 1 T = ambient temperature, deg K TQ = reference temperature, degK V = bias voltage V x = voltage at input terminals of mixer V 2 = voltage at output terminals of mixer + )X eq = terminal impedance of diode