A Variable Directional Coupler Using InSb Thin Films (Short Papers)

A variable directional coupler whose coupling is varied by an applied dc magnetic field is presented in this short paper. The directional coupler is of the two-hole type having InSb thin films in the coupling apertures to which the magnetic field is applied perpendicularly. The directional coupler was tested at room temperature at frequencies from 32 to 36 GHz. At a frequency of 33.1 GHz and magnetic flux densities of up to 13 kG, the coupling varies from 14.2 to 40.2 dB with the directivity exceeding 24.6 dB, the insertion loss of about 1 dB, and the VSWR of 1.2.     

A New Class of Nonreciprocal Components Using Slot Line (Short Papers)

The authors present an experimental and theoretical study of edge modes in a ferrite-loaded slot line. Nonreciprocal properties are obtained over a broad frequency band. Added microstrip lines provide suitable transitions. A theory based on magnetic boundary conditions shows good agreement with the experimental results and allows a comparison with stripline devices described by Hines. In particular, the characteristics of the slot-line isolators are satisfactorily explained by this theory.     

Resistivity of Thin Metal Films (Short Papers)

It is shown that the sheet resistance, and hence the resistivity, of very thin metal films (<100 /spl aring/) can be determined conveniently and accurately by microwave measurements. Accuracy is limited by VSWR measurement, film-holder design, and short-circuit quality. DC and microwave resistivity measurements are given for gold films on cleaved mica.     

A Method of Fabrication for Waveguide Nonreciprocal Toroidal Ferrite Phasers (Short Papers)

An improved technique for latching ferrite-phaser construction is described. It is particularly attractive when magnetostrictive ferrites or garnets are employed and for configurations utilizing high-dielectric-constant loading. The technique is capable of yielding phasers with very uniform characteristics, large figures of merit, low loss, and excellent average power capability.     

Microwave Properties of Lithium Ferrites (Short Papers)

Low-power loss and high-power threshold properties have been measured between 3.0 and 17.2 GHz on three Li-Ti ferrite compositions of magnetizations 1250, 2250, and 3600 G. In each composition the use of cobalt resulted in a linear increase in mu/sub 0/ and h/sub crit/. Temperature measurements were performed at 9.2 GHz on the 2250-G material. An illustration of how the data might be applied is given.     

A New Mixer Design for 140-220 GHz (Short Papers)

A new Schottky-diode mixer is described which has low noise and conversion loss in the 140-220-GHz band. At 170 GHz mixer noise temperatures of 1100-1300 K [Single sideboard (SSB)] have been measured, with 6.2-7.2-dB SSB conversion loss. The design should be usable up to -300 GHz with appropriate scaling. The mixer has been successfully used in airborne radiometers on the NASA Convair 990 and C-141 aircraft.     

Cryogenically Cooled GaAs FET Amplifier with a Noise Temperature Under 70 K at 5.0 GHz (Short Papers)

A 4.5-5.0-GHz gallium arsenide field-effect transistor (GaAs FET) amplifier cryogenically cooled to approximately 70 K is described. A noise temperature of under 70 K is achieved over the hand. Power gain for the two-stage amplifier is 20 dB. A noise analysis is performed to predict noise-temperature dependence on the temperature of the amplifier.     

Schottky Barrier Impedance Measurements at UHF (Short Papers)

The observed frequency dependence of the real part of the small signal impedance of Schottky barrier varactor diodes has previously been explained via physical phenomena. A detailed experimental investigation shows that the frequency dependence is due to inevitable systematic errors in the measurement procedure used.     

Performance of GaAs MESFET's at Low Temperatures (Short Papers)

The noise- and s-parameters of a GaAs MESFET with 1-mu m gate Iength are characterized versus temperature. At room temperature, the noise figure measured at 12 GHz is 3.5 dB. At 90 K, the noise figure decreases to 0.8 dB (T/sub e/ = 60 K). The associated gain is 8 dB. The design of a cooled amplifier for the 11.7-12.2-GHz communication band is discussed. At 60 K, the three-stage amplifier exhibits 1.6-dB noise figure (T/sub e/ = 130 K) and 31-dB gain.     

