應用於手持行動裝置之複合型多頻天線設計

Abstract

本論文旨在小型化行動裝置天線之研究，包含小型化寬頻天線以及整合於金屬機殼兩方面的應用。本研究所提出的天線設計，均具備結構簡單、製造與整合容易、低成本，以及良好的阻抗匹配、穩定的輻射場型與良好的輻射效率等特性。 首先，就行動裝置應用方面，由廣泛應用之單極天線技術開始，探討雙導體單極天線的共振模態，討論其兩共振模態間可結合與無法結合之情況條件，觀察發現在雙導體單極天線上除了基礎的四分之波長共振外，會產生一個二分之波長的共振，適當調整此共振模態有助於兩共振模態間的結合，並提出模態結合時的等校電路及無法結合時的解決方案。接著，利用此方法設計出一種具有寬頻及小尺寸之四導體單極手機天線，藉由適當地選擇相關變數達成多頻操作頻率，涵蓋 800 MHz 到 1000 MHz 及 1600 MHz 到 2500 MHz，其天線所需的淨空區域僅 7 mm，小於文獻中其他的天線設計，非常適合於手機應用。此外，亦利用電容性耦合可使多個共振模態結合以增加頻寬之方式，設計出應用於USB Dongle之小型化數位電視寬頻多導體單極天線，由實驗量測結果顯示，該天線的操作頻帶涵蓋 400 MHz 到 1200 MHz，頻寬達 800 MHz，不僅可涵蓋數位電視頻段，且可以一併支援應用於行動電話700 MHz 到 960 MHz 的頻段。 再者，由於行動裝置的堅固耐用性及外型美觀，金屬成為不可或缺之元素，但金屬接地面靠近天線會直接影響傳統天線特性，例如單極天線或是平面倒F天線。本論文提出一種結合單極天線與槽孔天線所組成之複合架構，可結合於手機大面積之金屬背蓋。此結構將單極模態與槽孔模態結合達到高頻寬頻效果，由實驗量測結果顯示，該天線的操作頻帶在低頻涵蓋LTE700頻段，而在高頻頻寬可達 2500 MHz，涵蓋 1700 MHz 到 4200 MHz，此高頻頻寬優於文獻中其它的天線設計涵蓋1700 MHz 到 2700 MHz。 此外，金屬邊框手機的外觀亦頗受歡迎，然而於其它文獻中數據顯示，連續無斷點之金屬邊框環繞於傳統天線會導致Q值提高，影響天線頻寬及輻射效率，所以市面上金屬邊框手機均有斷線，不但影響外觀且降低手機機構強度。本論文亦提出一種是適用於無斷線金屬邊框之雙槽孔寬頻手機天線，訊號由天線饋入端饋入後，先通過耦合饋入線支段，激發T型開路槽孔天線，再進入單極天線支段，此饋入結構不僅能提供阻抗匹配之外，同時也可成為主要的輻射體天線之一，除了可提供高頻頻段的共振輻射外，還是另一個耦合饋入結構，激發U型槽孔天線。結合兩槽孔天線達成寬頻的特性。由實驗量測結果顯示，該天線的操作頻帶可涵蓋790 MHz 到 1000 MHz，1550 MHz 到 2700 MHz，以及3300 MHz 到 3900 MHz。同時，也對於使用者手握金屬邊框手機時的影響進行探討，發現內置T型開路槽孔可有效降低使用者手握對天線之影響，提升使用者手握時的通訊品質。 最後，由於行動通訊系統種類日益增多，使用者對於資料的傳輸量要求也日提高，為了因應高速傳輸速率的要求，技術規範機構 3GPP介紹兩項嶄新技術規範，其為多用户多入多出技術(Multi User - MIMO)與載波聚合(Carrier Aggregation)，所使用的天線須同時涵蓋多個所使用的頻段。本論文提出一種小尺寸全頻段天線，結合超寬頻天線(Ultrawideband antenna)在高頻寬頻的優點，及偶合饋入結構在低頻的優點，設計出一種可以涵蓋現今所有手持行動通訊系統頻段的寬頻天線，由實驗量測結果顯示，該天線的操作頻帶可涵蓋690 MHz到1160 MHz與1600 MHz 到 6000 MHz。 比較模擬設計與實作量測結果，包含反射損失、輻射功率、天線增益，均具有良好的一致性。

This dissertation is focused on the design of the novel compact antenna development for handset applications. These antenna designs have the merits of simple in geometry, easy for manufacture and integration, low cost, and exhibits good radiation efficiency. Firstly, the common multi-strip structure of monopole antennas was classified. A comparison of the advantages of multiple-strip design with merged modes, and identified the root cause of modes failing to merge are presented. Based on these observations, a half wavelength mode exists on dual-strip monopole antenna is found, in addition to the fundamental quarter wavelength modes. This half wavelength mode can facilitate mode combination. To explain the mutual coupling effect occurred between any two adjacent traces of the dual-strips monopole antenna for modes mergence, a conceptual equivalent circuit is proposed. This dissertation also provides a layout configuration for exciting the half wavelength mode to resolve the issues preventing non-merged modes from achieving a continuous impedance bandwidth and compact size in proximity to the ground. Hence, a ground proximity multiple-strip monopole antenna with 7mm no-ground area for mobile phones applications is developed. Besides, a small size forked shape multiple-strip monopole antenna with 86% impedance bandwidth is proposed for DVB reception and mobile services applications. Secondly, the material design of metal has become popular and increasingly important. However, the bandwidth and radiation efficiency of conventional antennas in handheld devices tend to decrease when the antenna is in proximity of metal or surrounded by a conducting edge, which affects the impedance matching considerably and renders restoring the performance by adjusting the antenna parameters difficult, examples of these include the monopole antenna, planar inverted-F antenna (PIFA), and inverted-F antennas (IFA); these antennas are widely used in handheld devices. Hence, a compact multi-band antenna is proposed for metal casing mobile phone applications. This structure can generate four resonance modes, including two slot modes and two monopole modes. The advantage of proposed structure is to obtain wide bandwidth (1700-4200MHz) on the high frequency to cover the mobile broadband services. Moreover, a compact dual-slot antenna is proposed for full metal rim application. The dual slots are designed for generating several resonance modes, including loop mode, slot mode, and monopole mode. Each slot can support resonance at low and high frequencies simultaneously achieving a wide impedance bandwidth. In addition, the practical situation is also considered. The energy absorbed from a handset by the human hand is a critical concern because it can alter the radiation pattern and cause considerable degradation of phone performance, particularly in a metal rim handset. The proposed inner slot prevents this issue. Finally, to address the dramatic increase in the demand for mobile broadband services and to support wider transmissions bandwidths of multiuser MIMO (MU-MIMO) and carrier aggregation (CA) functions that fulfill the extremely high data throughput requirements of devices, a multiband and wideband antenna with UWB feeding structure is proposed. This antenna is integrated the advantages of the UWB antenna at high frequency and the coupled-fed structure at low frequency. The proposed structure can obtain a wide bandwidth at low and high frequency to cover all of the handset broadband applications.