天線共振長度

最近設計一個天線,類似fork shaped antenna
                                                                                
左右各伸出一隻arm,
                                                                                
目前遇到一個問題
                                                                                
模擬出來的結果和計算結果是
                                                                                
左邊的arm對應二分之波長的共振點
                                                                                
右邊的arm對應四分之波長的共振點
                                                                                
老師問我為什麼會左邊和右邊對應的共振長度一個是四分之波長,另一個是二分之波長
                                                                                
目前只能回答他計算出來結果就是這樣.....
                                                                                
老師對於這個答案不是很滿意,他希望我能解釋他的電波意義
                                                                                
有人知道為什麼嗎? 是否有相關的paper在探討這種問題?(有沒有關鍵字)
                                                                                
希望有大大可以幫我解惑,謝謝