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Sciences Laboratory

Nature Inspired Antenna Design

Thinned Aperiodic Arrays

A large grating lobe appears for an 8 element array
with a uniform spacing 0.8 λ when it is steered to 45°.

The scan volume of a thinned periodic linear phased array is proportional to the spacing between array elements. As the spacing between elements increases beyond a half wavelength, the scan range of the array will be significantly reduced due to the appearance of grating lobes. This research investigates a method of creating thinned aperiodic linear phased arrays through genetic algorithms that will suppress the grating lobes with increased steering angles. In addition the genetic algorithm will place restrictions on the driving point impedance of each element so that they are well behaved during scanning.

A non-uniformly spaced conformal array of microstrip patch antenna elements of length L, width w, and substrate thickness h.

A conformal array of microstrip patch antennas uniformly spaced at 0.85λ is perturbed using a GA to create an aperiodic array which simultaneously meets the grating lobe constraint and driving point impedance requirements.

Aperiodic arrays can have widely varying driving point impedances during scanning. To mitigate these effects the VSWR of each antenna element is bounded under 2:1 by using a GA to adjust the probe positions and element spacings.


..: References :..

1-) Optimization of Thinned Aperiodic Linear Phased Arrays Using Genetic Algorithms to Reduce Grating Lobes During Scanning
by Matthew G. Bray, Douglas H. Werner, Daniel W. Boeringer, and David W. Machuga

ABSTRACT: The scan volume of a thinned periodic linear phased array is proportional to the spacing between array elements. As the spacing between elements increases beyond a half wavelength, the scan range of the array will be significantly reduced due to the appearance of grating lobes. This paper will investigate a method of creating thinned aperiodic linear phased arrays through the application of genetic algorithms that will suppress the grating lobes with increased steering angles. In addition, the genetic algorithm will place restrictions on the driving-point impedance of each element so that they are well behaved during scanning. A genetic algorithm approach will also be introduced for the purpose of evolving an optimal set of matching networks. Finally, an efficient technique for evaluating the directivity of an aperiodic array of half-wave dipoles will be developed for use in conjunction with genetic algorithms.




2-) Matching Network Design Using Genetic Algorithms for Impedance Constrained Thinned Arrays
by Matthew G. Bray, Douglas H. Werner, Daniel W. Boeringer, and David W. Machuga

ABSTRACT: This paper investigates a technique for optimizing matching networks for thinned aperiodic dipole arrays to achieve a 2:1 or better VSWR for each antenna element over the entire scan range of the array. The thinned array is optimized via a genetic algorithm to have a suppressed grating lobe over the scan range of the array. In addition, the genetic algorithm will place restrictions on the driving point impedance of each element so that they are well behaved during scanning. The impedance constraint allows a three element reactive matching network to be optimized for each element of the array using a separate genetic algorithm.




3-) Thinned Aperiodic Linear Phased Array Optimization for Reduced Grating Lobes During Scanning with Input Impedance Bounds
by Matthew G. Bray, Douglas H. Werner, Daniel W. Boeringer, and David W. Machuga

ABSTRACT: The scan volume of a thinned periodic linear phased array is proportional to the spacing between array elements. As the spacing between elements increases beyond a half wavelength, the scan range of the array will be significantly reduced due to the appearance of grating lobes. This paper will investigate a method of creating thinned aperiodic linear phased arrays through genetic algorithms that will suppress the grating lobes with increased steering angles. In addition the genetic algorithm will place restrictions on the driving point impedance of each element so that they are well behaved during scanning.




4-) Efficient Impedance Interpolation and Pattern Approximation for Linear Microstrip Phased Arrays Using Neural Networks
by J. A. Bossard, D. H. Werner and M. G. Bray
2003 IEEE International Symposium on Antennas and Propagation and USNC/URSI National Radio Science Meeting Columbus, Ohio, June 22-27.
Go/


5-) Nature-based Design of Aperiodic Linear Arrays with Broadband Elements Using a Combination of Rapid Neural Network Estimation Techniques and Genetic Algorithms
by C. S. DeLuccia, and D. H. Werner
IEEE Antennas and Propagation Magazine, Vol. 49, No: 5, pp. 13 - 23, October 2007.


