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Microwaves, Antennas and Propagation, IEE Proceedings H

Issue 1 • Date February 1987

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Displaying Results 1 - 22 of 22
  • Effects of an intervening airgap on the two fundamental modes of a surface waveguide

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (577 KB)  

    The introduction of an intervening airgap in a circular surface waveguide is investigated. The radial field structure and the propagation characteristics of the two fundamental modes are shown, as well as their dependence on the airgap and the frequency. The thickness of the airgap is a new parameter that might be used to improve the propagation characteristics of the surface waveguide as a low-loss transmission line, or to control the penetration of the fields in the surrounding medium, allowing a design of the waveguide as a leaky transmission line. View full abstract»

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  • Variational method for coplanar waveguide with anisotropic substrates

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    Lower- and Upper- bound stationary expressions are derived for the line capacitance of the general structure of a coplanar waveguide (CPW) with layered anisotropic media for the first time. Numerical examples show the efficiency of the method, and how the margins of error can be contained within a very small range by the lowerand upper-bound calculations. View full abstract»

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  • New method for the analysis of dual-gate MESFET mixers

    Page(s): 11 - 15
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (509 KB)  

    A method for the analysis of a microwave mixer based on a dual-gate MESFET is presented. The method extends a previously published analysis technique for a single-gate MESFET mixer by treating the circuit as a threeport network. The device is described by a complete mathematical model and the harmonic balance technique is utilised for the large-signal analysis stage. This results in a relatively fast program. The method is demonstrated by applying it to the simulation of a mixer based on a Raytheon transistor RDX832 for which device data was available. The mixer was constructed and its experimentally obtained performance results show good agreement between the simulated and the measured conversion gain values through a wide range of local-oscillator input power. View full abstract»

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  • Rigorous analysis of dielectric rod waveguides with flat cross-section

    Page(s): 16 - 24
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (912 KB)  

    The mode-matching method is applied to the rigorous investigation of propagation characteristics of rod waveguides, such as an elliptically cored optical fibre or a rectangular waveguide with a flat cross-section, whose accurate analysis has been difficult so far. A high accuracy, to five significant figures, is achieved for the normalised propagation constant. Field distributions in several hybrid modes, as well as dispersion relations, are detailed. It is also confirmed that the hybrid mode analysis is not always necessary in the case of flat cross-section. The properties of higher-order mode cutoff and polarisation preservation in an elliptically cored fibre, whose investigation has not been always sufficient, are discussed more accurately. Through these analyses, it is also confirmed that the mode matching method is still a useful and reliable numerical method for rigorous analysis of the rodtype dielectric waveguide with an arbitrarily shaped cross-section View full abstract»

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  • Implementation of microwave diffraction tomography for measurement of dielectric constant distribution

    Page(s): 25 - 29
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (745 KB)  

    Diffraction tomography is a process that can infer the internal structure of an object from multiple views of its diffraction shadow. The procedure is sensitive to variations in the object's refractive index and there is interest in using the technique to measure permittivity distributions within dielectric objects and to image soft tissues for biomedical applications. To allow the inversion to proceed, a number of conditions have to be met. These determine the type of object to be studied, the geometry of the microwave system and surrounding environment. The optimal resolution distance obtainable is half a wavelength, but this can rarely be achieved because of practical limitations. Some procedures, however, are available to improve the practical resolution. One, which is suitable for microwave tomography, is to use multifrequency data and to combine the resulting images. A system operating over the X-Band microwave frequency range is described and some results for test objects in air are given View full abstract»

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  • Wavefront quality in antenna pattern measurement: the use of residuals

    Page(s): 30 - 34
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (638 KB)  

    The concept of the far-field residual source distribution is presented as a convenient and accurate means of assessing the quality of a wavefront employed in antenna measurements. The residual defines the errors in radiation pattern measurements in terms of the plane wavefront quality of the technique employed and can be used to examine the far-field range, the compact range and the near-field/far-field transformation. It is shown that the spherical wavefront of the farfield range can be analytically decomposed into a residual spectrum which can be used to explain the classical errors found in radiation patterns measured at a finite distance. The significance of different types of illumination is examined for the compact range. It is demonstrated that heavily tapered distributions can provide high accuracy at wide angles, whereas more uniform illumination results in better accuracy for near-in sidelobe measurements. Finally, the residual is used to quantify the accuracy offered by the near-field/far-field transformation and, as expected, demonstrates this to be the most accurate antenna measurement technique available View full abstract»

