Scalar Network Research Articles

Scaling for vibrational modes of fractals tethered at the boundaries

Using a mapping between a scalar elastic network tethered at its boundaries and a diffusion problem with permanent traps, we study various vibrational properties of progressively tethered disordered fractals. Different scaling forms are proposed for different types of boundary tethering and numerical investigation of the scaling is performed by the approximate diagonalization of the corresponding large, sparse transition probability matrices. Rather different localization behaviors are found for the leading modes depending on the type of tethering. For example, while the largest nontrivial eigenvalue for the tethering of the hull appears to scale by a power law of the cluster size S in an essentially same manner as the untethered case except for the amplitude which depends on the number of tethered sites, the corresponding quantity for the all-boundary tethering seems to scale logarithmically with S.

A microwave microstrip ring resonator as a moisture sensor for biomaterials: application to wheat grains

A miniaturized, non-destructive sensor employing a microwave microstrip ring resonator (MRR, GHz, mean diameter 3.69 mm) was developed for estimating the moisture content of a single wheat ( Triticum aestivum L) grain. A single wheat grain with a known amount of moisture was placed on the MRR at two different orientations ( and ) with respect to the feedline. The resonance frequency , bandwidth (B) and quality factor of the MRR were calibrated against the moisture content. The measurements were made with a scalar network analyser. The sensor was studied in the normal useful moisture range of 11-32% (on a wet-weight basis), the actual moisture values being obtained by an oven-drying method. The orientation was more sensitive to moisture than was the orientation. The total changes in for a 21% change in moisture content for and 90 orientations were 235 and 150 MHz, respectively. The errors in moisture estimation with for and were % and %, respectively. The corresponding values with B and for orientation were % and %, respectively. The proposed sensor is more sensitive than a reported waveguide resonator and is easy to operate, for the microstrip offers an open structure, thereby facilitating easy loading and unloading of the samples.

Characterization of high-Q resonators for microwave filter applications

A one-port reflection technique is developed to measure the unloaded Q and external Q of a microwave resonator. The unique procedure of measuring unloaded Q is outlined in three easy steps. A sample chart is provided to further simplify the process. This method is so simple that even a scalar network analyzer is adequate for the measurement. In addition, a time-delay response around the resonator resonant frequency is also derived and presented. This theoretical result, combined with the advanced capability of modern vector network analyzers, has been proven to be very useful for characterization and tuning of the external Q of a resonator. All the results derived are verified by practical measurement. Finally, this technique is applied to the realization and tuning of a six-pole dielectric loaded cavity filter.

A novel vector network analyzer

A calibration procedure for a perturbation two-port vector network analyzer is presented. It consists of a variable perturbation two-port placed between a device-under-test and a scalar network analyzer. A measured vector reflection coefficient is determined on the basis of amplitude-only measurements. A full correction of systematic errors is possible. The new principle was experimentally confirmed in the frequency band up to 14 GHz. The results enable prediction of an add-on for scalar analyzers, enabling vector measurements.

Hilbert-transform-derived relative group delay

Many common types of microwave circuits, particularly filters, are required to meet a group delay ripple specification. This is normally measured using a vector network analyzer (VNA) or some specialized test configuration. A new method of assessing the group delay ripple of a broad class of microwave circuits is presented, which uses a scalar network analyzer and a form of the Hilbert transform. Experimental results illustrating the usefulness of the technique are shown for a series of examples and the principal sources of error are analyzed.

EFFECT OF BOUNDARY TETHERING ON VIBRATIONAL MODES OF FRACTALS

We introduce a mapping between a tethered scalar elastic network and a diffusion problem with permanent traps. Various vibrational properties of progressively tethered fractals are discussed using this analogy both in terms of scaling ansatz and numerically by approximately diagonalizing the corresponding large random matrices, with the critical percolation cluster as an example of a fractal.

PCs for AP and other EM reflections

A FORTRAN subroutine is presented, which accurately determines the effective width of a waveguide and its length, by measuring the resonance frequencies of the cavity made of the same waveguide. This measurement method only necessitates a scalar network analyzer and standard waveguide components. >

Q-factor measurement with a scalar network analyser

An accurate determination of the unloaded Q-factor of RF and microwave resonators is required when the electrical properties of materials are being measured or when the resonator is to be characterised for an application in a filter or an oscillator. A procedure is described of weighted least-square curve fitting to the measured magnitude of the reflection coefficient. The accuracy of the results is significantly improved by incorporating coupling losses in the equivalent circuit model.

