合成孔徑雷達(SAR)和逆合成孔徑雷達(ISAR)是基於雷達技術的重要應用領域。本研究旨在利用有限時域差分法(FDTD)對ISAR進行研究。在研究動機部分，我們回顧了SAR和ISAR的歷史發展。SAR最早於1951年被提出，並在1953年獲得第一幅測量的影像。而ISAR則是基於SAR技術發展而來，旨在實現飛行器、船舶等目標物體的高解析度圖像。
在本研究中，我們使用ISAR和FDTD模擬方法對不同目標進行掃描。首先，我們對一個點和兩個點進行掃描，結果顯示，無論使用ISAR還是FDTD模擬的ISAR，都能成功成像出一個點或兩個點。其成像結果與實際距離大致相符。
接下來，我們將目標物改為飛機，利用ISAR和FDTD模擬的ISAR進行掃描。結果顯示，ISAR能夠成功重現出飛機的輪廓，而FDTD模擬的ISAR僅能大致描繪出飛機樣子。
綜合比較ISAR和FDTD模擬的ISAR，我們得出結論：對於一個點或兩個點的目標，無論是使用ISAR還是FDTD模擬的ISAR，都能成功成像出目標。然而，在處理複雜目標(如飛機)時，ISAR能夠更準確地重現出目標的輪廓，而FDTD模擬的ISAR僅能提供簡易的描繪。
這些研究結果顯示，ISAR和FDTD模擬的ISAR在不同場景中具有各自的優勢和限制。隨著雷達技術和信號處理算法的進一步改進，我們可以預期這兩種方法在未來的研究和應用中將發揮更重要的作用。

Synthetic Aperture Radar (SAR) and Inverse Synthetic Aperture Radar (ISAR) are important applications of radar technology. This study aims to investigate ISAR using the Finite-Difference Time-Domain (FDTD) method. SAR was first proposed in 1951 and obtained its first measured image in 1953. ISAR, on the other hand, is a development based on SAR technology and aims to achieve high-resolution images of targets such as aircraft and ships.
In this study, scans of different targets are conducted using theoretical ISAR and the FDTD simulated ISAR method. First, the object consisting of a single point and two points were scanned and the results showed that both theoretic ISAR and FDTD-simulated ISAR successfully imaged a single point or two points. However, FDTD resulted in double ghost image. But the center of the ghost image correctly represents the location of the object. The reconstructed images were generally consistent with the actual distances between objects.
Next, the target was changed to an actual aircraft and the image reconstruction was performed using ISAR and FDTD-simulated ISAR. The results showed that theoretical ISAR was able to successfully reproduce the contours of the aircraft, while the FDTD-simulated ISAR only provided a rough depiction of the aircraft's shape.
By comparing theoretic ISAR and FDTD-simulated ISAR, it can be concluded that both ISAR and FDTD-simulated ISAR can successfully image a single point or two-point targets. However, when dealing with complex targets like aircraft, theoretic ISAR was able to more accurately reproduce the target's contour, while the FDTD-simulated ISAR provided a simplified depiction.
These research findings indicate that theoretic ISAR and FDTD-simulated ISAR have their respective advantages and limitations in different scenarios. With further improvements in radar technology and signal processing algorithms, we can expect these two methods to play a more important role in future research and applications.

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