AD-.A= Oft ARMY ELECTRONICS RESEARCH AND DEVELOPMENT COMMANDO P0-ETC F/S 9f5MILLIETER-WALVESELF-MIXING INP AND GAAS GUNN OSCILLATORS. (U)

rt:CLASSIFIED DELET-TR-79-14 ML

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RESEARCH AND DEVELOPMENT TECHNICAL REPORT

DELET-TR-79-14

MILLIMETER-WAVE SELF-MIXING InP and GaAs GUNNSi OSCILLATORS

Samuel Dixon

ELECTRONICS TECHNOLOGY& DEVICES LABORATORYiI

June 1979

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TITLE (and Y5ublitle)TYEORERT&PIDCVRD

Millimeter-Wave Self-Mixing InP and GaAsC5 Guann Oscillators. e *clkep'

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US Army Electronics Technology &Devices Lab 6752~A9I7ERADCOM, ATTN: DELET-MJ20ii --Ft. Monmouth, NJ 07703 "' ~L

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III. SUPPLEMENTARY NOTES

I9. KEY WORDS (Continue on reverse aide if necessary mid Identify by block number)

Gunn Diode Conversion gainInPGaAsSelf-mixingMinimum detectable signal

20. PATRACT Continue on reverse aide it necessary and identify by block number)PSelf-oscillating mixers in both dielectric and waveguldL cavities have beeninvestigated in the 60 GHz frequency range. The devices zonsist of negativeresistance diodes of GaAs and InP material coupled to waveguide cavities or highresistivity dielectric cavities such as silicon or Al." Experimental measure-ments show that these devices have a sensitivity in tRie order of -8OdBm with theintermediate frequency at 60 MHz and an IF bandwidth of 120 MHz. Applicationsare suggested based on minimum detectable signal and RF power capabilities forsystems requiring small size and low cost.4__

DD 1JAN 73 14731, EDITION Of I NOV 65IS OBSOLETE - - - .

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CONTENTS

INTRODUCTION ........... ............................ . . 1

DEVICE DESIGN .......... ........................... . . 1

EXPERIMENTAL RESULTS ........ ........................... 3

DISCUSSION OF RESULTS ............ ........................ 10

CONCLUSIONS ........... ............................. .... 21

ACKNOWLEDGEMENT .......... ............... . . . ........... 21

REFERENCES ........... ............................. .... 22

FIGURES:

