隨著軍事技術以及現代探測技術的發展，戰鬥機在匿蹤外型設計上變為相當重要。傳統戰鬥機皆以敏捷的空氣動力外型設計為主要訴求，但現代為了要提高戰鬥機的視距外作戰能力及生存能力，先進戰鬥機不僅要具有良好的氣動特性，而且同時要具有低可被探測性。但由於匿蹤外型設計會限制其氣動特性及機動性，故要在兩者之間取得最佳的折衷。首先本研究以參考F-22建置匿蹤戰機外型，而進氣道口及噴嘴出口以金屬板覆蓋封閉以簡化模型，並利用ANSYS HFSS高頻電磁模擬軟體，以1 GHz (L-Band)雷達波，電場極化方向為水平極化，戰機表面設定為完美電導體材料，使用動差法(Method of Moment, MOM)求解，模擬分析F-22匿蹤戰機模型的單站及雙站雷達散射截面。其次為探討戰鬥機的常見外型部件中，各部件對於匿蹤戰機雷達散射截面的貢獻度，以F-22戰機外型的單站雷達散射截面結果為基礎，分別與去除機翼、去除水平尾翼和去除垂直尾翼之單站雷達散射截面結果進行差異比較，得出其垂直尾翼的貢獻度最高。本研究將F-22匿蹤戰機之垂直尾翼外傾角進行參數化研究，結果發現單改變垂直尾翼外傾角並未有較好的匿蹤效果。因而參考YF-23及近期巴黎航空展展出的Future Combat Air System (FCAS) 第六代戰機設計，上述戰機結合垂直尾翼及水平尾翼功能成V型尾翼設計。將F-22匿蹤戰機去除垂直尾翼，改變F-22水平尾翼傾斜角度，進行V型尾翼設計參數化的雷達散射截面分析。最終分析結果發現匿蹤戰機V型尾翼外傾角大於50°之設計能有效縮減雷達散射截面，達到更佳的匿蹤效果，相比F-22原型戰機，平均雷達散射截面可降低約5 dBsm。
以上探討外型設計時皆以金屬板覆蓋進氣道口及噴嘴出口之簡化模型，並無考慮進氣道對於雷達散射截面的影響。然而進氣道之設計卻是對於匿蹤戰機非常重要的一環，由於進氣道為管狀空腔，會產生空腔效應 (cavity effects)造成雷達波多次反射後，威脅到前向關鍵區域，使得敵軍更容易偵測且預防來襲戰機，故本研究建立具有進氣道設計的F-22模型，並進行分析具有進氣道與將進氣道填滿兩者之間的雷達散射截面差異。明顯得出具有進氣道之模型前向雷達散射截面較大，由於進氣道會造成空腔效應，即使F-22之進氣道已採用S型進氣道設計，但還是會有些微地導致雷達回波產生，大約增加10 dBsm。

In this thesis, Radar Cross Section (RCS) analysis of F-22 is performed to study how to design aerodynamic components of stealth fighter design. F-22 model used in this study is a simplified one that its inlet and nozzle are blocked with metal plates. The RCS of F-22 at 1 GHz horizontally polarized radar wave from different directions are analyzed by using Method of Moment (MOM) in ANSYS HFSS high frequency electromagnetic simulation software. All the surfaces are assumed to be perfect electric conductor in the simulation. In this study, RCS contribution of each exterior components of F-22 are discussed. The results show that the vertical stabilizers have the highest contribution among all. It is also found that the tilt angle (27°) of current F-22 vertical stabilizers is verified to be optimized tilt angle for its minimum RCS. In the mean time, a new V-tail design is introduced to reduce RCS of stealth fighters. RCS analysis of different tilt angles of V-tail design are performed. The results show that the V-tail tilt angle more than 50° effectively reduces its RCS and gets better stealth effects. Compared with the baseline F-22, the average RCS can be reduced by about 5 dBsm. In this study, a F-22 model with an inlet design is also established to study the RCS difference with and without inlet cavity effects. The results show that the forward RCS of the model with the inlet is larger, because of the inlet cavity effects. The forward average RCS of the model with the inlet is higher by about 10 dBsm.

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