horn. The radiation pattern of the antenna is tested in the near- field anechoic chamber. Figure 9 shows the simulated and meas- ured radiation patterns of the reflectarray antenna for co-polar and cross-polar components both in E-plane and H-plane at the center frequency of 13.58 GHz. As shown in Figure 9, the simulated antenna gain is 30.04 dB at the center frequency of 13.58 GHz with the 3-dB beam- width of 4.958 in both E-plane and H-plane. The simulated results of side lobe levels are below 218.8 dB with regard to the peak level. The measured gain levels 29.8 dB is obtained at 13.58 GHz with the 3-dB beamwidth of E-plane and H-plane both are 4.968. The measured side lobe levels are below 218 dB with regard to the peak level of both the H-plane and E- plane. The measured cross-polarization levels are below 235 dB for the E-plane and 228 dB for the H-plane. The simulation results are performed using the real material to coincide with the measurement condition. In practice, the air layer is substi- tuted by a cellular board. Besides, clear epoxy adhesive is used to bind the cellular board and substrate layer. The measured peak gains against frequencies from 12.58 to 16.58 GHz are shown in Figure 10. It can be concluded that the measured bandwidth, defined from the gain variation with fre- quency (1 dB drop in peak gain is considered), reaches 15.3%. The small difference between simulation and measured results are due to the fabrication and the measurement errors. The blockage of the foam and bracket and the feed misalignment are the reasons for the disagreement between simulations and meas- urements as well. 4. CONCLUSION A novel fractal microstrip reflectarray element with a single- layer substrate has been proposed and studied. The analysis of the fractal element shows that the proposed element can provide sufficient phase variation range with good linear reflection phase and gentle slope. The reflection phase curses of different fre- quencies indicate that the fractal element has broadband prop- erty. A concentric circle reflectarray which is composed of lots of the proposed fractal elements is designed, fabricated and measured. The measured 1-dB gain bandwidth reaches 15.3%. REFERENCES 1. F.E. Tsai and M.E. Bialkowski, Designing a 161-element Ku-band microstrip reflectarray of variable size patches using an equivalent unit cell waveguide approach, IEEE Trans Antennas Propag 51 (2003), 2953–2962. 2. D. Cadoret, A. Laisne, R. Gillard, L. Le Coq, and H. Legay, Design and measurement of new reflectarray antenna using microstrip patches loaded with slot, Electron Lett 41 (2005), 623–624. 3. J. Huang and J.A. Encinar, Reflectarray antennas, Wiley, Hoboken, NJ, 2008. 4. M.R. Chaharmir, J. Shaker, M. Cuhaci, and A. Ittipiboon, Broadband reflectarray antenna with double cross loops, Electron Lett 42 (2006), 65–66. 5. E. Carrasco, J.A. Encinar, and M. 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DESIGN OF UWB MICROSTRIP BANDPASS FILTER USING STUB-LOADED QUINTUPLE-MODE RESONATOR Elif Gunturkun Sahin, 1 Ali Kursad Gorur, 2,3 Ceyhun Karpuz, 2 and Adnan Gorur 1 1 Department of Electrical and Electronics Engineering, Nigde University, Nigde 51245, Turkey; Corresponding author: elifgunturkun35@hotmail.com 2 Department of Electrical and Electronics Engineering, Pamukkale University, Denizli 20070, Turkey 3 Department of Electrical and Electronics Engineering, Nevsehir Haci Bektas Veli University, Nevsehir 50100, Turkey Received 7 July 2015 ABSTRACT: Design of a novel ultra-wideband (UWB) microstrip bandpass filter is presented by using a square loop quintuple-mode reso- nator (QMR) having open-circuited stubs. The proposed resonator has five resonant modes in UWB band range and is coupled to Input/Output (IO) ports by parallel-coupled feed lines. The first three resonance modes are resulted from the stub loaded square loop resonator, whereas the remaining two modes can be formed by means of the coupling between the open-circuited stubs and the resonator. The designed UWB filter has totally seven poles including two poles resulting from the nature of the coupling sections and five poles from the QMR. Theoreti- cal analysis of the resonator is realized by defining the equivalent cir- cuit model. Coupling scheme and coupling matrix of the designed filter are also extracted to clarify the filter topology. In addition, two patch perturbation elements are used to control the in-band return loss levels. A seven pole UWB bandpass filter is designed, analyzed, and fabricated. Measurement results show a good agreement with the predicted results. V C 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:662– 666, 2016; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.29649 Key words: UWB; bandpass filter; multi-mode resonator; open- circuited stub 1. INTRODUCTION In 2002, ultra-wideband (UWB) frequency spectrum is released from 3.1 to 10.6 GHz by US Federal Communication Commission [1] for commercial use. Recently, UWB communication systems have gained great interest to be used at a very low energy level for short-range and high-bandwidth communications. One of the essential components of these systems is UWB filters. 662 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 58, No. 3, March 2016 DOI 10.1002/mop