The Phase Shift Through Symmetrical 3-Port Circulators (Short Papers)

Simple approximate formulas are derived for the phase shift through matched circulators---with and without transformer coupling---using expressions for the eigenadmittances Y/sub 0/, Y/sub -1/, and Y/sub 1/ which have recently been proposed. These formulas allow one to predict the phase shift from measurements of the VSWR in one case and from a knowledge of the transformer admittance Y in the second. They have been confirmed experimentally for strip-Iine circulators and indicate that in this respect circulators behave like electrically long transmission devices.     

Application of Ferrite to Electromagnetic Wave Absorber and its Characteristics

An electromagnetic wave absorber utilizing ferrite or rubber ferrite composed of ferrite powder and rubber is described. In our investigation, the existence of a matching frequency f/sub m/ and a matching thickness t/sub m/ has been found. The terms f/sub m/ and t/sub m/ mean that the ferrite which is backed with a conducting plate can be a perfect absorber only under the conditions that the frequency of the incident wave is f/sub m/ and that the thickness of the ferrite is t/sub m/.Each ferrite has two matching frequencies f/sub m1/, f/sub m2/, (f/sub m1相似文献   

Analysis of Four-Frequency Nonlinear Reactance Circuits

Several advantages of multiple-frequency nonlinear reactance circuits are described in this paper. In particular, a circuit is considered in which a nonlinear reactance couples four basic frequencies: /spl omega//sub 0/, /spl omega//sub 1/,/spl omega//sub 2/, and /spl omega//sub 3/; these are so related that /spl omega//sub 2/ = /spl omega//sub 0/ + /spl omega//sub 1/ and /spl omega//sub 3/ = /spl omega//sub 0/ - /spl omega//sub 1/. Here, /spl omega//sub 0/ is taken to be the power source or pump. It is found to be desirable to allow for the possible presence of the pump harmonic, 2/spl omega//sub 0/, and individual cases are characterized by whether 2/spl omega//sub 0/, is present or not. The major results are as follows: 1) Unlimited amplification gain is theoretically possible at frequencies higher than the pump, by reflecting negative input resistance at /spl omega//sub 2/, but without relying on any effects due to pump harmonics. 2) Unlimited up- or down-conversion gains between /spl omega//sub 1/ and /spl omega//sub 2/ are theoretically possible in the additional presence of the first pump harmonic, but without reflecting negative input or output resistance. 3) Unlimited amplification gain is theoretically possible at frequencies both lower and higher than the pump fundamental, without reflecting negative input resistance.     

Product and interleaving of anticodes

Two techniques are presented for constructing new anticodes from known anticodes, namely the product and interleaving of anticodes. The product of anticodes (m/sub 1/, k/sub 1/, delta /sub 1/) and (m/sub 2/, k/sub 2/, delta /sub 2/) produces an (m/sub 1/m/sub 2/, k/sub 1/k/sub 2/, delta ) anticode, where delta /sub 1/ delta /sub 2/>     

A dual-frequency Wilkinson power divider: for a frequency and its first harmonic

A Wilkinson power divider operating not only at one frequency f/sub 0/, but also at its first harmonic 2f/sub 0/ is presented. This power divider consists of two branches of impedance transformer, each of which consists of two sections of 1/6-wave transmission-line with different characteristic impedance. The two outputs are connected through a resistor, an inductor, and a capacitor. All the features of a conventional Wilkinson power divider, such as an equal power split, impedance matching at all ports, and a good isolation between the two output ports, can be fulfilled at f/sub 0/ and 2f/sub 0/, simultaneously.     

New View on an Anisotropic Medium and Its Application to Transformation from Anisotropic to Isotropic Problems