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  • Novel cylindrical-wave spectrum for analysis of scattering by multiple bodies

    Page(s): 35 - 44
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1116 KB)  

    A new technique based on the spectrum of cylindrical waves and successive scattering is developed to evaluate the scattered field due to two parallel cylindrical scatterers to any desired degree of accuracy. The salient features of the method are discussed and the results are presented for some practical configurations, namely two parallel circular cylinders and two semi-infinite wedges. The proposed technique is also applicable for scattering by multiple bodies of arbitrary cross-sectional shape once the scattering by each body in isolation is manageable. The numerical results for the scattering by two cylinders agree with the available exact boundary-value solution, whereas for the double wedge the transmission coefficient compares favourably with the exact values for the special case of a slit geometry and with two other asymptotic solutions for wide separations View full abstract»

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  • Noise considerations in active monopoles

    Page(s): 45 - 49
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    Limitations in the noise performance of untuned active monopoles are discussed with respect to their low radiation resistance. The noise performance of tuned active monopoles is analysed and shown to be much superior to the untuned monopole. The method of analysis is based on lumped equivalent circuits for both antenna and amplifier, and a figure of merit for comparing the noise performance of passive and active antennas is proposed. Experimental results for the noise output of ¿¿/20 and ¿¿/10 tuned active monopoles are presented to confirm the analysis View full abstract»

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  • Simplified design procedures for Butler matrices incorporating 90¿¿ hybrids or 180¿¿ hybrids

    Page(s): 50 - 54
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (636 KB)  

    This paper gives detailed procedures for designing Butler matrices up to 128 ¿¿ 128 using 90¿¿ or 180¿¿ hybrids. A formula is given for calculating the number of fixed phase shifters in each row for matrices using 180¿¿ hybrids and the positions and magnitudes of these phase shifters are shown. The phase shifts obtained across the output ports are specified, together with the input ports that produce these phase shifts. Design procedures for larger Butler matrices are also indicated View full abstract»

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  • Role of particle-size distributions on millimetre-wave propagation in sand/dust storms

    Page(s): 55 - 59
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (630 KB)  

    Particle size distributions of sand and dust are surveyed. Various assumptions for the theoretical prediction of the effect of particles on MMW propagation are discussed and justified. A general formula of the propagation parameters, for any particle shape and any distribution, is developed. It is found that the MMW propagation depends strongly on the probability density function of particle size distribution. A simplelinear relationship is shown between `¿¿, ¿¿¿¿ and an `effective radius¿¿ of the storm. Attenuation and phase shift due to spherical and ellipsoidal particles are calculated for four distributions, namely power law, exponential, lognormal and normal. Results are presented and the role of the distributions is discussed View full abstract»

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  • Gain enhancement of antennas over finite ground plane covered by a dielectric sheet

    Page(s): 60 - 64
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    In the paper the problem of gain enhancement for radiating elements between two finite plane reflectors, one of which is a partial reflector and the other a perfect conductor, is investigated. The problem is studied numerically using the method of moments and the effect of different parameters is investigated. It is shown that, as is similar to infinite structures, the antenna gain can be increased with finite size reflectors. Furthermore, for finite structures, the gain enhancement can be made larger than that of infinite structures. However, for optimum gain enhancement, the structure parameters must be selected with care View full abstract»

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  • Long-range propagation experiment to investigate the incidence of anomalous propagation in the North Atlantic

    Page(s): 65 - 70
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (831 KB)  

    The significance of enhanced range on air-to-ground paths is reviewed and an experiment described which collected maximum range data on an oversea path. A secondary surveillance radar sited in the Hebrides was used to observe civil air traffic crossing the North Atlantic, and a cumulative distribution of range extending to 0.1% of the year obtained based on 14 months of observation. About 99% of the observations are shown to be satisfactorily modelled by employing an exponential atmosphere with linear N profiles as measured by a suitably sited radio-sonde station to model the first 1 km of height. The remaining 1% of observations, the extreme range cases, are examined in some detail and are attributed to ray bending in passage through elevated layers View full abstract»

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  • Analysis of multipath fading on line-of-sight links in the presence of an elevated atmospheric duct

    Page(s): 71 - 76
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (716 KB)  

    Multipath propagation on microwave line-of-sight links is analysed in the presence of an elevated inversion atmospheric layer and a reflecting earth. A bilinear height profile for the modified refractive index is adopted. Simple mathematical relations are derived for the number of rays hitting the receiver, and a graphical solution is presented for the launching and arrival angles. It is shown that path inclination tends to reduce the number of rays reaching the receiver. When more than three rays are received, signal enhancement, due to ducting, is more likely to occur. On the other hand, signal fading is more probable in the presence of two or three rays View full abstract»

