Contains reports on three research projects.Joint Services Electronics Program (Contract DAAB07-71-C-0300)National Science Foundation (Grant GP-40485X

Adler, Richard B.

Blake, David H.

Burke, Bernard F.

Freund, Robert W.

Gupta, Madhu S.

Gwarek, Wojciech K.

Haschick, Aubrey D.

Kyhl, Robert L.

Lo, Kwok-Yung

Penfield, Paul L., Jr.

Rossin, Brian J.

Staelin, David H.

Walker, Robert C.

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VII. MICROWAVE AND MILLIMETER WAVE TECHNIQUESAcademic and Research StaffProf. Richard B. Adler Prof. Madhu S. Gupta Prof. David H. StaelinProf. Bernard F. Burke Prof. Robert L. Kyhl Dr. Mikail TyukhtinProf. Paul L. Penfield, Jr.Graduate StudentsWesley G. Brodsky Wojciech K. Gwarek Charles E. SimmonsRobert W. Freund Aubrey D. Haschick Robert C. WalkerKwok-Yung LoA. LOW-TEMPERATURE MILLIMETER WAVE RECEIVERS JSJoint Services Electronics Program (Contract DAAB07-71-C-0300)1. SUMMARY OF RESEARCHRichard B. Adler, Madhu S. Gupta, Robert L. Kyhl,Paul L. Penfield, Jr., David H. StaelinExperimental projects in progress include a 20-GHz single-diode mixer instrumentedfor detailed microwave measurements, a 20-GHz double-diode balanced mixer assemblyto test performance in a cooled mixer mode, and a 118-GHz single-diode mixer for radioastronomy use. All units use the GaAs Schottky-barrier diodes on Lincoln Laboratorychips.Room temperature measurements and preliminary cooled measurements with the20-GHz research mixer are reported in Section VII-A. 2. The design work on the bal-anced mixer, which uses packaged Lincoln Laboratory chips, has been completed andfabrication has begun. The 118-GHz mixer is in the assembly stage. Fabrication prob-lems that have been solved include forming a . 001" silica dielectric sheath on a . 005"tungsten post and soldering a . 0007" gold-plated tungsten whisker to the post.Parallel analytic studies of mixer behavior continue. One example is the improvedmethod of local-oscillator current and voltage waveform calculation which is describedin Section VII-A. 3. Such waveform calculations are basic to low-level signal analysis.2. K-BAND GaAs SCHOTTKY-BARRIER DIODE MIXERRobert W. Freund, Robert L. KyhlOne of the major goals of this project is to increase the understanding of millimeter-wave single-diode mixers. Toward this end, an experimentally measurable K-bandmixer has been fabricated using GaAs Schottky-barrier diodes. The type of diodes,mounting configuration, and a portion of the waveguide mount were described in Quar-terly Progress Report No. 113 (page 35). JSQPR No. 114Fig. VII-1. Complete K-band mixer mount.ALIGNMENT PINSPIECES 6 AND 76 AND 7GOES INTO4 AND 5Fig. VII-2. Perspective assembly drawing for a single K-band mixer mount.ixRI:nDIODETERMINALSFig. VII-3.Equivalent circuit for waveguideembedding network.QPR No. 114PIECE 3PIECE 2.PIECE I(VII. MICROWAVE AND MILLIMETER WAVE TECHNIQUES)Several different diode "dots" on a single chip were successfully incorporated into a JSworking mixer. Various overall mixer system measurements were performed, includingnoise temperature and conversion loss. A typical value of double-sideband system noisetemperature was 900*K. This value is based upon the following conditions: (a) an IFamplifier with a noise temperature of 240"K, (b) IF matching adjusted for optimumnoise performance, and (c) no microwave matching. This value of system noise tem-perature implies a double-sideband mixer noise temperature of 360*K. Because of theunknown effect of the microwave mismatch, this is a pessimistic value for this mixerand it should decrease with source optimization.The complete K-band mixer assembly is shown in Fig. VII-1, and a perspectivedrawing of the assembly in Fig. VII-2. The mount is composed of a tapered section ofridged waveguide, a uniform length of ridged waveguide, a back-short, and an elaborateIF filter section. Ridged waveguide was used to facilitate impedance matching of thediode to the transmission line. The taper section acts as a broadband matching trans-former to standard waveguide with a VSWR of less than 1. 