Showing papers in "IEEE Transactions on Antennas and Propagation in 1983"

The resonant cylindrical dielectric cavity antenna

Abstract: An experimental investigation of the radiation and circuit properties of a resonant cylindrical dielectric cavity antenna has been undertaken. The radiation patterns and input impedance have been measured for structures of various geometrical aspect ratios, dielectric constants, and sizes of coaxial feed probes. A simple theory utilizing the magnetic wall boundary condition is shown to correlate well with measured results for radiation patterns and resonant frequencies.

Effect of mutual coupling on the performance of adaptive arrays

Abstract: The effect of mutual coupling between array elements on the performance of adaptive arrays is examined. The study includes both steady state and transient performance. An expression for the steady state output signal-to-interference-plus-noise ratio (SINR) of adaptive arrays, taking into account the mutual coupling between the array elements, is derived. The expression is used to assess the steady state performance of adaptive arrays. The transient response is studied by computing the eigenvalues associated with the signal covariance matrix. The steering vector required to maximize the output SINR of Applebaum-type adaptive arrays in the presence of mutual coupling is also given.

Analysis and optimized design of single feed circularly polarized microstrip antennas

Abstract: Analysis and optimized designs are presented of three types of single feed circularly polarized microstrip antennas, namely, a diagonal fed nearly square, a truncated-corners square and a square with a diagonal slot. The Green's function approach and the desegmentation methods are used. The resonant frequencies are calculated for two orthogonal modes which together yield circular polarization. Optimum feed locations are determined for the best impedance match to a 50 \Omega coaxial feed line. Axial-ratio bandwidths, voltage standing-wave ratio (VSWR) bandwidths and radiation patterns are evaluated and verified experimentally.

Considerations for millimeter wave printed antennas

Abstract: Calculated data are presented on the performance of printed antenna elements on substrates which may be electrically thick, as would be the case for printed antennas at millimeter wave frequencies. Printed dipoles and microstrip patch antennas on polytetrafluoroethylene (PTFE), quartz, and gallium arsenide substrates are considered. Data are given for resonant length, resonant resistance, bandwidth, loss due to surface waves, loss due to dielectric heating, and mutual coupling. Also presented is an optimization procedure for maximizing or minimizing power launched into surface waves from a multielement printed antenna array. The data are calculated by a moment method solution.

High frequency scattering by a thin lossless dielectric slab

Abstract: A high frequency solution for scattering from a thin dielectric slab is developed, based on a modification of the uniform geometrical theory of diffraction solution for a haft-plane, with the intention of developing a model for a windshield of a small private aircraft. Results of the theory are compared with experimental measurements and moment method calculations showing good agreement. Application of the solution is also addressed.

The finite ground plane effect on the microstrip antenna radiation patterns

Abstract: The uniform geometrical theory of diffraction (GTD) is employed for calculating the edge diffracted fields from the finite ground plane of a microstrip antenna. The source field from the radiating patch is calculated by two different methods: the slot theory and the modal expansion theory. Many numerical and measured results are presented to demonstrate the accuracy of the calculations and the finite ground plane edge effect.

Direction finding with an array of antennas having diverse polarizations

Abstract: The advantages of using diversely polarized antennas to determine bearings of multiple cochannel narrow-band signals are shown Three bearing estimation algorithms-maximum likelihood (ML), adapted angular response (AAR), and Music (multiple signal classification)-are extended to handle antenna arrays with diverse polarizations; the maximum entropy method does not readily extend The proposed algorithms are applicable to arbitrary antenna locations and directional characteristics and arbitrary noise correlations between the antenna outputs The algorithms are compared on the basis of multiple signal resolution and bearing accuracy in the presence of noise The Music algorithm exhibits superior performance at moderate to low signal-to-noise ratio (SNR)

Electric field probes--A review

Abstract: Electric field probes consisting of a dipole antenna, RF detector, nonperturbing transmission line, and readout device have been implemented in a variety of ways. Three orthogonal dipoles are generally used in an E -field probe to provide a response which is nearly isotropic for all polarizations of the incident field. Diode detectors have been used with electrically short or resistivity loaded dipoles to produce very broadband devices (0.2 MHz to 26 GHz). Thermocouple detectors are used to provide true time-averaged data for high peak-power modulated fields. Optical fibers, together with a suitably modulated light source, may be used to form a wide-band nonperturbing data link from the dipole and detector to a remote readout. Application of E -field probes range from the measurement of fields in living animals exposed to nonionizing radiation to the measurement of fields in air for electromagnetic compatability or radiation safety purposes. Probes are available that can measure field strengths from less than 1 V/m to over 1000 V/m (rms).

