M-type Hexaferrite for Gigahertz Chip Antenna Applications

We demonstrate that Sn/Zn-substituted strontium M-type hexaferrite (SrSn_2.5Zn_2.5Fe₇O₁₉ = Sn/Zn-SrM) can provide high performance and a uniform radiation pattern over a wide frequency band for gigahertz chip-antenna applications. Saturation magnetization and coercivity were 68.5 emu/g and 46 Oe. Real parts of permeability and permittivity were 1.37 (loss tan δ_μ = 0.13) and 22.2 (loss tan δ_ε = 0.09) at 2.44 GHz, respectively. A Bluetooth Sn/Zn-SrM chip antenna has a bandwidth of 780 MHz (2.15-2.93 GHz) at S₁₁ <; -10 dB, maximum three-dimensional (3-D) peak gain of 1.25 dBi, and radiation efficiency of 60% at 2.4 GHz. Our antenna performance simulation suggests that radiation efficiency can be increased up to 98% with a low magnetic loss tan δ_μ of 0.01. 3-D radiation patterns were omnidirectional in the Bluetooth frequency range. Therefore, Sn/Zn-substituted strontium M-type hexaferrite is a promising magnetic material for future gigahertz antenna applications.