Theoretical And Applicational Studies Of Phased Antenna Arrays Based On Irregular Subarray Techniques

Phased antenna arrays have been widely used in various radio systems due to their salient features such as enhanced system gain,flexible beam scanning and beamforming.With the rapidly more and more complicated electromagnetic environment,phased antenna arrays are facing more and more challenging requirements.In order to meet the demands of low sidelobes,high gains and multi-function integration,phased antenna arrays need to be developed towards large scale,which poses great challenges to the design of the arrays.First of all,each element should be connected to a T/R module.However,traditional T/R modules have the disadvantage of highly integrated structure,expensive,and huge power consumption.Furthermore,all the connections at the back of a large-scale array are constrained to the same area of each antenna element.This limited space constraint presents severe engineering challenges to the antenna array with the increase of operating frequency.Therefore,starting from the radiation mechanism of phased arrays,it is necessary to explore the possible form of new array antenna to increase its design freedom and reduce the number of T/R modules.By using irregular subarray techniques,the uniformly spaced antenna array elements can be irregularly divided into subarrays fed by only one T/R module separately to reduce the cost and power consumption of the phased array.Therefore,amplitude and phase excitations of the elements in a subarray are fixed.Due to that all the elements in an irregular array are involved in radiation in contrast to those traditional thinned or sparse arrays,irregular arrays are able to achieve higher gain and angular resolution,thus having great potential to deal with the new challenges of low cost and high gain phased arrays.This dissertation takes irregular arrays as the research object and focuses on their radiation mechanism and synthesis methods.Moreover,combined with the typical system application,the design scheme of maximum spectral efficiency of large-scale MIMO base station based on irregular subarrays is also discussed.The main research content and innovation results of the dissertation are summarized as follows:1.Aimed at the synthesis problem of large-scale irregular arrays,an optimization model for irregular arrays based on maximum entropy principle is proposed.The entire algorithm is divided into two steps: Firstly,the optimal layout is optimized by using genetic algorithm based on maximum entropy principle;Secondly,the beam synthesis at the desired angle is carried out according to the fixed layout.This method utilizes the concept of array entropy to redefine the irregular array from another dimension,thus decomposing the original complex problem into two relatively simple problems and greatly improving the efficiency of the whole optimization process.2.For solving the problem of smaller interelement spacing of the tightly coupled wideband phased arrays,a sparsely excited tightly coupled array based on irregular subarrays is developed for the first time.While saving half of T/R modules,the proposed array is still able to achieve ?60° scanning in 8-12 GHz and the performance remain unchanged in the range of ?30° scanning.The T/R modules spacing of this sparsely excited tightly coupled array is 0.576 times the high frequency wavelength,which successfully solves the problem that tightly coupled array interelement spacing can not greater than half of the highest frequency wavelength.Hence,this technique has the potential to overcome the installation difficulties of connectors at higher frequencies,and is also beneficial to reduce the number of high cost of T/R modules and the cooling module design difficulties.3.Two synthesis methods for low thinned factor high-gain irregular arrays is presented.Firstly,after fully analyzing the radiation mechanism of irregular arrays,it is concluded that the relative wave path difference is the fundamental reason for the reduction of the directivity when irregular arrays scanning at large angles.The larger size of subarrays and the wider scanning angle will inevitably enlarge relative wave path differences,thus resulting in the reduction of directivity.For limited field of view applications,the directivity at large angle scanning can be improved only by optimizing the shape of subarray and array layout.In addition,in view of the wide angle scanning applications,through the unequal phase feeding for the elements in a subarray and the design of end-fire pattern,directivity in large angle scanning can be greatly improved.Compared to traditional phased arrays with same number of T/R modules,the proposed irregular array can achieve a benefit of nearly 3d B gain over the entire scanning range.4.A new one-dimensional irregular array structure for 5G base station platform is invented.Aiming at the mixed arrangement of different sizes of subarray with thinned elements,a mixed integer second-order cone programming model is established through convex analysis and transformation.At the same time,the generalized Benders decomposition algorithm is innovatively introduced to decompose the original complex problem into several simple problems,thus realizing the rapid solution of large-scale onedimensional irregular array layout problem.The irregular subarray partitioning strategy is based on the active coefficient and active pattern of each element obtained from the full wave simulation of finite array.Considering the effect of the joint effect on the realizable gain,all the degree of freedom are used to achieve the improvement of final performance.5.Finally,for the next generation MIMO array,irregular subarrays are innovatively introduced into traditional full digital beamforming(DBF)arrays and hybrid digital beamforming(HBF)arrays.The transmission models of full digital irregular array(FDIA)and hybrid digital irregular array(HDIA)are established,respectively.A minimum mean square error(MMSE)method has been applied to optimize the layout of irregular arrays.Numerical simulations show that the irregular array architecture outperforms conventional DBF and antenna selection architecture under the same power constraint and number of RF chains.