Simple method for pattern nulling by phase perturbation

Abstract: A method of sidelobe hulling, which involves perturbing the array illumination phase only, is presented. The general nonlinear problem is linearized by assuming the perturbations to be small, and an analytic solution is derived. Illustrative examples of sinc and Chebyshev patterns with imposed nulls are given.

The synthesis of surface reactance using an artificial dielectric

Abstract: A thin artificial dielectric layer consisting of a rectangular array of closely spaced, thin conductive cylinders (pins), was constructed above a perfectly conducting ground plane. The reactance of the surface was measured at 4.8 GHz for a variety of pin heights and dielectric embedding material by measuring the height-gain profile of a transverse magnetic (TM) surface wave launched across it. Design equations using the theories of artifical dielectrics and propagation in anisotropic media are given. These can be used to predict the surface reactance providing a correction factor accounting for fringing fields at the tops of the pins is included. Using an embedding dielectric tends to reduce this fringing effect.

Nonstationary probabilistic target and clutter scattering models

Abstract: A probabilistic model for nonstationary and/or nonhomogeneous clutter and target scattering is proposed and developed. The first-order probability density of the scattered power is treated as the expected value of a conditional density that is a function of random parameters. The family of gamma densities is a general solution for the density function of the intensity reflected by objects comprised of several scatterers and is selected as the conditional density. In the general case, the gamma density is a function of two parameters: the mean and the inverse of the normalized variance. Assuming various distributions for a random mean, expressions for the first-order density of the scattered power are derived and used to explain previous experimental and theoretical results. An example of detection performance for nonstationary target fluctuation based on the developed model is also presented.

An efficient computational method for characterizing the effects of random surface errors on the average power pattern of reflectors

Abstract: Based on the works of Ruze and Vu, a novel mathematical model has been developed to determine efficiently the average power pattern degradations caused by random surface errors. In this model, both nonuniform root mean square (rms) surface errors and nonuniform illumination functions are employed. In addition, the model incorporates the dependence on F/D in the construction of the solution. The mathematical foundation of the model rests on the assumption that in each prescribed annular region of the antenna, the geometrical rms surface value is known. It is shown that closed-form expressions can then be derived, which result in a very efficient computational method for the average power pattern. Detailed parametric studies are performed with these expressions to determine the effects of different random errors and illumination tapers on parameters such as gain loss and sidelobe levels. The results clearly demonstrate that as sidelobe levels decrease, their dependence on the surface rms/ \lambda becomes much stronger and, for a specified tolerance level, a considerably smaller rms/ \lambda is required to maintain the low sidelobes within the required bounds.

Cylindrical-rectangular microstrip antenna

Abstract: Resonant frequencies f_{r} of a cylindrical-rectangular microstrip antenna are theoretically calculated. Comparison is made to f_{r} for a planar rectangular patch antenna, including the simplest planar patch modes having no field variation normal to the patch surface. The validity of using planar antenna patches to characterize microstrip antennas is examined.

First-order equivalent current and corner diffraction scattering from flat plate structures

Abstract: The equivalent current concept is used to compute the scattering patterns of flat plate structures. It is also used to obtain the broadside scattering lobe for any incidence plane. The essential feature introduced in this paper is that only the components of the equivalent current perpendicular to the incidence plane are used. No special treatment of the singularity in the plane wave diffraction coefficient (which is the basis of the equivalent current concept) is required. Instead, this choice of equivalent current components is such that the singularity at one edge segment is canceled by the singularity at the opposite edge segment. For modern day computers there is sufficient accuracy that the main scattering lobe can be obtained in the limit as one approaches broadside. The same results can be obtained for plate structures made of straight edges by using a new corner diffraction analysis. For certain cases where the observation angle is sufficiently removed from normal incidence to an edge, the corner diffraction analysis appears to yield more accurate results.

Fourier transform of a polygonal shape function and its application in electromagnetics

Abstract: The shape function s(x, y) of a planar aperture \Sigma is defined ashaving value one inside \Sigma and zero outside. The two-dimensional Fourier transform of s(x, y) when \Sigma is an N -sided polygon is considered, and a closed-form exact solution is presented. Applications of these results are described for 1) the calculation of the secondary pattern of a reflector antenna with a noncircular aperture, and 2) high-frequency transmission through a periodic frequency selective surface.

