from the connectors, microstrip lines, and microstrip-SIW transi- tions is about 1.7 dB, and the measured return loss is lower than -19 dB. The bandwidth is about 3.6 GHz. For wideband filters, flat group delay in pass-band is usually required to reduce the signal distortion. Figure 6 presents the measured group delay for this Ka-band filter. It is seen a variation of less than 0.5 ns in pass-band is achieved. The substrate used for the Q-band filter is Rogers 5880, whose relative permittivity is 2.2 with a height of 0.254 mm. Measured results are shown in Figure 7. Four poles and two transmission zeros are clearly observed from the measure- ment. The measured insertion loss in pass-band is about 2.39 dB, which includes the losses of the connectors, 10 mm microstrip lines, and the transitions. We measured the performance of one section of 10-mm microstrip line, which are used in the filter design for comparison and find the transmission loss is about 1.35 dB at 41 GHz. Excluding the above extra losses, the real insertion loss for the filter should be smaller. 4. CONCLUSIONS A novel SIW dual-mode filter with controllable bandwidth using circular high-order mode cavities has been proposed. The mea- sured results are in good agreement with the simulation. High- performance, low-cost, and low-profile make it very promising for high-frequency application. ACKNOWLEDGMENTS This work is supported by National Science Foundation under Grant NSFC60621002. REFERENCES 1. D. Deslandes and K Wu, Single-substrate integration technique of planar circuits and waveguide filters, IEEE Trans Microwave Theory Tech 51 (2003), 593–596. 2. Z.C. Hao, W. Hong, X.P. Chen, J.X. Chen, K. Wu, and T.J. Cui, Multilayered substrate integrated waveguide elliptic filters, IEEE Mi- crowave Wireless Compon Lett 15 (2005), 95–97. 3. T.M. Shen, C.F. Chen, T.Y. Huang, and R.B. Wu, Design of vertically stacked waveguide filters in LTCC, IEEE Trans Microwave Theory Tech 55 (2007), 1771–1779. 4. H.J. Tang, W. Hong, J.X. Chen, G.Q. Luo, and K. Wu, Development of millimeter-wave planar diplexers based on complementary characters of dual-mode substrate integrated waveguide filters with circular and el- liptic cavities, IEEE Trans Microwave Theory Tech 55 (2007), 776 – 782. 5. Y. Tao, W. Hong, and H.J. Tang, Design of a Ka-band bandpass filter based on high order mode SIW resonator, International Conference on Antennas, Propagation & EM Theory (ISAPE06), Guilin, China, 2006, pp. 1–3. 6. B. Potelon, J.C. Bohorquez, J.F. Favennec, C. Quendo, E. Rius, and C. Person, Design of Ku-Band filter based on substrate-integrated circular cavities (SICCs), IEEE MTT-S Int, San Francisco, CA (2006), 1237– 1240. © 2009 Wiley Periodicals, Inc. ULTRAWIDEBAND BANDPASS FILTER WITH A CONTROLLABLE NOTCHED BAND Shanshan Gao, Shaoqiu Xiao, and Bing-Zhong Wang Institute of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, People’s Republic of China; Corresponding author: xiaoshaoqiu@uestc.edu.cn Received 27 October 2008 ABSTRACT: A compact ultrawideband (UWB) bandpass filter with a controllable notched band within the UWB passband is proposed on the basis of a stub-loaded modified stepped impedance resonator (SIR) and two identical interdigital feed-lines. In the design, the modified SIR and the interdigital feed-lines can work together properly to make up the desired UWB passband. The stubs loaded at each side of the modified SIR can generate a desired notched band within the UWB passband to avoid the interference from wireless local-area network. There are good agreements between the simulated and measured results. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1745–1748, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24455 Key words: ultrawideband; bandpass filter; stepped impedance resona- tor (SIR); controllable; notched band 1. INTRODUCTION In recent years, ultrawideband (UWB) wireless communication technology has attracted a wide attention since the Federal Com- munications Commission (FCC) released the unlicensed use of frequency range from 3.1 to 10.6 GHz for commercial communi- Figure 6 Measured group delay of the Ka-band circular cavity filter Figure 7 Measured (solid line) and simulated (dashed line) results of the fabricated circular cavity filter in Q-band DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 7, July 2009 1745