Design Of Ultra-Wideband Antennas And Research On Synthesis For Conformal Arrays

The applications of modern electromagnetic theory in radiation and scattering problems benefit from the optimization technique to a large extent. However, the optimization cost functions in electromagnetic field are always highly nonlinear, nondifferentiable and have multiple peaks, which bring about much challenges for the classically mathematic programming methods in solving the practical problems. Therefore efficient and intelligent optimization methods are urgently desired.The development of ultrawideband (UWB) technique spurs the demand of UWB antennas in practical system. However, there still exists several narrow bands for other communication systems over the designated frequency band, such as:the wireless local area network (WLAN) operating at5.15-5.35GHz and5.725-5.825GHz, WiMAX system operating at3.3-3.6GHz, which may cause severe electromagnetic interference to the UWB system. Therefore, the investigation on the design of the UWB antennas with band-notched characteristic has great values for the practical engineering problems.With the development of wireless communication and modern military, conformal antenna arrays have attracted more and more attention in recent years. This is because conformal antenna arrays can not only provide the desired performance, but also have slight effect on the aerodynamic performance and the antenna performance. Thus, the research on the conformal arrays has broad engineering applications.This dissertation makes deeply insight into the design of efficient hybrid optimization algorithm, ultrawideband printed antenna with band-notched characteristics, together with the synthesis of conformal antenna arrays. The author’s major contributions can be summarized as follows:1. Aiming at overcoming the drawbacks of standard genetic algorithm (SGA), such as prematurity and easily trapping in local optimum in solving complex problems, an improved genetic algorithm (IGA) is proposed, in which some improved mechanisms according to non-linear ranking selection, competition and selection among several crossover offspring and adaptive change of mutation scaling are adopted. Besides, the effects of these improved mechanisms on the proposed algorithm have been analyzed. The numerical results validate the performance of the improved genetic algorithm. 2. On the basis of investigating the search process of particle swarm optimization (PSO), a novel enhanced particle swarm optimization (EPSO) algorithm is proposed. The optimum search ability of PSO is improved by introducing a new velocity updating process, novel exceeding boundary control strategy and global best perturbation manipulation. Then, the influences of different parameter values on the convergence of EPSO are investigated. The effectiveness of EPSO is verified by the numerical simulation results.3. Motivated by the idea of grafting in botany, a new hybrid improved genetic particle swarm optimization algorithm called HIGAPSO is proposed by combining IGA with EPSO to integrate their advantages. The combination of these two different optimization mechanisms, not only improves the diversity of the offspring, but also maintains the balance of global search and local search, so the entire optimum search speed of the algorithm is accelerated. What’s more, the computation complexity of the proposed algorithm is analyzed and conclusion can be drawn that HIGAPSO basically has the same computation complexity as GA in each iteration. Typical benchmark functions and pattern synthesis of different arrays are used to illustrate the efficiency of the proposed algorithm.4. Employing the proposed hybrid algorithm and HFSS, a spade-shaped ultrawideband printed planar monopole antenna is designed. By embedding different shapes of slots on the radiating patch and the ground plane, or by introducing resonant structures behind the radiating patch, different notched frequency bands can be achieved. The variations of the notched bands with different lengths of resonant structures have been studied. Then, a planar ultra-wideband monopole antenna with dual band-notched characteristics is fabricated. Besides, to overcome the disadvantages that band-notched antennas rejecting the WLAN bands up-to-date has rejected entire5-6GHz frequency band which makes any useful information contained in the frequency band of5.35-5.725GHz lost, a novel planar UWB antenna with triple notched bands is provided to efficiently guarantee the information transmission between the frequency band of5.35and5.725GHz. Furthermore, the sensitivities of the finite ground size and fabrication variation to the designed triple notched bands antenna as well as the mutual influences among these notched bands are investigated. Finally, the proposed antenna has been successfully fabricated and measured.5. The low sidelobe and pattern reconfigurable of cylindrical conformal arrays are studied. Firstly, uniform and nonuniform cylindrical conformal arrays with low sidelobe are designed. During the optimized design process, considering the effects of the platform and the coupling between elements on pattern reconfiguration, the array patterns are obtained by directly importing all of the active element patterns to improve the reliability of the designed results. Then, the uniform and the nonuniform reconfigurable cylindrical conformal arrays are designed respectively. Finally, according to the optimized results, the uniform cylindrical conformal array is manufactured and its radiation characteristic is measured. The good measurement results indicate the validity and efficiency of the proposed synthesis.6. Three dimensional pattern syntheses of conical and spherical conformal phased arrays are investigated. Firstly, dual polarized patch antenna using two individual feeds is designed to conveniently adjust the desired polarization in the scanning process. Then, effects of the distance between array elements on the radiation pattern of the conformal arrays are discussed in detail to determine the rational arrangements of the conical and spherical conformal arrays. Finally, the modified Bernstein polynomial is employed to obtain the excitation amplitudes of the conical and spherical conformal phased arrays, with the purpose of overcoming the drawbacks of high oscillation amplitude weights across the phased array and significantly reducing the optimized variables in the syntheses process. Simulation results show that the optimized array patterns can totally achieve the design targets, which reveal the validity of the proposed method.