在無線區域網路的應用，需要一支可以同時在兩個頻帶進行收發的雙頻帶天線，且滿足無線通訊產品的輕、薄、短、小的訴求，達到天線尺寸縮小的目的。本論文裡提出一個S形平面雙頻單極天線，該天線被設計操作在無線區域網路規格，符合IEEE 802.11a/b/g (2400-2484MHz)和(5150-5825MHz)，本設計天線的共振路徑只有一條，而這條共振路徑可以激發出兩個模態，高頻共振模態的主要共振路徑長度為5.25GHz的四分之ㄧ波長，而低頻共振模態的主要共振路徑為2.45GHz的四分之ㄧ波長。利用HFSS軟體分析各個參數對天線特性的影響，以利於設計出最佳參數，還有分析接地板的參數，證明寬度參數的改變影響天線特性比長度參數大，此外比較模擬和量測遠場輻射場型圖，兩個輻射場型是相近的，在x-y平面， 曲線近似於圓形，在x-z和y-z平面上，呈現不完美的蝴蝶結對稱型式，因為本實驗的天線為不對稱的曲折線。
在實作方面，分別在FR4及氧化鋁為基板，設計符合WLAN，即操作頻帶為2.45和5.25 GHz的雙頻天線。FR4基板的厚度為0.8mm，相對介電常數為4.4，而氧化鋁基板的厚度為1mm，相對介電常數為9.8。實作結果和模擬分析皆非常相近，FR4基板天線的低頻頻寬為300MHz(12.5％)，而高頻頻寬為1075 MHz (20％)；而氧化鋁基板天線的低頻頻寬為400(17.3％)，而高頻頻寬為1000MHz(19.3％)。在FR4上，天線的低頻增益為2.3-3.35dBi，高頻增益為1.73-2.97dBi，在氧化鋁上, 天線的低頻增益為2-2.76dBi，高頻增益為0.15-1.55 dBi。

For the practical applications of wireless local area network (WLAN), the size of dual-band antennas, which can transmit and receive electromagnetic radiation simultaneously, is required to be small. To meet the requirement, we proposed an S-shaped planar dual-band monopole antenna which is suitable for 2.4 and 5GHz WLAN systems according to the IEEE 802.11 standards. The proposed antenna had a resonent path for the excitation of the two modes. One mode corresponded to a λ/4 radiator of 2.45 GHz and the other, 3λ/4 radiator of 5.25 GHz. To determine proper design parameters, the antenna was first analyzed by using the HFSS software. The simulation also demonstrated that the width of the ground imposed more influence on the antenna than the length of the ground did. The S-shaped antennas were realized on FR4 (εr4.4 ) and Al2O3(εr=9.8 ) substrates, respectively. The measured 10 dB bandwidths of the FR4 antenna were 300 MHz centered at 2.3 GHz and 1075 MHz centered at 5.4 GHz. And the measured 10 dB bandwidths of the Al2O3 antenna were 400 MHz centered at 2.35 GHz and 1000 MHz centered at 5.2 GHz. The gains of the FR4 antenna were 2.3-3.35 dBi for the 2.4 GHz band and 1.73-2.97 dBi for the 5.25 GHz band. And the gains of the Al2O3 antenna were 2-2.76 dBi for the 2.4 GHz band and 0.15-1.55 dBi for the 5.25 GHz band. The measured results agreed with the simulations. For the far-field radiation, the measured and simulated results were close on the x-y plane and a little different on the x-z and y-z planes.

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