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Antennas and Propagation, IEEE Transactions on

Issue 2 • Date March 1977

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Displaying Results 1 - 23 of 23
  • [Front cover and table of contents]

    Publication Year: 1977 , Page(s): 0
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  • Editorial: Page charges and the waiting list

    Publication Year: 1977 , Page(s): 161
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  • Corrections to "On an inverse scattering method" and "On the feasibility of an inverse scattering Method"

    Publication Year: 1977 , Page(s): 286
    Cited by:  Papers (1)
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  • Comparison of uniform asymptotic theory and Ufimtsev's theory of electromagnetic edge diffraction

    Publication Year: 1977 , Page(s): 162 - 170
    Cited by:  Papers (20)
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    High-frequency asymptotic solutions of electromagnetic edge diffraction by two different theories are studied. One is the uniform asymptotic theory which is a refinement of Keller's geometrical theory of diffraction. The other is Ufimtsev's theory of the edge wave, representing an improvedment over the classical physical optics theory. These two theories are summarized, their features compared, and their relations discussed. When the observation point is away from shadow boundaries and caustics, both uniform asymptotic theory and Ufimtsev's theory, up to (and including) order k^{-1/2} , agree with Keller's theory. Near or on shadow boundaries, uniform asymptotic theory gives an explicit field solution, while Ufimtsev's result contains a physical optics integral. The evaluation of that integral is not a trivial task. In a two-dimensional test problem, it is shown that both theories do give, up to order k^{-1/2} , an identical field solution everywhere including the edge, shadow boundaries, and transition regions. View full abstract»

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  • Temporal radio frequency spectra of multifrequency waves in a turbulent atmosphere characterized by a complex refractive index

    Publication Year: 1977 , Page(s): 254 - 260
    Cited by:  Papers (9)
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    Ishimaru's formulation for the amplitude and phase spectra for radio waves propagating in a turbulent medium is extended to cover the case where the refractive index is complex and frequency dependent. New static limits for the amplitude and phase spectrum are derived. The temporal radio frequency spectra give an estimate of the short time variations (i.e., tenths to tens of seconds) that tend to occur when radio waves propagate in a turbulent medium. For example, the refractive index is complex in a dispersive medium with a Lorentzian line shape, such as the earth's atmosphere over the the range of 50 to 70 GHz, due to resonant frequencies of molecular oxygen. The results for the amplitude and phase spectrum corresponding to radio links on earth (altitudes less than 5 km) indicate that turbulence does not significantly alter the radio frequency spectrum even for radio frequencies separated by 3 GHz. By contrast, the impact of turbulence is to make the details of the spectrum due to an isolated oxygen line in the 60 GHz band time dependent and, therefore, not readily compensated for by an equalizer. An isolated line in the 60 GHz oxygen band does constitute the propagation medium for radio links at altitudes greater than 25 km. View full abstract»

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  • A technique for the rapid measurement of bistatic radar cross sections

    Publication Year: 1977 , Page(s): 243 - 248
    Cited by:  Papers (4)  |  Patents (2)
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    Numerous techniques for measuring monostatic (backscatter) radar cross sections (RCS) are well known, but bistatic RCS measurements are inherently more difficult. In this paper we describe a bistatic RCS measurement technique which circumvents the major obstacles. It uses a variation of the CW "null-balance" approach resulting in rapid measurement times. A network analyzer and process computer were incorporated into an existing image ground plane system to improve the bistatic capability and add flexibility. Several objects were measured and compared with their known bistatic RCS to demonstrate the validity and utility of the technique. View full abstract»

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  • Rain-scatter interference on aneEarth-space Path

    Publication Year: 1977 , Page(s): 287 - 288
    Cited by:  Papers (7)
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    The rain-scatter coupling between the multiple beams of an earth-station antenna viewing several synchronous satellites was calculated. The results are summarized in a simple formula. A previous terrestrial experiment on forward rain-scattering showed the validity of the single scattering assumption. View full abstract»