ABSTRACT: The developmetns presented in this paper address the challenge of determining the optimal element positions in nonuniformly spaced broadband phaased-array antennasin order to best meet desired performance criteria. Specifically, this is accomplished by introducing a new nature-based design technique that couples a robust genetic-algorithm (GA) optimizer with rapid neural-network (NN) estimation procedures. These provide performance criteria as functions of the element positions over the entire scanning range and bandwidth of operation. The objective of this GA-NN technique is to determine the optimal element position for a broadband aperiodic linear phased-array antenna in order to minimize element VSWRs and sidelobe levels. The NN estimation procedurs circumvent the need for computational intensive full-wave numerical simulations during the optimization process, which would ordinarily render such an optimization task impractical. The effectiveness of the new GA-NN design synthesis technique is demonstrated by considering an example where a nonuniform spaced linear phased array of ten stacked patch antennas is optimized for operation within a given bandwidth and scanning range.




6 -) Design of Broadband Planar Arrays Based on the Optimization of Aperiodic Tilings
by Thomas G. Spence, and Douglas H. Werner
IEEE Transactions on Antennas and Propagation, Vol. 56, No. 1, January 2008

ABSTRACT: Antenna arrays based on aperiodic tilings have been shown to exhibit low sidelobe levels and modest bandwidths over which grating lobes are suppressed. In addition, compared to conventional periodic arrays, these arrays are naturally thinned (i.e., mean interelement spacing is greater than λ / 2). The generation of these arrays involves placing array elements at the locations of the vertices of an aperiodic tiling. To obtain a realizable design, the entire array is then scaled and truncated to achieve a desired minimum element spacing and aperture size. This paper demonstrates that it is possible to greatly extend the bandwidth of these arrays by incorporating a simple perturbation scheme into the basic array generation process. The implementation of this perturbation scheme is straightforward and it lends itself well to being combined with an optimization technique such as the genetic algorithm. It is successfully used to generate arrays that have large bandwidths (peak sidelobe level < -10 dB with no grating lobes) of up to a minimum element spacing of 5 λ . Moreover, the flexibility of this technique will be further demonstrated by introducing a slight variation of the basic scheme that is capable of generating arrays with extremely wide bandwidths. An example will be presented for an array design that has a bandwidth corresponding to a minimum element spacing of up to 11 λ .




7 -) The Pareto Optimization of Ultrawideband Polyfractal Arrays
by Joshua S. Petko, and Douglas H. Werner
IEEE Transactions on Antennas and Propagation, Vol. 56, No. 1, January 2008

ABSTRACT: The application of global optimization techniques, such as genetic algorithms, to antenna array layouts can provide versatile design methodologies for highly directive, thinned, frequency agile, and shaped-beam antenna systems. However, these methodologies have their limitations when applied to more demanding design scenarios. Global optimizations are not well equipped to handle the large number of parameters used to describe large-N antenna arrays. To overcome this difficulty, a new class of arrays was recently introduced called polyfractal arrays that possess properties well suited for the optimization of large-N arrays. Polyfractal arrays are uniformly excited with an underlying self-similar geometrical structure that leads to aperiodic element layouts. This paper expands on polyfractal array design methodologies by applying a robust Pareto optimization technique with the goal of reducing the peak sidelobe levels at several frequencies specified over a wide bandwidth. A recursive beamforming algorithm and an autopolyploidy based mutation native to polyfractal geometries are used to dramatically accelerate the genetic algorithm optimization process. This paper also demonstrates that the properties of polyfractal arrays can be exploited to create designs that possess no grating lobes and relatively low sidelobe levels over ultrawide bandwidths. The best example discussed in this paper maintains a -15.97 dB peak sidelobe level with no grating lobes from a 0.5 λ , to more than a 20 λ minimum spacing between elements, which corresponds to at least a 40:1 bandwidth for the array.




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