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In this paper, we introduce a novel design for a high‐directivity Electromagnetic Band Gap (EBG) resonator antenna that utilizes a frequency‐selective surface (FSS) superstrate. The above type of superstrate is proposed as an alternative to an EBG type of dielectric superstrate—investigated previously by the authors—to reduce its height and facilitate the fabrication process. Although FSS superstrate and the patch antenna comprise a composite resonator, we begin by investigating the FSS structure characteristics first before dealing with the combination. We vary several important parameters, such as the distance between the FSS superstrate and the ground plane of the antenna, and the dimensions of the FSS superstrate, to determine their effect on the resonant frequency and the quality factor of the unit cell of the FSS. The above study enables us to derive some guidelines for an optimum array size of the FSS superstrate that eventually leads to a maximum directivity for the FSS antenna composite, as evidenced via a comparison of the quality factors of the FSS, the unit cell, and the composite. It is demonstrated that the directivity of the antenna with an optimized array size of the FSS superstrate increases by 17.29 to 24.92 dBi for three different strip‐dipole lengths, as compared to that of the patch antenna alone (maximum 6 dBi). © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 462–467, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20502

A novel fractal DGS has been presented. The DGS lattice is a fractal Sierpinski-carpet type, instead of the rectangular holes used previously so that DGS can be adjusted by the filling factor. Simulation has shown that the proposed fractal DGS can provide more efficient size-reduction of the microstrip structure and better bandgap characteristics than the dumbbell-shaped DGS. A lowpass filter with the fractal DGS is designed and fabricated. Simulation and measurement confirms the validity of the proposed fractal DGS and the LPF configuration and design procedure. The LPF is simple. Additionally, the power-handling capability of low-pass filters can be improved by using the microstrip line with DGS. EFFICIENT ANALYSIS OF A CLASS OF MICROSTRIP ANTENNAS USING THE CHARACTERISTIC BASIS FUNCTION METHOD (CBFM)

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In this letter, a method to enhance the bandwidth of a double dipole quasi-Yagi antenna using a stepped slotline structure is presented. A stepped slotline with different widths is employed in the coplanar strip line connecting the two dipoles in order to improve impedance matching over a wide frequency band. In addition, two parasitic strip directors are appended to the antenna to enhance the gain in the high-frequency region. A detailed design procedure for the proposed antenna is explained, along with a performance comparison of the input impedance, voltage standing wave ratio (VSWR), and broadside gain. To demonstrate the effectiveness of the proposed design method, a prototype antenna operating in the 1.60-3.60 GHz frequency range with a gain > 6 dBi is designed and fabricated on an FR4 substrate. Experiment results show that the proposed antenna has the desired impedance characteristics with a frequency band of 1.59-3.64 GHz (78.4%) for a VSWR < 2, and a stable gain of 6.4-7.4 dBi in the 1.60-3.60 GHz frequency range. Moreover, a measured front-to-back ratio > 10 dB is obtained. Index Terms-bandwidthenhancement, stepped slotline structure, strip directors, double dipole quasi-Yagi antenna (DDQYA), mobile communications 1536-1225 (c)

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