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Antennas and Propagation, IEEE Transactions on

Issue 3 • Date May 1971

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

    Publication Year: 1971 , Page(s): 0
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    Freely Available from IEEE
  • [Back cover]

    Publication Year: 1971 , Page(s): c4
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    Freely Available from IEEE
  • Image theory for bianisotropic media

    Publication Year: 1971 , Page(s): 451 - 452
    Cited by:  Papers (4)
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    Image theory in bianisotropic media in the presence of a perfectly conducting plane is derived. The conventional image theory is shown to apply for crystals with two principal axes parallel to the conducting plane, for gyrotropic media with magnetostatic fields perpendicular to the plane, and for all such media uniformly moving parallel to the plane. View full abstract»

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  • Optimum pulse transmission through an exponential plasma inhomogeneity

    Publication Year: 1971 , Page(s): 453 - 455
    Cited by:  Papers (2)
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    The optimum transmission of electromagnetic waves through a thin exponentially inhomogeneous plasma region is treated in this communication. Matched filter theory is used in obtaining integral expressions for optimum transmitted signals, which result in received signals that have the largest possible amplitude when transmitted through the plasma region. The fast Fourier transform algorithm is used in obtaining signal waveforms for a number of examples. View full abstract»

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  • Correlating antenna array

    Publication Year: 1971 , Page(s): 447 - 450
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    A set of arbitrarily located receiving antenna elements, each connected with an appropriate network, can be used to construct a matched filter where the antenna array response results in an autocorrelation of a specified desired signal, correlating over time and space coordinates simultaneously. A receiving system using such a signal processing antenna can discard interferences which do not have the same spectral characteristics as the desired signal, or which do not originate from the same point as the desired signal source. Examples of correlating antenna arrays for various arbitrary intelligence modulations of the desired signal are discussed in this communication. View full abstract»

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  • Aperture matching for an infinite circular polarized array of rectangular waveguides

    Publication Year: 1971 , Page(s): 332 - 342
    Cited by:  Papers (3)
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    This paper studies the polarization of the main beam radiated from an infinite array of rectangular waveguides, and in particular, illustrates the matching procedure for the design of a circularly polarized array. It is demonstrated that the use of resonant irises at the waveguide openings together with a conventional matching junction inside the waveguides can improve both the power and the axial ratio of the main beam in a circularly polarized array. In general, a good matching design is the one which gives a proper compromise between the power and the polarization, and is not necessarily the one minimizing the reflection. View full abstract»

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  • A generalized expansion for radiated and scattered fields

    Publication Year: 1971 , Page(s): 348 - 358
    Cited by:  Papers (85)
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    At a given frequency every perfectly conducting obstacle has associated with it a particular set of surface currents and corresponding radiated fields which are characteristic of the obstacle shape and independent of any specific excitation. These characteristic modes form a useful basis set in which to expand fields radiated or scattered at a great distance from the obstacle. Once these modes are known for a given obstacle, the scattering of plane waves incident from arbitrary source directions into arbitrary receiver directions may be evaluated concisely. To support the theory, a method is described for determining characteristic mode currents on thin wires of general shape and is applied to several shapes to generate certain backscattering and input admittance data. Wherever possible comparison is made with existing data. View full abstract»

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  • Analysis of multiple-arm conical log-spiral antennas

    Publication Year: 1971 , Page(s): 320 - 331
    Cited by:  Papers (4)  |  Patents (1)
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    An N -arm log-spiral antenna may be excited in N - 1 orthogonal modes of N -tuple input. A rigorous solution to the spiral antenna of more than two arms is obtained by numerical solution of the integral equations. Results for a four-arm spiral, including current distribution, half-power beamwidth, beam orientation, and gain and phase centers, are presented. The propagation constant of the current waves along each spiral arm is found to be approximately the speed of light. An approximate k-\beta diagram is given which may be used to estimate the size of the antenna for each mode of operation. View full abstract»

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  • A comparison of the full-wave and WKB solutions of a plane wave with impulsive time variation reflected from a sech2electron-density profile

