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Antennas and Propagation, IEEE Transactions on

Issue 2 • Date March 1982

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Displaying Results 1 - 25 of 27
  • [Front cover and table of contents]

    Publication Year: 1982 , Page(s): 0
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  • Effect of record length on the correlation of complex exponentials

    Publication Year: 1982 , Page(s): 267 - 272
    Cited by:  Papers (1)
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    The correlation coefficient is one measure of how well two signals can be resolved. The effect of record length on the correlation of complex exponentials is examined. For two decaying exponentials of complex frequencies s_ {1} = \sigma _{1} + j\omega _{1} and s_ {2} = \sigma _{2} + j\omega _{2} with \sigma _{2} > \sigma _{1} , it is shown that a finite time record length \Delta may be considered as though it were infinite, provided \Delta > 2/ |\sigma _{1}| . This is also the condition for near-orthogonalization of a set of complex exponentials, with small error. View full abstract»

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  • Comments on "Simple formulas for designing an offset multibeam parabolic reflector

    Publication Year: 1982 , Page(s): 323
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    First Page of the Article
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  • [Back cover]

    Publication Year: 1982 , Page(s): c4
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    Freely Available from IEEE
  • Spatial correlations in adaptive arrays

    Publication Year: 1982 , Page(s): 212 - 223
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (944 KB)  

    A receiving array antenna can steer its main beam toward any direction by adjusting the complex weight in each element. However it cannot always steer one beam and one null toward two prespecified directions simultaneously with a single set of weights. The ability for an array to steer one beam and one or more nulls simultaneously is determined by five factors: 1) element positions, 2) orientations of elements, 3) antenna patterns of elements, 4) polarizations of signals, and 5) directions of the beams and/or nulls. A coefficient is defined, called spatial correlation, which includes these factors and completely characterizes array beam pointing and nulling. Its application to adaptive arrays is demonstrated. The adaptive array performance is dominated by this coefficient and can be improved by properly choosing the first three factors. Several examples on the selection of element placement in adaptive arrays are presented. View full abstract»

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  • Resonant behavior of a small aperture backed by a conducting body

    Publication Year: 1982 , Page(s): 205 - 212
    Cited by:  Papers (27)
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    The problem of an electrically small aperture in a conducting screen backed by a conducting body is analyzed. It is found that aperture-body resonances can occur for which the power transmitted through the aperture backed by a conducting body is much larger than that when the body is not present. An example is an electrically small aperture resonated by a capacitor across its midpoint. In the loss-free case, the transmission cross section of a small resonated aperture is 3\lambda ^{2}/4\pi independent of the size or shape of the aperture. For actual conductors, the transmission cross section will be increasingly reduced by conduction loss as the aperture is made smaller. View full abstract»

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  • Synthesis of offset dual reflector antennas transforming a given feed illumination pattern into a specified aperture distribution

    Publication Year: 1982 , Page(s): 251 - 259
    Cited by:  Papers (4)
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    The problem of transforming a given primary feed pattern into a desired aperture field distribution through two reflections by an offset dual reflector system is investigated using the concepts of geometrical optics. A numerically rigorous solution for the reflector surfaces is developed which realizes an exact aperture phase distribution and an aperture amplitude distribution that is accurate to within an arbitrarily small numerical tolerance. However, this procedure does not always yield a smooth solution, i.e., the reflector surfaces thus realized may not be continuous or their slopes may vary too rapidly. In the event of nonexistence of a numerically rigorous smooth solution, an approximate solution that enforces the smoothness of the reflector surfaces can be obtained. In the approximate solution, only the requirement for the aperture amplitude distribution is relaxed, and the condition on the aperture phase distribution is continued to be satisfied exactly. View full abstract»

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  • A spectral-iteration approach for analyzing scattering from frequency selective surfaces

    Publication Year: 1982 , Page(s): 303 - 308
    Cited by:  Papers (31)
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    A novel technique, called the spectral-iteration approach, for analyzing the problem of scattering from periodically perforated screens which find useful applications as radomes, optical filters, artificial dielectrics, and so on is applied. The formulation is carried out in the spectral domain where a set of algebraic equations is obtained directly for the spectral coefficients of the aperture field distribution (or the induced current density) rather than via an integral equation formulation. These equations are then solved simultaneously using an iterative procedure developed in this paper that circumvents the need for matrix inversion. Because the matrix solution is avoided in the spectral approach, it is capable of handling large aperture sizes in a computationally efficient manner. The efficiency of computation results from the use of the fast Fourier transform (FFT) algorithm which is employed in the derivation of the algebraic equations and in the iteration procedure. A unique feature of the spectral-iteration approach is that it has a built-in boundary-condition check which provides a reliable indication of the accuracy of the solution. It is also shown that the spectral domain technique can be applied to even a wider class of geometries, e.g., the step discontinuity in a waveguide. View full abstract»

