制定饋入低剖面天線的標準流程圖及使用反射相位萃取人造磁導體頻帶

Abstract

在設計低剖面天線時最常使用的方法就是將傳統天線和高阻抗平面組合在一起，這是因為高阻抗平面可以模擬完美磁導體的特性，而用以增加天線的輻射。但儘管如此，如何去饋入這樣的低剖面天線仍然是一個很大的研究課題，這是因為高阻抗平面雖然擁有可以近似人工磁導體的條件，但卻被頻率所限制。這代表高阻抗平面只能在特定的頻率範圍內才能擁有完美磁導體的特性，而這個頻帶就稱為人工磁導體頻帶。目前對於低剖面天線已經有了非常多且深入的研究資料，但仍然沒有一個有系統的饋入方法。有鑑於此，制定一個具有可重複性的系統方法去匹配低剖面天線就成為了我們想要達成的目的。

為了實現我們的想法，我們必須先了解反射相位，這是因為當我們談論到高阻抗平面結構時，很多研究者會使用反射相位來描述它的人工磁導體的頻帶，此頻帶位於反射相位±45°之間(其反射相位0°具有完美磁導體的特性)。儘管如此，這並沒有考慮到傳統天線的輻射場型。由於一般在定義反射相位時，最常見的是使用垂直入射的電磁波去測量，但在高阻抗平面上的傳統天線所發出之電磁波並非只有垂直入射。因此，我們的首要任務就是去了解並分析傳統天線的場型，再用以萃取人工磁導體頻帶。

A popular way to design a low profile antenna is by combining the traditional antenna with a high impedance surface (HIS), because the HIS can mimic the property of the perfect magnetic conductor (PMC) to improve the radiation. However, the way to feed the low profile antenna is still a big issue because the artificial magnetic conductor (AMC) condition of the HIS is a frequency-dependent property. It means the frequency band in which the PMC property of the HIS prevails is limited. This band is termed as the AMC region. There had been intensive research performed on the low profile antenna but there has not been a consistent, let alone identical method for feeding the low profile antenna. In consideration of that, matching the low profile antenna by a systematic way is our purpose.

To fulfill our idea, we should introduce the reflection phase first, because when talking about the HIS structure, many researchers usually characterize the AMC region of the HIS by the frequency range in which the reflection phase lies between ±45° (0° of reflection phase pertains to PMC property). However, this does not consider the radiation pattern of the traditional antenna. Because the reflection phase of the general definition is defined by the normal incident wave, the waves excited by the traditional antenna on the HIS are not all normal incident waves toward the HIS. Therefore surveying the pattern of the traditional antenna becomes the priority to extract the AMC band.