Comments on "A Relationship Between the Scattering Parameters of a Passive Lossy Nonreciprocal Two-Port" (Short Papers)

An inequality relating the scattering coefficients of a passive Iossy-reciprocal or nonreciprocal two-port is derived. For the reciprocal two-port the inequality reduces to that presented by Uhlir.     

Avalanche Diode Noise Sources at Short Centimeter and Millimeter Wavelengths (Short Papers)

Semiconductor noise sources for microwave frequencies have been constructed using commercial avalanche diodes in waveguide mounts. For the diodes and waveguide configurations reported here the upper usable frequency is approximately 40 GHz. The measurements are in limited agreement with previous predictions. It is possible that a reduction in package and diode parasitic would improve this agreement, and raise appreciably the upper usable frequency of such noise sources.     

Slot-Line Transitions (Short Papers)

Coax-slot and microstrip-slot transitions are discussed. Experimental VSWR and impedance data are presented and compared with values computed using equivalent circuits for these transitions. Thick-film chip terminations are also investigated.     

Highly Stabilized IMPATT Oscillators at Millimeter Wavelengths (Short Papers)

Highly stabilized IMPATT oscillators at millimeter wavelengths have been developed. The IMPATT diode is mounted in the coaxial-waveguide circuit at the detuned open position, and is series-resonant at the design frequency. The frequency stability and power output of /spl plusmn/5x10/sup -5/ / /spl plusmn/20/spl deg/C and 50 mW,, respectively, have been obtained at 80 GHz.     

Double-Amplification Mode Maser (Short Papers)

A chromium-doped rutile traveling-wave maser utilizing simultaneously two signal frequency transitions has been designed and a prototype section tested.     

The Edge-Guided-Wave Circulator (Short Papers)

A complete study is presented on "edge-guided-wave" circulators (EGC). The fundamental physical principles which underlie EGC's operation are established and exploited to construct a broad-band circulator in the 8-12-GHz band. The performance data are compared to those of a "continuous tracking" circulator (CTC) and a traditional Y-junction circulator.     

Ridged Circular Waveguide (Short Papers)

Characteristics of wave propagation inside a ridged circular waveguide are studied. The waveguide is a hollow, conducting circular cylinder with a pair of semicircular conducting ridges diametrically attached to its inside wall. Results of a perturbation analysis suggest that in this device a lower attenuation and a wider bandwidth than those of a conventional circular waveguide can be achieved. Certain numerical results are graphically presented.     

High-Frequency Gunn Oscillators (Short Papers)

Recent work to achieve high output power of fundamental mode Gunn-effect oscillators at frequencies ranging from 25 to 71 GHz is described. Ambient powers of 370 mW at 6.7-percent efficiency at 25 GHz, 260 mW at 4.5-percent efficiency at 38 GHz 150 mW at 4-percent efficiency at 54 GHz, and 30 mW at 1-percent efficiency at 71 GHz were obtained from single-diode structures. Combining two diodes in a push-pull circuit yielded 400 mW at 3.5-percent efficiency at 32 GHz and 260 mW at 4.0-percent efficiency at 42 GHz. This represents some of the highest powers and efficiencies reported to date from millimeter-wave Gunn-effect oscillators.     

Mixed Mode Filters (Short Papers)

Mixed mode bandpass filters are described which utilize alternating TE/sub 011//spl deg/ and TE/sub n11//spl deg/ circular waveguide cavity modes. This novel filter configuration exhibits both excellent unloaded Q and spurious mode response characteristics. The use of mixed resonant modes makes possible the design of microwave filters for both in-line side wall connected cylindrical resonators as well as folded planar filter configurations, whereby cross-coupling between selected resonators can be realized.     

Mic Ku-Band Upconverter (Short Papers)

An MIC S- to Ku-band upper-sideband upconverter has shown a pump efficiency of 25 percent and 3.8-dB signal gain. When used as a lower-sideband upconverter, gains of 13 dB and 100- MHz bandwidth were measured.     

Electrostatics of the Microstrip-Revisited (Short Papers)

The well-known integral-equation formulation of the microstrip problem is solved by a projective method using trial functions that preserve the essential singularity in charge distribution at the strip edges, Suitable computer programs are presented. This formulation is believed particularly useful in the analysis of strip discontinuities, where details of the charge distribution cannot easily be traded off against speed of computation.