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  • Analysis of rectangular horn antennas via uniform asymptotic theory

    Publication Year: 1982 , Page(s): 241 - 250
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (896 KB)  

    Approximate analytic expressions for the far-field radiation pattern and modal reflection coefficient of the three-dimensional horn antenna have been developed. Based upon a multiple-image model of the two-dimensional horn-waveguide structure, this approach offers greater generality than previously proposed ray analyses with comparable complexity and accuracy. The uniform asymptotic theory (UAT), which is employed throughout, provides information when this approach is valid for a desired degree of accuracy in the solution. It is demonstrated that, in most cases, the far-field pattern of the horn is reducible to the pattern of a simple slit in an absorbing screen illuminated by an array of patterned line sources. The measured patterns of several horns are convincingly recovered by the prediction of the analytical model. The same model is used to calculate the modal reflection coefficient of the horn-waveguide structure and, again, comparison with measured results is excellent. View full abstract»

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  • Resonant scattering for characterization of axisymmetric dielectric objects

    Publication Year: 1982 , Page(s): 168 - 172
    Cited by:  Papers (19)
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    Resonances in the electromagnetic scattering by dielectric objects are investigated both numerically and experimentally with particular emphasis on their direct application to object characterization. Low ka calculations for spheres and an infinite circular cylinder illustrate the modal nature of the resonances and the dependence of the resonance spectra on refractive index and size. Experiments show that the specific wavelengths at which resonances occur in the scattering intensity from a glass fiber can be used to determine its diameter to a high accuracy. The extended boundary condition method is used to calculate the low ka resonances of a prolate spheroid and a finite circulate cylinder with the anticipation that the scattering resonances may be particularly suitable for characterizing randomly oriented nonspherical objects. View full abstract»

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  • Synthesis of antenna patterns with prescribed nulls

    Publication Year: 1982 , Page(s): 273 - 279
    Cited by:  Papers (27)
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    The least mean square pattern synthesis method is extended to include constraints such as pattern nulls or pattern-derivative nulls at a given set of angles. The problem is formulated as a constrained approximation problem which is solved exactly, and a clear geometrical interpretation of the solution in a multidimensional vector space is given. The relation of the present method to those of constrained gain maximization and signal-to-noise ratio (SNR) maximization is discussed and conditions for their equivalence stated. For a linear uniform N -element array it is shown that, when M single nulls are imposed on a given "quiescent" pattern, the optimum solution for the constrained pattern is the initial pattern and a set of M -weighted (\sin Nx)/\sin x -beams. Each beam is centered exactly at the corresponding pattern null, irrespective of its relative location. For the case of higher order nulls, the n th pattern derivative is similarly canceled by the n th derivative of a (\sin Nx)/\sin x -beam. In addition, simple quantitative expressions are derived for the pattern change and gain cost associated with the forced pattern nulls. Several illustrative examples are included. View full abstract»

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  • Radiation from a small monopole in a uniaxially anisotropic plasma

    Publication Year: 1982 , Page(s): 235 - 240
    Cited by:  Papers (2)
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    The radiation field of a small monopole over a ground plane covered with a uniaxially anisotropic plasma with an arbitrary inclination of the optical axis is studied. A steepest descent evaluation of the field integrals has been performed under the elliptic condition, and some calculated power patterns have been studied in comparison with those for a small dipole in an unbounded uniaxially anisotropic plasma. For an arbitrary inclination of the optic axis, considerable differences between the power patterns of the two configurations have been observed. Lateral waves and concentrated field regions are found to occur from mode coupling at the surface of the ground plane. View full abstract»

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  • Ice depolarization of the COMSTAR beacon at 28.56 GHz during low fades and correlation with radar backscatter

    Publication Year: 1982 , Page(s): 183 - 190
    Cited by:  Papers (1)
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    Radar correlation with significant ice depolarization events accompanied by low copolarization fades of the 28.56-GHz COMSTAR beacon signal are described for an experimental program at Wallops Island, VA. Using a Faraday switch at the front end of the receiver, the copolarization and cross-polarization levels of the 28.56-GHz beacon signal are sequentially monitored. A nearby high resolution S -band radar pointing along the Earth-satellite path monitors the simultaneous ice and rain reflectivity. Excellent correlation is noted between the cross-polarization events and relatively large and extended ice reflectivities along a segment of the Earth-satellite path at altitudes near and above the 0°C isotherm. The radar and receiver data strongly suggest the cross-polarization mechanism is due to a hailshaft which intersects the path at altitudes well below the 0° isotherm. Since the intervening ice results in a cross-polarization signal which either adds or subtracts to the cross-polarization antenna residual, a method is described to remove the residual from the resultant measured cross-polarization level, without employing a phase measurement. Cumulative, month-of-year and time-of-day statistics associated with the depolarization signals are established. View full abstract»

