已知空气中电偶极子辐射的远场如下式,则波阻抗是( )<img src="https://static.zxtiku.com/wangke/imgs/topic/6fe4bf7a3d02de62e2a80f14a1fa4147.png"/><img src="https://static.zxtiku.com/wangke/imgs/topic/a12bd4ec81963ae7b8fe92cff89d6f27.png"/>