Hesham. A. Mohamed 1, IEEE Member, Heba B. El-Shaarawy 2, Esmat. A.F. Abdallah 1, and Hadia El-Hennawy 3

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1 International Journal of Engineering & Technology IJET-IJENS Vol:4 No:0 9 Reconfigurable Compact Dual Mode Resonators UWB-BPF Using DGS and RF PIN Diodes Hesham. A. Mohamed, IEEE Member, Heba B. El-Shaarawy, Esmat. A.F. Abdallah, and Hadia El-Hennawy Abstract High-selectivity microstrip wideband bandpass filter with two transmission zeros using DGS and PIN diode concepts is proposed. The bandwidth and locations of the transmission zeros can be adjusted by changing the characteristic impedance of open stub and coupling coefficients of the dual mode resonators. A prototype of planar wideband bandpass filter with -db fractional bandwidth 6% ( GHz) is designed and fabricated. The proposed filter topology employs RF PIN diodes as the switching device. RF PIN diodes are used to reject band from UWB by changing the location of diode. This filter can be adapted between a narrowband state with a 4% bandwidth and an ultra wideband state with a 6% bandwidth and compactness of up to 78% to be obtained compared to other filters. This filter achieves a passband reconfiguration ratio greater than 4:. The measured and simulated results indicate good performances high selectivity and second harmonic suppression. Index Term Dual mode resonators, Even mode, Odd mode, RF PIN diode, Defected Ground Structure (DGS), and Notched band. I. INTRODUCTION Many existing microwave systems and applications have multifunction capabilities, meaning that there is a demand for reconfigurable filters []. Additionally, new applications are emerging for multi-functional RF systems with more demanding and diverse requirements for reconfigurable filters e.g. to allow system reconfiguration from radar to communications. Consequently, reconfigurable filters are essential for future RF systems across commercial, defense and civil sectors. In all these areas reconfigurable filter technologies hold the key to controlling the spectrum of RF signals and eliminating interference and preserve the dynamic range under any signal receiving conditions. Reconfigurable filters can be realized in a variety of ways, but no matter what method of tuning used they must conserve their transmission and reflection co-efficient over the specified tuning range. Many traditional methods such as filter banks are being phased out due to reconfigurable filters having advantages such as flexibility and smaller footprints. Many tunable filters have been investigated in the past which control the center frequency and band width [-4]. In this letter, a novel miniaturized dual-mode resonator with reconfigurable frequency bands and UWB filter with DGS is proposed. The characteristics of the proposed dual mode resonators are investigated numerically and validated experimentally. This filter has the advantage of compact size, low insertion loss, sharp rejection and high out-of-band attenuation. The designed and fabricated filter is done on Rogers substrate (RO00) with thickness of 0.65 mm, relative dielectric constant of 0., loss tangent= 0.00 and the metallization thickness is 0.07 mm. II. STRUCTURE OF THE DUAL MODE RESONATOR The structure of the proposed dual-mode resonator was initially analyzed in [5-7], which consists of a microstrip resonator with internal coupled lines and quarter-wavelength open-circuited stub, as displayed in Fig., where,, and denote the characteristic admittances and electric lengths of the microstrip line and open stub, respectively., odd and indicate the odd- and -mode characteristic admittances and electrical length of the coupled lines. Since the resonator is symmetrical in structure, the resonant condition can be analyzed by the classical method of -and odd-mode excitation as listed in Table. For odd-mode excitation, there is a voltage null along the symmetrical plane A-A'. The circuit structure is shown in Fig.. Taking = = = for convenience, we can derive the input impedance (admittance) [5]. The coupling structure makes it possible for the filter to generate one finite transmission zero at the lower or upper stopband. Fig., shows the resonance frequencies of the degenerate modes. The horizontal axis is, when varied from 0.0 S to S, the resonance frequency of the mode decreases almost linearly from.5 to.4ghz, while the resonance frequency of the odd mode is almost constant (around.8 GHz). Electronics Research Institute, El-Tahreer St. Dokki, Giza, Egypt Electronic and Communication Department, Faculty of Engineering, Cairo University, Giza, Egypt. Electronic and Communication Department, Faculty of Engineering, Ain shams University, Cairo, Egypt Corresponding author: hesham_80@yahoo.com IJET-IJENS February 04 IJENS

