只使用一階藕合的小型偶極天線陣列的互藕補償方法

Abstract

本論文提出只採用相位天線陣列單元間的一階藕合常數來作為補償小型相位天線陣列互藕的方法。首先提出一個簡化且直觀的藕合機制模型，基於這個模型定出一階藕合常數，並提出使用單一量測點求出一階藕合常數的方法，再透過藕合機制模型解釋如何用一階藕合常數如同傳統方法，例如：傅立葉分解法，點匹配法等一般找到互藕補償矩陣，進而補償相位天線陣列的互藕。不是每個情況都適用一階藕合常數進行補償，本論文也會指出哪些情況能夠合理忽略高階藕合常數。 為了評估藕合補償的效果時，避免其他非理想效應出現，例如貼片天線的邊緣繞射(edge diffraction)，天線單元輻射場型不是全向性的(omnidirectional)等因素參雜其中，將情境複雜化，論文中採用半波長的偶極天線作為天線單元。 對小型的一維偶極天線陣列，不僅使用本論文提出的一階藕合常數補償法，也同時使用傅立葉分解法，點匹配法一起比較。除了利用補償前後的單元激勵場型(active element pattern)評估補償效果，也考慮了相位陣列理論的(1)改變相位-波束掃描(beam scanning)、(2)改變振幅- 卻比雪夫分布(Chebyschev distribution)等補償前後的差異。二維偶極天線陣列只使用一階藕合常數補償法。以上的情況，一階藕合常數補償法都得到良好的補償效果。 本論文使用了ANSYS HFSS進行模擬和MATLAB進行計算驗證。

關鍵字:相位天線陣列、互藕、單元激勵場型、波束掃描、互藕補償

Based on first order coupling between element within the phased array, a technique for mutual coupling compensation in small phased antenna array is presented in this thesis. First of all, a simple but intuitive coupling mechanism model is proposed. On the basis of this model, first order coupling coefficient is defined and also a method by using only one observation point to determine first order coupling coefficient is given. From the point of view of the model, it can be explained how a compensation matrix which is used in compensation of mutual coupling in phased array can be achieved by means of first order coupling coefficient, as well as that by traditional methods such as Fourier decomposition method and point matching method. Not all cases of coupling can be compensated by first order coupling method. The cases that higher order coupling coefficient can be reasonably neglected in compensation matrix are also indicated. To evaluate the performance of the compensation of coupling, avoiding other non-ideal effect, for example, edge diffraction in patch antenna, non-omnidirectional pattern, etc included in the system to make the situation more complicated, we use half -wave dipole as radiating element in an array. In the case of small linear dipole antenna array, we compare the performance of the first order coupling method, Fourier decomposition method and point matching method. For small planar dipole antenna array, only first order coupling coefficient method has been evaluated. In addition to using active element pattern with and without compensation to evaluate the performance of compensation, we also compare the compensated and uncompensated patterns in the following two cases: (1) beam steering by phase difference between elements and (2) element amplitude by Chebyschev distribution. In all the above cases, first order coupling method performs rather good. In this thesis, we use ANSYS HFSS to do EM simulations and MATLAB to do calculations and verifications.

Keywords: phased array, mutual coupling, active element pattern, beam scanning, mutual coupling compensation.