多頻帶阻絕天線之設計與電路模型分析

Abstract

本論文提出了多頻帶的多輸入多輸出天線系統，相較於大部分的多頻天線用結構上的延伸來增加額外的頻帶，本論文以頻帶阻絕的方式來達到多頻的效果。本論文中先分析V形槽孔濾波器在傳輸線時的特性，再與超寬頻天線整合，將過V形槽孔做適當的調整後，過濾掉不需要的頻帶，即可設計出一個多頻帶的天線。此流程的優點在於天線本身不需要重新設計，只要將V形槽孔的參數重新調整後，就可以將天線做不同的應用。 除了與天線整合，我們也將同樣的概念用於提高天線之間的隔離度。兩支天線在近距離擺放時，由於共用接地面，容易產生電磁耦合的效應，造成天線匹配與效率變差，在天線共用的接地面加上槽孔，可以利用其頻帶阻絕的特性抑制電流，提升兩支天線間的隔離度。 本論文中提出了槽孔型濾波器、單極超寬頻天線以及帶阻天線之等效電路模型，由電路模型可以更加理解其工作原理，天線的部分也透過實作與模擬結果互相驗證，量測與模擬結果相當吻合。

In this thesis, a multi-band MIMO antenna system is proposed. Compared to the traditional multi-band antennas using extended geometry to obtain additional operation bands, we employed the band-notching concept to achieve multi-band operation. We started with the analysis of the microstrip line over a V-shaped defected ground structure. Then, we applied V-slots on the UWB monopole antenna. By properly designing the slot dimension, we can notch out unwanted bands to complete a multi-band antenna. Using the proposed design method, the antenna can be easily modified for various applications simply by re-designing the V-slots without changing the antenna dimension. The mutual coupling is a critical issue when two antennas are closely spaced. We also applied the band-notched slots on the common ground. The isolation of two antennas was successfully enhanced. The equivalent circuit models of V-shaped DGS, UWB monopole and tri-band notched antenna are proposed. Through the circuit model, we have a deeper insight of the working principle of our designs. The prototype of UWB monopole antenna, tri-band notched antenna and multi-band MIMO antenna system were designed, built, and tested with a very good agreement between the simulated and measured results.