A new procedure for improving the solution stability and extending the frequency range of the EBCM

Abstract: The extended boundary condition method (EBCM) has been frequently used to obtain the absorption and scattering characteristics of axisymmetric dielectric objects. For applications involving relatively high-loss dielectric objects, however, the method was usable only at frequencies below resonance. In this paper a new procedure for improving the stability and extending the frequency range of the EBCM is presented. This new procedure has two main features: 1) it is iterative, since it starts with a known solution that approximates the scattering problem, and 2) it involves separate field expansions in each of the overlapping subregions which describe the total interior volume of the object. For example, for high-loss dielectric objects, such as the biological models of humans and animals, the first step in the procedure is to replace the lossy dielectric object with a perfectly conducting one of the same shape and solving the scattering problem to determine the current density on the surface of the conductor. This surface current is then used to calculate the induced field expansions inside the dielectric object. It is shown that the numerical stability of the solution is further improved by dividing the interior region of the object into overlapping subregions, in each of which a separate field expansion is assumed. The electric and magnetic surface currents so obtained from the solution of the internal problem are then used to improve the initial estimate of the current density on the surface of the object. The iterative procedure continues until convergent values of the surface currents and the fields are obtained. Numerical results illustrating the improved stability of the iterative EBCM (IEBCM) solution at higher frequencies as well as its accuracy in calculating the absorption characteristics of a spheroidal model of man in the resonance and the postresonance frequency range are presented.

Rectangular microstrip patch antennas with infinite and finite ground plane dimensions

Abstract: The rectangular microstrip patch antenna has been extensively analyzed with regard to its input impedance and resonant frequency, both for infinite and finite ground plane dimensions. For infinite ground planes existing formulas have been compared and improved parameters presented. The influence from the side current radiation has been discussed as well. For finite ground plane dimensions the contribution from the ground plane edge diffraction has been accounted for in an equivalent radiation conductance and an equivalent diffraction susceptance. Formulas for these parameters have been developed on the basis of different theories. They are valid under the condition that only one of the ground plane dimensions are finite at the same time. Experimental investigations are carried out to test the accuracy of the developed formulas, showing good accuracy under the given conditions.

A comparison of methods for randomizing phase quantization errors in phased arrays

Abstract: Beamsteering for phased arrays normally employs electronically switchable digital phase shifters. These can only approximate to the desired phase distribution across the array, and if a straightforward rounding off is used, a periodic phase error arises which causes a pointing deviation of the main beam and introduces a parasitic sidelobe. Various methods have been given in the literature for randomizing the phase errors to reduce these problems. Here a general formula is derived to evaluate the parasitic sidelobe level for different methods. The various methods are compared with reference to 1) the parasitic sidelobe level, 2) the variances of the field pattern and the pointing direction, 3) gain reduction, and 4) any extra array hardware requirements and beamsteering unit resources.

Coherent scattering of a spherical wave from an irregular surface

Abstract: The scattering of a spherical wave from a rough surface using the Kirchhoff approximation is considered. An expression representing the measured coherent scattering coefficient is derived. It is shown that the sphericity of the wavefront and the antenna pattern can become an important factor in the interpretation of ground-based measurements. The condition under which the coherent scattering-coefficient expression reduces to that corresponding to a plane wave incidence is given. The condition under which the result reduces to the standard image solution is also derived. In general, the consideration of antenna pattern and sphericity is unimportant unless the surface-height standard deviation is small, i.e., unless the coherent scattering component is significant. An application of the derived coherent backscattering coefficient together with the existing incoherent scattering coefficient to interpret measurements from concrete and asphalt surfaces is shown.

On the eigenfunction expansion of electromagnetic dyadic Green's functions

Abstract: A relatively simple approach is described for developing the complete eigenfunction expansion of time-harmonic electric ( \bar{E} ) and magnetic ( \bar{H} ) fields within exterior or interior regions containing an arbitrarily oriented electric current point source. In particular, these results yield directly the complete eigenfunction expansion of the electric and magnetic dyadic Green's functions \bar\bar{G}_{e} and \bar\bar{G}_{m} that are associated with \bar{E} and \bar{H} , respectively. This expansion of \bar\bar{G}_{e} and \bar\bar{G}_{m} contains only the solenoidal type eigenfunctions. In addition, the expansion of \bar\bar{G}_{e} also contains an explicit dyadic delta function term which is required for making that expansion complete at the source point. The explicit dyadic delta function term in \bar\bar{G}_{e} is found readily from a simple condition governing the behavior of the eigenfunction expansion at the source point, provided one views that condition in the light of distribution theory. These general expressions for the eigenfunction expansion of \bar\bar{G}_{e} and \bar\bar{G}_{m} reduce properly to those obtained previously for special geometries by Tai.

