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INTRODUCTIONRecently, there has been much interest in developing high-datarate systems, known as ultra-wideband (UWB) communication systems, with available bandwidths that cover 3.1 to 10.6 GHz. One of the most important issues in a UWB system is to develop compact-sized and wideband antennas. Printed slot antennas, especially coplanar waveguide (CPW)-fed slot antennas, exhibit a number of merits such as wide bandwidth, omnidirectional radiation pattern, ease of design and fabrication, and the capability be integrated with monolithic microwave integrated circuits (MMICs). These advantages make it an attractive candidate for UWB application. Many attempts have been made to increase the Other design schemes, such as those using a folded-slot [7], circular-slot [8], or multislot [9] structure, have also been proposed to achieve wideband performance.In this paper, a novel UWB slot antenna fed by a grounded CPW is proposed. For this design, a forklike tuning stub and a polygonlike wide slot are employed in order to enhance its operation bandwidth. An impedance bandwidth of about 3.2:1 is achieved. The characteristics of the antenna's radiation patterns and gain over the entire operation frequency range are also given and discussed. DESCRIPTION OF THE ANTENNAThe schematic diagram of the novel antenna and its dimension parameters are shown in Figure 1. The antenna is fabricated on a dielectric substrate with relative permittivity r ϭ 2.65, loss tan ␦ of 0.001, and thickness h ϭ 1 mm, and it has a compact volume of 36 ϫ 33 ϫ 1 mm 3 . The antenna is fed by a grounded CPW. As shown in Figure 1, the size of the back ground plane is only 30 ϫ 5.5 mm 2 ; thus, there is no conductor ground plane on the back of the wide slot. A forklike tuning stub and a polygonlike wide slot are designed to increase the antenna's operation bandwidth. EXPERIMENTAL RESULTSThe return loss of the antenna is calculated using Zeland's IE3D and measured using Agilent's HP8720E vector network analyzer. The calculated and measured results are given and compared in Figure 2. It is observed that the impedance bandwidth for return loss of less than Ϫ9.5 dB is from 2.89 to 9.19 GHz. Thus, an impedance bandwidth of about 3.2:1 has been achieved.Radiation patterns of the antenna in the z-y and z-x planes at three different frequencies over the operation frequency range are measured in a chamber and given in Figure 3. We can observe that relative constant radiation patterns and good omnidirectional performance can be achieved over the entire frequency range. Thus, the operation bandwidth of the antenna can be determined to be the same as its impedance bandwidth. The antenna gain is also measured in a chamber, as shown in Figure 4. We can see from the figure that gain flatness with a maximum variation of about 2 dB can be achieved. CONCLUSIONA novel compact UWB slot antenna fed by a grounded CPW has been proposed, and the calculated and experimental results have been presented. From the measured results, UWB performance of more than 3.2:1 and omnidirectional p...

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A novel, miniature balanced antipodal printed slot antenna for ultra‐wideband applications is proposed. The antenna is fed by strip‐line with a fork‐like stub. By employing balanced antipodal structure, not only good omnidirectional performance but also compact size is achieved. Several properties of the antenna, such as return loss, radiation pattern, and gain, have been investigated numerically and experimentally. As is reported, the operation bandwidth of the antenna is from 2.95 to 12 GHz, which is about 4:1. Stable omnidirectional radiation pattern with good polarization purity and flat gain performances over the whole frequency range can be achieved. Furthermore, the size of the antenna is more compact than conventional printed slot antennas for ultra‐wideband applications. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1943–1945, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21827