Miniaturised slot loop antennas on dielectric and magnetic substrates

Digital cellular handsets and other portable devices are widely used in everyday life. Therefore, it is a challenge to miniaturise antennas into very limited space inside mobile terminals. The traditional narrow band antenna miniaturisation loads the antenna with different materials, especially very high permittivity dielectric materials (permittivity is from 9 to 100). However, degradation of antenna performance and difficulty of impedance matching are the two main drawbacks to this material loading miniaturisation method. A newly-developed method is to load composite magneto-dielectric materials instead of pure dielectric ones. Applying magnetic material can improve bandwidth and efficiency performance while suppressing field confinement. Furthermore, because the characteristic impedance of magneto-dielectric material is close to the surrounding medium, it is much easier for impedance matching in a wider bandwidth. Recently, an organic magnetic material was introduced and manufactured in China. This material has stable magnetic performance and high relative permittivity and permeability. It is suitable for designing compact and broadband microstrip antennas. The research done by Chinese scholars shows that the new organic magnetic material can reduce the antenna size from approximately 32% to 40% while improving impedance bandwidth from 3.2 to 6 times compared with normal dielectric materials. A novel technology applied to antenna miniaturisation is folded patch antenna, which has been reported in the literature. The antenna patches or strips are folded in multi-layers to form a 3D antenna model. Therefore, the antenna length is increased efficiently to keep the antenna geometry more compact than the conventional planar design. The research results showed that the folded patch antenna can achieve nearly 40% miniaturisation. Moreover, decreasing the separation distance between the folded patches can lower the resonation frequencies. Instead, folded slot loop antennas fabricated on dielectric or organic magnetic substrate are reported in this paper with a consideration of their applications for WLAN and UWB applications. The effect of organic magnetic material will be discussed and compared with normal FR4 material. The measured S-parameters and far-field patterns will also be presented.