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Communication & Space
Sciences Laboratory

Conformal Antennas

Conformal Antennas Mounted on Large Platforms

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1-) A Reciprocity Approach for Calculating Radiation Patterns of Arbitrarily Shaped Microstrip Antennas Mounted on Circularly Cylindrical Platforms
by Douglas. H. Werner, Rene J. Allard, Rodney A. Martin, and Raj Mittra

ABSTRACT: This paper presents a convenient and efficient approach, based on the reciprocity theorem, for calculating the radiation patterns of arbitrarily shaped microstrip antennas with dielectric substrate and superstrate layers mounted on circularly cylindrical platforms. A detailed theoretical development followed by examples with numerical and graphical results illustrate the versatility of the technique. The reciprocity approach presented is very flexible and may be used in conjunction with any of the commonly employed computational electromagnetics modeling approaches such as the method of moments, finite-element methods, and finite-difference time-domain techniques.

2-) Radiation Pattern Synthesis for Arrays of Conformal Antennas Mounted on Arbitrarily-Shaped Three-Dimensional Platforms Using Genetic Algorithms
by Rene J. Allard, Douglas H. Werner, and Pingjuan L. Werner

ABSTRACT: A domain-decomposition/reciprocity procedure is presented which allows the radiation patterns of microstrip patch antennas mounted on arbitrarily-shaped three-dimensional perfectly electric conducting (PEC) platforms to be computed accurately as well as efficiently. The utility of this technique is demonstrated by considering an example consisting of a nine-element conformal array of microstrip patch antennas mounted axially along a finite-length PEC circular cylinder. It is shown that the elements close to the ends of the cylinder have significantly different patterns than those close to the center of the cylinder. The results from this example suggest that the common practice where all the individual element patterns are assumed identical is not always valid and, in fact, can lead to significant performance degradation in the design of conformal phased arrays. This observation is supported by the fact that an attempt to steer the main beam of the nine-element conformal array to an angle θ = 60 using a standard uniform progressive phase shifting technique proves unsuccessful. Next a genetic algorithm (GA) synthesis procedure is introduced that is capable of determining the optimal set of element excitation phases required to yield a desired or specified far-field radiation pattern. The results of this GA phase-only optimization are shown to yield the desired main beam steered to the correct angle for this nine-element linear array mounted on a circularly cylindrical platform. The GA radiation pattern synthesis procedure introduced appears to be a highly effective means of correcting for platform effects on the individual element patterns of a conformal phased array.

3-) Efficiency-Constrained Particle Swarm Optimization of a Modified Bernstein Polynomial for Conformal Array Excitation Amplitude Synthesis
by D. W. Boeringer and D. H. Werner
IEEE Transactions on Antennas and Propagation, Vol. 53, No. 8, pp. 2662-2673, August 2005.

ABSTRACT: As various enabling technologies advance, conformal phased arrays are finding more numerous applications. Because a conformal array is curved, new far field pattern behaviors emerge and many of the traditional linear and planar phased array synthesis methods are not valid. This paper starts by reviewing the equations for the far field of a curved phased array, and provides a generalized definition of aperture efficiency appropriate for conformal arrays. A modified Bernstein polynomial, defined with just five parameters, is introduced which provides a flexible method to specify a variety of smooth unimodal amplitude distributions that are shown to give good sidelobe levels and aperture efficiencies. By using particle swarm optimization of the modified Bernstein polynomial parameters constrained to provide a specified aperture efficiency, a family of aperture distributions and corresponding far field patterns is produced that allows aperture efficiency to be traded for sidelobe level.

4-) Bézier Representations for the Multiobjective Optimization of Conformal Array Amplitude Weights
by Daniel W. Boeringer and Douglas H. Werner
IEEE Transactions on Antennas and Propagation, Vol. 54, No. 7, pp. 1964-1970, July 2006.

ABSTRACT: For conformal phased arrays, generally the excitation amplitude of the array elements must be adjusted in order to maintain low sidelobes as the array is scanned. While the desired phase weights for maximum gain are deterministically set by the array geometry and scan angle, the representation of optimum low sidelobe amplitude weights remains an open problem. Following up on prior work using the efficiency-constrained optimization of a modified Bernstein polynomial for low sidelobe conformal array synthesis, a Bézier surface is shown to provide a good representation of the optimized amplitude weights with a reduced number of parameters, while demonstrating -constraint multi-objective optimization of conformal aperture efficiency versus sidelobe level. These results are extended to include a Bézier volume representation for the multiobjective optimization of conformal aperture ef ficiency versus both sidelobe level and scan angle.

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