應用單脈衝振幅比較技術於定位系統之開發

Abstract

本論文提出了一種機械式掃描之振幅偵測器，其工作頻段為2.4GHz。整套系統運作以電腦程式控制，可判斷待測物所在之方位。本系統參考單脈衝系統之架構，以兩支八木-宇田天線作為接收天線。兩路接收訊號經由180°分合波器後得到和(Σ)與差(Δ)的值。透過數學證明以及電磁模擬軟體皆可發現在待測物所在之角度，(Σ-Δ)的振幅將會有一個最大值，以此將可判別待測物之方位。有別於傳統架構將Σ與Δ各別經由對數放大器處理至直流電壓(射頻處理器)，本系統使用射頻切換開關將Σ與Δ分時進入同一射頻處理器，消除傳統兩路所造成傳輸相位及振幅的誤差。此方法大幅減少微波元件之使用，包含低雜訊放大器、帶通濾波器等，可降低成本、減少系統功率消耗。此外，本系統利用NI Lab VIEW DAQ系統整合射頻電子系統與機械掃描裝置，包含控制脈波寬度調變、射頻開關切換、資料接收、後續處理運算及繪圖顯示。實驗結果證實本系統能精確的判斷來波之方位角，所有實驗量測結果平均誤差約為1.34°。

This thesis presents a new type of mechanical steering amplitude detector, operating at 2.4 GHz. The system, which can determine the direction of DUT (device under test), is automatically controlled by computer program. Using the configuration of modern mono-pulse radar system, this work uses two Yagi-Uda antennas as receiving antennas. Sum and difference patterns are obtained after rotating the receiving antennas and the signal processing by rat-race ring. It is proved mathematically and confirmed numerically that the difference between two channels will have a maximum while the boresight of receiving antenna is in alignment with DUT, which enables the system to determine the direction. Distinct from conventional configuration utilizing two independent channels for sum and difference, this research exploiting a microwave switch to combine sum channel and difference channel in different time division, and thus the inaccuracy of circuitry fabrication in two channels can be avoided. Moreover, this method can decrease the usage of microwave components such as LNA (low noise amplifier) and BPF (bandpass filter), lowering cost, and reducing power consumption. In addition, this system employs NI LabVIEW DAQ to integrate RF electronic system and mechanical scanning device, which control the pulse width modulation, RF switching, signal processing, and data display. Finally, the experiment confirms that the proposed system can calculate the direction angle of incoming wave accurately. The average measurement deviation is about 1.34 degree.