Coaxial Impedance Inverter Design (Short Papers)

It is shown that the effects of discontinuity capacitances associated with the abrupt change in the center conductor diameter of a coaxial bandpass filter can readily be anticipated at the designing stage.     

Measurements of Intercavity Couplings (Short Papers)

This short paper describes the determination of couplings within a system of coupled cavities by measuring frequencies at which the phase of the input reflection coefficient is either 0/spl deg/ or 180/spl deg/. A high degree of accuracy may be achieved and corrections can be made for finite cavity Q.     

Very Large Impedance Steps in Microstrip (Short Papers)

Experimental determination of an equivalent circuit for very large impedance steps in microstrip is described. The equivalent circuit is shown to be valid in the frequency range from 1 to 2 GHz on 0.0635-cm-thick alumina substrate, although the experimental method used is applicable to any frequency range and any geometry.     

Noise Reduction in GaAs Schottky Barrier Mixer Diodes (Short Paper)

The sensitivity of heterodyne receivers operating at millimeter and submillimeter wavelengths is limited by the noise produced in the mixer element. In this paper we investigate the presence of excess noise in GaAs Schottky barrier mixer diodes. Comparison of the measured noise data with that predicted from noise models indicates that these devices typically exhibit excess noise. An additional fabrication step, which removes several hundred angstroms from the GaAs surface before the anode contact is formed, greatly reduces this excess noise. This additional step is outlined, and experimental evidence is presented.     

Correction for Adapters in Microwave Measurements (Short Papers)

A measurement on a standard termination provides sufficient information for making corrected measurements through an adapter, if the dissipative loss of the adapter can be neglected. This approximation often gives more consistent results than calibration techniques that require highly reflecting standards.     

Probe Mutual Impedance in a Rectangular Waveguide (Short Papers)

The mutual impedance between two probes, arbitrarily located on the broad walls of a rectangular waveguide, is derived by using the reaction concept. This mutual impedance is found to depend on the location and height of the probes and their separation distance. For probes of equal height, it reduces to the probe self impedance, as the probe separation distance approaches zero. The convergence of the solution and the effects of a terminating short circuit on the mutual impedance are also studied and discussed.     

Swept Frequency Impedance Indicator Using Directional Couplers (Short Papers)

A swept frequency impedance indicator which consists of directional couplers and detectors is described. Experimental equipment was made at a 17.5-19.5-GHz band, and successfully operated.     

Normalized Impedance Graphs for Exponential Transmission Lines (Short Papers)

Sign errors in an existing closed form solution for the reflection coefficient along an exponentially tapered transmission line have been corrected and the solution has been modified by the use of electrical line length. This allows useful graphs for the input impedance of the tapered line to be computed which are normalized with respect to frequency and system impedance. The graphs clearly demonstrate both the broad-band and narrow-band properties of the tapered line.     

Active Stabilization of Crystal Oscillator FM Noise at UHF Using a Dielectric Resonator (Short Papers)

A low-noise 600-MHz crystal oscillator circuit is described. It uses a dielectric oscillator as the dispersive element of a discriminator in an active frequency stabilization loop which reduces the near-carrier FM noise. The innovation in the circuit is an essentially noiseless active carrier suppression loop, which allows maximum utilization of a low-noise RF amplifier to reduce the discriminator threshold (Delta f/sub rms/) to 2.5x10-5 Hz in a 1-Hz bandwidth. The FM noise 1 kHz from the carrier was reduced by 44 dB to this threshold, equivalent to a phase-noise spectral density of -152 dBc/Hz.     

Notes on the Conjugate Matched Two-Port As an UHF Amplifier (Short Papers)

Because of the relative simplicity of measurement of scattering parameters of active two-ports at frequencies up to the lower microwave region, investigations have been made into the application of these parameters to the design of UHF amplifiers. The theory of generalized scattering parameters has been developed by Kurokawa, applied to two-port power-flow analysis by Bodway, and used in the design of a single-stage UHF amplifier by Froehner. In this last paper, the bandwidth limitations imposed by the matching networks were not considered, nor was the capacitive matching arrangement to a purely resistive load fully developed. Both of these topics are the subject of this short paper, in which the relevant design expressions are also given.     

