微帶漏波模之孔徑耦合激發及模耦合現象之研究

Abstract

本論文探討微帶第一及第二高階漏波模之特性及其應用，包括其有效之饋入結構、微帶線間之相互耦合效應、不同漏波模間之耦合效應、以及多種天線之設計應用。整篇論文均採用頻域分析法做為微帶漏波模傳播特性分析之工具。 本論文之第一部份探討有關微帶第一高階漏波模（微帶奇次模）之特性及應用。孔徑耦合激發微帶第一高階漏波模之設計方法在此被提出。將輻射單元與其他元件以接地面隔離可提供此二部份個別之最佳化設計，因此能將微帶漏波天線之寬頻、高天線增益及頻率掃描特性充分展現。Ｘ波段之斜向及橫向天線驗證了此種設計方法。Ｋ波段之單波束及數種雙波束天線陣列與Ｓ波段基地台天線之應用亦被設計完成。結合多層結構技術的優點可提供無線通訊應用有效、簡單、多樣性以及高天線增益之設計。此外，因第一高階漏波模所產生微帶線間耦合現象亦被討論。我們發現無限長耦合微帶線間之共振現象，此現象肇因於耦合微帶線內緣之邊界條件配合微帶第一高階漏波模為場源所形成。於耦合微帶線之奇對稱及偶對稱分別產生不只一個漏波模，而這些模有相互耦合的現象。 本論文之第二部份探討有關微帶第二高階漏波模（微帶偶次模）之特性及應用。微帶偶次模之耦合現象在此被討論。此現象發生於當微帶漏波主模的色散曲線與偶次模接近時。改變微帶之金屬帶寬及基板厚度可觀察到有趣的模演化遷移現象，並由此得知偶次模間漏波模之相互關係。我們發現偶次模本身之頻域間隙乃為漏波主模與漏波偶次模發生耦合的結果。短路之共平面波導饋入與微帶線饋入方法被採用以有效激發微帶第二高階漏波模。分別激發具有漏波主模及不具漏波主模之第二高階漏波模之實驗顯示了漏波主模對第二高階漏波模天線設計之影響。

This thesis investigates the properties and applications of the first two higher order leaky modes of the microstrip, which include efficient feeding structures, mutual coupling on microstrips, coupling effect in different leaky modes, and several antenna applications. The spectral domain analysis is employed to solve the propagation characteristics of the microstrip leaky modes throughout this study. The first part of the thesis pertains to the first higher order leaky mode (odd mode) of the microstrip line. The design procedure of the microstrip first higher order leaky-mode antenna excited by aperture-coupling method is presented. Separating the radiators from other components with the ground planes provides optimal design of both parts respectively so that the inherent broadband, high gain and frequency-scanning properties of the leaky-wave antenna can be exploited. Tilted- and broadside-beam antennas are designed in X-band. Single and dual beams arrays in K-band and a base-station antenna application for S-band are also implemented. The required elements were reduced markedly in comparison with the patch antenna for higher gain design. Versatile designs combining the merits of multilayer technology offer simplicity and efficient design for many wireless applications. In addition, the coupling effects in the coupled microstrips, which caused by the first higher order leaky mode on the microstrip, are investigated. The resonance phenomena found between the strip of the infinite coupled microstrips are owing to the inner edges of the coupled microstrips forming the resonant boundary and the leaky modes of the microstrips serving as the resonant sources. For even- and odd-symmetry of the coupled microstrips, more than one leaky mode are found in both cases, and these leaky modes couple with each other. The second part of the thesis treats the subjects of the microstrip second higher order leaky mode (even mode). Mode-coupling phenomena of the even modes on microstrip is investigated. These phenomena occur when the dispersion curve of the leaky dominant mode of the microstrip is close to those of the even higher order modes of the microstrip. Interesting patterns of the migration of mode evolution, obtained by varying the ratio of the strip width to the substrate thickness, exhibit the relationships between the even higher order modes and the leaky dominant mode. The spectral gap effect of the even higher order modes is the result of the coupling between these modes and the leaky dominant mode. Design of the even higher order leaky mode as a line source should be based on the physical implications of these phenomena. Short-end CPW and microstrip feeding method are used to excite the second higher order leaky mode. Experimentally exciting the second higher order leaky mode with and without the leaky dominant mode reveals the interference between these two leaky modes.