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Microwave Theory and Techniques, IEEE Transactions on

Issue 4 • Date April 1969

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Displaying Results 1 - 14 of 14
  • Table of contents - April 1969

    Page(s): 177
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    Page(s): 240
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  • Design and Computed Theoretical Performance of Three Classes of Equal-Ripple Nonuniform Line Couplers

    Page(s): 218 - 230
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    The purpose of this paper is to provide an accurate theoretical picture of three classes of tapered-line couplers. The coupler taper is approximated with a cascade of short equal-length coupled line segments whose coupling values match those of the taper at one end of each segment. Exact analysis of the even-mode transmission-line analogy is then performed by evaluating the ABCD matrix of the cascade as a function of frequency with the aid of a digital computer. The computed response converges to that of the smooth tapered coupler as the number of line segments increases, total length being held constant. An exact asymptotic high-frequency model for asymmetric couplers is presented which provides improved prediction of coupler performance, as verified by computer analysis. The associated design procedures are given explicitly. The insertion phase dispersion of the 90° and Σ - Δ magic tee devices is treated. Comparisons with the insertion phase dispersion of various stepped coupling 90° designs are provided. View full abstract»

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  • Fields in Waveguide Bends Expressed in Terms of Coupled Local Annular Waveguide Modes

    Page(s): 210 - 217
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    The fields in waveguide bends with arbitrary curvature and cross section are expressed in terms of "local" annular modes. The coupling between the local mode amplitudes is derived by evaluating the differential scattering coefficients between two adjacent infinitesimal annular waveguides. Comparison of these solutions with an earlier analysis of the problem shows that the coupling terms for the local annular modes are smaller for gradually curved bends since they are proportional to the derivative of the curvature. Furthermore, the significant scattered annular modes are bunched more tightly about the incident mode. The coupled differentiaI equations for the annular mode amplitudes may therefore be solved by considering relatively fewer scattered modes. View full abstract»

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  • A General High-Order Finite-Element Analysis Program Waveguide

    Page(s): 204 - 210
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    A very general computer program for determining sets of propagating modes and cutoff frequencies of arbitrarily shaped waveguides is described. The program uses a new method of analysis based on approximate extremization of a functional whose Euler equation is the scalar Helmholtz equation, subject to homogeneous boundary conditions. Subdividing the guide cross section into triangular regions and assuming the solution to be representable by a polynomial in each region, the variational problem is approximated by a matrix eigenvalue problem, which is solved by Householder tridiagonalization and Sturm sequences. For reasonably simple convex polygonal guide shapes, the dominant eigenfrequencies are obtained to 5-6 significant figures; for nonconvex or complicated shapes, the accuracy may fall to 3 significant figures. Use of the program is illustrated by calculating the propagating modes of a class of degenerate mode guides of current interest, for which experimental data are available. Numerical studies of convergence rate and discretization error are also described. It is believed that the new program produces waveguide analyses of higher accuracy than any general program previously available. View full abstract»

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  • A High-Resolution Swept-Frequency Reflectometer

    Page(s): 185 - 188
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    A simple swept-frequency reflectometer is described that is capable of measuring reflection coefficients as low as 0.001 and is particularly suitable for precise impedance matching. With the exception of a length of accurate plain waveguide, used as a standard, the instrument contains no critical components and requires no tuning adjustments. The reflection coefficient is displayed on an oscilloscope or X-Y recorder on an almost linear scale that is only slightly affected by departures from square-law detection. View full abstract»

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  • The Stepped Digital Elliptic Filter

    Page(s): 178 - 184
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    The design and synthesis of various types of microwave elliptic function filters has been accomplished by a number of authors. However, one problem in this field which remains is the realization of compact narrow-band bandpass elliptic function filters. In this paper, a procedure is presented which enables this class of filters to be constricted in a compact digital form. Since the physical realization is in the form of an n-wire line, one-quarter of a wavelength Iong at the center frequency of the passband, where the impedance levels are stepped along the center of the coupled lines, the filter has been termed the stepped digital elliptic filter. The absence of awkward interconnections in the filter due to the stepped digital structure inherently implies that reasonable insertion loss characteristics may be achieved in the X-band region and above, and also simplifies the mechanical construction. It is shown that the resonant elements in the filter, due to the design procedure adopted, are relatively insensitive to the absolute bandwidth of the filter, and consequently fractional bandwidths of approximately 30 percent and below may be readily achieved while the normalized impedance values of the elements in the network remain of the order of unity. This latter result is similar to that obtainable from conventional interdigital filters but in the case of narrow bandwidths the stepped digital filter is considerably smaller in physical size. A systematic procedure is also formulated for the inclusion of the parasitic lumped end effect capacitances into the overall design procedure in order to maintain the equiripple passband and stopband responses. Experimental results are presented for a five-element, 11 percent bandwidth filter and are shown to be in good agreement with theoretical predictions. View full abstract»

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  • The Design and Synthesis of a Class of Microwave Bandpass Linear Phase Filters

    Page(s): 189 - 204
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    This paper is concerned with the design procedure and synthesis of a class of microwave bandpass linear phase filters which simultaneously exhibit a maximally flat amplitude and delay response about band center. In the first part of the paper a systematic procedure is developed for the construction of a nonminimum phase transfer function which exhibits a maximally flat delay and maximally flat amplitude characteristic. In the second part, a synthesis procedure is presented for the realization of the general nth-ordered transfer function by a generalized interdigital network. To simplify the design and construction of this filter, typical characteristics for filters of degree n = 3,4,5,6,7 are graphically presented together with a tabular representation of the polynomials which are required to design the filter. Finally, the results of an experimental filter of degree 3 are incorporated to illustrate that this class of nonminimum phase filters may readily be constructed in practice. View full abstract»

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The IEEE Transactions on Microwave Theory and Techniques focuses on that part of engineering and theory associated with microwave/millimeter-wave components, devices, circuits, and systems involving the generation, modulation, demodulation, control, transmission, and detection of microwave signals. This includes scientific, technical, and industrial, activities. Microwave theory and techniques relates to electromagnetic waves usually in the frequency region between a few MHz and a THz; other spectral regions and wave types are included within the scope of the Society whenever basic microwave theory and techniques can yield useful results. Generally, this occurs in the theory of wave propagation in structures with dimensions comparable to a wavelength, and in the related techniques for analysis and design..

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