Dielectric constants of rubber and oil palm leaf samples at X-band

The paper reports on the measured dielectric constants of leaves of two tropical crops, namely rubber and oil palm, as a function of moisture content at X-band. Using a microcomputer-based automated system consisting of a Wiltron scalar network analyzer and a slotted waveguide, the measurements are done based on the waveguide thin sheet technique. Theoretical values from the dual-dispersion model by Ulaby and El-Rayes [1987] and from the simple dielectric theory of Fung and Fung [1977] are compared with the experimental data. The model from Ulaby and El-Rayes is found to be able to give good estimates of the dielectric constants for the two types of leaf samples at X-band.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Unambiguous through-bond sugar-to-base correlations for purines in 13C, 15N-labeled nucleic acids: The HsCsNb, HsCs(N)bCb, and HbNbCb experiments

A set of three 3D (1H,13C,15N) triple-resonance correlation experiments has been designed to provide H1'-H8 intraresidue sugar-to-base correlations in purines in an unambiguous and efficient manner. Together, the HsCsNb, HsCs(N)bCb, and HbNbCb experiments correlate the H1' sugar proton to the H8 proton of the attached base by means of the (H1', C1', N9, C8, H8) heteronuclear scalar coupling network. The assignment strategy presented here allows for unambiguous H1'-H8 intraresidue correlations, provided that no two purines have both the same H1' and C1' chemical shifts and the same C8 and N9 chemical shifts. These experiments have yielded H1'-H8 intraresidue sugar-to-base correlations for all five guanosines in the [13C,15N] isotopically labeled RNA duplex r(GGCGCUUGCGUC)2.

Existence and uniqueness of travelling waves for a neural network

SynopsisA one-dimensional scalar neural network with two stable steady states is analysed. It is shown that there exists a unique monotone travelling wave front which joins the two stable states. Some additional properties of the wave such as the direction of its velocity are discussed.

Rapid High Temperature Measurement of Microwave Dielectric Properties

ABSTRACTPractical high temperature (above 500°C) dielectric measurement techniques are reviewed stating both advantages and limitations of known methods. Details of a new and practical dual frequency microwave high temperature dielectrometer are discussed. This dielectrometer technique is capable of measurements beyond 2000°C. Both heating of the small samples and the measurement of their complex dielectric constant is done simultaneously using both a medium power (60W) microwave source and a low power scalar network analyzer. Good accuracy is obtained and the measurement is capable of being totally automated. Presently, a measurement and heating cycle time of about 20 s is needed to completely characterize the sample's microwave dielectric response from 300°C to 1600°C. A second high temperature dielectrometer technique is discussed which requires only one microwave source of medium power level (60W). This method requires only the reflected power to be monitored during the microwave heating of the sample to obtain the complex permittivity versus temperature curve.

Scalar network analysers operating at Ka- and W-bands

Scalar network analysers measuring the amplitude of the reflection/transmission coefficients of waveguide structures have been realised at Ka- and W-bands. Their accuracy derived by using standard mismatches is excellent at Ka- band and fairly good at W-band. To our knowledge this is the first instance where the accuracy of measurements obtained from a scalar network analyser was checked over full waveguide bands with the aid of standard mismatches. The reported reflectometers are precursors of vector network analysers based on six-port reflectometers. Methods aimed at increasing the signal-to-noise ratio (SNR) of the measurements have been developed, while proposals for improving the dynamic range of these network analysers are put forward.

Development of mode converters for 28 GHz electron cyclotron heating system

Small circular waveguide mode converters used in the 28 GHz, 200 kW ECH system for the Hitachi tokamak HT-1 have been developed. In order to convert from the TE02 to the TE11 mode, TE0202-to-TE01 and TE01-to-TE11 mode converters are used. Both converters use periodic waveguide wall perturbations, the case of the former, circularly symmetric perturbations, and in the case of the latter, curvature perturbations. The lengths of the mode converters were successfully shortened with high mode conversion efficiencies by decreasing the number of periods and then optimizing the periods using quite a small diameter for the converters. The 30ϕ TE02-to-TE01 mode converter is 103 · 34 mm long and its mode conversion efficiency measured by a scalar network analyser is 96% at 28GHz. The TE01-to-TE11 mode converter is 427 · 38 mm long and has an efficiency of 79%, which is 10% lower than the design value. This discrepancy resulted mainly from mode conversion from the TE11 to the TE12 mode, caused by the smaller number of...

