http://docs.google.com/viewer?a=v&q=cache:o4L9mrY3KxoJ:see.xidian.edu.cn/microwave/jcja/science3/Ch6.pdf+%22%E5%BD%AD%E5%8A%A0%E5%8B%92%E5%8F%98%E6%8D%A2%E6%9C%AC%E8%B4%A8%22&hl=zh-CN&pid=bl&srcid=ADGEESiyTiGk0xbuJ-6n7Tg_72FBmowWkM1cd8VuMb9ssfXR4cd4RisW6waAIxUaV9DpDpStDoaii5M_Zuhijt9i9LL0sQ6N-hPmde3L8y3XOZvXQS1Vndyl6w6emY0_SahwEGaQpkzJ&sig=AHIEtbRGAWxQESn1b4t04ErbWYmmQCXjPA