雙頻與壓抑後波瓣之高增益行波天線設計

Abstract

本論文將提出兩種行波天線設計，第一種設計是雙頻可回授式之半模基板合成波導洩漏波天線，其操作頻率為5.2 和5.8 GHz。傳統的洩漏波天線，通常會在天線的尾端接上一個負載，讓殘餘未輻射的能量不會反射，減少反射波，以壓低後波瓣。並且傳統的洩漏波天線，天線長度必須要到一定的長度，才能讓能量有效的利用，所以天線的面很大。而回授式之半模基板合成波導洩漏波天線，可以藉由回授網路，讓殘餘未輻射的能量再回到天線，可以增加增益。而天線的長度也可以變得比較短，不但有效率地使用能量，也相對的減少使用面積。第二種設計是單一導體行波天線的改良設計，此天線容易實現高增益以及寬頻的特性。由於單一導體帶第一高階模的行波天線的基本物理特性為完美電牆(perfect electric wall)中心對稱，縱向電流為奇對稱分布，而橫向電流為偶對稱分布，所以藉由平衡轉非平衡轉換器饋入激發，使單一導體帶第一高階模之行波天線具備寬頻以及高增益的特性。並且單一導體帶第一高階模之行波天線的正規化相位常數β/k0 在其頻寬內都相當接近1，所以場型幾乎為水平方向(end-fire)的輻射場型，但其場型會有後波瓣而可能會對後端電路造成輻射干擾，所以利用調整天線寬度的方法，以壓低後波瓣，讓天線場型有顯著的改善，不會對後端電路產生干擾。

In this thesis, a dual-band half-mode substrate integrated waveguide(HMSIW) traveling-wave antenna(TWA) with feedback network and a single-conductor tapered strip traveling- wave antenna are proposed. The classical TWAs are always terminated at the end of antenna. Because the remaining power reflected from the end of TWA may excite back lobe to spoil the radiation pattern. Otherwise, its longitudinal length requires 5~10λ to radiate efficiently, and it will occupy too much space to fabricate in low price. In our first design, using feedback network of HMSIW TWA allows the remaining power which is non-radiating to re-radiate, it can not only enhance the gain of TWA but also suppress back lobe level. The length of HMSIW TWA with feedback network requires only 1~2λ, which is shorter than the classical TWAs, it would also reduce the area. In our second design, the improvement of single-conductor strip TWA is easy to achieve high gain and broadband performance. For the first higher mode in this structure, a virtual perfect electric wall is assumed at the center of the strip, which means that the longitudinal currents are odd-symmetric and the transverse currents are even-symmetric with respect to the center. A wide-band microstrip balun to feed this structure is needed to excite the first higher leaky mode. The normalized phase constant is very close to one in the space-wave leaky region. We observed that the main beam of this antenna is almost fixed at the end-fire direction in the operation band. From the radiation pattern of this structure, we find that the back lobe is very large, its radiation may interfere the circuits which are behind the antenna. So we taper the width of the single-conductor strip TWA to suppress back lobe level. After tapering the width of antenna, we can observe the improvement on the back lobe level.