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Antennas and Propagation, IEEE Transactions on

Issue 5 • Date September 1982

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Displaying Results 1 - 25 of 42
  • [Front cover and table of contents]

    Publication Year: 1982 , Page(s): 0
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    Freely Available from IEEE
  • Comments on "Nonuniqueness in inverse source and scattering problems"

    Publication Year: 1982 , Page(s): 1037 - 1039
    Cited by:  Papers (1)
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  • Comments on "Nonuniqueness in inverse source and scattering problems"

    Publication Year: 1982 , Page(s): 1039 - 1042
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  • A correction to the available formula for the GTD near-field patterns of conical horns

    Publication Year: 1982 , Page(s): 1042 - 1043
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    An error in the geometrical theory of diffraction (GTD) near-field analysis of a conical horn published earlier is pointed out. This error is corrected, and the correct expression for the near-field patterns for the conical horn is presented. Computations based on the corrected formulas correlate better with results based on measurement as well as aperture integration technique [4]. View full abstract»

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  • Comments on "GTD analysis of the near-field patterns of conical and corrugated conical horns"

    Publication Year: 1982 , Page(s): 1043 - 1044
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    For original paper see ibid., vol.AP-25, no.3, p.447 (1977) which presents a novel technique for the analysis of the principal plane near-field patterns of conical and corrugated conical horns with small and wide flare angles excited in the dominant mode using the uniform theory of diffraction (UTD). The authors apply a slope diffraction correction, which is necessary in cases where the incident field is rapidly varying at the edge View full abstract»

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  • Reflections from linearly vibrating objects: plane mirror at oblique incidence

    Publication Year: 1982 , Page(s): 898 - 903
    Cited by:  Papers (7)
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    The reflections from a perfectly conducting plane in sinusoidal vibration are evaluated. The incident wave is a time-harmonic plane wave at oblique incidence. The solution is essentially based upon expansions of the scattered fields in infinite series of evanescent, and propagating plane waves. The expressions obtained by this method are compared to the expressions obtained by the quasistationary method and to the expressions obtained by means of the special theory of relativity. View full abstract»

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  • Theoretical limitation of the sea on the detection of low Doppler targets by over-the-horizon radar

    Publication Year: 1982 , Page(s): 837 - 845
    Cited by:  Papers (6)
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    A theoretical model for the Doppler spectrum of high frequency (HF) backscatter from ocean waves (sea clutter) is used to determine the limitations that this clutter could impose on the detection of ships by skywave over-the-horizon radar (OTHR). Sea clutter spectra were computed as functions of radio frequency, sea state, radar-to-wind angle, and the amount of coherent integration employed in the processing of these spectra. Target-ship radar cross sections of 30 dBm2and 50 dBm2were utilized, and a radar antenna aperture of 2.5 km (yielding a 0.5\deg azimuthal resolution at 15 MHz) and a range resolution of 1.5 km were assumed for this study. The results of this analysis are presented in graphical form in terms of target ship detectability as a function of radial velocity, assuming that a minimum signal-to-clutter ratio of 10 dB is required. It is generally concluded that target detection is better at lower sea states, higher radio frequencies, and when coherent integration time is increased. The best computed capability exists at 25 MHz, where positive detection is predicted for both 30 dBm2and 50 dBm2targets with radial velocities either near zero or in excess of 10 knots, in any sea state. This capability is typical for daytime ionospheric propagation conditions. At a frequency of 7 MHz-and for small target ships-the detection capability is much more sensitive to the sea state; this capability is quite viable for stationary or transiting ships in sea state 2, but marginal for target ships in sea state 8. View full abstract»

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  • Theory of the frequency responses of uniform and quasi-taper helical antennas

    Publication Year: 1982 , Page(s): 1017 - 1021
    Cited by:  Papers (2)
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    A theory is presented for the frequency responses of uniform and quasi-taper helical antennas radiating in the axial mode. Based on a model assuming a single traveling wave of current, expressions for the far-zone electric field are obtained by summing the contributions of the current elements from one end of the helix to another. These expressions are used to study the variation of the axial electric field with frequency, first assuming the Hansen-Woodyard (HW) condition and then assuming Sensiper's solution for the phase velocity. It is found that the HW condition leads to the result that the electric field increases monotonically with frequency over the entire axial mode range, which is in violation with the recent experimental measurements of King and Wong. On the other hand Sensiper's phase velocity yields frequency response curves that are consistent with King and Wong's measurements. Numerical results are given for uniform helices and quasi-taper helices consisting of two uniform sections of different diameters. View full abstract»

