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Microwave Theory and Techniques, IEEE Transactions on

Issue 5 • Date May 1988

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Displaying Results 1 - 13 of 13
  • Millimeter-wave diode-grid phase shifters

    Page(s): 902 - 907
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    Monolithic diode grids have been fabricated on 2-cm square gallium-arsenide wafers with 1600 Schottky-barrier varactor diodes. Shorted diodes are detected with a liquid-crystal technique, and the bad diodes are removed with an ultrasonic probe. A small-aperture reflectometer that uses wavefront division interference was developed to measure the reflection coefficient of the grids. A Phase shift of 70° with a 7-dB loss was obtained at 93 GHz when the bias on the diode grid was changed from -3 V to 1 V. A simple transmission-line grid model, together with the measured low-frequency parameters for the diodes, was shown to predict the measured performance over the entire capacitive bias range of the diodes, as well as over the complete reactive tuning range provided by a reflector behind the grid, and over a wide range of frequencies form 33 GHz to 141 GHz. This shows that the transmission-line model and the measured low-frequency diode parameters can be used to design an electronic beam-steering array and to predict its performance. An electronic beam-steering array made of a pair of grids using state-of-the-art diodes with 5-Ω series resistances would have a loss of 1.4 dB at 90 GHz View full abstract»

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  • Characteristic impedance of a coaxial system consisting of circular and noncircular conductors

    Page(s): 917 - 921
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    Two types of equivalent eccentric coaxial lines are described whose eccentricities vary with the ratio of inner and outer conductors, for a coaxial system consisting of circular and noncircular conductors. The equivalent lines can provide a smooth transition between extremes of a small wire and a wire near contact. The results obtained are simple analytical expressions for fast computation of the characteristic impedance or for the computer-aided design (CAD) of coaxial components. The accuracy of the expression is confirmed by comparison with accurate numerical data View full abstract»

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  • The history of electromagnetics as Hertz would have known it

    Page(s): 806 - 823
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    Highlights of the separate developments of the sciences of electrostatics and magnetostatics are traced through the end of the 18th century, climaxed by the work of Coulomb and Poisson. The linkage of these two sciences due to the discoveries of Oersted, Ampere, Biot and Savart, and Faraday are described, followed by the theoretical culmination embodied in the work of Maxwell. It is shown how Maxwell's prediction of the existence of electromagnetic waves set the stage for the epochal experiments of Hertz View full abstract»

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  • Oscillator priming and preoscillation noise in a gyrotron

    Page(s): 891 - 901
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    Phase control is achieved in a pulsed gyrotron oscillator both by applying an external priming signal directly to the oscillator and by applying the signal to a prebunching cavity. A pulse-to-pulse phase jitter of greater than 2.5° is achieved in the gyrotron at drive-to-oscillator power ratios of -36.6 dB (drive signal-to-noise power ratio of 36 dB) in the direct injection case and -71 dB (drive signal-to-noise power ratio of 22 dB) in the prebunched case. A lumped-element theory is compared to the experimental results. The theoretical description seems valid when the drive frequency is within about 5 MHz of that of the oscillator. Preoscillation noise in the gyrotron is about 10 μW, larger than expected from either shot noise thermal noise but in the vicinity of spontaneous cyclotron emission. Convective radio-frequency noise growth is investigated. No evidence of the electrostatic cyclotron instability was seen. All growth observed is attributed to the gyroklystron amplification mechanism. However the noise growth per unit length is not as large as that of a narrow-band drive signal View full abstract»

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  • Complex modes in boxed microstrip

    Page(s): 865 - 874
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    A method is described for obtaining the propagation coefficients and field patterns of a large number of modes for microstrip with a minimum of computational effort. The method uses a discrete space-domain formulation to calculate a large number of higher-order modes in a way which leads to their fast location and which ensures that node modes are missed. This includes those pairs of modes with complex conjugate propagation constants of the type reported for finline, as well as the normal evanescent modes. In addition, the characteristic impedance of microstrip is efficiently calculated. The results presented are obtained using the generally accepted power-current definition and are in agreement with other published results View full abstract»

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  • The first century of microwaves-1886 to 1986

    Page(s): 830 - 858
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    The author reviews the first century of experiments into microwaves, which he considers began with the experiments of Heinrich Hertz, between 1886 and 1889, using what are now called microwave circuits and techniques. Hertz's thorough investigations validated the Faraday-Maxwell theory of electromagnetism, opened up the electromagnetic spectrum between DC and light for scientific and practical uses, and opened up a new line of investigation in the ultraviolet. The author's work is in two parts. Two of the objectives of the first part are to identify, and establish a uniform nomenclature for, the apparatus used by Hertz in his experiments, and to serve as a guide to the understanding of the work of Hertz in electromagnetics, especially his experiments. After briefly reviewing Maxwell's contributions, Hertz's career is discussed with emphasis on the work in understanding and using Maxwell's work (the Berlin Prize Problem). The discovery by Hertz of a method to generate and detect electromagnetic waves is then detailed. The second part outlines his succeeding work to the early 1940s. Examples of some of the ensuring advances described are drawn from a search of historical records and from personal correspondence and interviews with some pioneers in microwave devices and applications View full abstract»