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  • Electromagnetic fields near a concave perfectly conducting cylindrical surface

    Publication Year: 1982 , Page(s): 280 - 292
    Cited by:  Papers (9)
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    Although no shadowing or diffraction effects occur, the surface fields excited by a high frequency source located on a perfectly conducting concave cylindrical boundary cannot be analyzed by geometrical optics since the caustics for rays, which have experienced many reflections, accumulate. In a previous study, alternative field representations in terms of whispering gallery (WG) modes, canonical integrals, and hybrid ray-mode combinations have been explored to compensate for the failure of geometrical optics. As the source and/or observation points move off the boundary, the number of relevant multiply reflected rays decreases, and the caustics eventually become separated sufficiently to be treated as isolated. Ray optics is then expected to apply provided that uniform corrections near caustics and their endpoints are included. This conjecture is confirmed in the present investigation, which tracks the field continuously from the "boundary layer" near the concave surface, where ray optics is invalid, to off-surface points where it applies, by generalizing the alternative field representations used previously. A rich variety of hybrid ray-mode combinations exists for off-surface source and observation points. Especially intriguing is the possibility of choosing a hybrid mix that completely avoids the need for the caustic (and endpoint) correction functions in a purely ray-optical formulation. The utility, accuracy, and range of validity of the various field representations is assessed by numerical comparison with a reference solution in terms of WG modes plus a continuous spectrum. View full abstract»

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  • SEM parameter extraction through transient surface current measurement using King-type probes

    Publication Year: 1982 , Page(s): 260 - 266
    Cited by:  Papers (1)
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    The well-known miniature loop technique pioneered by R. W. P. King and his co-workers for probing surface currents is considered for the case of measuring transient surface currents-in particular, for the use in performing singularity expansion method (SEM) extraction measurements. The theoretical performance of electrically small loops is reviewed and interpreted in the transient regime. Measured probe responses are presented and viewed against the backdrop of theory. Results are presented for current measurement on a cylindrical scatterer illuminated by a transient spherical wave and compared with numerical predictions. Singularity expansion descriptions extracted from the measured data are presented and ramifications regarding their accuracy and recoverability are discussed. View full abstract»

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  • Analysis of a large linear antenna array of uniformly-spaced thin-wire dipoles parallel to a perfectly conducting plane

    Publication Year: 1982 , Page(s): 230 - 234
    Cited by:  Papers (2)
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    A method of moments solution is presented for the analysis of a large linear antenna array of uniformly spaced thin-wire dipoles parallel to an infinite perfectly conducting plane. A single piecewise sinusoidal expansion and testing function per dipole is used in a Galerkin procedure. This results in a symmetric Toeplitz generalized impedance matrix requiring approximately 2N^{2} multiplications and divisions to determine the unknown dipole currents. The solution corresponds to a savings of a factor of N/6 over a Gaussian elimination solution. Computed results are given for a 1000- element dipole array. View full abstract»

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  • Wide-band diffraction improved dual-shaped reflectors

    Publication Year: 1982 , Page(s): 173 - 176
    Cited by:  Papers (2)
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    Modified dual-shaped reflectors are discussed. These antennas have improved gain and gain over noise temperature (G/T) performance over the conventional uniform illumination design when diffraction effects are considered. A further advantage of the present design approach is its inherent broad-band characteristics. These considerations are vital for ultra-low noise systems as employed in the deep space telemetry service. View full abstract»

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  • Slant path fade and rain-rate statistics associated with the COMSTAR beacon at 28.56 GHz for Wallops Island, Virginia over a three-year period

    Publication Year: 1982 , Page(s): 191 - 198
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB)  

    Rain-fade and rain-rate statistics covering a three-year period for Wallops Island, VA are presented. The attenuation statistics were derived from continuous measurements of beacon signals at 28.56 GHz emanating from the COMSTAR ( D_{2} and D_{3} ) geostationary satellites. The rain-rate statistics were determined from continuous measurements of precipitation with tipping-bucket rain gauges. Descriptions are given of the yearly, overall average, monthly, and time-of-day fade as well as the yearly and overall rain-rate distributions. Relatively small year-to-year variations are noted for both the fade and rain-rate statistics; however, relatively large year-to-year changes are noted for the monthly and time-of-day cases. For example, the extreme average probability variations for the year-to-year cases are within \pm20 percent relative to the average distribution over the fade interval from 3 to 25 dB. Over the rain-rate interval, 4-50 mm/h, the extreme probability deviations are within \pm25 percent relative to the three-year average rain-rate distribution. Probability deviations of factors of two or more are noted, however, for the yearly variations in both the monthly and time-of-day statistics. Using effective parameter concepts coupled with the 28.56-GHz attenuation and rain-rate measurement, the cumulative fade distribution at 19.04 GHz is predicted. This, as well as the measured 28.56-GHz fade distributions are compared with those predicted using the International Radio Consultative Committee (CCIR) global model, and excellent agreement is noted. View full abstract»