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  • Measurements of ice depolarization at 28.56 GHz using the COMSTAR Beacon simultaneously with a 16.5 GHz polarization diversity radar

    Publication Year: 1982 , Page(s): 858 - 866
    Cited by:  Papers (6)
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    Measurements on ice depolarization made at the National Research Council in Ottawa, using a 16.5-GHz polarization diversity radar concurrently with the 28.56-GHz COMSTAR beacon, are reported. The radar, which is normally operated in a circular polarization mode, provides data on polarization parameters such as the cancellation ratio and the degree of preferred orientation. Frequently, the differential propagation parameters can be determined. From these data, identification of different kinds of hydrometeors (i.e., rain, melting layer, and ice crystals) along the path is possible. The beacon receiver measures the differential attenuation and the differential phase shift between two linear orthogonal components of the received signal, and the copolar attenuation. Several occurrences of ice depolarization in the presence of rain were observed. From radar data, identification of the hydrometeors was made and the contribution of each type toward the differential propagation parameters was determined. Good agreement between radar and beacon receiver measurements was obtained. Also several events of ice depolarization in the absence of rain are reported. The results presented here provide new data on ice depolarization and demonstrate the usefulness of simultaneous polarization diversity radar and beacon measurements for obtaining a better understanding of the nature of ice depolarization. Because of the limited observation period, emphasis is given to the nature of the phenomenon rather than to the statistics of its occurrence. View full abstract»

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  • A note on utilizing far-field phase information

    Publication Year: 1982 , Page(s): 1008 - 1010
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    The far-field phase information available from an antenna pattern is discarded in most system applications. Making use of such information for an angle-of-arrival estimation application across a relatively wide region of space is discussed in this note. The far-field phase difference response from two simultaneous shaped beam receive patterns generated by a linear array antenna is shown to provide an appropriate relative phase property for making unambiguous angle determinations. View full abstract»

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  • A broad-band annular-ring microstrip antenna

    Publication Year: 1982 , Page(s): 918 - 922
    Cited by:  Papers (59)  |  Patents (1)
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    A heuristic discussion of the radiation properties of the transverse magnetic (TM11) and (TM12) modes of the annular-ring microstrip antenna is presented, indicating the possibility of the TM12mode as a superior microstrip antenna. Rigorous analyses of the resonant frequency characteristics of the antenna are then performed with the matched asymptotic expansions technique and the perturbation approach. The analyses show that the TM12mode is decidedly the best mode for microstrip antenna applications while the TM11mode, having a high Q -factor, is best reserved for resonator applications. The analyses include the study of the resonant frequencies, bandwidths, and radiation pattern of the antenna. The matched asymptotic expansions technique and the perturbation approach are also shown to agree excellently with each other within their domain of validity. View full abstract»

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  • A new expression for the scattering of a Gaussian beam by a conducting cylinder

    Publication Year: 1982 , Page(s): 881 - 887
    Cited by:  Papers (12)
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    The scattering of a Gaussian beam with phase distribution by a conducting cylinder is analyzed for the H and E waves. A simpler expression than in conventional analysis is successfully obtained by using a new method of solution. The expression of the beam is represented as a product of a well-known scattering of a plane wave and a weighting function. This analysis is still valid for the case where the diameter of the cylinder is comparable or equal to the beamwidth. The Poynting vector and the amplitude of the total Gaussian beam near the cylinder are sketched in two-dimensional space. The amplitude and phase of the total beam are compared with experimental results. The surface current distribution and scattering patterns are also described. View full abstract»

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  • Simple formulas for transmission through periodic metal grids or plates

    Publication Year: 1982 , Page(s): 904 - 909
    Cited by:  Papers (54)  |  Patents (2)
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    A simple closed-form approximate solution is given for the transmission coefficient of a normally incident electromagnetic plane wave through a screen made of periodic metal grids (inductive screen), or made of metal plates (the complementary capacitive screen). Explicit formulas are also presented for cascading screens and dielectric slabs. When compared with the exact solution, our approximate simple formulas show good numerical accuracy. View full abstract»

