不對稱共平面波導饋入槽孔天線暨雙頻圓極化L型槽孔天線設計

Abstract

本篇論文包含兩個部分，第一部分是不對稱共平面波導饋入的槽孔天線陣列，第二部分是雙頻圓極化L型槽孔天線 第一部分提出的不對稱共平面波導槽孔天線 是由一三階共平面波導帶通濾波器所改良而成，此三階共平面波導帶通濾波器是由共平面波導傳輸線及電容性凹槽所構成，本隻天線的架構系將此共平面波導之一邊的共地結構縮小，使此地的接地特性遠遜於另一邊未受影響的部分，而產生不理想接地的特性，該結構會使不對稱結構兩邊的電場也產生不對稱的現象，此一現象導致此結構原本在帶通濾波器上行走的能量輻射到空氣中進而可以作為天線之應用 此天線是由32mil的FR-4作為介質基板，操作頻率在5.2~5.8GHz之間，適合作為WiMAX及WLAN基地台之應用。 第二支天線是一隻操作於1.5~1.7GHz及2.4~2.5GHz的雙頻圓極化天線，此一天線是在接地面製作出兩組L型槽孔，並於表面上使用一倒C型結構微帶線饋入，此一微帶線之垂直轉角之結構及L型槽孔之結構使得輻射電場變成一組隨相位變化的正交電場，此正交電場遂使天線能產生圓極化傳送波，大的L型槽孔產生1.5~1.7GHz之共振頻率，小的L型槽孔產生2.4~2.5GHz之共振頻率。 此天線能夠接收GPS L1頻段之圓極化波亦能收發於 2.4~2.5GHz頻段之無線通訊之應用(Bluetooth, WiMAX)，進而能做為整合兩組頻段之應用的天線

This thesis includes two parts of research. Part one of this thesis proposes a asymmetric type of coplanar waveguide antenna and part two would purpose a L-shape slot circular polarized antenna. In the first part, an asymmetric coplanar waveguide antenna is proposed. Manufacturing by 0.8mm FR-4 substrate, a 50mm*50mm size antenna can radiate at endfire derictions instead of broadside. The theory of band-pass filter is referred in making this antenna. Traditionally, making a coplanar waveguide transmission line would include a symmetric and large enough – can be seemed as infinite ground – ground plane. By letting one side of ground become as small as comparing to another side of ground. The unbalance ground plane makes one side of E-field weaker from another. The stronger side of E-field make the whole structure vulnerable to radiate. The second part of this thesis proposes an L-shape circularly-polarized slot antenna which works at two different frequencies. Slot antenna is always a good choice for making circularly- polarized antenna. In this work, the L-shape slot on the ground plane would cause two different linearly-polarized E-fields therefore it generates a circularly-polarized E-filed. By using the two 90 degree corner microstrip line feeding, the two linearly-polarized E-field become sameamplitude so the axial ratio of circularly-polarized E-field is low. The two different size of L-shape slot generate two different resonant frequency bands. One work at 1.5GHz ~ 1.7GHz (which covers GPS L1 band 1.575GHz) and another work at 2.4GHz ~ 2.5GHz(which covers WiMAX band of 2.45GHz ).This antenna can be used to receive and transmit circularly-polarized signal at two different frequency bands.