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  • Design of microstrip antennas covered with a dielectric layer

    Publication Year: 1982 , Page(s): 314 - 318
    Cited by:  Papers (43)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    The design of a microstrip antenna covered with a dielectric layer is presented. Due to loading, the resonant frequency of the antenna changes. The absolute value of the change increases with the operating frequency, the relative permittivity (except plasma), and the thickness of the dielectric layer. This change may cause degradation in performance due to the inherent narrow bandwidth of microstrip antennas if the effect of loading is not considered in the design. The curves presented here may be used to design microstrip antennas that may be subjected to icing or a plasma environment or coated with protective layers. Numerical and experimental results for the fractional change in the resonant frequency are round to be in good agreement. View full abstract»

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  • The analysis of the RF response of a solid wire excited by a focused laser beam

    Publication Year: 1982 , Page(s): 177 - 182
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    The solution is presented for the current excited on a solid cylindrical wire with a flat endcap which is excited by a short current filament oriented parallel to the wire axis and located on or near the endcap surface. This wire/source geometry has become of interest as a result of experimental findings in which transient source filaments have been excited on metal targets due to the incidence of a high-power short-pulse laser beam. Steady-state solutions are developed which show the basic characteristics of the responses and their dependence on critical wire and source parameters. Transient responses also are presented and shown to exhibit excellent agreement with measured results. View full abstract»

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  • Antenna beamwidth independence of measured rain attenuation on a 28-GHz Earth-space path

    Publication Year: 1982 , Page(s): 165 - 167
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    Rain attenuation measured at 28 GHz on an earth-space path is independent of antenna beamwidth for beamwidths as small as 0.1\deg and for attenuations up to 30 dB. The measurements imply that angle-of-arrival fluctuations are less than 0.02\deg . View full abstract»

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  • A propagation experiment combining reflection and diffraction

    Publication Year: 1982 , Page(s): 318 - 321
    Cited by:  Papers (7)
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    Measurements of propagation at a frequency of 1090 MHz over terrain that produces specular reflection and knife-edge diffraction are in good agreement with model calculations that use images to represent the effect of reflection. A hill covered with a pine forest formed the diffracting mask, and an airport area formed the reflecting surface. Agreement between measurements and model calculations required that the diffracting knife edge be located at treetop level. Optimum propagation into the shadow region was obtained when a maximum in the reflection-lobe pattern coincided with the mask angle. View full abstract»

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  • A dual-band TEM lens for a multiple beam antenna system

    Publication Year: 1982 , Page(s): 224 - 229
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    A three-dimensional electromagnetic (TEM) lens is made of many printed circuit cards for future satellite multiple beam antenna applications. To obtain a low scan aberration lens combined with cross-polarization suppression, the lens array faces have a nonuniform distribution of element rotational orientations, making the array faces electrically nonuniform as to mutual coupling. An experimental procedure is presented for developing dual-band active impedance matched lens elements. Using such elements, a lens is built and tested to verify the adequacy of the design procedure. View full abstract»

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  • Phase linearization of a broad-band antenna response in time domain

    Publication Year: 1982 , Page(s): 309 - 313
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    Broad-band antennas often introduce phase distortions to their associated signals. A digital technique is introduced to correct (linearize) the antenna phase response in the time domain without use of the fast Fourier transform (FFT) which in a minicomputer requires extensive computer time and storage for its implementation. The process can be performed in real time. It is accomplished by appropriately piecewise linearizing the phase response and correcting each linear phase (constant time delay) segment with respect to a time reference. The correction is performed with the application of a relative time delay and phase offset. View full abstract»

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  • Transmission through slits formed by inclined planes

    Publication Year: 1982 , Page(s): 199 - 204
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    The phase and the amplitude of electromagnetic fields transmitted through two-dimensional slits are investigated both theoretically and experimentally. The slits are formed by two inclined perfectly conducting planes. The approximate theory employed is based on the modification of the high frequency diffraction by a half-plane (modified geometrical theory of diffraction (GTD)). The experimental measurements were performed using a parallel-plate range. Results indicate that the effect of the relative inclinations of the planes tends to be of importance only for the cases of narrow slits, i.e., \lambda /3 or less. View full abstract»

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IEEE Transactions on Antennas and Propagation includes theoretical and experimental advances in antennas.

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Editor-in-Chief                                                 Kwok W. Leung