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Bayside, N. Y.IT HAS BEEN SHOWN in the literature1 that the power output from tunnel-diode oscillators, under certain assumptions, is inversely proportional to the series inductance L of the oscillator circuit ( Figure 1) :For cavities small compared t o a wavelength, L can be expressed as2where h is the height, r2 is the radius of the cavity conductor that can be substituted for the nonuniform ( Figure 21, and Teff designates the radius of a cylindrical radius of the junction and the leads connecting the junction to the end-'plates of the package.To obtain large power output we therefore want T~~~ large and r2 small. The effective radius of the tunnel diode, yefj, cannot be influenced by the circuit designer. On the other hand, ~2 can be made as small as the outside dimensions of the diode. A cavity with such minimum dimensions is shown in Figiure 3. The major disadvantages of this arrangement are, first, the frequency of oscillation is completely determined by the diode parameters, particularly the junction load to the cavity by means of a probe or loop, due to capacitance; and second, it is very difficult to couple the the small dimensions involved. These shortcomings can be resolved by increasing the electrical length of the cavity radius by X/Z; Figure 4. Instead of a physical short circuit, a voltage node is then located at T Z . The frequency of oscillation can now be controlled by the dimensions of couple the load to the electric or magnetic field. Unfor-the transmission line. In addition, space is provided to tunately, this solution creates another problem. The diode can now oscillate also on a lower mode with the much larger inductance L' consisting of the total length of transmission line short-circuited at r3. The realization of a lower mode.usef,ul circuit thus depends on our ability to supress the We have approached this problem by introducing a damping resistance R d in shunt with the diode at r3. Since rg is t o be kept small in order to keep L small, it is

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