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The program 'Equivalence Principle As Applied To Conical Arrays' has been successfully completed. The equivalence principle pattern synthesis technique has been used to provide aperture distributions for an experimental conical array. The array consisted of thirty-seven crossed-slot elements on a cone of half-angle 10.25 degrees and was operated at 3.185 GHz. Radiation patterns were measured for two beam pointing directions, one 50 deg. from the cone tip and the second normal to the conical surface. Excellent agreement was obtained bewteen measured patterns and calculated patterns. It is concluded that the technique can be used successfully to synthesize radiation patterns from arrays on conical and other curved surfaces. (Author)

Flush mounted slot antenna systems on metallic cones or ogival surfaces can be inertialessly scanned in the required direction. Since scanning over a wide angular region is generally desired, the radiation characteristics, including the effect of mutual coupling on the radiating elements, must be investigated before the more detailed system aspects are considered. To this end, various approximation techniques have been examined for use in pattern calculations and in impedance calculations. These include the approximate asymptotic approach and the equivalence principle technique. The approximation techniques provide simplified computations as compared with the exact technique, and are not applicable to all conditions. A combination of exact and approximation techniques is generally required to design or analyze an array. The approximate asymptotic approach, which allows the separation of the diffracted field and geometrical optics fields, has been examined in detail. It appears that the asymptotic representation of the Legendre function chosen for the analysis leads to divergent expressions as the mode number m is increased, and hence limits the usefulness of the asymptotic approach in the present problem. The divergent nature of the asymptotic expression is verified by computed radiation patterns of several azimuthal modes. A computer program is being developed to apply the equivalence principle technique to a conical surface.

Excellent agreement has been shown between element patterns of circumferential and radial slots on a cone, computed with the normal mode series computer programs, and patterns measured with an experimental model with both types of slots. When the modal series is used for the computation of exact patterns, the number of modes required for convergence of the series increases as the distance of the slot location from the tip of the cone increases. Computational difficulties from accumulated round-off errors also affect the accuracy and limit the applicability of the modal series program to element positions not too far from the cone tip. The approximate asymptotic approach, on the other hand, allows the separation of the diffracted field and the geometrical optics field. More specifically, the asymptotic approach resulted in complete expressions for the E sub theta and E sub phi radiation fields in terms of optical, transition, and diffraction fields. The complete expressions for each of the two field components, in a form suitable for numerical computation, were included in the Final Report on Contract No. N00019-74-C-0127. An examination of these expressions indicates that the diffraction coefficients of both field components are only a function of the angular coordinates and not of the location of the radiating element.

The report contains the results of a study of techniques for obtaining extended coverage element patterns for use on hemispherically scanned phased arrays on cylinders of large radius of curvature. It contains experimental patterns of slot radiators on such a cylinder covered with surface wave structures. Experimental patterns of slots coupled to parasitic dipoles extended around the cylinder are also included. An analysis that treats sources on reactive cylinders is performed to determine what type of surfaces will give extended coverage when the polarization is parallel to the cylinder axis. The results of the study indicate that improved coverage can be obtained using reactive surfaces that are selected to affect TE waves and TM waves in different manners. Such surfaces can be constructed by combining corrugated conductors and dielectric slabs. The combination can be selected to provide effectively the proper surface reactance to allow radiation near the horizon for both polarizations., See also report dated Dec 73, AD-779 695.

For missile seeker radars, the use of mechanically scanned antenna systems becomes increasingly difficult as the requirements for the aerodynamic and electrical performance of missiles become more demanding. One possible alternative to the use of mechanically scanned antennas lies in the application of flush-mounted slot antenna systems on metallic cones or ogival surfaces. These antenna systems would be inertialessly scanned in the required directions. The curvature of the particular conformal surfaces and the positional relationships of the radiating elements, however, introduce many problems which are different than those associated with planar electronically controlled arrays. As a consequence of these positional relationships, there may be no element that can be considered 'typical' so that impedances, patterns, and polarizations may vary significantly among the elements, in contrast to the conditions that are obtained in planar arrays for elements not too near the edge. In addition, since the radiating elements are not all similarly oriented, there may be a significant cross polarized component in the array pattern that could interfere with the desired system operation., Also available as Rept. no. HAC-REF-2753/1691. DDC Form 55 not necessary for document request.