1. Cutaway view of waveguide self-oscillating mixer ......... 2

2. Image guide self-oscillating mixer coupling to

waveguide ............ ......................... 4

3. Cutaway view of dielectric waveguide self-oscillatingmixer .......... ............................... 5

4. Exploded view of dielectric image guide self-oscillatingmixer ............. ........................... 6

5. Assembled dielectric waveguide self-oscillating mixer. 7

6. Characteristics of InP waveguide cavity oscillator ........ 8

7. Block diagram of measurements system for minimumdetectable signal ....... ........................ 9

8. IF output versus signal power for GaAs Gunn diode inwaveguide cavity ........ ..................... . .11

9. IF output versus signal power for InP Gunn diode inwaveguide cavity ........ ..................... ... 12

10. Conversion gain versus signal power for a GaAs Gunndiode in waveguide cavity ...... ................. ... 13

11. Conversion gain versus signal power for InP Gunn diodein waveguide cavity ........ .................... ... 14

i

12. Characteristics of GaAs dielectric waveguideoscillator ......... ......................... .... 15

13. Characteristics of InP dielectric waveguideoscillator ......... ......................... .... 16

14. IF output versus signal power for GaAs Gunn diode

in dielectric waveguide ......... .................. 17

15. IF output versus signal power for InP Gunn diode

in dielectric waveguide ...... .................. ... 18

16. Conversion gain versus signal power for GaAs Gunndiode in dielectric waveguide ..... ............... ... 19

17. Conversion gain versus signal power for InP Gunndiode in dielectric waveguide ....... ............... 20

Ai

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INTRODUCTION

The self-mixing Gunn oscillator has been of considerable interest inrecent years' ,2 3 because of the fact that this device embodies simplifi-cations for the circuitry of electronic receiving systems. Schottky barrierand other rectifier diodes suffer from the disadvantage of fragility and lowburn-out power levels. Bulk effect self-oscillating mixers using the non-linearity of transferred electron (Gunn) devices offer competitive sensiti-vities and the attractive alternative of a high power handling capability.In conventional mixers, there usually exist a signal frequency, a mixer diodeof the rectifier type, and a separate local oscillator. In the self-oscillating mixer, the mixer diode is eliminated. The Gunn diode will serveboth as a local oscillator, and because nonlinearities are always presentin an oscillator, as a mixing element. With the Gunn diode oscillatorserving both these functions, a receiver front-end becomes extremelysimplified and compact, especially when the dielectric image line approach isused. In the latter arrangement, the signal is fed directly into theoscillator and a suitable IF (intermediate frequency) probe will remove the IFpower for use in subsequent amplifier stages. What makes self-mixingoscillators different intrinsically from the conventional mixing process withpassive devices such as the Schottky junction diode is that self-mixing canoccur with conversion gain (rather than loss) similar to parametricamplification4 .

One of the objectives of this report was the design of self-mixingoscillators with considerable simplication and hence reduction in cost. Inthe quest for lower cost, the image line technology was applied using a Gunndiode in a simply constructed cavity, in a self-excited oscillator-mixermode of operation. Both GaAs and InP Gunn diodes were imbedded in an aper-ture which was cut in high resistivity A120 3 ceramic waveguide. Metal wave-guide cavity self-mixing oscillators were also evaluated for comparison. Thesignificance of the dielectric waveguide technology is that active devices,as well as passive components, can be developed in-situ in circuit modules toconstruct functional integrated sub-systems.

DEVICE DESIGN

The metal waveguide self-mixing oscillators utilized a coax-waveguidehybrid circuit as shown in Fig. 1. The packaged diode is imbedded in acopper heat sink at the end of a coaxial line section. A large portion of theouter conductor is removed with the removed section facing the waveguideopening to form a broadband coaxial-to-waveguide transition. A wide-bandchoke is used to terminate the opposite end of the line. The dc bias to theGunn diode and extraction of the IF power is also provided at this end.

The dielectric image line oscillator cavity design is based on an imageline concept first formulated by Marcatili5 and later modified for milli-meter waves 6, . The fundamental electromagnetic wave propagating in an

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for proper operation should be on the order of one wavelength in the mediumin width, and less than one-half wavelength in height. The cross-sectionaldimensions of alumina at 60 GHz which has a dielectric constant of approx-imately 9.0, were slightly greater than 1 millimeter in height and about 2milli eters in width. Experiments indicated that in this oversized condition,

the E mode dominated. The resonant length of the dielectric section inback 64 the diode was chosen for optimum power. This was approximated to be(2n+l) O/2 in length.

A simplified schematic of the self-mixing oscillator is shown in Fig. 2.

This indicates the manner of coupling to the metal waveguide showing one endof the resonant cavity being taperea. The dielectric image guide taper can

effect a low loss waveguide to image guide transition by simply insertinginto the full height waveguide opening and adjusting the protrusion for max-imum power transfer. This matched condition also yielded optimum IF outputwhen an RF input signal was introduced. Figure 3 gives a more detailed cut-away view of the image guide device investigated. As can be seen, the IFexits out of the top of the structure with a metal disc being utilized as a

matching element from Gunn diode to image guide. Figure 4 shows an explodedview of the self-mixing oscillator which utilized a tuneable short as animpedance matching device and Fig. 5 shows the same unit ready for operation.

Referring to Fi*. 4,the metal diode housing was designed for minimumradiation leakage with dimensions that were oversized with respect to WR-15waveguide. The Gunn diode is mounted flush with the bottom of the metal

structure. The aluminum oxide (A10 3 ) dielectric waveguide with taperedfront end was bonded to the metal housing in such a way that the Gunn diode

tip protruded up into the dielectric. A .045" hole in the dielectric wave-guide allowed the IF and bias voltage post to make a pressure contact withthe top of the Gunn diode. This made it possible to mount a slidina short

behind the image guide for impedance matching and tuning.