Coupling Errors in Cavity-Resonance Measurements on MIC Dielectrics (Short Papers)

Measurements on MIC dielectrics have been made by applying the theory of resonant cavities to either wholly or partly metallized substrates. Two different schemes of coupling are employed, depending upon the metallization. Errors occur in the derived value of /spl epsi/, due to the coupling, and are of opposite sense for the two methods discussed. They may be averaged to improve the overall measurement precision (0.5 percent).     

Characteristic Impedance Design Considerations for a High-Speed Superconducting Packaging System (Short Papers)

The characteristic impedance influences of superconducting packaging systems (in particular, Josephson packaging) on the degradation in transmitted signal rise time, amplitude distortions and crosstalk, signal propagation delay, and amplitude decay at the inductive and resistive connectors with matched capacitors are quantitatively evaluated by using the ASTAP computer simulation. The present choice of the characteristic impedance Z/sub 0/ = 10- 12 Omega for a superconducting stripline is inadequate. Higher impedances of Z/sub 0/=40-50 Omega are useful from the standpoint of noise performance improvement. At the same time, a higher impedance choice can make the ground connector numbers of each connector decrease, which is preferable for a large-scale packaging system.     

Characteristic Impedance of the Slab Line with an Anisotropic Dielectric (Short Papers)

The characteristic impedance of the slab line with a circular conductor having an anisotropic dielectric is presented by rising the affine and conformal transformations. Moreover, a simpler approximate formula of the impedance expressed in term of epsilon /spl par/, epsilon /spl perp/, and r/h is also presented, where epsilon /spl par/, epsilon /spl perp/ r, and h, are the principal axes-relative dielectric constants of the anisotropic dielectric, the inner conductor radius, and the half Iength between ground planes, respectively.     

Equivalent Representation of an Abrupt Impedance Step in Microstrip Line (Short Papers)

The equivalent electrical lengths of uniform microstrip line associated with an abrupt impedance step are first evaluated, under static assumptions. The importance of these results in establishing a reference plane for the step, and in the application of calculations of capacitance associated with the step, is then demonstrated. Furthermore, some interesting dualities are discerned from the results.     

Faster Impedance Estimation for Coupled Microstrips with an Overrelaxation Method (Short Papers)

Using the Frankel-Young method, fast estimation of the potential distribution for a microstrip structure is obtained when an accelerating factor /spl omega/ is introduced in the finite-differences (relaxation) method. It is possible to calculate such a factor by an iterative technique, but the time of computation needed to find /spl omega/ annihilates the theoretical gain. In this short paper, the authors present a method which gives an analytical expression for /spl omega/. The realistic case examined here, as an illustration, is that of the suspended microstrip couplers for which odd and even impedances are the interesting parameters. Given an analytical expression for /spl omega/, the overrelaxation method appears as a very powerful and attractive method for finding the solution of any type of microstrip structure.     

Analysis of Automatic Homodyne Method Amplitude and Phase Measurements (Short Papers)

A system employing RF substitution techniques for automatic phase and intensity measurement of microwave fields is described. The system uses homodyne detection to generate error signals for servomechanisms which balance the attenuation and phase secondary standards. Accuracy and dynamic range of this method of measurement can be strongly dependent on the method of modulation employed. This paper analyzes errors from this cause and indicates what means are available to minimize them. This method of measurement is less expensive than some alternate techniques, and, at the present stage in the evolution of microwave near field measurements, its errors are less serious than uncertainties introduced by absorber reflections, probe characteristics, and mechanical positioning errors.     

Slotted Line Measurements for Propagation Constant in Lossy Waveguide (Short Papers)

The propagation coefficient in a slotted waveguide partially loaded with a lossy dielectric can be determined accurately, in terms of the measured standing-wave pattern, by means of a computer program solving a set of transcendental equations. This determination is a necessary step in a permittivity measurement technique which was recently proposed by several authors.     

Determination of the Characteristic Impedance by a Step Current Density Approximation (Short Papers)

The step current densities are used to determine the characteristic impedance of a transmission line with rectangular shape of the conductors. Numerical results for different rectangular lines with asymmetrical position of the inner conductor are presented. The comparison of the results for the square and rectangular coaxial lines shows quite good agreement with the known data.     

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.