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  • Angle estimation with adaptive arrays and its relation to super-resolution

    Page(s): 77 - 82
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (673 KB)  

    The paper discusses the angle estimation problem for an adaptive array for the case where the interference covariance matrix alone is measured (signal absent adaptation). It is shown that derivative constraints for the main beam do not solve the problem. The optimum weight for angle estimation derived from maximum likelihood estimation is given. This weight is shown to be closely related to a maximumlikelihood super-resolution method. This method is therefore proposed as an alternative to adaptive nulling View full abstract»

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  • Engineering model for arbitrarily shaped microstrip antennas based on the collocation method

    Page(s): 83 - 86
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (373 KB)  

    A new method for the analysis of microstrip antennas is suggested in the paper. In the method, the least-square collocation method of the method of weighted residuals (MWR) is used. The round patch antenna is analysed using the method and the results show good agreements between the calculations and experimental data. The method is conceptually simple and computationally easy. It is particularly suitable for microcomputers View full abstract»

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  • Convergence phenomenon in the solution of dichroic scattering problems by Galerkin's method

    Page(s): 87 - 92
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    The convergence problem that arises when the scattering problem of dichroic surfaces is solved numerically by means of Galerkin's method and Floquet's theorem is investigated. A theoretical discussion is outlined showing that a truncation of the infinite Floquet spectrum is actually equivalent to modifying the used basis functions. Examples of modified basis functions due to different Floquet-mode truncations and the effect on the numerical results are demonstrated for the particular cases of arrays of thin dipoles and crossed dipoles. Some useful truncation rules are also presented, and the theories are verified by comparing predicted values with experimental results obtained by waveguide simulator measurements View full abstract»

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  • Evaluation of Sommerfeld integrals arising in the ground stake antenna problem

    Page(s): 93 - 97
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (575 KB)  

    A novel approach is described to the numerical evaluation of Sommerfeld integrals, which offers a compromise between efficiency and simplicity. In this method, the real-axis path of integration is deformed to a contour, which is the steepest-descent path for the exponential function present in the integrand. This new contour also avoids the singularities of the integrand which occur near the original path. The proposed technique is applicable if the radial displacement of the source and field points is electrically small and is most efficient if this displacement is smaller than the vertical separation between these points. Such conditions prevail, for example, in the analysis by means of the integral equation technique of a thin, vertical wire antenna, which penetrates the interface between two media (the so-called ground stake antenna) View full abstract»

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  • Technical memorandum: Conductance Of A Longitudinal, Resonant Slot In A Ridge Waveguide

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (212 KB)  

    The conductance of a longitudinal, resonant slot in a ridge waveguide is calculated under the assumptions that Stevenson made for the rectangular waveguide in 1948 [1]. The results obtained with these assumptions are compared with experimental data View full abstract»

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  • Single Sided Slotline Microstrip Transition

    Page(s): 101 - 102
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    A single-sided microstrip-slotline transition is described. It uses a balun in the form of an open ring consisting of two microstrip lines connected to a slotline through a pair of coupled microstrip. The transition transforms an unbalanced microstrip to a balanced slotline and also serves as an impedance matching network between the two lines. An experimental and theoretical study is presented. Different parameters of the transition are optimised to obtain best results View full abstract»

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  • New method for the measurement of coupling coefficients of transmission cavities

    Page(s): 103 - 105
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    A new automatic technique for measuring the coupling coefficients, resonant frequency and quality factors of transmission resonators is presented. It is based on the simultaneous measurement of the transmitted and reflected power near resonance. A linear regression analysis provides the resonator parameters with good accuracy. The accuracies of the measurements are 1 part in 107 for the resonant frequency, 0.1% for the quality factor and 1% for the coupling coefficients View full abstract»

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  • Technical memorandum: Highly Shaped Beam Telemetry Antenna For The ERS-1 Satellite

    Page(s): 106 - 108
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (653 KB)  

    The paper describes a highly shaped beam telemetry antenna developed for the ERS-1 satellite payload. The antenna comprises a symmetric reflector of shaped profile and a circularly polarised dual-mode feed horn excited by a crossed dipole. Measured radiation patterns are shown for the antenna in free space and in the presence of the satellite back structure View full abstract»

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