theoretical maximum value of the antenna gain is 19.5 dB. The gain of the patch antenna with metamaterial structure is already very close to the theoretical maximum value of antenna with the same size and operating frequency. CONCLUSIONA new patch antenna with a metamaterial cover has been designed. Then, the radiation characteristics of a patch antenna with and without metamaterial structure are measured. The measured results show an about 10 dB addition in the antenna gain in comparison with the conventional antenna, thus the radiation characteristics of antenna with metamaterial structure are remarkably improved. Since, the ring aperture lattice is insensitive to the direction of arrival wave and independent to the wave polarization, this structure is much more useful than some kinds of EBG covers in some specific applications. REFERENCES

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Abstract-In this paper we develop a new impulse-radio-based RF front-end module for ultrawideband communications. The proposed transceiving module is designed based a novel compact microwave sampler. The microwave sampler consists of a multilayered magic-T and a balanced sampling bridge. By utilizing a wideband microstripto-slotline Marchand balun, the newly proposed magic-T features an improved bandwidth of 94.2%. The design concept, circuit topology, and experimental results of the magic-T and microwave sampler are investigated in the first half of this paper. By utilizing the equivalent time sampling theory, in the second half of this paper we investigate an impulse-radio-based ultrawideband transceiving front-end module. Two transmission data rates, 90 and 270 Kbps, are demonstrated with various bit patterns. The experimental results reveal that the transceiving module has a coverage range up to 4.5 m. The circuit configuration, modulation scheme, and system performance of the front-end module are discussed thoroughly. The tradeoff for increasing the data rate is discussed at the end of this paper as well.