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  • Microwave relay fading statistics as a function of a terrain clearance factor

    Publication Year: 1977 , Page(s): 269 - 273
    Cited by:  Papers (1)
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    Three sources of microwave relay fade statistics are examined to show that their differences may be explained on the basis of ground clearance at midpath. An empirical expression is suggested that combines the three sets of data into one that is useful over a considerable range of ground clearance. This is then used to calculate a microwave link composed of N hops between ground and tethered balloons. It is shown that at the short and long extremes of range, the results match known performance. View full abstract»

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  • A new approach based on a combination of integral equation and asymptotic techniques for solving electromagnetic scattering problems

    Publication Year: 1977 , Page(s): 187 - 197
    Cited by:  Papers (34)
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    We introduce a new approach for combining the integral equation and high frequency asymptotic techniques, e.g., the geometrical theory of diffraction. The method takes advantage of the fact that the Fourier transform of the unknown surface current distribution is proportional to the scattered far-field. A number of asymptotic methods are currently available that provide good approximation to this farfield in a convenient analytic form which is useful for deriving an initial estimate of the Fourier transform of the current distribution. An iterative scheme is developed for systematically improving the initial form of the high frequency asymptotic solution by manipulating the integral equation in the Fourier transform domain. A salient feature of the method is that it provides a convenient validity check of the solution for the surface current distribution by verifying that the scattered field it radiates indeed satisfies the boundary conditions at the surface of the scatterer. Another important feature of the method is that it yields both the induced surface current density and the far-field. Diffraction by a strip (two-dimensional problem) and diffraction by a thin plate (three-dimensional problem) are presented as illustrative examples that demonstrate the usefulness of the approach for handling a variety of electromagnetic scattering problems in the resonance region and above. View full abstract»

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  • A comparison of quadrature and single-channel receiver processing in adaptive beamforming

    Publication Year: 1977 , Page(s): 209 - 218
    Cited by:  Papers (3)
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    A performance comparison between two different types of receivers in an HF adaptive array application is presented. The data used for the study were recorded using a bistatic HF radar located in the central valley of California. Eastword-looking transmissions were generated using a continuous sweep-frequency (chirp) format with a sweep repetition rate of 60 Hz. Backscatter signals, produced by a one-hop forward ionospheric path followed by a one-hop ionospheric return path were received using eight adjacent 32-element linear subarrays spanning a total linear aperture of 2.5 km. Single-channel receivers at each of the eight subarrays were employed for deramping and conversion to baseband. The overall system bandwidth was 960 Hz, and a common local oscillator was used for the receivers. All adaptive processing was carried out off-line using digitized data recorded simultaneously at the eight receiver outputs. The objective of the study described in this paper was to compare the results obtained using the receiving system described above with those which would be obtained using quadrature receivers at the subarray outputs. In the latter case, dual common local oscillator injection, with a 90\deg phase difference, is employed to obtain two receiver outputs, (in-phase and quadrature components) for each receiver. The component outputs then each have a bandwidth equal to one-half that of the single-channel receiver or 480 Hz for both the in-phase and quadrature signals. One advantage of quadrature reception is that a single real multiplying weight can be used at the two outputs to obtain a frequency-independent gain and phase-shift across the received bandwidth, a property which is not easily obtained for all azimuths in the single-channel receiver structure. The study described in this paper was undertaken to quantitatively determine the importance of this difference in an adaptive beamforming system. The approach taken was to synthesize quadrature receiver signals from the recorded single-channel data using Hilbert transform methods. Comparisons between the two receiving systems were then carried out using identical data sets. The results obtained illustrate that minor differences (less than 5 dB) exist in the processed outputs provided that the same num- ber of adaptive degrees of freedom are used in the two processors. As a result, decisions as to the specific form of a receiver to be used in an HF radar should be based on considerations relating to ease of implementation rather than the overall performance of the adaptive processor. View full abstract»

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  • High-frequency diffraction of a line-source field by a half-plane: Solutions by ray techniques