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  • Low-frequency ground wave propagation over narrow terrain features

    Publication Year: 1982 , Page(s): 831 - 836
    Cited by:  Papers (1)
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    Solutions of the one- and two-dimensional integral equations that describe ground wave propagation are presented and compared. The one-dimensional equation is shown to be inaccurate at low frequencies for obstacles narrower than about 10 km and typical pathlengths. In such cases, the two-dimensional equation is needed to account properly for the signal's dependence on obstacle width, recovery at long distances, and transverse diffraction pattern. The one- and two-dimensional solutions approach each other at large distances beyond very wide obstacles. View full abstract»

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  • Using site-diversity reception to overcome rain depolarization in millimeter wave satellite communications systems

    Publication Year: 1982 , Page(s): 990 - 991
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    The concept of attenuation diversity gain in a single-polarized site-diversity receiving system can be extended to an analagous quantity called isolation diversity gain in a dual-polarized site-diversity system. Isolation-diversity gain can be calculated from single site attenuation if the attenuation diversity gain is known. View full abstract»

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  • On the index for array optimization and the discrete prolate spheroidal functions

    Publication Year: 1982 , Page(s): 1021 - 1023
    Cited by:  Papers (11)
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    A class of array optimization problems is considered in which we seek to optimize the array response in a specified angular sector. The optimization of array directivity is shown to be a special limiting case of these problems as the width of the specified angular sector approaches zero. The optimum array patterns are also shown to be related to the well-known prolate-spheroidal functions. View full abstract»

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  • The response of a two-wire transmission line to incident field and voltage excitation, including the effects of higher order modes

    Publication Year: 1982 , Page(s): 998 - 1003
    Cited by:  Papers (10)
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    The surface currents on a two-wire transmission line induced by incident field excitations are investigated using the spectral concept. A simple solution is obtained for plane wave excitation. A solution for voltage source excitation, in which the induced current may be given, at least approximately, by means of the so-called leaky-wave concept, is considered. The influence of the electrical dimensions of the structure on the currents and the relative importance of the higher modes are examined by numerical examples. View full abstract»

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  • Studies on radio duct occurrence and properties

    Publication Year: 1982 , Page(s): 853 - 858
    Cited by:  Papers (1)
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    It is necessary to clarify radio duct properties in order to estimate propagation characteristics for radio system design. In this paper, radio duct properties are statistically analyzed using aerological data observed at six typical stations in Japan over seven years, and meteorological data observed near the ground by a balloon or tower. Radio refractivity gradient statistics are then compared with duct occurrence probability and fading occurrence probability. Consequently, it was possible to evaluate quantitatively a probability of duct occurrence using refractivity statistics. Certain properties of the radio duct were also quantitatively obtained. View full abstract»

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  • Extremely low frequency quasi-static propagation measurements from a calibrated electric field source in the ocean

    Publication Year: 1982 , Page(s): 825 - 831
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    Experimental data are presented that verify a theoretical model for subsurface-to-subsurface quasi-static propagation from a horizontal electric dipole in a semi-infinite conducting half-space. The data were taken in an ocean environment in a frequency range from 1 to 10 Hz. Horizontal source/sensor separations from 180 to 450 m and depths from 46 to 100 m were used. Comparisons are made between the data and model predictions, relative to range dependence and magnetic field strength. The model predicted magnetic fields were found to agree with the experimentally measured fields approximately within experimental uncertainty. View full abstract»

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  • Sidelobe control in cylindrical arrays

    Publication Year: 1982 , Page(s): 1027 - 1031
    Cited by:  Papers (13)  |  Patents (7)
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    Low sidelobe patterns in cylindrical arrays are synthesized through the use of an artificially created noise source environment. Pattern/excitation pairs are generated by an exact formal process which optimizes the array performance. For symmetric patterns this process minimizes the signal-to-noise power ratio. For optimum antisymmetric patterns the on-axis boresight error is minimized. Sidelobe levels and rate of decay are controlled by proper selection of the angular variation of the noise amplitude. View full abstract»

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  • Estimating wind speed from HF skywave radar sea backscatter