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  • Flexible dielectric waveguides with powder cores

    Page(s): 882 - 890
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    Flexible dielectric waveguides have been demonstrated at 10 GHz and 94 GHz using thin-wall polymer tubing filled with low-loss, high-dielectric-constant powders. Absorptive losses of the order of 10 dB/m were measured at 94 GHz. with nickel-aluminium titanate and barium tetratitanate powder in polytetrafluoroethylene (PTFE) lightweight electrical tubing. Bending losses at 94 GHz were negligible for curvature radii greater than 4 cm. M.H. Kuhn's (1974) theory of three-region cylindrical dielectric waveguide was used to calculate dispersion curves for the lower-order modes for several combinations of dimensions and dielectric constants. Good agreement was obtained between experimental and theoretical values of guide wavelength. A scheme is proposed for classifying hybrid modes of three-region guides based on the ratio |Ez/Hz|. For two-region guides, this reduces to E. Snitzer's (1961) familiar scheme View full abstract»

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  • Heinrich Hertz: a short life

    Page(s): 802 - 805
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    The author presents a biography of Heinrich Rudolf Hertz (1857-94). After brief mention of Hertz's childhood, his education and papers on electrical theory are reviewed. Investigations conducted on electromagnetic wave propagation phenomena are recounted View full abstract»

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  • A new six-port microwave network; six-port magic junction

    Page(s): 859 - 864
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    A six-port junction is proposed that consists of an H-plane symmetrical waveguide Y-junction with a coaxial line on one side of its axis and a circular waveguide on its other. The scattering matrix of the junction in an ideal case is derived using the symmetry properties of the structure. If both the coaxial and the circular waveguide arm are matched without destroying the symmetry, the arms of the junction are automatically matched and isolated as well, similar to the side arms of a conventional magic T. Therefore, the proposed device is called a six-port magic junction. These properties are confirmed experimentally in X-band. Some interesting applications based on the properties of the six-port junction are discussed View full abstract»

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  • Heinrich Hertz-theorist and experimenter

    Page(s): 824 - 829
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    It is argued that when Heinrich Hertz was appointed professor of physics at Karlsruhe in 1885 he was uniquely prepared for his historic experiments that opened the radio spectrum. Hertz made the first antennas and transmitter-receiver radio system and conducted a series of experiments which establish that radio waves are identical to light except for their much greater length. His description of the radiation phenomenon remains the best ever written, revealing his tremendous depth of understanding of the subject. Hertz's training studies, and experiments are recounted and measurements with a replica of his apparatus are described View full abstract»

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  • Green's function for layered lossy media with special application to microstrip antennas

    Page(s): 875 - 881
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    Suitable Green's dyadics are determined for the fields generated by a surface current density in a plane parallel to the interface of a layered isotropic structure. Special care is taken to ensure that Green's function can still be calculated in the source region by circumventing the numerical problems using analytical procedures. The obtained Green's function is used to calculate the power deposition from a microstrip antenna inside a layered biological tissue, the media involved can be highly lossy. An analytical method is developed to avoid numerical problems arising from the exponential decay of the fields due to these losses View full abstract»

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  • Comparison of power deposition by in-phase 433 MHz and phase-modulated 915 MHz interstitial antenna array hyperthermia systems

    Page(s): 908 - 916
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    The interstitial microwave antenna array hyperthermia (IMAAH) system produces a pattern of specific absorption rate (SAR) that is nonuniform within a 2-cm square array when driven in phase at 915 MHz. It was found that phase modulation makes the time-averaged SAR pattern significantly more uniform in planes perpendicular to the antennas. To drive antennas in phase at 433 MHz similarly improves SAR uniformity when the antennas are of resonance length View full abstract»

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  • Mode stability of radiation-coupled interinjection-locked oscillators for integrated phased arrays

    Page(s): 921 - 924
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    An analysis is presented of a two-element, 10-GHz array consisting of two oscillators coupled solely by means of the free-space interaction between their respective antenna elements. The oscillators are modeled as energy-storing L-C tank circuits in parallel with voltage-dependent negative conductances. A simplified far-field slot antenna model is used to derive the mutual admittance of the two antennas. Even-odd mode analysis yields the normal modes of the system, and a theorem from averaged potential theory is used to determine which mode is stable. Two microstrip Gunn diode oscillators were built to verify the essential features of the model. Oscillator frequencies, relative phases, and radiation patterns were measured as functions of the interantenna distance, and the periodic alternation of modes with distance predicted by theory was confirmed quite well 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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