The inverse of a block-circulant matrix

Abstract: The inverse A^{-1} of a block-circulant matrix (BCM) A is given in a closed form, by using the fact that a BCM is a combination of permutation matrices, whose eigenvalues and eigenvectors are found with the help of the complex roots of unity. Special results are also given when A is block symmetric or symmetric.

Directivity of planar array feeds for satellite reflector applications

Abstract: Array-fed reflector antennas are used extensively in today's contour and multiple beam satellite antennas. To determine the directivity of these antennas theoretically, the total radiated power of the array feed must be accurately computed. In this paper, a closed-form expression for the radiated power is obtained for arrays with the well-known (\cos \theta)q -type element patterns. The formulation is general, and takes into account polarization, nonsymmetric E - and H -plane element patterns, nonuniform element spacings and arbitrary complex excitation coefficients. Selective numerical data are presented to demonstrate the usefulness of this result. Comparisons are made with the available results obtained using direct numerical integration techniques, and with other available data based on less general formulations. Excellent agreement is observed for all cases. In particular, data are presented on the directivity of seven-element cluster feeds used in multiple beam designs, and an array feed for producing a contour beam covering the United States Eastern Time Zone (ETZ).

Reflection from a periodically perforated plane using a subsectional current approximation

Abstract: The scattering from a zero thickness plane having finite sheet resistance and perforated periodically with apertures is calculated for arbitrary plane wave illumination. The surface current density within the unit cell is approximated by a finite number of current elements having rooftop spatial dependence. The transverse electric field is expressed in terms of the current, and the electric field boundary condition is satisfied in an integral sense over the conductor, generating a finite dimension matrix equation whose solution is the current density. Since the conductor shape is defined through the locations of subsectional current elements, arbitrary shaped apertures can be handled. The reflection coefficient and current distribution are calculated for square apertures in both perfectly conducting and resistive sheets, and for cross-shaped apertures. Finite resistivity is shown to cause the magnitude of the transverse magnetic (TM) reflection coefficient to decrease more rapidly and its phase to decrease less rapidly, as the angle of incidence approaches glancing. Through detailed plots of the current density, the current crowding around the apertures is made clearly evident.

Creeping waves and resonances in transient scattering by smooth convex objects

Abstract: Scattering by smooth convex objects, excited by a transient field with broad spectral content, has been analyzed either by ray formulations, which are useful at observation times descriptive of the early arrivals, or by the complex resonances of the singularity expansion method (SEM), which are most appropriate at intermediate and late observation times. Within the framework of SEM, efforts have recently been made to show that in a grouping of the resonances along "layers," rather than along the conventional "arcs" based on an angular harmonic field representation, the higher order resonances behave collectively like a wave traveling circumferentially around the object. This observation has provided the stimulus for the present investigation in which the relation between the wavefront arrivals (creeping waves) and the SEM resonances is placed on a rigorous basis. Using a perfectly conducting circular cylinder as a canonical model, this is done by direct application of the theory of characteristic Green's functions to construct alternative field solutions, and by collective summation of groups of wavefront arrivals or groups of resonances. The connection between creeping waves and resonances thus having been established, hybrid formulations are developed which combine the creeping waves and the SEM resonances within a single rigorous framework so as to maximize the utility of each over the entire range of observation times. These results are then generalized to smooth cylindrical objects with noncircular convex shape.

Hybrid solutions for scattering from perfectly conducting bodies of revolution

Abstract: A current-based hybrid formulation is developed for predicting the electromagnetic scattering from conducting bodies of revolution (BOR). The electric field integral equation (EFIE) formulation of the problem is solved by incorporating the Fock solution for the surface currents on the scatterer into the method of moments (MM) solution. To treat oblique illumination, the Fock results are extended to arbitrary surfaces with torsion. The formulation is illustrated for spheres and conespheres with smooth and discontinuous joins. The analysis includes nonspecular phenomena such as creeping wave effects. Application of the physical optics (PO) approximation in this hybrid formulation is discussed. The formulation is shown to be accurate even for scatterers in the near-resonance range (i.e., ka \simgtr 7.5 ).