Parametric mixing in a nonlinear TlCaBaCuO thin film resonator at microwave frequencies

The RF nonlinear behavior of a TlCaBaCuO thin film at 77 K is investigated. The film is patterned to form a disk with small annular perforations along the outer edge, and a dielectric resonator is used to couple to the structure. Thinning of the film with a bromine etch greatly enhances the reactive nonlinearity of the resonator structure. Scalar network analyzer measurements revealed sufficient nonlinearity to achieve parametric amplification at 7.2 GHz. The nonlinearity is tentatively attributed to RF-induced flux in the superconducting film.

Mode filter for high-power microwaves

A resistive-wall mode filter in which the axisymmetric (TE/sub 01/ and TE/sub 02/) modes pass almost without attenuation and the nonaxisymmetric (TE/sub 11/ and TM/sub 11/) modes attenuate has been developed for 28-GHz high-power microwave applications. Pyrolytic graphite having an anisotropic resistivity was installed in the mode filter so that the normal direction to the deposition surface of the pyrolytic graphite was in the axial direction of the mode filter. Mode attenuation and return losses in the mode filter were measured for the four modes using a scalar network analyzer with mode converters that convert from the rectangular TE/sub 10/ mode to the circular modes. Measured attenuation was 2.4+or- 0.3 dB for the TE/sub 11/ mode, 5.5+or-0.2 dB for the TM/sub 11/ mode, and 0.0+or-0.2 dB for the TE/sub 01/ and TE/sub 02/ modes at 28 GHz. Return losses were in the range of -20 to -25 dB for each mode.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Multistate instrument for characterising 2-ports

A general method is reported for measurement of the complex reflection and transmission coefficients of a two-port device by connecting it between a reflectometer and a sequentially mismatched detector. The coefficients are determined from the ratios of outputs from two power sensors to that of a third, so that the method may be of use for adapting a scalar network analyser for measuring complex quantities. Experimental results from a waveguide WG22 implementation are described.

Determination of the functionally important heme peripheral vinyl group orientation in paramagnetic hemoprotein by 2D NMR

2D NMR spectroscopies have been successfully used to characterize the heme peripheral vinyl groups in paramagnetic hemoprotein in spite of the difficulties from the rapid paramagnetic relaxation and the low digital resolution of the 2D NMR map. The scalar coupling network system among the vinyl protons is clearly identified in the COSY spectra from its characteristic cross-peak pattern and the dipolar coupling connectivities of the vinyl proton resonances with other heme side-chain proton resonances not only provide the specific assignment of vinyl β-proton resonances but also allow the determination of the vinyl group orientation with respect to the heme plane.

Accuracy assessment of the scalar network analyzer using sliding termination techniques

In the absence of phase response the major, if not the primary, sources of error in the scalar network analyzer are the imperfect directivity, etc., associated with its internal and frequently inaccessible test set or measurement network. An explicit expression is obtained for this error in terms of the observed response to a sliding termination and sliding short. This has made possible a more complete error expression than would have otherwise been obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ultra broad band measurements on high T/sub c/ ceramic superconducting transmission lines

Transmission lines were fabricated on high-T/sub c/ ceramic conductor thin films by means of a lithographic technique. A scalar network analyzer was used to perform measurements from 10 MHz to 26.5 GHz of the transmission and reflection characteristics of superconducting transmission lines at 4.2 K, 77 K, and room temperature. The lines were fabricated from 0.8- mu m-thick YBa/sub 2/Cu/sub 3/O/sub 7/ on 1.0-mm-thick SrTiO/sub 3/ substrates. Characteristic impedance, attenuation constant, phase constant, group time delay and group velocity were calculated by a novel algorithm which is processed in real time. Time domain responses, e.g., pulse delay and waveform distortion, were also easily obtained by a computer technique. The degradation due to the etching process is investigated, and a comparison is made of copper and ceramic transmission lines. >