Exact element patterns computed from expressions of two potential functions representing the model fields of arbitrary apertures on a conducting cone were compared with measured patterns. Circumferential and radial slots 6.22 lambda from the tip of a 10 deg half angle cone were used in the pattern measurements. Measured and computed patterns are in very good agreement. During this same period, an asymptotic approximation of the contour integrals representing the fields of the circumferential slot was carried out, resulting in approximate expressions for both field components. These expressions describe the component fields in terms of optical, transition and diffraction fields. The diffracted field is a product of a frequency-independent angular function and a simple function containing the position of the radiating element. Such representation of the fields is better suited for numerical computation than the modal series. Recommendations for further investigative work on the topic of conformal arrays are also included.

Two methods of synthesizing patterns from conical arrays were investigated during this period. In the first method the equivalence principle was used to synthesize patterns that are approximate duplicates of the patterns of representative planar arrays. This is done by evaluating on the surface of the cone the near field of a centrally located and mechanically steered hypothetical planar array. These near fields are used to calculate the required complex excitations of real elements on the surface of the cone to nearly duplicate the pattern of the hypothetical planar array. Patterns are presented of the results for two beam pointing directions. In the second method of synthesizing patterns from a conical surface, a heuristic approach was taken wherein the placement of the elements on the surface was based on extrapolations from linear and circular array theory and practice. Several element configurations are considered and numerous computer patterns are presented. The characteristics of these patterns are summarized by comparing in graphical form grating lobe levels, first sidelobe levels, and back-lobe levels for all of the patterns.

Two distinct aspects were investigated. The first one is concerned with the synthesis of far field patterns from sources on the conical surface. Three different approaches were undertaken: (1) An equivalence principle was used to determine the distribution of sources on a cone to produce a prescribed pattern in the far field. (2) Roots of two transcendental equations were calculated for appropriate parameters. The numerical values are needed for a theoretical solution of the radiation fields and mutual coupling effects in a region bounded by a conducting cone. (3) Computation of patterns from discrete radiators placed on a conical surface was continued. The signal-to-noise ratio is optimized in the beam pointing direction. The second aspect included the design, fabrication and testing the scanning capabilities of a linear array of crossed slots on a large ground plane. The array was designed so that each radiating element could be matched in the presence of the others, its phase and amplitude could be arbitrarily set and the active impedance measured. The array scanned from broadside to 80 degrees (10 degrees from endfire) with satisfactory beam patterns and sidelobe levels.

Several topics relating to conformal arrays have received detailed attention in the last few years. These topics include pattern synthesis, types of appropriate radiating elements, and their impedance and mutual coupling characteristics, and wide angle scanning of linear arrays located on planar and conical surfaces. In the present report, the computation of an exact element pattern is described. The report begins with the general expressions for two potential functions representing the modal fields of arbitrary apertures on a conducting cone. Expressions for the electric field components are then derived from the potential functions for circumferential and radial slots with particular slot excitations. The field expressions are the basis for a computer program which computes radiation patterns from both circumferential and radial slots. The appropriate approximations for the Legendre functions and the spherical Bessel functions used for their computations are summarized in this report. The computer program is a modification and extension of one described by Pridmore-Brown and has been executed on the IBM 370 computer system, now operational at the Hughes Aircraft Company. The program computes the special functions in DOUBLE PRECISION, thus giving the required accuracy of the computations.

This report presents the results of a study dealing with the effects of factors such as high temperature and vehicle maneuvers on a rectangular flat plate slot array antenna for lift-reentry vehicles. Specifically, the study consisted of two parts. The first part dealt with an investigation of slot closure techniques which will preserve the electrical performance of the antenna under severe environmental conditions. This consisted of a materials study to determine suitable metals and dielectric materials which have compatible thermodynamic characteristics up to temperatures of 2500F. The second part of the study consisted of an investigation of the problem of beam stablization in the presence of vehicle pitch, roll and yaw maneuvers. Two aspects of the problem were considered. First, the regions within which beam pointing control is required were determined by applying various combinations of pitch and roll to the vehicle carrying the antenna. Second, for the type of antenna being considered, the region of possible beam positions was investigated. Devices and techniques for accomplishing the beam positioning were also considered. The high temperatures of the antenna and components ruled out the use of most conventional phase shifting devices.

