無線人體區域網路之超寬頻-場型分集天線之小型化設計

Abstract

本篇論文設計一支可運用在人體區域網路系統當中的人體無線通訊系統 (Body Wireless Communication System；BWCS)，其高度為0.64公釐且半徑為20公釐圓板狀的新型平面式微小化之超寬頻-場型分集 (UWB-Pattern Diversity) 天線。其操作頻段滿足美國聯邦通訊委員會所認定的 3.1 GHz -10.6 GHz 超寬頻帶。在天線設計當中吾人經由微帶傳輸線輸入端，再利用耦合方式至非共平面漸近式開槽天線 (non-coplanar tapered slot antenna) 結構，使槽狀天線呈阻抗漸近改變來達成寬頻的效果。同時，為了適用於人體的各種行動姿勢及各種環境下，將具備兩埠端的場型分集型式，以確保人體之間的通信可靠度。其架構創新為一對非共平面漸近式開槽天線，在底部的內部漸近邊共用一個橢圓型接地面，可解決以往共面結構當中的漸近邊之輻射體結構重複設計，如此可達成小型化且降低成本的實際需求；且非共平面漸近式開槽天線單元之間呈相互垂直，使非共平面漸近式開槽天線單元間之電流路徑互為正交，所產生之天線輻射場型達成場型分集的效果；並能夠保證兩支非共平面漸近式槽狀天線能夠相互降低干擾，提高兩支非共平面漸近式槽狀天線間之隔離度。因為其輻射場型本身具備朝人體外，且平行於人體之指向性，可應用於人體無線通訊系統。如此之輻射場型特性不需反射體結構設計，以節省整體天線體積。其輻射場型增益約在3 dBi~6 dBi 之間。 最後，為了改善超寬頻–場型分集天線因小型化設計，所產生的單元天線之間在低頻帶的高相互耦合、低隔離度的問題。因此，在場型分集天線的底部接地面中央加上M字型之蜿蜒狀槽線結構；並在非共面漸近式開槽天線的外部漸近邊之頂邊上，加上鋸齒狀 (corrugated) 的開槽結構，使天線在超寬頻段的相互耦合大小均在-15 dB之下、單元天線之間相關度係數均在-20 dB之下，使其具備良好的通道差異，並保持天線原有之特性，達到微小化之超寬頻–場型分集天線具備隔離度之最佳化。

In this thesis﹐we designed a novel planar miniaturized ultra-wide-band (UWB) pattern diversity antenna system (two elements) with its height is 0.64mm and a radius of 20 mm of circular plate﹐used for BWCS application in Wireless Body Area Network (WBAN). This antenna operates frequency range which is 3.1GHz – 10.6GHz﹐meets the U.S. Federal Communications Commission (FCC) identified the operating band of UWB. In this design﹐the proposed diversity antenna consists with a pair of non-coplanar tapered slot antenna (NCTSA) structure fed by micro-strip transmission line and used by coupling method. The tapered structure is designed for gradual variation of the impedance of the NCTSA and achieves ultra-wide bandwidth. In order to apply in various actions of human body and environment﹐we present the pattern-diversity form with two-port termination to ensure the reliability of communication between human body. The innovative design of the structure is that each side of the two NCTSA structures commonly used the same elliptic ground plane. It could achieve the demands of miniaturization design and low cost. In addition, the two NCTSA structures are perpendicular with each other. It could be ensured that two NCTSA’s current paths are orthogonal to achieve the pattern diversity﹐reduce the interfering with each other﹐and enhance the isolation between the two NCTSAs. Owing to its radiation patterns are spontaneously directional with their directions are out of and parallel with body, the proposed diversity antenna doesn’t add reflectors. Therefore, it could reduce total volume of the proposed antenna and be suitable for BWCS application. The radiation gain of the proposed diversity antenna is about 3 dBi~6 dBi. Finally, to improve the problem that high mutual coupling and low isolation between the two elements in lower-band frequency because of the miniaturized design, we add two isolated structures such as meander slot-line and corrugated structures. It could be achieve optimizations of the isolation with the values of mutual coupling and correlation coefficient between the two elements are below -15 dB and -20 dB respectively.