主動式微帶洩漏波天線陣列之研究

Abstract

本篇論文主要是著重於主動式微帶洩漏波天線陣列應用於波束掃瞄的功能。 一般相位陣列天線(Phased antenna array)在從事二維掃瞄時須要二維的相位陣列天線以及移相器﹐或者利用基座馬達來進行二維掃瞄, 不僅體積大不夠輕巧而且價格昂貴。本論文結合了微帶洩漏波天線在第一高階模的操作頻率下具有波束頻率掃瞄 (Frequency Scanning, H-plane Scanning) 的特性與無移相器之一維主動掃瞄天線陣列( E-plane Scanning) ﹐提出一個新型無移相器之一維主動天線陣列來實現二維的波束掃瞄理念。 本論文在於將微帶洩漏波天線應用於主動天線陣列中以完成二維掃瞄無移相器之一維主動天線陣列﹐所以一開始我們先研究微帶洩漏波天線﹐從歷史文獻中找出合適的饋入結構以便有效的激發微帶洩漏波天線的第一高階模﹐並且有效地抑制微帶洩漏波天線主模的激發﹐同時我們也進行壓控振盪器以及匹配網路的研製﹐並將壓控振盪器與微帶漏波天線透過匹配網路結合起來﹐成為單一單元之主動天線。利用壓控振盪器來控制操作頻率﹐實現波束頻率掃瞄。接下來﹐我們研製天線單元之間的耦合網路﹐以實驗的方法找出恰當的耦合係數。主動天線單元之間的注入信號透過耦合網路耦合到相鄰的天線單元﹐利用末端壓控振盪器來進行E-plane 的波束掃瞄。對４單元的主動微帶洩漏波天線而言﹐實驗結果表明當操作頻率從8.24 GHz改變到9.15GHz﹐主波束可以連續地從 68° 掃到 40° 。當微調末端壓控振盪器的操作頻率時﹐主波束可以在一角錐面上進行水平掃瞄掃瞄角度可從 -26° 到 +10° 。 此外﹐我們也嘗試將各種不同饋入結構﹐比如CPW-CPS, CPW-Slot Line, Aperture Feeding等﹐應用於主動微帶洩漏波天線的電路□﹐以提供電路應用的多元性。另外，因為甘式二極體(Gunn Diode)有著比三端元件都高的截止頻率，所以它是最適合作高頻單石(Monolithic)微波源的器件。所以，一個使用甘式二極體的X頻帶共平面轉槽線饋入之對稱結構雙單元主動微帶洩漏波天線陣列被成功的製造出來。當改變其中一個甘氏二極體的操作偏壓時﹐天線陣列的操作模式可以在奇模與偶模之間切換﹐輻射場型也隨之改變。此種雙單元主動背對背微帶洩漏波天線陣列可激發出對稱的雙波束﹐因此這種天線陣列可應用於汽車的防撞系統上﹐更由於此電路無須挖洞穿孔(Via Hole)﹐且甘氏二極體是兩端元件﹐所以此電路可以用到更高的頻率及MMIC的製程。

This thesis demonstrated an active phased array design for electronic two-dimensional beam scanning using a phase-shifterless linear one-dimensional active leaky-wave antenna array. The varactor-tuned voltage controlled oscillators (VCOs) and coupling network are implemented in this array. Three coupling networks are designed and compared for optimum coupling strength between each VCO elements. Here, we demonstrated an asymmetric microstrip line fed linear active phased antenna array with two-dimensional beam-scanning capability without using phase shifters. The coupling transmission line enhances the mutual synchronization of the active antenna array. The controlling of the free-running frequency is achieved by tuning the varactor's DC bias, which also gives an additional advantage of fine tuning the scanning angle of the array. The measured pattern of a 4×1 active leaky-wave antenna array shows that the main beam can be continuously scanned from 68°to 40°in elevation as the frequency varied from 8.24 GHz to 9.15 GHz. This is equivalent to over 10% electronic tuning bandwidth. By tuning the free running frequencies of the end elements, the main beam can be continuously scanned from -26°to +10°from broadside with azimuth symmetry in a conical scan manner. Beside, we also used the other feeding structures (for examples, the CPW-CPS, CPW-slot line and aperture feedings) in the active microstrip leaky-wave antenna arrays for more applications. In this thesis, a new spatially power combining array using microstrip antenna as radiating elements are also be developed, which possesses two switching radiation modes. It is shown that a simple lumped element coupled oscillator theory, with compared experimental results, can predict the frequency and phase behavior of a network of two-element coupled oscillators. A two-element dual-beam back-to-back CPW-slotline fed active microstrip leaky-wave antenna array was demonstrated to verify the mode-switching phenomena. The CPW-slot has been shown to be a correct feeding structure for the excitation of the leaky mode. The dual-beam is achieved in the H-plane radiation patterns. Two-way switching phenomenon of the radiation patterns in the quasi-E-plane was achieved by controlling the dc bias of one of the Gunn devices. The initial results show a good potential of using this circuit for low cost transmitters, spatial power combiners and collision warning radar applications. Furthermore, two-terminal devices, for example, the Gunn diodes have the advantages over three terminal devices such as higher cutoff frequency, simpler bias circuit, and they are suitable for monolithic millimeter-wave integration circuit.