Electromagnetic scattering from perfectly conducting rough surfaces in the resonance region

Abstract: A rigorous integral formalism for the problem of scattering of electromagnetic radiation from a cylindrical, perfectly conducting rough surface of arbitrary shape is introduced. The computer code obtained from this theory enables us to show that the range over which the incident field affects the surface current density is of the order of the radiation wavelength. This phenomenon is explained using a new approximate theory, able to express the scattered field in the form of an integral whose integrand is known in closed form. Using the rigorous computer code, we show that the new approximate theory is better than the Kirchhoff approximation in the resonance region. Finally, it is shown that the phenomenon of short interaction range of the incident field permits the rigorous computation of the field scattered from a rough surface of arbitrary width.

Combined E - and H -plane phase centers of antenna feeds

Abstract: The feed efficiency, a first approximation to the aperture efficiency of a paraboloid or a conventional Cassegrain antenna, is used to define uniquely a combined E - and H -plane phase center of the feed pattern. A formula for numerical calculation of the combined phase center is presented, as well as theoretical results of the feed position tolerances and the efficiency loss due to differences in the principal plane phase patterns.

The accuracy of Norton's empirical approximations for groundwave attenuation

Abstract: In his papers on the numerical evaluation of the Sommerfeld surface wave attenuation, Norton gave the results primarily in graphical and tabular form, but he also included some empirical approximations. These approximate expressions are simple and readily programmed on hand calculators, while the exact expression involves the complementary error function with complex argument. The accuracy of the approximations is therefore of practical interest; the results of numerical checks of the accuracy of the various approximate expressions are reported here.

Time domain sensors for radiated impulsive measurements

Abstract: Discussion of various sensors and radiators commonly used for time domain antenna measurements is presented. The sensors and radiators discussed here are passive and analog devices which convert the electromagnetic quantity of interest to a voltage or current at their terminal ports. Moreover they are primary standards in the sense that their transfer functions can be calculated from their geometries and are flat (constant) across a wide frequency range. One of the major requirements for these sensors and radiators is that the electromagnetic far field, transmitted or received, is a replica or high fidelity derivative of the original pulse. Note that the transmitting transfer function of an antenna is proportional to the time derivative of the receiving transfer function of the same antenna, which follows from the reciprocity theorem. For electric field strength measurements, linear antennas loaded nonuniformly and continuously with resistance, or with both resistance and capacitance are discussed. Also, a conical antenna and an asymptotic conical antenna are discussed from the standpoint of improved characteristics. For an improved directivity, various types of transverse electromagnetic (TEM) horns are considered, e.g., a conducting TEM horn, and a resistively loaded TEM horn.

A spectral-iteration technique for analyzing scattering from arbitrary bodies, Part I: Cylindrical scatterers with E-wave incidence

Abstract: In the past, methods for solving electromagnetic scattering problems in the frequency domain have been developed largely for the low-frequency (moment method) and high-frequency (asymptotic techniques) regimes. The intermediate frequency range has been analyzed by combinations of these two approaches or by separation of variables, when possible. This paper is devoted to the development of an independent approach, viz., the "stacked spectral-iteration technique," which is capable of handling arbitrary scatterers with dimensions ranging from small to moderately large. The method takes advantage of the simplicity with which the planar-source planar-field relationships are expressed in the spectral domain. The boundary conditions or constitutive relationships, on the other hand, are expressed most simply in the spatial domain. Alternating between the two domains is carried out with the aid of the fast Fourier transform (FFT) algorithm. The spectral-iteration technique (SIT) was applied in the past to thin planar structures which allow the analysis to be carried out on a plane. The generalization of the two-dimensional formulation to arbitrary three-dimensional bodies can be accomplished by sampling the current distribution on the scatterer over a number of parallel planes, and using the simple spectral-domain interaction relationships between the planes. This new approach involves no matrix inversion and is capable of analyzing scatterers whose sizes far exceed those treatable by the moment method. In addition to being arbitrarily shaped, the scatterer may be conducting, dielectric, or lossy dielectric. Thus, the SIT provides an efficient approach to filling the much-needed gap between low- and high-frequency conventional techniques, e.g., the moment method (MoM) and the geometrical theory of diffraction (GTD), and to extending the range of applicability to dielectric scatterers, with or without loss. Though the concepts presented herein are applicable to arbitrary three-dimensional scatterers, the problem of arbitrary cylinders with E -polarized excitation is addressed in this paper, while the H -case is treated in an accompanying work. The three-dimensional case is to be reported in a future communication which treats the problem of scattering by a lossy inhomogeneons dielectric cylinder of finite length.