The metric factor is defined as m(epsilon*/sub x/, epsilon*/sub y/, theta/sub x/) = /spl radic/ cos/sup 2/theta/sub x/ / epsilon*/sub x/ + sin/sup 2/theta/sub x/ / epsilon*/sub y/ in the radial direction, with the angle theta/sub x/ from the x axis being one of the principal axes in an anisotropic dielectric medium filling the two-dimensional space. The normalized metric factor is defined as n(epsilon*/sub x/, epsilon*/sub y/, theta/sub x/, beta) /spl equiv/ m(epsilon*/sub x/, epsilon*/sub y/, theta/sub x/) / m(epsilon*/sub x/, epsilon*/sub y/, beta) in the form normalized by the metric factor in the direction with the angle beta from the x axis. The effective path length d'/sub P1P2/ between the points P1 and P2 is defined as d'/sup P1P2/ = n(epsilon*/sub x/, epsilon*/sub y/, theta/sub x/, beta)d/sub P1P2/ where d/sub P1P2/ is the actual path length of the straight line P1P2 with the angle theta/sub x/ from the x axis. We propose the minimun principle of the effective path length for electric flux in the region with multilayered anisotropic media. It is applied to solving the electrostatic problem with two anisotropic media whose principal axes are different. We show by using the normalized metric factor that the anisotropic problem can be transformed into the isotropic problem.     

Active-redundancy allocation in systems

An effective way of improving the reliability of a system is the allocation of active redundancies. Let X/sub 1/, X/sub 2/ be s-independent lifetimes of the components C/sub 1/ and C/sub 2/, respectively, which form a series system. Let us denote U/sub 1/ = min(max(X/sub 1/,X),X/sub 2/) and U/sub 2/ = min(X/sub 1/, max(X/sub 2/, X)), where X is the lifetime of a redundancy (say R) s-independent of X/sub 1/ and X/sub 2/. That is, U/sub 1/(U/sub 2/) denote the lifetime of a system obtained by allocating R to C/sub 1/(C/sub 2/) as an active redundancy. Singh and Misra (1994) considered the criterion where C/sub 1/ is preferred to C/sub 2/ for the allocation of R as active redundancy if P(U/sub 1/ > U/sub 2/) /spl ges/ P(U/sub 2/ > U/sub 1/). In this paper, we use the same criterion of Singh and Misra (1994). We investigate the allocation of one active redundancy when it differs depending on the component with which it is to be allocated. We also compare the allocation of two active redundancies (say R/sub 1/ and R/sub 2/) in two different ways; that is, R/sub 1/ with C/sub 1/ & R/sub 2/ with C/sub 2/, and viceversa. For this case, the hazard rate order plays an important role. We furthermore consider the allocation of active redundancy to k-out-of-n: G systems.     

Diagnostics of asymmetrically coated semiconductor lasers

The authors present a simple diagnostic procedure for lasers that have a priori unknown facet reflectivities. The most important laser parameters that can be extracted are the cavity decay rate Gamma /sub c/ (equal to the inverse of the photon lifetime), the mirror loss coefficient alpha /sub m/ identical to -1/2 L In R/sub 1/R/sub 2/, the internal loss coefficient alpha /sub i/, the facet reflection coefficients R/sub 1/ and R/sub 2/, the spontaneous emission factor n/sub sp/, and the differential gain xi /sub l/. The authors have verified the procedure by applying it to lasers with a priori known facet reflection coefficients, these lasers were weakly index guided (VSIS and CSP types).<>     

Correction To "Asymptotic High-Frequency Modes of Homogeneous Waveguide Structures With Impedance Boundaries"

The treatment of Section V in the above paper was incomplete and, as such, a bit misleading. In fact, the existence question for solutions of equation (53) for f/sub 2/ = (pi/sub 2/, m/sub 2/) did not properly take into account the degeneracy of the basic modes f/sub 1/ = (pi/sub 1/, m/sub 1/). It is known that for a solution to exist, the right-hand side of a deterministic equation like (53) must be orthogonal to all solutions of the homogeneous adjoint problem, which in this case is the basic problem with solutions f/sub 1/. Without degeneracy, equation (56) would be that condition. However, since there are at least two linearly independent solutions f/sub 1i/, there are at least two such conditions, which leads to a contradiction except if f/sub 1/ in (53) is chosen in a special way. Let us denote the admissible f/sub 1/ in (53) by f'/sub 1/ and it can be written as a linear combination of any complete set of degenerate basic modes corresponding to the same parameter beta/sub 1/:f'/sub 1/ = Sigma alpha/sub i/f/sub 1i/.     

