Frequency Modulation of a Millimeter-Wave IMPATT Diode Oscillator and Related Harmonic Generation Effects

A continuous wave (CW) millimeter-wave silicon I M P A T T diode oscillator was used satisfactorily as a local oscillator in an experimental pulse code modulation (PCM) millimeter-wave repeater system. 1, 2 That oscillator circuit used a radial-line resonant cavity whose resonant frequency was the primary factor determining the oscillation frequency. The oscillator was difficult to tune either mechanically or electronically. While such characteristics are desirable for fixed frequency local oscillator applications, other applications which demand wideband * The essential results of this paper were presented at the 26th annual conference on Electron Device Research, Boulder, Colorado, June 19-21, 1968. 143 144 T H E BELL SYSTEM T E C H N I C A L J O U R N A L , JANUARY 1969 performance and tunability are also of interest. For example, a millimeter-wave frequency deviator using an I M P A T T diode would bs advantageous over the L-band deviator and up-converter combination in the P C M repeater system. The I M P A T T diode oscillator could deliver power at least one order of magnitude greater than the up-converter. A previous paper showed that the circuit inductance of the radialline cavity in shunt with the diode was much smaller than the diode inductance. 1 Therefore, the oscillation frequency could be tuned only a few hundred megahertz by varying the diode bias current.* In addition, the radial-line cavity was loosely coupled to the external waveguide circuit so that a tuning range of only 300 MHz was obtained when a varactor diode was used for frequency deviation.