In this article, a miniaturization method for a ultrahigh frequency radio frequency identification reader antenna using an artificial magneto‐dielectric is proposed. The miniaturization was achieved using an artificial magneto‐dielectric, realized using a split ring resonator (SRR). The 10 dB return loss bandwidth of the designed antenna ranges from 908.5 to 914 MHz. The measured peak gain is −3.75 dBi and the axial ratio is below 3 dB over the frequency band of interest. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1926–1930, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25423

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This paper proposes a method for improving the isolation characteristic of multi-input multi-output (MIMO) antennas using a split ring resonator (SRR) array structure between the two radiating elements. The fabricated antenna satisfies the 10 dB return loss requirement in the Mobile-WiMAX frequency band from 3.4 GHz to 3.6 GHz. The isolation between the two radiating elements is improved by approximately 20 dB at the center frequency by inserting a SRR array structure. The measured peak gains of the two elements are 2.3 dBi and 2.4 dBi, respectively. Ⅰ. IntroductionCurrent mobile communication systems require high data rates and large channel capacity in order to satisfy the various demands of users. A MIMO antenna system has a higher data rate and larger channel capacity compared with a conventional wireless system. A MIMO system is therefore a suitable candidate for fourth generation mobile communication systems requiring high speed and quality transmissions involving large amounts of data transfer. In the MIMO system, two or more antennas are used on both the transmitter and receiver sides. However, the antenna elements are strongly coupled with each other, as well as with the ground plane, because they share the common surface current [1]. Several techniques have been introduced to improve the isolation characteristic, such as using the resonating slot on the ground plane [2] and using the isolation elements between the radiating elements [3]. However, these techniques limit the available space for other system components and do not guarantee a uniform radiation pattern. A metamaterial technique [4] might be a good candidate for overcoming some of these drawbacks.Metamaterials can be defined as man-made homogeneous electromagnetic structures with unusual properties that are not readily available in nature. When electrical property has negative permeability or negative permittivity (μ<0 or ε<0), the medium has an evanescent wave. An evanescent wave is an electromagnetic wave that decays exponentially with distance. Negative permittivity and permeability materials can usually be obtained using the wire and split ring resonator (SRR) at a specific frequency band. The resonance frequency is determined by the capacitance and inductance of the structure [5]. This paper proposes a method for improving the isolation performance of a MIMO antenna for the MobileWiMAX frequency band using the negative permeability property of an SRR array structure. Ⅱ. Antenna Design and Performances 2-1 Antenna StructureThe configuration of the proposed MIMO antenna is shown in Fig. 1. The antenna was implemented on two FR4 substrates (εr=4.4) of different thicknesses; it consisted of two radiating elements, the ground plane, and the SRR array structure. The radiating elements and ground plane were printed on a 0.8-mm-thick FR4 substrate (sub #1). The two radiating elements of the MIMO antenna were symmetrically printed with respect to the center and were placed near the corners of the top edge of the ground plane.As shown in...

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