Study On Linear Dipole Array Antennas With Parasitic Elements

With the development of electronic communication technology, antennas which plays an very important role in modern communication system need to work in a very complex electromagnetic environment, so antenna arrays with low sidelobe level has strong anti-interference feature. Based on the new electromagnetic technology in recent years, in the view of the common problems in projects, in this paper we study how to control the sidelobe of antenna arrays by changing the space between antenna elements and adding parasitic array elements.This paper first introduces the basic concept of antenna array and the general analysis method, besides, the method of moments is used to model and analyse the wire dipole antenna, and the calculated result agreed well with commercial calculation software feko which illustrate the validity of the algorithm. Then standard particle swarm optimization algorithm is presented in this paper, and a quantum well is introduced to improve the search ability of the algorithm, the test functions show that the improvement is effective. At the end of the paper dipole antenna arrays which has parasitic array elements and unequal space between array elements are modeled with the method of moments and optimized by the quantum particle swarm optimization(QPSO) algorithm, the range of the space between array elements is set appropriately according the projects. And according to the arrangement of the dipole antenna elements, the flush arrangement and coaxial arrangement array are both respectively analyzed and calculated, the conclusion is that this method is essentially changing the energy distribution by the coupling of the array, so as to realize the low sidelobe characteristic. In this paper a large number of analysis calculation are made respectively according to the following four different situation,1. An active array is placed above the ground plane, the space between array elements are used to control sidelobe level of the array, without considering the coupling effect, the sidelobe level of the flush arrangement array can be reduce to-17 d B and the coaxial arrangement array can be reduced to-19 d B. While when the coupling effect is considered, the sidelobe level of the flush arrangement array can be reduce to-17 d B and the coaxial arrangement array can be reduced to-17 d B. Besides, the ground and the distance between the array and the ground also can influence the sidelobe level.2. A parasitic array is placed above the active array, and the space of the active array is unchanged, just control the array sidelobe level by changing the space of the parasitic array, and the ratio of number of the parasitic array and the active array is respectively 1,1.5 and 2. The sidelobe level of the flush arrangement array can be reduce to-20 d B while the sidelobe level of the coaxial array is-19 d B,-18 d B and-15 d B.3. For further reducing the sidelobe level, changing the space of the the parasitic array and the active array simultaneously, ratio of number of the parasitic array and the active array is 1,1.5 and 2. In this situation, The sidelobe level of the flush arrangement array can be reduce to-20 d B while the sidelobe level of the coaxial array is-20 d B,-20 d B and-16 d B.4. For the irregular ground problem, a layer of parasitic array is used to replace the ground, the whole array similar with the quisi-yaga antenna arrays. In this situation the sidelobe level in the upper half space is easy to be reduced to-20 d B.Through all the analysis and calculation in the paper, using this method to control the sidelobe level of the array is feasible, and this method works better when the dipole arrangement is coaxial. At the end of the paper according to the optimized analysis results, an array with feeding structures are established in the computing software HFSS, among them, the parasitic array is equivalent to a layer of metamaterials structure, the active array is built as a printed dipole array, the result is very consistent with the method of moments, which verified the correctness of the calculation results in this paper.