階梯型微帶天線之改善設計

Improved Design for Ladder-Shape Microstrip Antenna

石士平(Shih-Ping Shih)

指導教授 ： 謝東宏

義守大學/電機資訊學院/電子工程學系/碩士(2016年)

摘要

為了改善階梯型微帶天線次要輻射強度過高之問題，以提高階梯型天線的適用頻帶，本論文的做法是針對產生輻射的磁流源進行改變，在原結構加上凹槽或雙摺疊結構。其中凹槽結構會增加磁流源之數目，而雙摺疊結構使電場振幅翻轉改變磁流方向，兩種方式皆增強磁流互相抵銷之效果，次要輻射強度降低的目標就可達成。
針對這個階梯型微帶天線，本文先利用已有的理論分析與模擬軟體兩種方式探討此天線的特性，進而點出產生輻射問題之所在。而當凹槽與雙摺疊這兩種改善結構各別套用至這個天線上，兩種改善方式所得之定性分析、模擬以及實驗的數據都顯示天線三個模態的次要輻射強度都在可接受範圍之內，且主要輻射也呈現良好的狀況，所以天線是維持三頻操作之功能。而當摺疊程度不同時，共振頻率之變化並不大，這種摺疊程度在15~30%時，改善效果最佳。又在特定頻率之應用設計方面，模擬與實驗的數據結果彼此符合，所以天線可選用的頻帶是明顯增加的。
本論文是利用定性分析的方式處理改善前與後的天線參數，這樣循序漸進的方式免去複雜的計算過程且又能快速的掌握天線特性。雖然有兩種不同的改善方案，但只要定性分析的方法運用得當，不論磁流源方向以及位置，甚至輻射場狀況都能有效掌握。又定性分析、模擬以及實驗結果都相符合，不只設計理念的可被驗證，而且定性分析的方式處理天線的相關參數也具有可信度。

關鍵字

階梯型微帶天線 ； 凹槽結構 ； 雙摺疊結構 ； 三頻操作

並列摘要

In order to improve the high cross-polarization radiation and increase available frequency band of the ladder-shape microstrip antenna, this thesis uses concaved structure and double-folded structure to change the radiation magnetic currents. By the technique, the number of magnetic currents can increase due to a concaved structure, the amplitude of electric field in a cavity can also flip. Both two approaches can increase the cancellation between magnetic currents themselves, the reduction of crosspolarization radiation could achieve.
For this antenna, the thesis first uses available theoretic formulation and commercial software to investigate antenna characteristics and reveal radiation problem. As the concaved and folded structures are used, the results from theoretical, simulated, and experimental date all show that the co-polarization radiations is in a good shape, and cross-polarization radiations are within an acceptable range for three different modes. As the folded extention varies, the resonant frequency does not change too much, and the optima design occurs as the folded extention is between the range of 15~30%. As the improved technique is applied at specific frequency band, simulation and experiment agree with each other, so that the available frequency band obviously increases.
This thesis also uses theory to process parameters of antennas before and after improvement. The method in thesis is straight-forward and simple, antenna characteristics can be obtained without any problem. As long as the improved technique can be applied properly, the direction and position of magnetic currents, and even
radiation can be handled effectively. Since theory, simulation, and experiment all agree with each other, not only design concept is verified, but the data from theory is also convincing.

並列關鍵字

Ladder-shape microstrip antenna ； folded structure ； concaved structure ； tri-band operation

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