Studies On The Antenna Arrays Based On Four Dimensional Antenna Theory And Strong Mutual Coupling Effect

With the development of various modern wireless electronics systems, multifunctional antenna systems with high performance and low manufacturing cost are highly demanded. Single element antenna, due to its limited performance, is often not enough to meet various technical needs such as shaped beam pattern synthesis, beam scanning capability, low sidelobe level, and so on. However, by arraying many antennas in space, the resulted antenna array provides a powerful solution to the aforementioned requirements. At present, theory and techniques of antenna arrays have been well described in many technical books, and one may think that modern antenna array theory is rather mature. Nevertheless, most of the antenna arrays being used are still designed with the principles originally developed during the period of 1920s to 1940s, we call such antenna array technique as“conventional antenna array design method”. Antenna array designed with conventional method is being rather difficult to meet various challenges now. In recent years, with the development of various subject branches in the research field of electromagnetics, many novel ideas have emerged and then have been taken as new techniques for high performance antenna array designs. We call these novel antenna array design methods as“antenna array design methods based on new physical insights”. However, these techniques are rarely studied in antenna array research field, since their theory and practical implementation technique depart too far away from those of classic antenna arrays, and they are also unfamiliar to modern antenna array research field. Therefore, in order to realize various high performance antenna arrays using such new methods, it is necessary to study these techniques from the aspects of fundamental theory, practical techniques, experimental method, and potential applications.With this purpose, this dissertation carries out the studies on the“antenna array design method based on new physical insights”from new perspectives. Firstly, enlightened from the Doppler effect of high speed moving objects, we introduce the“four dimensional antenna theory”into the antenna array design, making the conventional amplitude-phase weighting be realized by time weighting and thus adding a new design freedom into the antenna array design. Secondly, motivated from the wideband properties of FSS with closely spaced dipoles, we develop various wideband phased antenna arrays by introducing strong mutual coupling effect between adjacent antenna elements. Moreover, we propose several design guidelines for antenna arrays with different specifications. The new phased array technique breaks out the framework set up by conventional antenna array design method, and it provides a novel design method for developing wideband/ultra-wideband phased array antennas. The outlines and conclusions are summarized as follows:1. Modern optimization algorithm based on population evolution methodWith the purpose of antenna array optimization, a careful study on modern optimization methods is carried out. By introducing the refreshing distribution operation, the fittest individual refinement operation, the dynamic differential evolution strategy and a novel individual modification scheme into the original differential evolution strategy, a modified differential evolution strategy (MDES) is proposed. Numerical results demonstrate that MDES has the following advantages: (1) a balanced relationship between the high convergence rate and robust exploration ability is built up; (2) the low convergence rate in nonconvex optimization problems is significantly improved; (3) poor exploration ability such as stagnation and premature convergence in nonconvex optimization problems is avoided. In order to design antenna arrays involving digital phase shifters and analog amplitude controllers, a hybrid differential evolution strategy (HDES) is proposed, which can be used to deal with optimization problems with both discrete and continuous design parameters. Furthermore, considering antenna array synthesis problems with multiple conflict objectives, a multiobjective optimization method based on the differential evolution operator and objective decomposition scheme is proposed to optimize antenna arrays with multiple disparately-scaled conflicting objectives. Numerical results show that this method excludes the tedious and difficult task of weighting factor selections in single objective optimization methods. Moreover, as compared to single objective optimization approaches, the main advantage of the present multiobjective optimization method is that many Pareto-optimal solutions can be obtained in a single run.2. Efficient pattern synthesis method for four dimensional planar antenna arraysFor planar array synthesis problems solved with population-based optimization method, the most time-consuming part in the iterative procedure is the conventional element-by-element field calculation of the synthesized pattern. Therefore, a method based on 2D IFFT is proposed to accelerate the evaluation of array patterns for planar array synthesis problem. In this method, the angle domain of an array pattern is mapped to the transform domain of 2D IFFT, then the conventional element-by-element field calculation is fulfilled by the inverse fast Fourier transform, thus the pattern computation efficiency is improved. Moreover, an efficient array synthesis technique based on MDES and 2D IFFT is developed for the design of optimal monopulse antennas in four dimensional planar arrays with triangular lattices and hexagonal boundaries. Finally, a novel modified 2D Woodward-Lawson method is proposed to pursue high efficiency pattern synthesis for complicated shaped beams with low sidelobe level. In this method, a Taylor aperture distribution is employed to serve as the local basis function for the representation of the desired far field. Consequently, the sidelobe level of the synthesized shaped beam can be well controlled by only adjusting the design parameters in the Taylor synthesis method. It is worthy to note that all the array beams with low sidelobe level is realized with low dynamic range ratio or even uniform amplitude distribution, which is almost impossible in conventional antenna arrays.3. Studies of the potential applications of the four dimensional antenna arrayFirstly, a novel monopulse antenna for a tracking radar system is proposed using the four dimensional linear antenna arrays. The time modulation technique applied in the antenna arrays overcomes the usual need for compromise design between sum and difference beams and avoids the need for implementation of two separate feed networks. The four dimensional antenna array also relaxes the error tolerance of the tracking accuracy from the amplitude and phase errors, due to the new design freedom of‘‘time''which can be controlled precisely and quickly. Moreover, the position of the target can be recovered by two reflected echoes from one previously transmitted pulse, thus the tracking errors resulting from the excitation errors and receiver noise in conventional antenna arrays can be greatly alleviated. Secondly, in order to apply the four dimensional antenna array in smart antenna systems, a flexible approach based on a hybrid differential evolution strategy was developed for adaptive pattern nulling with four dimensional linear antenna arrays. The hybrid differential evolution strategy adjusts only the least significant bits of the digital phase shifters and the on–off time sequence to minimize the total output power; deep nulls can then be placed in the direction of the interferences without much compromise of the shape of the main beam. Thanks to the new design freedom introduced in four dimensional antenna arrays, this adaptive nulling approach exhibits better performance over the traditional phase-only, amplitude-only, and phase-amplitude adaptive nulling methods, in terms of the practical implementation, nulling depth, and pattern deterioration.4. Studies of wideband phased arrays based on strong mutual couplingConsidering the practical implementation of the novel wideband phased array design method, a wideband phased antenna array based on closely spaced dipoles is studied firstly, and then a novel wideband phased antenna array based on closely spaced octagonal ring elements is proposed. Based on the theoretical and experimental studies on the two types of wideband phased antenna arrays, the general relationship among the ground plane, operation bandwidth, and gain is discovered, and a“gain-bandwidth”compromise design guide line is presented. Theoretical and experimental results show that the dipole antenna array has a wide bandwidth of 6: 1 and a maximum beam scanning angle of±45°. Moreover, theoretical and experimental results show that the octagonal ring antenna array has a 4.5: 1 bandwidth and a maximum beam scanning angle of±45°.5. Low-profile wideband microstrip antenna design method based on strong couplingA bandwidth enhancement method based on the strong coupling effect and inductance & capacitance tuning technique is proposed. Both theoretical and experimental results show that the thickness of a conventional wideband microstrip antenna can be reduced from 8% wavelength to 4.3% wavelength, while the wide bandwidth performance is still kept. It is the first time that inductance&capacitance tuning technique is applied in wideband low-profile microstrip antenna design. This method also greatly enriches the existing wideband microstrip techniques.