The experimental and theoretical investigations performed during this program indicate that wide angle scanning can be realized with linear arrays located on groundplanes and also located on a generatrix of a 20 deg cone. Scanning from broadside to 10 deg from endfire for the planar arrays and in a direction along the tip of the cone was obtained. Measured far-field patterns and impedances of the radiating elements were in very close agreement with predictions based on simplified theoretical models. (Author)

Several interrelated topics necessary for the development of overall Integrated Conformal Arrays were studied. A method was devised that allows the determination of sources required on conical surfaces to produce certain prescribed patterns. The effects of element location and spacing on pattern characteristics were studied so that the number of radiating elements can be minimized. Fields in the vicinity of cones were analyzed to aid in the prediction of mutual coupling effects and the improvement of pattern analysis capability. An experimental radiating element was selected, constructed, and tested in a ground plane and a 20-degree cone with a base diameter of eight inches was fabricated. Possible system configurations were reviewed, and two approaches to the scan control problem were examined. The studies made significant progress toward the solution of the overall problem of developing an electronically steered conformal array on a cone. (Author)

This program is directed toward the evaluation of the feasibility of electronically scanned arrays conformal with the surface of aerospace vehicles namely, missiles. For purposes of analysis conical geometry has been adopted. Sum and difference patterns which can be scanned from broadside through the axis of the cone have been analysed. Expressions for mutual coupling have been derived and applied to a linear array. (Author)

Analytical and experimental approaches are combined in an analysis of the performance of phased arrays when they are fed by arbitrary feeding networks. The array is described in terms of its element patterns and its scattering matrix, while the feeding network is described by its scattering matrix. Measured array meters, obtained with a 16-element phased array, were used with theoretical feeding parameters in a specially derived computer program that calculated array gains, patterns, and impedances for various feeding arrangements and scan angles. Calculated values of gains are compared with optimum gain values. The digital computer program written in FORTRAN is given in an appendix, as is a matrix formalism for the description of large arrays. (Author)

The report contains analyses of the radiation characteristics of grounded dielectric slabs fed by slots in a groundplane. It also contains experimental patterns of such configurations. In Addition, measured patterns of slots with parasitic radiating elements, and of combinations of slots, surface wave structures and parasitic elements, are included. It is shown that significant improvement of radiation at the horizon can be obtained in the E-plane and that significant broadening of the pattern can be obtained in the H-plane. Patterns of a linear array of slots in a groundplane with curved extensions, electronically scanned in the E-plane show that significant improvement in radiation at endfire can be obtained using a surface wave structure. Recommendations for further study are included. (Author)

The report contains analyses of the radiation characteristics of grounded dielectric slabs fed by slots in the groundplane. Two configurations are examined, one in which a semi-infinite slab covers the slot, a second in which a finite slab does not extend over the slot. The slots are parallel to the slab edges so that only TM mode propagation is considered. Integral equations are derived for the fields at the ends of the slabs and approximate solutions are obtained. Numerical results in the form of radiation patterns are given for the case of the semi-infinite slab. It is found that the feed pattern is very close to the space-wave that would exist if the slab were infinite, but differs from it in the region near the horizon. The results can be applied to studies of electronic scanning of finite arrays of slots in the presence of surface wave structures. Recommendations for further study are included. (Author)

A technique was developed for optimizing under certain constraints, the power transferred from an arbitrary antenna array to a receiving antenna in some spatial direction. In certain practical cases this optimization reduces to that of maximizing directive gain; in others it reduces to optimizing the so called effective gain. The optimization technique is formulated for several of these cases and is applied to three numerical examples. (Author)

This report investigates the changes in input admittance of a rectangular waveguide terminated in a groundplane covered by a uniform plasma slab contiguous with the groundplane. Such radiators provide wide angular pattern coverage and find application as telemetry and communication antennas in reentry vehicles. Numerical calculations were performed for the case of lossless plasmas in which the electron densities are all below the critical density, i. e., the effective relative permittivity of the slab ranges between zero and unity. Curves of input conductance and susceptance for this configuration are given as a function of relative permittivity for several slab thicknesses. These admittance values are used to compute reflection coefficients and signal loss resulting from mismatch. These are also presented graphically. The calculations show that, except for thin slabs, the aperture admittance is very close to that for a slab of infinite thickness. A qualitative explanation of this effect is also given. (Author)