2 International Journal of Engineering & Technology IJET-IJENS Vol:4 No:0 0 Fig.. Structure of the proposed dual-mode stub-loaded resonator, Resonance frequencies of the degenerate modes and transmission-zero frequency against the different values of susceptance in Siemens (S) Fig.. Simulated current distributions for the two modes of the proposed resonator, odd mode, mode. TABLE. RESONANT CONDITIONS OF THE EVEN-AND ODD-MODE EXCITATION[5]. Odd mode (tan( )) o odd C tan ino j tan( )( ) tan ( K fodd L eff Even mode ine tan o tan[ ] tan j tan [ ] K f C tan ( L eff ) K ) frequency of the proposed resonator can be flexibly controlled while the fundamental odd-mode resonant frequency is unaffected. Besides, it can be seen from Fig. that there is a transmission zero inherently through the stopband. The transmission-zero frequency of the resonator can also be tuned by varying the value of. As increases, the transmission zero will shift from the upper to lower stopband. This unique property allows an easy design of asymmetric responses with improved selectivity below or above the passband, by just varying the width of the opencircuited stub (W ) as listed in Table. Where C is the speed of light in free space, L is the length of the microstrip line, and denotes the effective dielectric constant eff of the substrate. As a result, the fundamental -mode resonant frequency of the proposed resonator can be flexibly controlled while the fundamental odd-mode resonant frequency is unaffected. Slow-wave structure can be implemented with simple modification by etching a rectangular slot as shown in Fig. incorporated in the open stub, thereby this aperture tend to decrease the quality factor of filter, thus increasing the bandwidth[7-8]. Coupling coefficient of resonator plays a key role in determining the bandwidth of a filter [9]. A full-wave EM eigenmode simulator CST 0 ready-made software package was used to characterize the current patterns for the resonator. Fig. and show the current patterns of the resulting two fundamental eigenmodes. At the fundamental odd-mode resonant frequency, there is no current flowing on the open-circuited stub, and the open-circuited stub does not perturb the fundamental resonant current distribution in Fig.. On the other hand, at the fundamental -mode resonant frequency, there is current flowing on the open-circuited stub, which changes the current distribution path, thus changing the resonant frequency in Fig.. The normalized element values of the Chebyshev low-pass filter prototype with 0.0 db ripple can be obtained from [9] as, g 0 =, g = , g = , g =.007 that improves the passband and out-of-band performances [7]. The initial dimensions can be chosen using the above design procedure and then the CST 0 is used to optimize the dimensions for.8ghz GSM applications. III. DUAL-MODE COUPLED LINE RESONATOR It can be seen that the line width was chosen to give the characteristic impedance of 50Ω and coupled line length and open stub are quarter wavelengths at mid frequency.8 GHz of GSM applications of the symmetrical structure as shown in Fig.. In addition, the impacts of some parameters on frequency characteristics of the filter are analyzed in detail as shown in Fig.. A result, the fundamental -mode resonant IJET-IJENS February 04 IJENS Fig.. The geometric description of the BPF (all dimensions in mm). Frequency responses of the filter ageist width of the open-circuited stub W. We can predict and obtain the transmission zero from the analysis of the transmission coefficient S [7]. The simulated and measured the return loss of the filter is 0.7 db and insertion loss is 0dB at.8 GHz, while the insertion loss is 6 db, and return loss is 0.9 at.88 GHz. The response exhibits a transmission zero located at.5 GHz and a bandwidth of 70 MHz (4.5%) as shown in Fig4. The fabricated filter is depicted in Fig. 4.