    Publication Year: 1971 , Page(s): 456 - 458
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    This communication compares a more general numerical point-to-point transient wave propagation program to a known analytical (full-wave) solution based upon a certain special geometry and ionospheric profile. The main purpose of the comparison is that of using the known analytical results as a test case for the numerical program. The parameters of the ionosphere were chosen to purposively tax the condition of requiring a slowly varying medium in using the Wentzel-Kramer-Brillouin (WKB) method (i.e., the parameters chosen lead to a sporadic E -type layer). With the results favorable for this case, the application of a numerical procedure, based upon the WEB method, to the more slowly varying F region would definitely be acceptable. Based upon the full-wave and WKB solutions, results are given in the form of time-domain waveforms due to reflection of a transient wave from the ionosphere. View full abstract»

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  • Phase properties of backscattered fields from thin rods

    Publication Year: 1971 , Page(s): 450 - 451
    Cited by:  Papers (1)
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    Numerical and analytical calculations show the phase of backscatter fields from thin perfectly conducting rods at constant distance from the scatterer to become essentially independent of aspect angle for rod lengths less than \lambda /2 , to approach a limit near 180\deg for shorter rods, and in broadside directions to depend only on rod thickness when rod lengths are an integral multiple of \lambda . View full abstract»

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  • Multiple scattering of EM waves by spheres part II--Numerical and experimental results

    Publication Year: 1971 , Page(s): 391 - 400
    Cited by:  Papers (11)
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    In [8], both low- and high-frequency solutions to the two-sphere problem were presented in a form suitable for efficient computer solution, Here, numerical results are presented using a method which has enabled the first appearance of reliable results for the scattered field from two spheres of radii larger than one wavelength and as large as ten or more. Radar cross sections (RCS) are computed for numerous configurations of two spheres of various materials. Results for scattering by three collinear spheres are also given. An experimental program was undertaken and is briefly described. Whenever possible, these results are compared with the theory. In all cases the agreement is excellent. Depolarization due to multiple scattering is also investigated, revealing some interesting effects and practical applications to scattering range calibration. View full abstract»

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  • Computer-aided analysis of a finite arbitrarily shaped dielectric antenna

    Publication Year: 1971 , Page(s): 444 - 445
    Cited by:  Papers (2)
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    A numerical method of analysis is developed to determine the characteristics of a homogeneous dielectric antenna of arbitrary shape based on a general expression of electromagnetic wave scattering by a homogeneous dielectric body derived by Barrar and Dolph. This method is tested on a dielectric-disk antenna. View full abstract»

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  • Synthesis of the fields of a transverse feed for a spherical reflector

    Publication Year: 1971 , Page(s): 310 - 320
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1056 KB)  

    The problem of designing a transverse feed for a spherical reflector is considered and a method is presented for synthesizing the fields on a surface of a sphere enclosing a feed that will produce a specified reflected field at the surface of a spherical reflector. The method identifies the reflector and a spherical surface enclosing the feed as a boundary value problem and uses a finite set of spherical waves to approximate the boundary conditions. A feed designed to excite this field will in turn produce the desired reflected field at the surface of the reflector, under the condition that that portion of the reflected field which is scattered by the feed may be neglected. It is shown that the feed need produce only a small part of the synthesized field to obtain an antenna efficiency of more than 70 percent. Some typical field distributions will be shown so as to indicate a method for designing a feed and to point out the correlation between the polarization of the synthesized field and the polarization of the reflected field at the surface of the reflector. View full abstract»

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  • Radiation from a slot antenna in a ground plane coated with a moving plasma sheath

    Publication Year: 1971 , Page(s): 401 - 405
    Cited by:  Papers (1)
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    The electromagnetic radiation from a slot antenna in a conducting plane coated with a moving isotropic cold plasma layer is considered. It is assumed that the direction of motion of the layer is across the slot, which is taken to be infinitely long. An integral representation for the field radiated through the plasma layer is obtained and evaluated asymptotically in the far zone by the method of steepest descents. The migration of the poles in the integrand of this integral representation as the speed of the slab is varied is discussed and related to several calculated radiation patterns. It is found that the motion of the plasma layer has the greatest effect on the radiation pattern when the wave frequency and plasma frequency are nearly equal. View full abstract»