EXPERIMENTAL RESULTS

Figure 6 shows the output power and frequency characteristics of an InPdiode in a waveguide cavity as a function of the bias voltage. It should benoted that the frequency can be tuned over a range of 280 MHz with a changeof bias of 1.2 volts. This change in bias voltage gave a change in output

power from 19 to 23 mW. Similar characteristics were obtained with the GaAsGunn diode in a waveguide cavity except that the peak bias voltage was in the

order of 4.5 volts with peak powers of 6.5mW. These peak output powers aretypical of those used in the self-mixing experiments. Figure 7 shows a block

diagram of the RF circuit used in evaluating the two types of self-mixingGunn oscillators. A backward wave oscillator in a mechanically tuneable modewas used as the signal source. The single frequency outputs from this sourcewere stablewithin +.001% with non-harmonic spurious signals that are 40dB

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down. This highly stable signal was tuned 60 MHz above or below the Gunnoscillator frequency to produce an IF frequency. The difference signal at60 MHz was displayed on the face of the spectrum analyzer oscilloscope. Byincreasing attenuation in the signal channelthe IF energy pulse could bemade to decrease and disappear into the noise level of the spectrum analyzer.The attenuation was then decreased until the detected IF power is 3dB abovethe noise level. At this point the signal level is equal to the noise leveland this IF power is defined as the minimum detectable signal power measuredin decibels referred to 1mW. The oscillating diode was tuned by the biasvoltage above the threshold field and also by the RF circuit to achieve thedesired operating point. Care was taken to insure that no spuriousoscillations or bias circuit instabilities were present. The amplitude ofthe IF power in dBm was compared with measured values of input signal powerfor conversion gain or loss measurements. Figure 8 shows the IF outputpower as a function of signal power input for a GaAs Gunn diode in a wave-guide cavity. Figure 9 shows the same variables utilizing a metal wave-

guide cavity for an InP Gunn diode. The data point at the lowest signalpower indicates the point where the IF output power disappears into the noiselevel of the spectrum analyzer. As can be seen, the GaAs and InP Gunn diodeshave a minimum detectable signal (MDS) in the order of -77 and -81 dBm,respectively. This minimum detectable power is the principal parameter fordetermining the sensitivity of a self-mixing oscillator, that is, how weaka signal the device can detect. Figure 10 shows the conversion gain

measured on the GaAs self-mixing oscillator. Figure 11 shows the same inform-ation for the InP device. As can be seen, the gain is in the order of 12dBfor the InP oscillator while for GaAs it is 9dB. The data also indicates thatthe conversion gain increases as the signal power decreases.

In the quest for a much lower cost device, GaAs and InP Gunn diodes wereimbedded in an image guide cavity structure and their performance evaluated.Figure 12 shows the output power and frequency characteristics of a GaAsdiode, imbedded in image guide, as a function of the bias voltage. Figure 13shows the same variables with respect to an InP diode. The data indicatea frequency-bias tuning range of 120 MHz for the GaAs device and 220 MHz forthe InP self-mixing oscillator. However, the frequency tuning rate is muchsteeper for the InP diode as a function of the bias voltage, which is veryadvantageous for certain system applications. Figures 14 and 15 show theIF output power as a function of signal power input for both the GaAs and InPself-mixing oscillators respectively. The sensitivities of the image guidedevices are in the same order of magnitude as that of their waveguide counter-parts. Figures 16 & 17 show the conversion gain measured with image guideself-mixing oscillators, which was again comparable to that measured withwaveguide devices.

