thermograph, antenna with no excitation, was subtracted from each of the 11 remaining thermographs to obtain the increase in temperature caused by Joule heating for each frequency of the RF generator. 3. RESULTS The heating of a planar dipole antenna due to ohmic losses was visualized through thermographs for different frequencies of the supplied voltage. Results showed a well-defined increment of the antenna temperature for each voltage frequency, and allowed to find the maximum change induced on its surface by visual comparison. The more representative thermographs of the heating process are shown in Figures 2(a)–2(d). Figure 2(a) shows the antenna at room-temperature without any RF excitation (25  C) so no heating was expected. The biggest temperature increase on the dipole surface was reached by tuning the voltage to 833 MHz corresponding to Figure 2(c), which agrees with the theoretical resonance value, at this value a higher current density is expected on the antenna. Finally, Figures 2(b) and 2(d) were taken at frequencies below and above the antennas’ resonance where the transfer of energy between the antennas and source is not optimum. The mean temperature increase for each frequency is shown in Figure 3(a). The results follow the frequency behavior of the half-wave dipole showing that the induced current increases sig- nificantly when resonance is achieved around 833 MHz. It is worth noting that also a thermal drift of the signal is observed (red line). This is caused by the heating of the substrate which can be seen in Figure 2. To remove the substrate heating effect, it is assumed in a first approximation that the temperature of substrate increases linearly with the frequency of excitation, so a straight line is fit- ted to the first four points of the curve and the room- temperature thermograph with no heating. Figure 3(b) shows the pure contribution of the antenna where the heating of the sub- strate was subtracted. 4. CONCLUSION In this work, a novel method of testing based on infrared ther- mography was used to find the resonant frequency of a planar half-wave dipole designed to work at the UHF band. By using an infrared camera, it is possible to visualize the thermal heating of an antenna of which the induced currents are responsible. This makes possible to characterize planar antennas in a nonin- vasive way, which might be useful for in-situ evaluation and characterization of antennas where there would be no need to take the antenna to a special antenna-characterization facility. REFERENCES 1. J.D. Kraus and R.J. Marhefka, Antennas for all applications, McGraw-Hill, New York, 2002. 2. C.A. Balanis, Antenna theory analysis and design, Wiley, New York, NY, 1997. 3. W. Hong-Jian, F. Bin, Y. Min, G. Fu-Ling, L. Guang, C. Xue, X. Yan, H. Jianguo, C. Minghui, and L. Shihua, Inflatable antenna for space-borne microwave remote sensing, IEEE Antennas Propag Mag 54 (2012), 58–70. 4. D.G. Fang, Antenna theory and microstrip antennas, CRC Press, Boca Raton, FL, 2010. 5. S. Yun, Y. Kirn, J. Park, J. Eun, and S. Lee, Error Testing at Planar Near-Field and Far-Field range of Anechoic Chamber, In: Proceed- ings of the International Symposium on Antennas, Propagation and EM Theory (2003), 385–388. 6. A. Rao, S. Varughese, and M.S. Easwaran, Anechoic chamber related issues for very large automated planar near field range, In: International Conference on Electromagnetic Interference and Com- patibility (1997), 75–82. 7. P. Li and L. Jiang, An iterative source reconstruction method exploiting phaseless electric field data, Prog Electromagn Res 134, (2013), 419–435. 8. F.J. Zucker, Antenna theory, McGraw-Hill, New York, 1969. V C 2014 Wiley Periodicals, Inc. VERY COMPACT PALMATE LEAF- SHAPED CPW-FED MONOPOLE ANTENNA FOR UWB APPLICATIONS Mohammad M. Fakharian and Pejman Rezaei Department of Electrical and Computer Engineering, Semnan University, Semnan, Iran; Corresponding author: m_fakharian@sun.semnan.ac.ir Received 5 November 2013 ABSTRACT: This article presents a very compact coplanar waveguide- fed planar monopole antenna for ultrawideband (UWB) applications. The antenna consists of a palmate leaf-shaped radiator with a modified shaped ground plane on the same side of the substrate. The measured impedance bandwidth of the proposed antenna is from 3.08 to over 14 GHz with a ratio of about 4.6:1 for VSWR  2. Experimental results show that the proposed antenna has stably omnidirectional H-plane radiation patterns with low cross-polarization level and average peak gain of 3 dBi across the UWB. The antenna dimensions are restricted to 13.5 3 14.8 3 0.8 mm 3 . V C 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1612–1616, 2014; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.28395 Key words: ultrawideband; coplanar waveguide; monopole antenna; compact size 1. INTRODUCTION Recently, ultrawideband (UWB) wireless systems have drawn a wide range of applications including ground penetrating radars, high-resolution microwave imaging, communication systems for military, body area networks, and UWB short pulse radars for automotive and robotics applications [1–3]. UWB systems are characterized by low complexity, low operating power level, high precision ranging, high data rates, very low interferences, and great capacity. One of the most fundamental parts of the UWB systems is antennas. They are required to operate in the ultrawide bandwidth of 3.1–10.6 GHz since the Federal Com- munications Commission (FCC) released its report in 2002 [4], be omnidirectional radiation patterns, be simple and compact with small dimensions and light weight. The monopole UWB antennas with various shaped planar ele- ments such as square, elliptical, triangle, circular, annual ring, pentagonal, and crescent geometries have been studied in previ- ous literature [5–9]. Most of the UWB antennas mainly focus on two types of feed structure, that is, microstrip [10, 11] and copla- nar waveguide (CPW) line. The CPW feed line is preferred due to its small size, low profile, low radiation loss, and easy integra- tion with microwave monolithic integrated circuit (MMIC). Hence, many planar CPW-fed antenna configurations have been designed and developed [12–14]. In this article, a novel leaf-shaped CPW-fed planar monopole antenna is presented for UWB operation with a compact size only 13.5 3 14.8 mm 2 , significantly less than those antennas 1612 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 56, No. 7, July 2014 DOI 10.1002/mop