    Publication Year: 1977 , Page(s): 171 - 179
    Cited by:  Papers (11)
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    The diffraction of an arbitrary cylindrical wave due to a line source and incident on a half-plane is treated by the uniform asymptotic theory of edge diffraction. For large wavenumber k , an asymptotic solution for the total field up to and including terms of order k^{-3/2} relative to the incident field is derived. This solution is uniformly valid for all observation points, including points near the edge and the shadow boundaries. In particualr, two special cases are considered: A) the line source is located on the half-plane, and radiates an E -polarized wave and B) the line source is located in the aperture complementary to the half-plane and radiates an H -polarized wave. A companion paper will show that our asymptotic solution for Case A) is in complete agreement with the asymptotic expansion of the exact solution. For the same diffraction problem, asymptotic solutions obtained by the method of slope diffraction coefficients and the method of equivalent currents are also discussed. It is found that the latter solutions agree with the exact one only when i) the observation point is away from the edge and the shadow boundaries, and/or ii) the terms of order k^{-3/2} in the field solution are ignored. View full abstract»

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  • Radio frequency transmission via a trolley wire in a tunnel with a rail return

    Publication Year: 1977 , Page(s): 248 - 253
    Cited by:  Papers (7)
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    An analysis is given for the transmission of electromagnetic waves along a circular tunnel in the presence of axial conductors. One of these conductors is an idealization of a trolley wire with its bonded feeder line that may be located anywhere in the tunnel. The other is a metal rail that is located within the homogeneous rock medium at a finite distance from the tunnel wall. A mode equation for the propagation modes is obtained that is used to obtain numerical results for the attenuation rate in the frequency range 50 to 800 kHz. It is shown that the attenuation rate is only weakly dependent on the burial depth of the rail conductor, at least in the range up to 50 cm. Also, it is found that the rail conductor for the model adopted carries an appreciable fraction of the total return current when typical rock conductivities are assumed. A thin layer of insulation on the rail appears to have a negligible effect. In fact, there is little change even if the rail is within the tunnel and just above the tunnel floor. View full abstract»

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  • A radiometric antenna gain calibration method

    Publication Year: 1977 , Page(s): 218 - 223
    Cited by:  Papers (2)
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    A radiometric method is presented for measuring the power gain of a microwave antenna. It is particularly applicable to horns with gains in the range 20-45 dB, and an absolute uncertainty ( 3\sigma ) of less than 0.1 dB is achievable in favorable cases. An absorbing screen with a circular aperture is placed in the far-field of the test antenna. The diameter of the aperture is chosen to subtend an angle much smaller than the main lobe of the radiation pattern of the test antenna. Then two sheets of microwave absorber (one at ambient temperature and the other cooled to the boiling point of liquid nitrogen) are alternately placed first behind the screen aperture and then, for normalization, across the aperture of the test horn. The ratio of the antenna temperature differences measured with a sensitive microwave radiometer is proportional to the effective antenna solid angle, and thus its directivity. Corrections must be applied for near-field effects, diffraction at the screen aperture, partial resolution of the screen aperture by the main lobe of the test antenna pattern, and ohmic losses. A comparison of black disk measurements using a large conical horn at 86 GHz with theoretical calculations confirms the accuracy of this gain calibration technique. View full abstract»

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  • Intensity scintillations of an EM wave in extremely strong turbulences

    Publication Year: 1977 , Page(s): 266 - 268
    Cited by:  Papers (2)
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    If one assumes Gaussian field statistics in extremely strong turbulence, the scintillation index of an arbitrary source approaches unity. This result is independent of whether the source is coherent or incoherent, provided that the response time of the measuring apparatus is short compared with the coherence time of the source. View full abstract»

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  • An antenna for limited scan in one plane: Design criteria and numerical simulation

