| Abstract: | 隨著無線通訊技術的快速發展，無線通訊應用也越來越廣泛。為了兼容多個通訊系統的標準，對於雙頻或是多頻天線之需求也與日俱增。而傳統的多頻天線通常以分集或是植入槽孔的設計架構，容易有體積大、占空間的問題。
本研究以全平面式的結構與直接饋入的方式來設計天線，使其與基板較易整合，採用厚0.8mm的FR4基板，以相對介電係數(Relative Permittivity)為4.4，Dielectric Loss Tangent為0.02，來進行模擬並和實驗相驗證，設計兩種雙頻天線架構，其涵蓋應用範圍包括PCS/WCDMA1900、PHS、TDS-CDMA、WCDMA/IMT-2000、WLAN(802.11a)和WLAN(802.11-a/b/g/n)。
首先，回顧操作在1/4波長的平面單極天線，以此作為天線的初始結構，為了進一步縮小天線的尺寸，吾人深入比較平面倒L型天線與平面倒F型天線的特性，並且嘗試將兩個倒F型天線以背對背的方式，形成π型天線，且探討此π型天線的特性，並針對倒F型天線的窄頻缺點進行改善，使在低頻帶呈現寬頻效果。接著，進一步縮小尺寸，以設計出具實用價值的WLAN雙頻天線。
一些天線原型的實作量測結果與模擬皆非常相近，頻寬方面，分別可使低頻段(WCDMA/IMT-200)頻帶的頻寬由8.78%增加至21.11%；高頻段WLAN頻帶則可由原來的9.27%增加至17.15%。輻射場型的部分，實測結果顯示其H-plane(XZ-plane)在各個共振頻率點上均能有不錯的全方向(Omni-Directional)輻射場型特性。
With the rapid development of wireless communication technology, applications of various wireless communication are wide spread. For those communication systems to be compatible with multiple standards, dual and/or multi-frequency antennas are continuously increasing in demand. The traditional multi-frequency antennas usually require multi-path architecture and/or slit design, which tend likely to occupy a relatively large volume.
In this study, uni-planar structure with a coaxial feed is utilized to design the antennas so that it is easy to integrate with the PCB. The FR4 substrate with thickness 0.8mm is used, while the relative dielectric constant of 4.4 and loss tangent of 0.02 is used for simulation. Experiments are conducted to verify the design of the dual-band antenna structures that cover the frequency bands of PCS/WCDMA1900, PHS, TDS-CDMA, WCDMA/IMT-2000, WLAN (802.11a) and WLAN (802.11-a/b/g/n), etc.
At first , the planar quarter-wavelength monopole antenna serves as an initial structure studied in this thesis. In order to reduce the antenna size, we compare the characteristics of the inverted L antenna and the inverted F antenna, and then examine the π-shape antenna, which can be viewed as resulted from two inverted F antenna with back to back, and to explore the characteristics of π-type antenna to overcome the narrowband shortcoming of the inverted F antenna. In addition to the bandwidth-broadening in the low-frequency band, we further introduce parasitic elements to achieve the a dual-band WLAN antenna design. Finally, try to reduce the size of the new design.
Several antenna prototypes are fabricated, while the measurement results show very good agreement with the simulation. As the bandwidth concerned the low-frequency (WCDMA/IMT-2000) bandwidth is increased from 8.78% to 21.11%, while the high-frequency WLAN bandwidth is increased from 9.27% to 17.15%. For the radiation patterns, experimental results show that the H-plane (XZ-plane) reveals a omni-directional characteristics at various frequencies. |