15 across the entire frequencyrange of 18 GHz to 26. 5 GHz.An equivalent circuit representation for the waveguide portion of the mixer mount isshown in Fig. VII-3. We now have a complete description of the taper section, which,together with small-signal microwave impedance measurements, permits evaluation ofthe elements. Comparison of the measured diode quality factors as defined by Kurokawaand Schlosserl and by theory, indicates that the model is valid. By using the equivalentcircuit and a circuit for the IF filter section, two-port mixer parameters can be deducedfor the diode mixer.To increase our understanding, mixer operation will be studied at cryogenic temper-atures. Preliminary results indicate improvements in mixer noise temperature, butthese data are incomplete and further work is anticipated.References1. K. Kurokawa and W. O. Schlosser, "Quality Factor of Switching Diodes for DigitalModulation," Proc. IEEE 58, 180-181 (1970).3. NONLINEAR COMPUTER-AIDED ANALYSIS OF AMICROWAVE MIXERWojciech Gwarek, Robert L. KyhlNonlinear large-signal analysis of local-oscillator current and voltage wave shapeswas made for mixers with Schottky-barrier diodes. The diode can be treated as a par-allel connection of the diode conductance characterized by the function ID = IS(exp(PV) -1)and the nonlinear capacitance CD= Co/ 1 _. 1/2, where c is the diode contact potential. JSQPR No. 114(VII. MICROWAVE AND MILLIMETER WAVE TECHNIQUES)JS VLO cos Glt Vdc I VLOCOSlIt Vd ct Vk Cos WG Vk cos nltCD(V) GD(V) Z () CD(V) GD(V)V V conlt- ZFig. VII-4. Fig. VII-5.Model of the diode circuit. Model used in the algorithm.Iv Fig. VII-6.Example of the diode voltage andcurrent waveforms.The microwave circuit seen from the diode point of view can be characterized by afrequency-dependent impedance Z(w) and a source voltage V . This situation is shown01in Fig. VII-4. Z(w) can be calculated by the method described by Eisenhart and Khan.This impedance characterizes the waveguide structure, and it is usually impossible tomake a reasonable approximation of it by a simple RLC network.The large-signal problem was solved by developing the following algorithm inFORTRAN for the model shown in Fig. VII-5.1. It solves the nonlinear circuit problem by the Runge-Kutta method of integration,under the assumption that Z(w) is the impedance of a simple RLC network.2. Within an iteration loop it introduces the voltage sources Vk ... Vk to bring1 nthe impedances at the frequencies Cl 1 ... n * wl to the values expressed by Z(w).For most practical calculations the method converged within 20 or 30 cycles ofoscillation. The results of calculations by this method were compared with resultsaccomplished by a frequency domain analysis using a method similar to that of Egami.2The comparison shows that the new method is faster and more convenient. One of thereasons is that in the frequency domain analysis we must guess the set of the solutions.The wrong guess can significantly slow down the program or even cause divergence ofJS the algorithm.QPR No. 114(VII. MICROWAVE AND MILLIMETER WAVE TECHNIQUES)Figure VII-6 shows an example of the results of calculations using the new technique JSfor a Schottky diode in a K-band waveguide structure.References1. R. L. Eisenhart and P. J. Khan, "Theoretical and Experimental Analysis of a Wave-guide Mounting Structure," IEEE Trans., Vol. MTT-19, No. 8, pp. 706-719, August 1971.2. S. Egami, "Nonlinear, Linear Analysis, and Computer-Aided Design of ResistiveMixers," IEEE Trans., Vol. MTT-22, No. 3, pp. 270-275, March 1974.B. MICROWAVE MEASUREMENTS AND INSTRUMENTATION:MICROWAVE APERTURE-SYNTHESIS INTERFEROMETERJoint Services Electronics Program (Contract DAAB07-71-C-0300)National Science Foundation (Grant GP-40485X)1. SUMMARY OF RESEARCHBernard F. BurkeAmong our objectives with the three-antenna aperture-synthesis system now underconstruction at the Haystack Observatory has been the measurement of atmosphericrefraction at millimeter and submillimeter wavelengths. The current work in the fieldindicates that atmospheric refraction limitations for stable image construction