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  • Radiation resistance of antennas in lossy media

    Publication Year: 1971 , Page(s): 443 - 444
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    Using the concept of modified power density, expressions are derived for the radiation resistance and efficiency of antennas in a dissipative medium. View full abstract»

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  • Multiple scattering of EM waves by spheres part I--Multipole expansion and ray-optical solutions

    Publication Year: 1971 , Page(s): 378 - 390
    Cited by:  Papers (55)
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    Solution to the multiple scattering of electromagnetic (EM) waves by two arbitrary spheres has been pursued first by the multipole expansion method. Previous attempts at numerical solution have been thwarted by the complexity of the translational addition theorem. A new recursion relation is derived which reduces the computation effort by several orders of magnitude so that a quantitative analysis for spheres as large as 10\lambda in radius at a spacing as small as two spheres in contact becomes feasible. Simplification and approximation for various cases are also given. With the availability of exact solution, the usefulness of various approximate solutions can be determined quantitatively. For high frequencies, the ray-optical solution is given for two conducting spheres. In addition to the geometric and creeping wave rays pertaining to each sphere alone, there are rays that undergo multiple reflections, multiple creeps, and combinations of both, called the hybrid rays. Numerical results show that the ray-optical solution can be accurate for spheres as small as \lambda /4 in radius is some cases. Despite some shortcomings, this approach provides much physical insight into the multiple scattering phenomena. View full abstract»

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  • High-frequency backscatter from terrain with cement-block walls

    Publication Year: 1971 , Page(s): 343 - 347
    Cited by:  Papers (1)
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    The measurements of high-frequency (HF) radar cross sections (RCSs) \sigma of trees on a large flat field were reported a few years ago by Steele. This work used a special adaptation of the standing-wave method to 26 MHz. Shortly afterward, the present author used the same apparatus to measure the (RCSs) of cement walls erected on the same terrain. Wall sizes ranged from 5 ft high by 10 ft wide to 20 by 20 ft. Angles of elevation \psi ranged from 2.5 to 22.5\deg . Using vertical polarization ( E field in the plane of incidence), cross sections increased with wall size. When a wall was thoroughly dampened, \sigma increased by 3 to 13 dB, depending on \psi , and wall size over \sigma was obtained when the wall was dry or partly damp. Chicken wire covering increased the 10- by 10-ft wall's cross section by 10 dB. Using horizontal polarization, cross sections were immeasurable for the smaller walls. For the 20- by 20-ft wall, \sigma was a smoothly increasing function with \psi . When this wall was wet, its cross section increased by 4 dB. The wall-ground combination was treated as a corner reflector, using a theory based on physical optics. The theory compares fairly well to experimental cross sections for the 20- by 20-ft wall. Extrapolation of the theory suggests that a 150-ft high by 100-ft wide building could have a cross section approaching 10^{4} m2at 26 MHz. View full abstract»

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  • Imperfectly conducting cylindrical antenna: Variational approach

    Publication Year: 1971 , Page(s): 435 - 436
    Cited by:  Papers (5)
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    Driving point admittances of resistive cylindrical dipoles are computed by a variational method, using the two-term trial function for current proposed by King and Wu. The theoretical admittances are in excellent agreement with experimental results. View full abstract»

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  • A technique for solution of Maxwell's equations in a moving dielectric medium

    Publication Year: 1971 , Page(s): 455 - 456
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    A simple technique is presented for converting a known solution for the electric and magnetic vector fields in a dielectric medium at rest into the corresponding fields in a moving dielectric medium. The technique combines methods presented by Tai [1] with a scaling procedure developed by Clemmow [2]. Tai's work reduces the moving medium problem to the solution of Maxwell's equations in a uniaxial medium, and Clemmow's procedure enables one to convert a known solution in an isotropic medium to the corresponding solution in a uniaxial medium. Thus by first solving for the fields in the medium at rest, then following Clemmow's procedure to obtain the fields in Tai's uniaxial medium, and finally applying Tai's reasoning, one may easily obtain the solution of Maxwell's equations in the moving medium. View full abstract»