    Publication Year: 1977 , Page(s): 232 - 243
    Cited by:  Papers (18)  |  Patents (1)
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    An analytical and numerical study has been performed on a novel design scheme for an antenna system for limited one-dimensional scan. The system has a number of control elements approximately equal to the minimum theoretically compatible with the aperture size and field of view (FOV). The radiating structure consists of a "bootlace" lens with linear outer and circular inner profiles. This geometry plays a basic role in determining excellent scan performance over a moderate frequency band. A linear array whose size depends critically upon the scan requirements and the lens focal length is located on the focal plane and is focussed onto the inner lens profile. The array is fed by a hybrid network (HN) performing a spatial Fourier transformation. The input ports of the HN are fed by the output ports of a beam forming network (BFN) through a set of variable phase shifters. The BFN has separate input ports for the sum and difference patterns, controlled independently, The system works as follows. The antenna illumination is synthesized as the weighted superposition of components illuminations or "overlapping subarrays" each of which is due to the excitation of one of the ports of the HN. The amplitudes of the subarray excitations are fixed and determined by the power divisions provided by the BFN. Their phases are controlled by the set of variable phase shifters. A desirable feature of the scheme is that for a fixed phase shifter setting neither the beam scan nor its width changes for a moderate frequency variation. Through a suitable design of the BFN, ultralow sidelobes outside the FOV can be achieved at the expense of a slight reduction of the illumination efficiency, which is, however, always high, since the aperture is fully used. Extensive numerical computations for an antenna having a half-power beamwidth of 1.2\deg show that the sum beam can be scanned in a sector greater than \pm3 beams, on a band of 20 percent with excellent performance form the viewpoint of gain and sidelobes-the scan sector being slightly less for the difference beam. View full abstract»

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  • Multiple scattering effect on backscattering from a random medium

    Publication Year: 1977 , Page(s): 205 - 208
    Cited by:  Papers (5)
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    The backscattering from a random medium is analytically studied. The result gives a mathematical foundation to the cumulative forward-scatter single-backscatter (CFSB) approximation proposed by de Wolf. The multiple scattering effects on backscattering of a plane wave incidence are examined for both Fresnel and Fraunhofer scatterings with various correlation functions of turbulence. As a result, it is found that the multiple scattering effect on the backscattering is sensitive to the statistical properties of the fluctuating medium. View full abstract»

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  • Electromagnetic coupling through small apertures in a conducting screen

    Publication Year: 1977 , Page(s): 180 - 187
    Cited by:  Papers (16)
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    The electromagnetic field coupling through small apertures illuminated by an arbitrary incident plane wave is discussed for general aperture shapes. A set of new integral equations in a form highly amenable to numerical solution techniques is derived. Based on the application of the Rayleigh series method, an analytical solution is obtained for the first few terms of the expansion of the aperture E - field of a circular aperture. Numerical results are also constructed for the aperture field and the diffracted field of small rectangular apertures and compared with those of the circular apertures. View full abstract»

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  • A spectral domain method for remotely probing stratified media

    Publication Year: 1977 , Page(s): 261 - 265
    Cited by:  Papers (5)
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    The problem of remotely probing a stratified, lossless, dielectric medium is formulated using the spectral domain method of probing. The response of the medium to a spectrum of plane waves incident at various angles is used to invert the unknown profile. For TE polarization, the electric field satisfies a Helmholtz equation. The inverse problem is solved by means of a new representation for the wave function. The principal step in this inversion is solving a second kind Fredholm equation which is very amenable to numerical computations. Several examples are presented including some which indicate that the method can be used with experimentally obtained data. When the fields exhibit a surface wave behavior, a unique inversion can be obtained only if information about the magnetic field is also available. In this case, the inversion is accomplished by a two-step procedure which employs a formula of Jost and Kohn. Some examples are presented, and an approach which greatly shortens the computations without greatly deteriorating the results is discussed. View full abstract»

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  • Polarizability of some small apertures

    Publication Year: 1977 , Page(s): 198 - 205
    Cited by:  Papers (28)
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    The basic integral equations for the electrostatic and magnestostatic problems are reviewed. These equations are solved with a digital computer for four typical aperture shapes. The results of the calculations are compared with Cohn's experimental values. Some data are given concerning the corresponding acoustic problems. View full abstract»

