平衡饋入印刷式多頻天線及鄰近導體對天線的影響

Abstract

本論文中，我們提出兩種型式的平衡轉非平衡轉換器。其中第一型平衡轉非平衡轉換器具有寬頻的效果，缺點是兩平衡輸出端相位差會隨頻率變化。第二型平衡轉非平衡轉換器，其在兩平衡輸出端設計為對稱性的物理結構，因而可造成兩平衡輸出端相位差差180°，且不隨頻率變化，缺點是無寬頻的效果。藉由加強微帶線間的偶合效應，來改進第二型平衡轉非平衡轉換器頻寬的缺點，使達到寬頻的效果，且兩平衡輸出端相位差差180°，誤差在1%以內。 利用先前設計的兩種平衡轉非平衡轉換器，分別在平衡輸出端接上印刷式迴路天線，造成平衡饋入印刷式迴路天線。並且藉由一對寄生金屬導體與迴路天線的產生的偶合效應，來改變天線的輻射阻抗值，以達到多頻的效果。 考量在天線系統週遭有鄰近導體情況下，比較以平衡饋入印刷式迴路天線與以共平面波導饋入相同的印刷式迴路天線，導體上電流分佈與S參數所受到的影響。證實平衡饋入印刷式迴路天線可減小受使用者手部與頭部的影響，且減低人體腦部受天線輻射的傷害。

In this thesis, we propose two kinds of balanced to unbalanced transformers (Balun transformer). The first kind of Balun transformer has wide-band result, but the defect is that phase different of two balance-output ports vary with frequencies. By designing the two balanced-output ports of second kind of Balun transformer have physical symmetry structure, we can produce 180° phase different of two balance- output ports, and the phase different do not vary with frequencies. The improvement on bandwidth of the second kind of Balun transformer by enhancing microstrip couple effect carries out wide-band result, and 180° phase different of two balance- output ports, error no more than 1%. We connect printed loop antenna with the balance-output ports of the two kinds of Balun transformers to form printed loop antenna with balanced feeds. By using the couple effect of parasitic conductor and the loop antenna to vary radiate impedance, then antenna system can achieve multi-band result. As nearby conductors surround antenna system, we compare the balance-fed loop antenna with conplanar waveguide feed same loop antenna, in the influence of current distribution on nearby conductor and S parameter. It verify that the effectiveness of using balanced-feed antenna system can reduce degration of antenna due to the body effect, and decrease the harm of human brain from antenna radiation.