Embedded-circuit and RIS meta-substrates for novel antenna designs

Abstract

1.Abstract: Antenna miniaturization with enhanced radiation performance is a contemporary problem with application in RF and wireless systems. The substrate and ground plane of antenna play a very important role in achieving the desired antenna characteristics. The focus in this paper is to present the applications of two types of meta-substrates for novel antenna designs, namely, Embedded-Circuit Meta-material (ECM) and Reactive Impedance Surface (RIS) substrates. ECM provides a way to fabricate an E-p substrate, allows antenna miniaturization with relatively high bandwidth and efficiency. Also, a novel compact RIS as the ground plane for a dual-band Eshaped patchislot antenna is proposed to reduce the interaction of antenna with its ground and design a miniaturized wideband antenna system. 2.Magneto-Dielectric Embedded-Circuit Medium: Antenna miniaturization using high permittivity materials as substrate has been attempted in the past [l]. Although miniaturization can be achieved using high dielectric materials, there are two drawbacks. One problem stems from the fact that the field remains highly concentrated around the high permittivity region (field confinement), which results in low antenna efficiency and narrowband characteristics. The second drawback pertains to the fact that the characteristic impedance in a high permittivity medium is rather low which creates difficulties in impedance matching of the antenna. These aforementioned problems can be effectively circumvented if one uses a magneto-dielectric material. Magnetodielectric materials can also miniaturize the antenna by the same factor however using moderate values of permittivity and permeability ( n = G ) . Therefore, the issue of strong field confinement is minimized and the medium is far less capacitive when compared to the dielectriconly high permittivity material. Furthermore, since the characteristic impedance of magnetodielectric medium (7 = 7 " m ) is close to that of the surrounding medium ( vo) it allows for ease of impedance matching over a much wider bandwidth.It has been shown by Hansen and Burke [2], that the zero-order bandwidth for an antenna over a magneto-dielectric substrate with thickness t can be approximated by Thus for a given miniaturization factor (constant 6) the antenna bandwidth can be enhanced by increasing ,u,/&, ( p , > 6,). However, the main engineering question is that "how one can obtain a magnetic material with relafively large permeability'. Basically, the naturally available magnetic materials operate only up to lower UHF band. It was demonstrated in [3] that a periodic structure of high Q resonant tank circuits embedded in a low permittivity dielectric material has the potential to successfully obtain an E+ medium at any frequency of interest. In this work we design a compact embedded-circuit structure which is constructed of miniaturized tank circuits made up a wire loop and an interdigated capacitor (see Fig. I). A unit cell transmission line model of the structure is shown in Fig. l(b). The magnetic flux l...

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