針對一個小型行動裝置的MIMO天線(e.g.2X2)，在空間有限的情況下，本論文提出一種雙頻的MIMO天線，且利用非對稱的結構來提高其隔離度的設計。 此MIMO天線由兩個具有類似結構(但有差異)的天線元件組成，天線元件的結構為一個以偶極天線當負載的狹縫(slit)，其中激發槽狹縫將負責高頻帶(5GHz-6GHz)的輻射，偶極負載則負責低頻帶(2.4GHz)的輻射，另一個天線元件則反其道而行，其激發狹縫負責低頻帶的輻射，偶極負載則負責高頻帶的輻射。 本論文針對厚度為0.8mm的FR4基板(相對介電係數為4.4)進行天線設計，模擬與實驗結果皆顯示，此一創新結構將可使隔離度更加提升(相較於對稱結構)，其原因在於負責相同頻率輻射的兩個天線輻射體，具有不同的幾何結構(分別為狹縫及偶極金屬導線)，導致輻射體之間的互耦量減少之故；此外，針對此一雙頻的MIMO天線，吾人使用一種系統化的天設計流程，此一流程是結合了直交表(orthogonal array; OA)和響應表面模型(response surface modeling ; RSM)的技術，非常適合針對此一非對稱高隔離度MIMO天線進行優化設計。 For the design of MIMO antennas (2x2 for examples) of a small mobile device with limited space, this thesis proposes a dual-band MIMO antenna design, and the use of non-symmetrical structure to improve the isolation of the elements. The proposed MIMO antenna consists of two similar (but yet different) elements. Both elements are in the form of the slit loaded with a dipole antenna. For one element the slit is responsible for the high-band (5GHz-6GHz) radiation, and the dipole is responsible for the low-band (2.4GHz) radiation. For the other element, the design logic is the opposite, of which the slit is responsible for the low-band (2.4GHz) radiation, and the dipole is responsible for the high-band (5GHz-6GHz) radiation.
In this thesis, the above MIMO antenna is assumed to reside on an FR4 board of the thickness of 0.8mm (relative dielectric constant of 4.4). Both simulated and experimental results show that the innovative structure can improve the isolation (as compared to the symmetric structure). Since the antenna radiators that are responsible the same frequency band have different geometries, and they are slit and dipole wire, respectively, such that the mutual coupling between them is reduced. Furthermore, for the proposed dual-band MIMO antenna, a systematic scheme is employed to carry out the antenna design instead of trial and error. The design scheme utilizes both the technology of orthogonal array (OA) and response surface model (RSM) and is well suited for the optimization design process to achieve the high isolation for the asymmetric MIMO antenna.