    Publication Year: 1982 , Page(s): 846 - 852
    Cited by:  Papers (3)
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    Linear expressions relating ocean surface wind speed to a theoretical estimate of the - 10 dB width of the high frequency (HF) sea echo Doppler spectrum (0.078 Hz Doppler shift frequency resolution) are derived for different radar frequencies. The -10 dB width, determined from theoretical model estimates of the Doppler spectrum as a function of radar frequency for a wide range of ocean wave conditions, changes in a complex way with the continuum of second-order echoes surrounding the stronger first-order echo. Because the amplitude of the second-order echoes is directly related to changes in the directional ocean wave spectrum, the wind speed estimates derived from these expressions are highly dependent on the wave field (both the total energy and its distribution with direction); significant differences in these expressions are also found, for example, between fetch-limited and fully developed seas, and for wind seas and swell. These expressions are extremely difficult to use experimentally to obtain reliable estimates of wind speed because a priori knowledge of the wave field is required to apply the correct expression, and yet this knowledge cannot be determined from the unresolved second-order structure at this spectral resolution. Several Doppler spectra recorded under known ocean wind and wave conditions illustrate the difficulty in applying these theoretical expressions to estimate wind speed. We conclude that the -10 dB width is not a good estimator of wind speed. Wind speed estimates are better obtained from HF radar spectra by first estimating the directional wind-wave spectrum from the second-order echoes (0.01 Hz Doppler shift frequency resolution) and then computing wind speed from a wind-wave prediction model. View full abstract»

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  • A hybrid diffraction technique--General theory and applications

    Publication Year: 1982 , Page(s): 888 - 897
    Cited by:  Papers (14)
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    A new method is presented for calculating the current on a perfectly conducting body. The starting point of the method is in the assumption that the dominant current on the scattering body is an optics type current close to 2\hat{n} \times \bar{H}^{i} . Near shadow boundaries, the current is represented by the moment method such that the total current in the vicinity of a shadow boundary is the sum of the optics current and the moment method current. (In this sense the method may be equivalent to the physical theory of diffraction.) The magnetic field integral equation is then used in an iterative procedure to obtain the correct current in the asymptotic regions (away from shadow boundaries) and in the moment method region. Because the iterative process starts with a current close to the true current, convergence is rapid with two or three iterations being typical. The general theory is presented and then applied to the infinite wedge problem and to the problem of a two-dimensional square cylinder. Results are compared with other independent solutions, and excellent agreement is demonstrated. A comparison is made with conventional physical optics. Application of the hybrid diffraction method to curved surfaces is discussed. Advantages and disadvantages of the method are also discussed. View full abstract»

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  • Error analysis of image representations for sources near to a dissipative earth

    Publication Year: 1982 , Page(s): 1005 - 1008
    Cited by:  Papers (5)
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    Various image representations for sources above a dissipative earth are introduced. A criterion for assessing their accuracy is given. Some of these image representations comprise purely discrete images, a purely continuous image or a mixture of both types. It is shown that the error in any representation is a function of the height of the field point from the earth's surface. A mixture of a discrete image and a simple continuous image can lead to a negligibly small error for field calculations over a wide range of the height of the field point. This means that the image theory can offer simplicity and accuracy in many application such as geophysical prospecting of the earth. View full abstract»

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  • Dispersion relation for general anisotropic media

    Publication Year: 1982 , Page(s): 991 - 993
    Cited by:  Papers (9)
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    The dispersion relation is derived for an anisotropic medium with arbitrary tensor permittivity and permeability. Particular cases and applications to layered media are discussed. View full abstract»

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  • The thin-substrate approximation for reflection from the end of a slab-loaded parallel-plate waveguide with application to microstrip patch antennas

    Publication Year: 1982 , Page(s): 910 - 917
    Cited by:  Papers (29)
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    Integrals arising in the Wiener-Hopf solution for wide microstrip antennas are approximated in closed form for the case of an electrically thin substrate. The resulting expressions are used to obtain simple, closed-form expressions for resonant frequency and unloaded radiation Q for rectangular microstrip patch antennas which are valid when commonly used quasi-static formulas no longer hold. Numerical comparisons show significant shifts in resonant frequencies as compared with existing theories. 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