A small antenna robust to metallic object inserted into antenna body

In this paper, an antenna which is robust to a metallic object is proposed. A metallic object is placed in the vicinity of the antenna, where a part of it is inserted into the element. The fluctuation of resonant frequency and reflection S11 are negligibly small in proposed antenna when the metallic object is placed symmetric. Furthermore, metallic object placed symmetric doesn't have influence on radiation pattern of the proposed antenna.