DISCUSSION OF RESULTS

In terms of sensitivity the data indicates that the InP self-mixingoscillator's performance in both image guide and metal waveguide cavities is

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better than that of the GaAs device. The reasons for superior performance of

the In? may lie in the following factors It has a current peak-to-valleyratio of 3.5 as opposed to 2.5 for GaAs". This, in theory, 9 will providehigher conversion efficiencies. In addition, the peak-to-valley ratio in InP

degrades less rapidly with temperature changes than GaAs and the thermal

conductivity is greater, thus favoring CW operation. An inherentcharacteristic indicated by the experimental data is that the sensitivity or

conversion gain increases as the signal level decreases. This characteristichas been reported by other investigators for waveguide self-mixingoscillators at 34 GHz1 , 4.

The major objective for this program was to design a low cost device,with simple construction and lightweight for application in integrated

circuit modules and sub-assemblies. The dielectric image line approach seemswell suited to accomplishing these objectives. The sensitivities of -77dBm

for GaAs and -8ldBm for InP self-mixing oscillators obtained in this develop-

ment make them attractive for application in mixer devices for certain

applications.

CONCLUSIONS

It has been shown that GaAs and InP diodes. imbedded in dielectric wave-

guide cavities in a simplified design circuit will give comparable sensitiv-ities to that of metal waveguide cavity self-mixing oscillators. Experimental

data indicates that the sensitivity of these devices are in the order of

-80dBm which made them competitive with other conventional mixers. However,the image guide device has the advantage of having simplified construction

with a high signal power burnout level coupled with very low unit cost.These characteristics make the image guide self-mixing oscillator, a viable

device in low cost receivers, expendable EW sensors, and short range terminal

guidance. In addition, the InP self-mixing device has great potential in

the higher millimeter-wave frequency region (n:ove 100 GHz) due to its higher

effective transit velocity and fast intervalley scattering.

ACKNOWLEDGEMENT

The author wishes to thank Dr. H. Jacobs of the Electronics Technologyand Devices Laboratory, ERADCOM, and M. M. Chrepta of Communications System

Center, CORADCOM for their valuable technical discussions and encouragement.

21 FM 270-80

REFERENCES

1. M. J. Lazarus, S. Novak and F. D. Bullimore, "A ;Ln-ii 'i. 'Killimeter-Wave

Self-Oscillating Gunn Diode Mixer, Proc. IEEE, Vol !' 8i ,-814.

2. M. Kotoni and S. Mitsui, "Self-Mixing Effect ol 'uwn, ucillator",

Electronics and Communications in Japan, Vol. , -B, N(. 12, PP 60-67,

1972.

3. S. Kwok, H. Nguyen-Ba and G. I. Haddad, PropLrt(-s and Potential of

BARITT Devices. Proc of Int Sclid-State Circ~itrs (onf., PP 180-181, 1,1

1974.

4. M. J. Lazarus, S. Novak, and E. 1). Bullimork,, " i.,... Yl]imeter-Vave

Receivers Using Self-Oscillating Gunn Diodc >11, i- . Microwave ]oijr.,,Vol 14, No. 7, July 1971, PP 43-45.

5. E. J. Marcatili, "Dielectric Rectangular Waveguide and Directicn; l

Coupler for Integrated Optics", Bell System Tech. Journal, Vol. 48, PP

2071-2102, Sep 1979.

6. H. Jacobs, G. Novick, C. M. LoCasio, M. M. Chrepta, Measurements of Gutid

Wavelengths in Dielectric Rectangular Waveguide, Proc. TEEE. ,,. .i-.

PP 815-812, November 1976.

7. K. Klohn, J. Armata, M. M. Chrepta, "Transverse Propagation Constants il;

Dielectric Waveguides, US Army Electronics Command, Fort Monmouth, NJ,

Tech Rpt 4242, August 1974.

8. R. J. Hamilton, Jr., R. D. Fairman, S. I. Long, M. Amori and F. B. Fank,

"InP Gunn Effect Devices for Millimeter-Wave Amplifiers and Oscillators

IEEE Transaction on MTT, Vol. MTT-24, PP 775-780, November 1976.

9. M. J. Lazarus, S. Novak, Private Communication.

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