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  • The cylindrical antenna as a probe for studying the electrical properties of media

    Publication Year: 1971 , Page(s): 406 - 416
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (864 KB)  

    When a base-driven cylindrical monopole (or center-driven dipole) is immersed in an arbitrary medium, the electric and magnetic fields on its surface depend not only on its length and radius but also on the effective conductivity and permittivity of the medium. These fields can be explored and measured with small probes designed to travel along the cylindrical surface of the antenna. The interpretation of the observations depends on the availability of a general theory that correctly describes the distributions of current and charge on the conductor. The results of a new theory that is valid for electrically thin monopoles up to 5\lambda /8 (dipoles up to 5\lambda /4) in length over all practical ranges of conductivity and permittivity of the ambient medium, including those characteristics of under- and overdense cold plasmas, are described together with their experimental verification. View full abstract»

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  • Transmission of electromagnetic waves into time-varying media

    Publication Year: 1971 , Page(s): 417 - 424
    Cited by:  Papers (18)
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    Expressions are obtained for the electromagnetic fields transmitted into the time-varying medium when a plane wave is incident upon either a dielectric or dispersive half-space. Solutions are obtained for the case when the medium is changed in a stepwise fashion, and also for the case when the medium varies slowly and continuously. View full abstract»

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  • Diffraction by arbitrary cross-sectional semi-infinite conductor

    Publication Year: 1971 , Page(s): 358 - 364
    Cited by:  Papers (17)
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    This paper investigates the problem of diffraction of an electromagnetic wave by a semi-infinite conductor by means of the computer method based on an integral equation formulation. The cross section of the conductor can have an arbitrary shape, provided the face shined by the incident wave is a uniform plane in the region far from the edge. In that plane region, the problem is simply that of reflection from a conductor wall for which a solution is known. This known part of the solution is analytically excluded to derive an integral equation describing the edge effect over a limited region. The limited region is unknown at first and must be determined from the results of some numerical computations. As a numerical example, a thick half-plane conductor is treated in which the electric field polarization is parallel to the conductor, i.e., the case of an incident E wave. View full abstract»

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  • Excitation of surface wave on circular-loop array

    Publication Year: 1971 , Page(s): 433 - 435
    Cited by:  Papers (2)
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    A method is presented of analyzing surface-wave excitation to an infinite periodic linear array in which only one element is excited and all others are parasitic. The approach taken in the analysis is based on the properties of the periodic structure. A formal solution for the current distribution on the array element is obtained, and the propagation constant of the surface wave is also found. In the case where the array consists of loop antennas, the surface wave can propagate only when the separation of the array element is less than one-half wavelength and the circumference of the loop is less than one wavelength. Calculated values of the propagation constant of an array are in good agreement with the measured results. View full abstract»

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  • On a method for array design by matrix inversion

    Publication Year: 1971 , Page(s): 446 - 447
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    Matrix methods described earlier for array design for a specified pattern are limited in that the number of values that can be specified in the far-zone field must equal the number of independent applied excitation voltages. In this communication an extension is described to handle cases where the number of specified values exceeds the number of independent applied excitations. View full abstract»

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  • An agar-agar chamber for study of electromagnetic waves in an inhomogeneous medium

    Publication Year: 1971 , Page(s): 365 - 377
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1216 KB)  

    A medium for the propagation of electromagnetic waves whose dielectric constant or loss tangent has a prescribed profile was fabricated by using a large quantity of agar-agar in simulation chambers. The dielectric constant of the agar-agar could be changed continuously by means of a controlled diffusion of ethyl alcohol. The loss tangent of the same medium could be changed continuously by means of a controlled diffusion of NaCl. This paper is concerned with the design and characteristics of the simulation chamber. Topics to be considered include the properties of agar-agar in a wide frequency spectrum, the diffusion profiles, a reexamination of the principle of simulation, and the construction of various types of probes and simulation chambers. View full abstract»

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Aims & Scope

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

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Meet Our Editors

Editor-in-Chief                                                 Kwok W. Leung