at radiowavelengths are roughly the same as at optical wavelengths; that is, the atmospheric"seeing" is of the order of magnitude of 1 arc-second. There are questions about the com-pletion of the analysis, however, on two gounds: First, the differential phase shift, evenat millimeter wavelengths, is seldom as great as 2,w. Second, the "phase closure" prop-erties of an interferometric system allow more complete control over the image reduc-tion process than in the optical analog.The antennas are ready for operation, the antenna wiring and preparation of the rail-road track are nearly complete, and when the Spring rains stop, the entire system shouldbe under test within a month. During the winter, work was concentrated on the elec-tronic systems and software. In particular, phase stability measurements of the 1-3 cmlocal oscillators were made, which have resulted in the development of phase-lockedsystems of high absolute stability.2. STABILITY OF 1. 3 cm OSCILLATORSDavid H. Blake, Aubrey D. HaschickTwo Gunn-diode oscillators were phase-locked to a harmonic of a Rubidium atomicfrequency standard, and their phase stability was compared. The limiting factor in thephase stability of the systems was the harmonic mixers, which had a temperature JSQPR No. 114(VII. MICROWAVE AND MILLIMETER WAVE TECHNIQUES)JS coefficient of 10 electrical degrees per degree C. The accuracy of the measurementswas 0. 1 electrical degrees at K-band, which corresponds to a difference in path lengthof 3 p.m to the two oscillators.3. HARD-WIRED TAPE CONTROLLERBrian J. RossinThe Nova 800 minicomputer that will control the interferometer system and reducethe data must spend an inordinate time at present in magnetic tape read and write sub-routines. The efficiency of the system has been greatly enhanced by development of atape control unit that performs all of the tape read and write subroutines with hard-wiredlogic. The unit is relatively simple and inexpensive, and should be of use to anyone whowishes to make more efficient use of a minicomputer system.C. VERY LONG BASELINE INTERFEROMETRYJoint Services Electronics Program (Contract DAAB07-71 -C-0300)National Science Foundation (Grant GP-40485X)Kwok-Yung Lo, Robert C. Walker, Bernard F. BurkeThe program to establish the long-term stability of microwave maser sources con-tinues. We have established that the 18-cm OH maser sources associated with HIIregions such as W49 and W3 appear to be stable in position and intensity over a periodof years. The H20 sources (at 1. 35 cm wavelength) are variable in intensity, but apaper has recently been completed, in conjunction with the Naval Research Laboratory,which demonstrates that the positions remain stable, to at least . 01 arc-second.A new type of maser source at 18 cm has been discovered by K-Y. Lo and K. Bechisof this laboratory. The star V1057 Cygni is an example of a young star that has recentlyappeared, either as a result of brightening as nuclear burning sets in, or by having itsdust cocoon blown away. A maser source, of unique type, has been discovered, whichexhibits maser action only at 1720 MHz. When the source was discovered, it was thebrightest known maser source in the sky. As time has progressed, however, the sourcehas steadily weakened, and it is probably not a suitable class of object to use in a long-term program such as in geodesy or an operating system. Our observations have shown,however, first by using the California Institute of Technology Owens Valley interferom-eter and then by an NRL-NRAO VLBI experiment, that the line has polarization and angu-lar properties that are completely consistent with a Zeeman effect in the maser. Themagnetic field would be approximately 1. 5 X 10- 3 G.Some work has been completed on a conceptual VLBI working system that could beJS used either for navigation or as a means of remote synchronization of time signals.QPR No. 114

Microwave and Millimeter Wave Techniques

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Microwave and Millimeter Wave Techniques

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