3 International Journal of Engineering & Technology IJET-IJENS Vol:4 No:0 Fig. 4. CST EM-simulated and measured S-parameters of BPF. Photo of fabrication. TABLE II INFLUENCE OF VARING OPEN STUB WIDTH (W ) IN FIG.4(A) (W ) (mm) A. f o (GHz) B. FBW (%) Trans. Zero(GHz) above, two transmission zeros resulting from the dual-mode resonator and the DGS coupling line can be found, as shown in Fig.5, DGS microstrip line is used to diminish the higher order harmonics of f o, at.8ghz. Under the considerations of compact size, sharp rejection band and high performance filter, a novel BPF was designed by the DGS geometries. Simulated and measured results are shown in Fig. 6. It shows that the measured results matches closely the simulation ones, The results show that the proposed BPF has high a good performance with respect to the db bandwidth GHz (FBW 6%), insertion loss of -0.5 db and sharpness (the transition band between stop-band and pass-band is only 0.048GHz from.798ghz to.8466ghz, the transition band between pass-band and stop-band is only GHz from.49 GHz to.4995 GHz), and the sharpness is 5dB/GHz in low frequency edge and 55 db/ghz in high frequency edge. UWB BPF has three transmission poles in the passband and two transmission zeros in the lower and upper stopbands to enhance selectivity. The experimental results show excellent agreement with the theoretical simulation results. Measurements were done using Agilent 789ES Network Analyzer with range 50MHz to.5ghz. IV. UWB BPF DESIGN USING DGS AND RECONFIGURABLE FREQUENC BAND The above bandpass filters, has one transmission zero, low sharpness factors and its bandwidth is limited to 4.5%, which is only suitable for narrow-band applications. To overcome this limitation, a defected ground structure (DGS) has been proposed and implemented in the fabrication. The advantages of using the DGS under the microstrip line is that it is possible to increase the characteristic impedance by additional effective inductance generated by the DGS [4], and suppression of the second harmonic[]. The broadened width of the DGS microstip line can be understood as the increased equivalent capacitance, which plays a great role in raising the phase constant and slow-wave effects. Fig. 5. Configuration of the microstrip UWB-BPF. (all dimensions in mm). Configuration of the proposed DGS. UWB transmission systems are characterized by using an instantaneous bandwidth greater than 500 MHz or a fractional bandwidth of more than 0%. In Fig.5, we have presented a novel DGS. To illustrate this, the -mode frequency is adjusted by d, when d is increasing, the -mode frequency shifts higher with a fixed odd-mode frequency. As discussed IJET-IJENS February 04 IJENS Fig. 6. UWB BPF using DGS, Simulated and measured S-parameters, S-parameters at D on state. The reconfigurable filter can be realized by using RF PIN diode HBND 4005 []. In comparison to tunability of center frequency, there has been very little effort made in tunability of bandwidth. A reason for this is the lack of methods in order to vary the perturbations of fields in DGS electronically, which is essential for bandwidth control. After a preliminary optimization,

4 International Journal of Engineering & Technology IJET-IJENS Vol:4 No:0 we have considered the configuration shown in Fig.5, in which three RF PIN diodes are able to guarantee a proper bandwidth of the operating frequency. The positions of the RF switches have been chosen by inspecting the path of the currents on the ground surface to individuate the most suitable placement of the diodes to guarantee the current flow. This electronically reconfigurable filter is done mainly by RF PIN diodes (D, D, and D 4 ) ON and OFF states in Fig.5, DGS has two distinct characteristics of slow wave effect in passband and distinct stopband properties. As it is known, any defect etched in the ground plane of the microstrip line disturbs its current distribution. This will increase the effective capacitance and inductance. Hence, by selectively switching PIN diode in DGS ON and OFF or altering the overall impedance of the filter changes the passband width. The simulated results with reconfigurable bandwidth are 8% at center frequency.77ghz for ON state which achieves