雙頻帶圓極化天線及雙頻帶高隔離度多重輸入多重輸出天線設計

Abstract

本篇論文提出兩種類型天線之設計。一是雙頻帶圓極化天線之研究，另一主題是探討高隔離度之多輸入多輸出天線 首先，針對第一個主題，由螺旋型圓極化天線做為理念，我們將以簡易的圓型分支路徑，使電流流向為圓形，產生圓極化之效果之天線。以不同分支使共振頻帶達到雙頻，再藉由主要路徑電流流向產生圓極化。除此之外，面臨正 Z 軸左手圓極化增益較小之問題，我們在背後基版增加一圓形貼片，將此圓型貼片當作反射鏡面使用。將邊緣波束整體往上反射。由模擬及實驗結果證明，此貼面確實可增加一部分之增益。 另一個主題，在此我們討論一種增加天線之間隔離度之方法，一般多輸入多輸出之天線，天線之間存在著很高的耦合量，對於訊號之傳輸有著干擾，為避免此問題，文獻[1]設計是在天線之間增加一電感性分支，亦或是增加一電感性元件，在文獻[2]提出，在接地面上設計一槽空，使其達到提高隔離度之效果。我們將參考之前論述，簡易的在接地面適當位置做出幾個凹槽，此凹槽可等效為電容電感元件串聯，當在適當頻率共振時，可視作此凹槽在輻射一部分能量，阻隔兩天線之間輻射之干擾。 此兩支天線皆設計在2.5GHz及5.2GHz，以供無線區域網路頻段之應用。

This paper proposes two designs of antennas. One is the research of the dual band circularly polarized antenna and another design is dual band high isolation multi input multi output (MIMO) antenna. For the first topic, according the spiral antenna, we designed the circularly polarized antenna with circular strips. It made the current go to circular paths. To improve the Left Hand Circularly Polarization (LHCP) gain at positive z axial. We added a circular pad on the back of the substrate. From the simulation and measurement, it observed that the LHCP gain enhanced, really. Then, another topic, we discussed the method to enhance the isolation between two port antennas. According some reference, high isolation was achieved by etching slits into the ground plane[2]. Ground branches were applied in to achieved low mutual coupling within a narrow frequency band. Parasitic elements were added to improve the port isolation of a MIMO antenna[1]. In this work, we studied the slot line on the ground, the slot line could equivalent to RLC series circuit, when it at resonant frequency it could radiate to decouple the two elements antenna. The two proposed antennas are designed at 2.5GHz and 5.2GHz, they could be applied on wireless communication.