Detection of buried targets via active selection of labeled data: application to sensing subsurface UXO

When sensing subsurface targets, such as landmines and unexploded ordnance (UXO), the target signatures are typically a strong function of environmental and historical circumstances. Consequently, it is difficult to constitute a universal training set for design of detection or classification algorithms. In this paper, we develop an efficient procedure by which information-theoretic concepts are used to design the basis functions and training set, directly from the site-specific measured data. Specifically, assume that measured data (e.g., induction and/or magnetometer) are available from a given site, unlabeled in the sense that it is not known a priori whether a given signature is associated with a target or clutter. For N signatures, the data may be expressed as {x/sub i/,y/sub i/}/sub i=1,N/, where x/sub i/ is the measured data for buried object i, and y/sub i/ is the associated unknown binary label (target/nontarget). Let the N x/sub i/ define the set X. The algorithm works in four steps: 1) the Fisher information matrix is used to select a set of basis functions for the kernel-based algorithm, this step defining a set of n signatures B/sub n//spl sube/X that are most informative in characterizing the signature distribution of the site; 2) the Fisher information matrix is used again to define a small subset X/sub s//spl sube/X, composed of those x/sub i/ for which knowledge of the associated labels y/sub i/ would be most informative in defining the weights for the basis functions in B/sub n/; 3) the buried objects associated with the signatures in X/sub s/ are excavated, yielding the associated labels y/sub i/, represented by the set Y/sub s/; and 4) using B/sub n/,X/sub s/, and Y/sub s/, a kernel-based classifier is designed for use in classifying all remaining buried objects. This framework is discussed in detail, with example results presented for an actual buried-UXO site.     

A Lower Limit on the Interaction Between Symmetrical Odd-Mode Fringing Capacitances (Letters)

Let us denote the familiar odd-mode fringing capacitance which is plotted in graphs given by Getsinger by C/sub f0/. It is further defined by Fig. 1(b) in the limit as the magnetic wall tends to infinity on the right. We also denote the corresponding fringing capacitance of the symmetrical coaxial structure of Fig. 1(a) by C/sub f0/. When the dimensions of Fig. 1(a) and (b) are such that s' = s, it is convenient to denote the difference between C/sub f0'/ and C/sub f0'/ by /spl utri/C/sub f0/, and define it as the interaction between the symmetrical odd-mode fringing capacitances. Clearly, /spl utri/C/sub f0/ has the property of approaching zero as w/ (b - t) /spl rarr/ 0 [w is defied in Fig. 1(a)]. Moreover, whenever /spl utri/C/sub f0/ is known, C/fub f0/ is also known.     

Data-dependent k/sub n/-NN and kernel estimators consistent for arbitrary processes

Let X/sub 1/, X/sub 2/,... be an arbitrary random process taking values in a totally bounded subset of a separable metric space. Associated with X/sub i/ we observe Y/sub i/ drawn from an unknown conditional distribution F(y|X/sub i/=x) with continuous regression function m(x)=E[Y|X=x]. The problem of interest is to estimate Y/sub n/ based on X/sub n/ and the data {(X/sub i/, Y/sub i/)}/sub i=1//sup n-1/. We construct appropriate data-dependent nearest neighbor and kernel estimators and show, with a very elementary proof, that these are consistent for every process X/sub 1/, X/sub 2/,.     

An optical investigation of electronic excitations in the high temperature superconductors YBa/sub 2/Cu/sub 3/O/sub 7- delta / and Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+ Delta /

The results of Raman scattering from superconducting gap excitations in the high T/sub c/ compounds YBa/sub 2/Cu/sub 3/O/sub 7- delta / and Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+ Delta / are compared. In the normal state, both materials exhibit strong electronic interband scattering which manifests itself as a broad background continuum having both A/sub 1g/ and B/sub 1g/ symmetry components. At low temperatures a redistribution of this electronic scattering occurs, indicative of the formation of a superconducting gap in these compounds. The two symmetries exhibit distinct redistribution, however, denoting strong anisotropy. At temperatures well below T/sub c/, both compounds exhibit residual low-energy scattering, a feature suggestive of the coexistence of normal electrons and superconducting quasi-particles.<>     

Field Theory Design of Rectangular Waveguide Broad-Wall Metal-Insert Slot Couplers for Millimeter-Wave Applications (Correction)

In the above paper, the designation of the columns "Slot Lengths (mm)" of Tables I-IV should have read "Half Slot Lengths (mm)," as is indicated correctly in Fig. 1 of the paper, by z = l/sub 1/, z = 2l/sub 1/, respectively, for the first slot. S/sub 1/, S/sub 2/,· · ·, in the figure of Table I, therefore, should have read 2S/sub 1/, 2S/sub 2/,· · ·, as shown above.     