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  • Estimating ionospheric reflection height from Doppler measurements

    Publication Year: 1977 , Page(s): 273 - 276
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    A method is described which allows estimating an ionospheric reflection height from Doppler measurements made over an oblique CW radio transmission. This method requires the presence of multihop signals. The assumptions pertaining to the method's validity are delineated and an example is illustrated. View full abstract»

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  • Capacitance bounds and equivalent radius

    Publication Year: 1977 , Page(s): 284 - 286
    Cited by:  Papers (3)
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    The isolated capacitance of conducting ellipsoids is calculated, and the resulting values are presented in the form of equivalent radii. These data are used to establish bounds for the capacitance of other conducting objects, namely, the right circular cylinder and the rectangular parallelopiped. View full abstract»

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  • On the cross polarization of asymmetric reflector antennas for satellite applications

    Publication Year: 1977 , Page(s): 276 - 283
    Cited by:  Papers (11)
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    It is well known that focussed, axial symmetrical reflector antennas collimate the co- and cross-polar components of the primary field separately, i.e., the reflector does not create a contribution to the cross polarization of the far-field. By a simple extension of a classical physical argument it is demonstrated that this separability does not depend on the symmetry of the antenna, and that it, therefore, holds even for off-set fed reflectors. A new mathematical formulation of the collimation is derived in which this is shown. Yet the separability does depend on how the co- and cross-polar fields are defined, and the cross polarization of feeds for asymmetric reflectors is discussed in detail in the light of this. It is further suggested how to design low cross polarization feeds for off-set fed antennas. As a consequence of the separate collimation such feeds will lead to low cross-polarization of the secondary fields. Two simple examples are treated. The only limitations of the results are those due to the application of the aperture field version of the physical optics approximation. View full abstract»

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  • Development of a superconducting ELF receiving antenna

    Publication Year: 1977 , Page(s): 223 - 231
    Cited by:  Papers (3)  |  Patents (6)
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    The development of an extremely low frequency (ELF) submarine receiving antenna that uses a triaxial array of superconducting quantum interference devices (SQUIDs) has addressed the following six problem areas: 1) achievement of a SQUID sensor with a sensitivity of 10^{-14} T-Hz-1/2; 2) acheivement of a SQUID linear dynamic range of 140 dB; 3) achievement of sensor orthogonality of 10^{-4} rad;4) stabilization of receiver platform motion to 10^{3} rad; 5) processing of SQUID outputs in order to remove residual motion noise;6) provision of a suitable cryogenic environment. The required sensitivity, approximate linear dynamic range, and sensor orthogonality were successfully obtained in a prototype point-contract type triaxial SQUID magnetometer. This magnetometer was used to detect the ELF signal broadcast from the U.S. Navy transmitter in Wisconsin, both in the atmosphere above the water surface and at a depth of 100 m below the ocean surface in a stationary configuration. No measurements have been made as yet with the magnetometer in a towed buoy. Achievement of the platform motion requirement was demonstrated by motion spectrum measurements on a hydrodynamically stabilized buoy designed to be towed by a submarine. Motion excursions within the ELF pass band of 30- 130 Hz were found to be about 10^{-4} rad. This amount of motion requires that motion-generated noise be further reduced by more than 80 dB. The required noise rejection can be achieved by adaptive determination of a vector that is approximately equal to the earth's magnetic field vector. When the adaptive vector is evaluated and combined vectorially with the SQUID outputs, a quantity proportional to the ELF signal vector results in which motion noise is suppressed. This adaptive processing has been studied using a computer simulation of the SQUIDs' motion noise derived from towed-buoy motion data. The feasibility of cooling the SQUID sensors with liquid helium was demonstrated by a prototype long-hold-time dewar of a size capable of fitting a towed communications buoy. The dewar successfully maintained the temperature of a volume sufficiently large to hold a triaxial SQUID sensor package at the temperature of - boiling liquid helium for a duration of 102 days. 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