Ferrite sheet loaded PIFA for critical couping

A method which can achieve the critical coupling of PIFA is proposed. It is accomplished by only attaching the ferrite sheet without changing the structure of the antenna. It is modeled by equivalent circuit based on transmission line modeling and the critical coupling can be confirmed by Smith chart of the antenna. The proposed antenna is verified by 3D EM simulator. The ferrite sheet loaded PIFA can easily attain to critical coupling and it has sufficient bandwidth, 880–1040 MHz (VSWR≪2).