a passband reconfiguration ratio greater than 4: as in Fig. 7. TABLE III OBSERVED RESULTS FROM THE RECONFIGURABLE FILTER IN FIG (5) PIN diodes Filter FBW Passband Trans. state All diodes off D ON D &D &D OFF D &D &D On and D OFF Type UWB BPF UWB with notched band Narrow band BPF S (db) S (db) (db) (MHz) zero % 586 two % 0 two % 70 one V. RESULTS AND DISCUSSION The overall dimension of the filter is 6 mm (length) x5 mm (breadth) x0.65 (height) mm, and the efficient electric size of the proposed filter is 0.4 x0.4 with size reduction 78% g relative to Table.4 and the fractional bandwidth of the UWB bandpass filter is about 6 %. The performances of the proposed filter along with the parameters of other BPFs in published literatures are compared in Table 4. g Par. Ref. TABLE IV COMPARISON AMONG VARIOUS UWB BPFS. [] [5] [8] [0] [] This work Permittivity Thickness(mm) Loss tangent f o (GHz).84.8 FBW 5.4% %.% 0% 4% 6% Trans. zero One Two One One Six Two Size (mm ) 6x6 5x 94x9 5x9 5x0 6x5 Size reduction 0% 75% 78% 8.8% 90% --- Publication year Fig. 7. S-parameters results for the narrow BPF at (D, D, and D4) ON state, Fabricated reconfigurable filter with DGS and RF PIN diode. In order to allow this structure to generate a narrow notched band inside the ultra-wide band as shown in Fig. 5, we found that the loading RF PIN diode (D ) in internal coupled lines in distance (K) to changes the length of the quarter wavelength to generate tuned notched bands to avoid interference of UMTS at.ghz, and the group delay as demonstrated in Fig.7. Fig. 7 illustrates the fabricated filter with bias lines to apply bias voltages to the circuit using HPND 4005 PIN diodes. The optimal positions of the RF PIN diodes are obtained on cut and trail basis. The simulated performance results of the filter in Fig.5 are summarized in Table III. VI. CONCLUSION In this letter, a dual-mode stub-loaded resonator with internal coupled lines is proposed. The properties of the resonator have been obtained by theoretical analysis and thereafter verified by simulation and experiment. The proposed resonator possesses the merit that its fundamental -mode resonant frequency can be flexibly controlled while the fundamental odd-mode resonant frequency remains unaffected. By adding the DGS to the filter the FBW rises from 4% to 6%. The sharpness increased from 46dB/GHz to 5dB/GHz at low frequency edge and from 97dB/GHz to 55dB/GHz for high frequency edge. However, there is an increasing demand for reconfigurable ultra wideband filters with/without notch band and high selectivity for wideband communications, radar and electronic warfare (EW) systems for processing signals involving large information with high data rate. Finally, results indicate that the proposed filters have IJET-IJENS February 04 IJENS

5 International Journal of Engineering & Technology IJET-IJENS Vol:4 No:0 properties of compact and miniature sizes, low passband insertion losses and high frequency selectivity. REFERENCES [] J.-S. Hong, Reconfigurable planar filters, IEEE Microwave Magzine, Vol.0, No.6, pp.7-8, Oct [] Z. Birto, I. Limas and S. Colpo, Precise frequency and bandwidth control of switchable microstrip bandpass filters using diode and microelectromechanical system technologies, IET Microw. Antennas Propag, Vol. 9, No. 4, pp. 7-77, 0. [] H. Zhang and K. Chen "A microstrip bandpass filter with an electronically reconfigurable transmission zero," European Microwave Conference, pp , 9- Sept [4] M. Hesham, H. El-Sharawy, E. Abdualla and H. El-Hennawy" Design of reconfigurable miniaturized UWB-BPF with tuned notched band" Progress In Electromagnetics Research B, Vol. 4, pp.97-09, 0. [5] C. Hua, C. Miao "Microstrip bandpass filters using dual-mode resonators with internal coupled lines," Progress In Electromagnetics Research, Vol., pp.99-, 0. [6] M. Matsuo and M. Makimoto, "Dual-mode stepped- impedance ring resonator for bandpass filter applications," IEEE Trans. Microw. Theory Tech., Vol. 49, No. 7, pp.5-40, 00. [7] R. Mongia, I. Bahl, and P. Bhartia, "RF and Microwave Coupled line Circuits, " Artech House, Norwood, MA, 007. [8] W. Apisak, and S. Kunthphong Stepped-impedance coupled resonators for implementation of parallel coupled microstrip filters with spurious band suppression, IEEE Trans. Microw. Theory Tech., Vol. 60, No.6, pp , June. 0. [9] D. M. Pozar, Microwave Engineering, 4th Ed. JohnWiley Inc., 0. [0] C. Wen and W. Guang "Effective design of novel compact fractal-shaped microstrip coupled-line bandpass filters for suppression of the second harmonic", IEEE, Microwave and Wireless Comp. Lett., Vol.9, No., pp , July 009. [] HPND 4005, Avago Technologies, United States. [] S. J. Xue, W. J. Feng, and W. Q. Che,"Microstrip wideband bandpass filter with six transmission zeros using transversal signal interaction concepts" Progress In Electromagnetics Research C, Vol. 4, pp.