Font Size: a A A

Iterative Fourier Techniques For The Synthesis Of Antenna Arrays

Posted on:2014-09-13Degree:DoctorType:Dissertation
Country:ChinaCandidate:X K WangFull Text:PDF
GTID:1268330398998468Subject:Electromagnetic field and microwave technology
Abstract/Summary:PDF Full Text Request
Comparing with a single antenna, antenna arrays could realize some electrical properties such as high gain, narrow beamwidth, low sidelobe, and so on. The properties enable them to get wide application in modern wireless electronic equipments. Array synthesis is one of the core issues in the design of antenna arrays, and developing better synthesis algorithms could facilitate designing high performance antenna arrays. Therefore, studying the high-efficiency synthesis method suitable for large antenna arrays has important theoretic and practical meaning.This thesis focuses on array synthesis methods, and the applications of Genetic Algorithm (GA), Invisive Weed Optimization (IWO), and the Iterative Fourier Technique (IFT) in synthesizing low-sidelobe antenna arrays are studied. The advantages of the IFT method and its modified version in the design of linear as well as large planar arrays are discussed in detail. The main contributions of this thesis could be summarized into the following points:1. A new crossover operator is presented to improve the global searching ability of the available real-coded GA. The improved GA is applied to the synthesis of low sidelobe linear arrays, the arrays have11-12dB sidelobe reduction than that obtained by the initial GA while meeting the requirement of beamwidth and null depth.2. Combining GA with the Invasive Weed Optimization (IWO), a hybrid algorithm called GA-IWO is proposed for antenna array synthesis. The method takes the results obtained by GA after a few evolutions (rough GA) as the initial solution, then, the IWO is employed to perturb the initial solution in order to improve the global searching ability and accelerate the convergence speed. Synthesis results for a20elements linear array show that the arrays obtained by GA-IWO have0.8-2dB sidelobe level reduction than that obtained by fine GA and IWO with nearly the same beamwidth and Null depth. The convergence speed of the GA-IWO is much faster than the fine GA, but slower than the IWO.3. Based on the Iterative Fourier Technique (IFT), an adaptive Iteration Fourier Technique (AIFT) is proposed for the synthesis of equal-spaced linear arrays. Comparing with the IFT algorithm, the new method does not need the sidelobe level threshold (SLLT) given in advance to get the optimum array. For the case that the array’s element excitations are massively truncated, the method could reduce the beam broadening through adaptively adjusting the values of far field pattern located in the edge region of mainlobe. Synthesis results for linear arrays with different design requirements using AIFT show that the antenna arrays have4-5dB sidelobe reduction than that obtained by the IFT method, while the arrays’beamwidths have tiny broadening.4. A modified Iterative Fourier Technique (MIFT) is proposed for synthesizing thinned linear arrays and large thinned planar arrays. When the MIFT method is used in the synthesis of thinned linear arrays, the computational time is about1/17of the time needed by IFT. When the method is used in the synthesis of large thinned planar arrays, the arrays have0.9-8.6dB sidelobe reduction than that obtained by using the IFT method when the array’s filling factor is greater than40%, while the pattern’s beamwidth is almost invariable. The array’s sidelobe reduction is4-5dB compared with the results obtained by the Deterministic Density Taper (DDT) method. Since the SLLT plays an important role in the MIFT method, a way to determine the scope of SLLT is also provided.5. When the arrays’filling factors drop below40%, the MIFT is not appropriate for thinning large thinned planar arrays any more, while the IFT method may trap in local minima. Therefore, a new method called IWO-IFT is proposed in the thesis. In the method, the initial population is produced by the IFT, then, the individuals in the population are perturbed by I WO in order to get the arrays with low sidelobe level. Simulation results demonstrate that the IWO-IFT could be used in the synthesis of the thinned planar arrays having arbitrary apertures and filling factors, and the arrays sidelobe reduction range in different levels with the maximum value of2.6dB.
Keywords/Search Tags:Genetic Algorithm, Invasive Weed Optimization (IWO), Linear Arrays, Iterative Fourier Technique, Large Thinned Planar Arrays, SidelobeLevel Threshold (SLLT)
PDF Full Text Request
Related items