The noise generator was a 0.005” diametermesa structurep+ nn4 silicon . The p-k material was formed by diffusing boron 3 microns into the n region and the p~timpurity density was approximately lOI9 per cm3. The n material, epitaxially grown on a heavily doped substrate, was approxi- matelyfour microns in thickness with animpurity density of 10’ percm3 10.5 21 cm). The crystal was mounted in a standard IN23 cartridge and tested in modifiedX-band mounts. Noise measurements in a crystal holder with anadjustable short to op- timize the noise output and with a matched termination in place of the short are presented, The results indicate that the diode itself is an inherently broad band noise sourceand that the circuitlargely determines the bandwidth of the noise source. The results of both continuously and pulse operated will be pre- sented. Note: Sponsored by Cayuga Associates, Ithaca, N. Y. I Val’d-Perlov,Krasilov, and Tager, “The Avalancing Transit-Time Diode- A New SemiconductorMicrowave Device,” Radio Engineering and Electron Physics (U.S.S.R.) No. 11, pp. 1764-1779, November 1966. 7.4 ANOISE REDUCTION DESIGN FOR IMPATT OSCILLATORS, E. J. Cook, Varian Associates, Beverly,Mass. This paper describes atechnique for achievingconsiderably lower noise figures for IMPATT oscillatorsthan have beenpreviously reported. With thesedevices used as local oscillators,receiver noise figures in X band within 10 dB (singleended mixer, 30 mcIF) and 0.2 dB(balanced mixer, 30 mc IF) of those produced with a klystronlocal oscillator have been ob- tained. Thetechnique alsoresults in a low oscillatorpushing figureand an accompanyingimprovement in thespectrum of the device when pulsed. No externalcavity stabilizationis involved, andthe oscillatorconsists only of adiode and a fundamental mode cavity. Detailed measurements of the AM and FM noise mmponents of the C. W. device indicate the primary reason for the improved performance as a local oscillator to be a 2 dB per octave slope in the AM noise component, a char- acteristicquite unlike the conventional IMPATT oscillator which exhibits a noise power independent of displacement from the carrier (at least out to a few hundred Kc wherethese measurements usually stop). For the reduced noise device,the AM noise in a 1-Kc band is an ordinary 103 dB below the carrierat 2-Kc displacement, but hasalready dropped to lessthan 113 dB below thecarrier at 100-Kc displacement. Although the detailed test data so far taken are at X band, preliminary operation of oscillatorsfrom C through Ku bandindicate the widespread validity of the approach. 7.5 NONLINEAROPERATING CHARACTERISTICS OF IMPATT DIODES, W. J. Evansand G. I.Haddad, University of Michigan, Ann Arbor, Mich. The nonlinear equations which describe the current and field in a Read- type’ IMPATT have been solved in closed form by assumingthat thetran- sit time of the carriers through the driftregion is small compared with the period of themicrowave oscillation. Using this solution thelarge-signal im- pedance of the diode isobtained. Impedance-plane plotsfor large-signal op- eration are presented. For small rdf voltages the results reduce to those ob- tained by Gilden an’d Wines2 Larger voltages result in a decrease in the neg- ativeresistance of the diode andthis leads to stableoscillator operation. A region of unstable operation similar to that found by Read’ is also predicted. The large-signalanalysis predicts a markedchange in thecurrent tuning of IMPATT diodes as compared to the small-signal case. Experimentshave been performed on an IMPATT diode in a reentrant coaxialcavity. The experimentalresults on frequencytuning, impedance ar..d otheroperating characteristics of theoscillator are in good agreement Note: This work was supported by a grant from Omni Spectra, Inc., Farm- ington, Mich. IW. T. Read. “A Proaosed High Freauencv Diode.” Bell System Tech. Jour., $01. 37, p’p. 401-4446, MarcK 1958. 2M. Gilden and M. E. Hines. “Electronic Tuning Effects in the Read Micro- wave ,” IEEE Trans. on Electron Devices. vol. ED-13. No. 1. pp. 169-175, January 1966.

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