-, 0. BIBLIOGRAPHIES Hesham A. Mohamed received a BSc. degree in Electronics and communication engineering from the University of Menofia in 00 and received his M.Sc. degree from Ain Shams University in 009. His M.Sc. is Miniaturization Techniques for Microstrip Filters. He is currently working toward the Ph.D. degree in the area of design and implementation of compact and reconfigurable planar filters at Ain Shams University. His research interests include the design and analysis of microstrip filters, microstrip antennas, and its application in wireless communication. He now holds an assistant research at the Electronics Research Institute (ERI) institute, Giza, Egypt. Esmat A. Abdallah graduated from the Faculty of Engineering and received the M.Sc. and Ph.D. degrees from Cairo University, Giza, Egypt, in 968, 97, and 975, respectively. She was nominated as Assistant Professor, Associate Professor and Professor in 975, 980 and 985, respectively. In 989, she was appointed President of the Electronics Research Institute ERI, Cairo, Egypt, a position she held for about ten years. She became the Head of the Microstrip Department, ERI, from 999 to 006. Currently, is the Microstrip Department, Electronics Research Institute, Cairo, Egypt. She has focused her research on microwave circuit designs, planar antenna systems and nonreciprocal ferrite devices, and recently on EBG structures, UWB components and antenna and RFID systems. She acts as a single author and as a coauthor on more than 60 research papers in highly cited international journals and in proceedings of international conferences in her field. Hadia M. El Hennawy received the B.Sc. and the M.Sc. degrees from Ain Shams University, Cairo, Egypt, in 97 and 976, respectively, and the Ph.D. degree from the Technische Universitat Braunschweig, Germany, in 98. In 98, she returned to Egypt and joined the Electronics and Communications Engineering Department, Ain Shams University, as an Assistant Professor. She was nominated an Associate Professor in 987 and then a Professor in 99. In 004, she was appointed as the Vice-Dean for graduate study and research. In 005, she was appointed as the Dean of the Faculty of Engineering, Ain Shams University. She has focused her research on microwave circuit design, antennas, microwave communication and recently wireless communication. She has been the Head of the Microwave Research Lab since 98. She has published more than 00 journal and conference papers and supervised more than 50 Ph.D. and M.Sc. students. Prof. El Hennawy was the Editor-in-Chief of the Faculty of Engineering, Ain Shams University, Scientific Bulletin from August 004 to August 005 and is a member of the Industrial Communication Committee in the National Telecommunication Regulatory Authority (NTRA), Educational Engineering Committee in the Ministry of Higher Education, and Space Technology Committee in the Academy of Scientific Research. She is deeply involved in the Egyptian branch activities. Heba B. El-Shaarawy was born in Cairo, Egypt, in 98. She has graduated from Electronics and Communication Dept., Faculty of Engineering, Cairo University, Egypt in 00 with honor, and worked as a teacher assistant in the same department. She has obtained her master degree in 005 from Electronics and Communications Dept., Cairo University, in the miniaturization of microstrip filters, and Ph.D. degrees in 009 from the University of Toulouse, Toulouse, France. Her fields of interest are microstrip components and antennas, electromagnetic bandgap structures, and defected ground structures IJET-IJENS February 04 IJENS