the maximum group delay is nearly 6 ns. So it proves that the antenna has a good time-domain characteristic and a small pulse distortion as well. Figure 8 shows the measured gain for the UWB antenna, it can be found that there are two sharp decreases at least 10 dB at 3.8 and 5.5 GHz for the frequency notched antenna, which has the same resonant point as the VSWR characteristic, and verified the band-stop function effectively. In practical applica- tions, we can consider that a meaningful rejection occurs only if the gain drops of at least 10 dB, so this design will have exten- sive application in the UWB sysyem. 4. CONCLUSION The design of a novel ultra-wideband monopole antenna with dual band-notched characteristic is presented. The fabricated antenna yields an impedance bandwidth of 3.1–10.6 GHz with VSWR <2, except the bandwidths of 3.3–3.8 GHz for WiMAX and 5.1–5.9 GHz for WLAN application. The dual stopbands function can be obtained with four u-shaped slots in the crescent radiating patch. The measured results show the broadband im- pedance matching, dual band-stop characteristic, which can sup- press the interference in UWB system, good radiation patterns, and near omnidirectional radiation pattern. REFERENCES 1. H. Schantz, The art and science of ultrawideband antennas, Artech House, Norwood, MA, 2005. 2. H. Zhou, Q. Liu, B. Sun, and Y. Yang, A band-notched swallow- tailed planar monopole antenna for UWB application, Microwave Opt Technol Lett 50 (2008), 793–795. 3. C. Sim, W. Chung, and C. Lee, An octagonal UWB monopole antenna with 5 GHz band-notch function, Microwave Opt Technol Lett 51 (2009), 74–78. 4. Y. Zhao, Y. Jiao, G. Zhao, L. Zhang, Y. Song, and Z. Wong, Compact planar monopole UWB antenna with band-notched char- acteristic, Microwave Opt Technol Lett 50 (2008), 2656–2658. 5. J. Kim, C.S. Cho, and J.W. Lee, 5.2 GHz notched ultra-wideband antenna using slot-type SRR, Electron Lett 42 (2006), 315–316. 6. H. Lee, Y. Jang, J. Kim, and J. Choi, Wideband monopole antenna with WLAN(2.4 GHz/ 5GHz) dual band-stop function, Microwave Opt Technol Lett 50 (2008), 1646–1649. 7. Q. Chu and Y. Yang, 3.5/5.5 GHz dual band-notch ultra-wideband antenna, Electron Lett 44 (2008), 172–174. 8. K. Yin and J. Xu, Compact ultra-wideband antenna with dual bandstop characteristic, Electron Lett 44 (2008), 453–454. 9. J. Ding, Z. Lin, Z. Ying, and S. He, A compact ultra-wideband slot antenna with multiple notch frequency bands, Microwave Opt Technol Lett 49 (2007), 3056–3060. 10. W.S. Lee, D.Z. Kim, K.J. Kim, and J.W. Yu, Wideband planar monopole antennas with dual band notched characteristics, IEEE Trans Microwave Theory Tech 54 (2006), 2800–2806. V C 2009 Wiley Periodicals, Inc. COMPACT SINGLE FEED CIRCULARLY POLARIZED FRACTAL BOUNDARY MICROSTRIP ANTENNA P. Nageswara Rao and N. V. S. N. Sarma Department of Electronics and Communications Engineering, National Institute of Technology, Warangal, India; Corresponding author: nrraop@yahoo.com Received 10 April 2009 ABSTRACT: Compact circularly polarized single feed microstrip antenna using fractal curve as boundary is presented. It is shown that by using fractal curve as boundary to the square patch the size can be reduced by more than 50% without much reduction in gain of the antenna. The antenna gives a good circular polarization with minimum axial ratio close to 0 dB at the center frequency of 2234 MHz. Three decibel axial ratio bandwidth of about 0.81% and 10 dB impedance bandwidth of about 3.25% are obtained with the proposed antenna. The antenna provides almost constant gain of about 4 dBi over the frequency band of operation. Measurement results are compared with simulated results and a very good agreement is obtained. V C 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 141–147, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24854 Key words: circularly polarized microstrip antenna; axial ratio; Koch fractal boundary; Minkowski fractal boundary 1. INTRODUCTION Circularly polarized microstrip antennas find applications in dif- ferent fields like WLAN, GPS, Mobile satellite, RFID applica- tions, etc. It is required to design antennas with compact size without degradation in gain of the antenna in the said applica- tions. Circular polarization is beneficial because current and future commercial and military applications demand the addi- tional freedom of not requiring alignment of the electric filed Figure 7 Measured group delay for the proposed antenna Figure 8 Measured gain for the proposed antenna DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 1, January 2010 141