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The design of an ultra‐wideband planar tapered slot antenna for use in a circular cylindrical microwave imaging system is presented. The antenna was designed assuming high dielectric substrate material Rogers RT6010LM to achieve its compact size. The developed antenna element (50 × 50 mm2) features a 10‐dB return loss bandwidth from 2.75 GHz to more than 11 GHz. The gain of the antenna is between 3.5 and 9.4 dBi over the 3–10 GHz band. The experimental tests showed that the manufactured antenna element supports transmission of narrow pulses with negligible distortions, as required in the microwave imaging system. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2212–2216, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21906

wavelength at the center frequency of the desired notched-band, where A denotes the arc length between the feedline and cutting pie. Figure 4 illustrates the characteristics of various flare angles at position ϭ 50°. The larger the flare angle , the wider the notched band. According to the above design criteria, with a ϭ 11.6 mm, ϭ 2°, and ϭ 50°, a UWB with a bandwidth range from 3.061 GHz was proposed with a notchedband range from 4.880 to 5.925 GHz. This feature meets the requirement for interference immunity at 5.2/5.8 GHz. Figure 5 plots the measured radiation patterns at 4.1 and 8.2 GHz, respectively. The measured radiation patterns of the proposed antenna are about the same as those of the reference antenna (without cutting pie, ϭ 0°). Figure 6 depicts the measured antenna gains of the proposed and the reference antennas with respect to frequency, indicating a sharp notched-band, suppressed by the cutting pie between 4.880 and 5.925 GHz. The antenna gain is about the same for both the proposed and the reference antennas for the frequencies outside the notched frequency band. CONCLUSIONSA circular slot antenna fed with an indented circular stub presented to achieve the band-notched characteristic has been proposed. The cutting pie helps determine the notched band. The proposed printed antenna has ultra-wideband frequency, but avoids interference with the 5.2/5.8 GHz bands, which are occupied by existing wireless systems. INTRODUCTIONRecently, there has been great interest in the development of the radio frequency identification (RFID) tags. As the use of RFID systems increases, manufacturers are pushing toward higher operating frequencies (UHF band) for long reading range, reading speed, and anticollision [1]. The technology used to realize the antenna is perhaps the most important technology in RFID development. Designing a passive tag antenna matched with the complex microchip impedance is the most challengeable factor, since a microchip has very high Q because of its small resistance and large capacitive reactance. To overcome this problem, the inductively coupled feed is used to achieve a wideband impedance match between the antenna and the chip [2]. Also, the impedance of an RFID tag antenna varies when it is mounted on different objects. Especially, metallic objects strongly affect the antenna performance by lowering the tag's efficiency. Therefore, tag antennas have to be designed to enable tags to be read near and on metallic objects without severe performance degradation. Several microstrip patch antennas mountable on metal platforms have been proposed [3,4]. In this article, a microstrip patch-type tag antenna mountable on various metallic platforms is proposed. The antenna is inductively coupled by a novel feeding structure placed on the side of the radiator. This allows control of both the real and imaginary parts of the antenna impedance to achieve conjugate match with the various values of the microchip impedances. STRUCTURE AND DESIGNThe structure and dimension of the proposed antenna are sh...

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