characteristics was tested by using an Agilent 8722ES Vector Network Analyzer at Iran Telecommunication Research Center, as indicated in Figure 7. A very good agreement between the simulated and measured results can be seen in Figure 7. The fig- ure clearly shows that the constructed antenna exhibits two notched bands of 3.25–4.25 GHz and 5.1–6 GHz, while main- taining wideband performance from 2.5 to 11.9 GHz for VSWR < 2, covering the entire UWB frequency band. Figure 8 shows the measured maximum antenna gain from 3 to 11 GHz for the proposed antenna with and without filter structures. The figure indicates that the realized dual band-notched antenna has good gain flatness except at the two notched bands. As shown in Fig- ure 8, gain decreases drastically at the notched bands. Figure 9 shows the measured radiation pattern in frequencies 3, 7, 9, and 11 GHz, in x-z and y-z planes. From an overall view of these radiation patterns, the proposed antenna behaves quite similarly to the typical printed monopoles in the lower and middle fre- quency bands. The H-plane patterns are almost omnidirectional but more directive in the higher band. 4. CONCLUSIONS A compact microstrip-fed printed monopole antenna with ultra- wideband performance and dual band-notched characteristics has been presented. The first band-stop characteristic is achieved by using a pair of mirror inverted L-shaped slots on the top side in the radiation patch, which exempt from interfaces with existing WiMAX and C operating bands. Also, the second notched band is achieved by using a pair of mirror inverted L-shaped slots on the bottom side in the radiation patch, which exempt from inter- faces with existing WLAN band. The measured results of a 12 mm  14 mm antenna on an FR4 substrate that has 1.6-mm thickness show a wide impedance bandwidth (131%) from 2.5 to 11.9 GHz, two notched bands centered at 3.7 and 5.5 GHz and an omnidirectional radiation. This antenna with two control- lable notched bands is suitable for ultrawideband systems with proper dimensions and aforementioned characteristics. REFERENCES 1. Q. Wu, R. Jin, J. Geng, and M. Ding, Printed omni-directional UWB monopole antenna with very compact size, IEEE Trans Antennas Propag 56 (2008), 896–899. 2. K. Thomas and M. Sreenivasan, Printed elliptical monopole with shaped ground plane for pattern stability, Electron Lett 45 (2009), 445–446. 3. D. Valderas, J. Melendez, and I. Sancho, Some design criteria for UWB planar monopole antennas application to a slotted rectangu- lar monopole, Microwave Opt Technol Lett 46 (2005), 6–11. 4. A. 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DESIGN OF COPLANAR WAVEGUIDE ULTRAWIDEBAND BANDPASS FILTER USING STUB-LOADED RESONATOR WITH NOTCHED BAND M. Amin Honarvar, 1 and R. A. Sadeghzadeh 2 1 Department of Electrical Engineering, Islamic Azad University Science and Research Branch, Tehran, Iran; Corresponding author: Amin.Honarvar@pel.iaun.ac.ir 2 Faculty of Electrical and Computer Engineering, K. N. Toosi University of Technology, Tehran, Iran Received 14 November 2011 ABSTRACT: In the present research, a novel compact ultrawideband (UWB) bandpass filter on coplanar waveguide (CPW) is examined and implemented. Pairs of three stepped-impedance open stubs are connected in shunt to a uniform high-impedance line to form a multiple- mode resonator (MMR). The physical dimension of the stepped- impedance stubs is regulated to allocate the first four resonant modes of the MMR within UWB passband (3.1–10.6 GHz).Thus, through etching a complementary split ring resonator on the CPW feed line, the narrow notched band having admissible rejection level is made. Subsequent to obtaining the optimization parameters from the electromagnetic full- wave simulation, the intended filter is fabricated. The level of agreement between the measured and the simulation results was excellent. The advantages of the proposed filter include compaction (0.55 k), flat group delay with maximum 0.17 ns variation in the passband, low insertion loss, and good return loss as well as improved upper stopband. V C 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2056–2061, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/ mop.26992 Key words: ultrawideband; bandpass filter; coplanar waveguide; multiple-mode resonator; notched band 1. INTRODUCTION There has been no scarcity of literature on the ultrawideband (UWB) bandpass filter from the time the Federal Communica- tion Commission allocated the frequency band 3.1–10.6 GHz for indoor wireless communication in 2002 [1]. To ensure high- quality signal transmission or reception, the UWB bandpass fil- ter requires both the ultrawide passband and high selectivity to reject signals from existing systems, for example, 1.6 GHz Global Positioning systems and 2.4 GHz Bluetooth systems. To date, numerous UWB filter design techniques have been sug- gested. The multiple-mode resonator (MMR) techniques have been frequently used to design high-performance UWB bandpass filters. The idea of MMR having a stepped-impedance resonator 2056 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 9, September 2012 DOI 10.1002/mop