Symmetry-Induced Modal Characteristics of Uniform Waveguides --- I: Summary of Results

The application of symmetry analysis to uniform waveguides is discussed. Symmetry analysis provides exact information concerning mode classification, mode degeneracy, modal electromagnetic-field symmetries, and the minimum waveguide sectors which completely determine the modes in each mode class. Tables are presented which list the possible mode classes and their degeneracies for the two general symmetry families, C/sub n/ and C/sub nv/, of uniform waveguides. Tables showing the azimuthal dependence of the longitudinal components of the electric and magnetic fields for each mode class are given. Based on this azimuthal dependence, figures showing the minimum waveguide sectors which are necessary and sufficient to completely determine the modes of the various mode classes are presented. The application of symmetry analysis is illustrated by considering uniform waveguides with C/sub 4/ and C/sub 6v/ symmetry.     

Balancing networks for symmetric antennas .I. Classification and fundamental operation

Emphasis has been placed on the quality of a metrology antenna system that allows it to be represented accurately using analytical or numerical models. Central to this capability is the efficacy of the balancing networks, sometimes referred to as balanced to unbalanced transformers (baluns). In this paper, we classify three fundamental types of baluns and show that all three can be derived from the 180/spl deg/, four-port hybrid network. Balanced antennas driven from coaxial feed lines and operated in the presence of an asymmetric scatterer present an intrinsically unbalanced load to the balun. We show that in such situations the current balun is the only appropriate balun to employ. For numerous antenna metrology applications, in particular, site attenuation measurements, 180/spl deg/, four-port hybrid networks have been employed as baluns. Network relations are derived relating the so-called voltage and current baluns to the 180/spl deg/, four-port hybrid network. It is shown that, in addition to acting as a 0/spl deg/ or 180/spl deg/ power divider, the hybrid network can serve as either a voltage or a current balun depending on the termination at the isolated port. In contrast to the traditional approach, it is shown that when using a 180/spl deg/ hybrid as a balun, the isolated port should be terminated in such a way that the hybrid behaves as a current balun as opposed to a 180/spl deg/ power divider. This will yield experimental results that can be more readily reconciled with models.     

Application of Submillimeter Spectroscopy to Magnetic Excitations

Magnetic excitations are the collective excitations of the magnetic moments in ferro- and antiferromagnets. The frequencies are mostly in the far-infrared spectral range. Their study is of current interest with respect to the properties of phase transitions, since in ordinary 3-dimensional crystals the dominating exchange interactions can be 3-dimensional (MnF/sub 2/, NiO) or may be restricted to 2 dimensions (K/sub 2/MnF/sub 4/CoCl/sub 2/ or even to 1 dimension (CsNiF/sub 3/, CoCI/sub 2/ 2H/sub 2/O). In this paper, an introduction and a review is given of the results on q = 0 magnon modes (ferro- or antiferromagnetic resonance) which can be studied rather directly by submillimeter-wave spectroscopy. Some results about 2 magnon bands are also mentioned. Experimentally, grating monochromators, Fourier-transform interferometers, FIR laser, and microwave techniques have been employed. In the past, not only pure materials have been studied but also doped crystals where localized magnon modes can occur (MnF/sub 2/ :Co/sup 2+/, CoF/sub 2/ :MnF/sub 2/, NiO :Co/sup 2+/).     

A Simple Method for Spacing the Adjacent Passbands of a Coupled-Line Filter

A bandpass filter using two coupled transmission lines is considered. Two ports of the coupled-line four port are both short-circuited (or open-circuited); the other two ports are terminated in the characteristic impedances of the lines (e.g., 50 Omega). For a constant coupling along the coupling section l the attenuation poles are fixed at l/lambda = n/2 (n = 0,1,2,...). If, however, the coupling changes along the coupling section in three steps with the coupling factors k/sub 1/, k/sub 2/, k/sub 3/ = k/sub 1/, the stopband between two adjacent passbands can be extended for certain values of k/sub 1/ and k/sub 2/. A simple calculation method for the coupling factors k/sub 1/ and k/sub 2/ is described. A practical design example shows good agreement with theoretical results.