Ultra Sharp Transition-Band Low-pass Filter with Miniaturized Size for GSM Applications

Transcription

1 RADIOENGINEERING, VO. 7, NO., JUNE 8 Ultra harp Transition-Band ow-pass Filter with Miniaturized ize for GM Applications Gholamreza KARIMI, Alireza GOETANIFAR, Amirhossein GHADERI, Navid AIMPOUR Electrical Department, Faculty of Engineering, Razi University, Kermanshah, Iran Young Researchers and Elite lub, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran ghkarimi@razi.ac.ir, Golestany9@yahoo.com, Amir9h@yahoo.com, Navid_salimpour@yahoo.com ubmitted May, 7 / Accepted January, 8 Abstract. In this paper, a microstrip low-pass filter (PF) using a bended transmission line is presented. The PF has a simple topology, which is composed of a T-shaped stub as main resonator, one conventional rectangular resonator (as suppressing stub) and two T-shaped stubs. To approach a high operation and small dimensions, this structure is bent. The proposed PF has a compact size (.9 λ g.9 λ g ) and presents an ultra sharp transition-band ( = 88.9 db/ghz) from.9 to.987 GHz with and db suppression levels, respectively. This filter, with - db cut-off frequency (f c ) of.9 GHz, is useful for GM applications. The performance of each section is investigated based on equivalent circuit. The designed filter is fabricated and measured. Also, the results exhibit an excellent figure of merit (FOM) of 97. Keywords ow-pass filter, T-shaped resonator, transmission zero, equivalent circuit. Introduction Microstrip low-pass filters (PFs) with benefits like small size, wide stop-band and sharp cut-off are emerging requirements for implantation in wireless communication circuits such as; high frequency mixers and demodulators to reject interferer signals []. In [], a microstrip PF with high insertion-loss in the stop-band using T-shaped and Z-shaped resonators was presented, to reduce the circuit size, transmission line was bent. In [], a dual-layer PF with wide rejection-band was depicted; however, enormous dimensions and slow cut-off are challenges of this work. In [], a low-pass filter using T-shaped resonator was introduced, which gradual transition-band and large dimensions are disadvantages of this filter. In [], a symmetrical PF with high return-loss in the pass-band using T-shaped resonators was reported. To increase the stop-band width, four stepped-impedance suppressors were adopted, even though this filter does not have a sharp cut-off and small size. A miniaturized PF with gradual cut-off frequency and narrow stop-band using funnel-shaped resonator was reported in [], so that four triangle resonators were utilized to increase the sharpness. A simple PF using steppedimpedance resonators was presented in [7]. This structure has a weak sharpness and large dimensions. In [8], an PF with sharp cut-off and compact size using T-shaped resonator was introduced. The presented PF in [9] was composed of several open-circuited stubs, which a fractal defected ground plane was embedded to decrease the circuit size. Also, this filter presents a slow transition-band and the limited stop-band. In [], a microstrip PF with acceptable stop-band width using T-shaped resonators was reported, but the circuit dimensions are large. To develop the stop-band of the low-pass filter in [], improved hairpin resonators were adopted; nonetheless the transition-band is slow. Multi-layer PFs such as defected ground structure (DG) [ 9], do not have a wide stop-band and sharp transition-band, moreover these filters suffer from complex structure. In this work, a microstrip PF with individual properties such as simple topology, ultra sharp transition-band, miniaturized size and very high FOM is proposed. To approach a sharp cut-off and wide stop-band, T-shaped and conventional rectangular resonators are employed. The simulation is performed by using the Keysight full-wave simulator Advanced Design ystem (AD). Also, the proposed filter is manufactured on a Rogers_RO substrate with ε r =.8, h =.8 mm and loss-tangent of... T-shaped Resonator Design In order to design a microstrip low-pass filter at GM band, an resonator for a -pole elliptic low-pass filter is proposed, based on Fig. a. The element values of this resonator are obtained using () and (), [] as follows: =. nh, =.8 nh, =. nh and =. pf. g Z i i f, () c g i i fcz () DOI:./re.8. EETROMAGNETI

2 G. KARIMI, A. GOETANIFAR, A. GHADERI, ET A., UTRA HARP TRANITION-BAND PF WITH MINIATURIZED Fig.. T-shaped resonator:, layout. where Z is the line impedance ( Ω). g i and g i are applied to denote the inductive and capacitive elements, respectively. Also, and are inductances of the transmission line. describes the inductance of high-impedance stub and is equivalent capacitances of the open-circuited and low-impedance stubs. The layout of the resonator is presented in Fig. b. The physical lengths of the T-shaped resonator are computed using () and (), []: l l arcsin, () g Z arctan Z () g c where λ g and λ g present the guided wave-length of high and low impedance lines, respectively. ω c is angular cut-off frequency, Z and Z show the characteristic impedance of transmission line with high and low impedances, respectively. In addition, line calculator of Keysight AD software can easily calculate the values of characteristic impedances. The EM and simulations results of the T-shaped resonator are illustrated in Fig. a, where there is a good agreement between them. This resonator generates two transmission zeros (T Z and T Z ) at.9 and GHz frequencies (seen in Fig. b) that the first transmission zero (T Z ) has more importance than another one, tuning the transition-band. Also, the second transmission zero (T Z ) can provide a wide stopband. The transfer function of the T-shaped resonator is obtained from its circuit as follows: where v v ( ) ab o ( r ) i a r r r ( ), b ( r ) r, () Fig.. T-shaped resonator: EM and simulations, EM simulation. Fig.. EM-simulation of T-shaped resonator for different values of and K. K (mm) (nh). 9 8 f z (GHz) imulated alculated.9..9 Transition-band (GHz) Tab.. Variations of f z for different values of and K. r is the matching impedance of input and output ports (r = Ω) and is equal to jπf where f is frequency. The equation of the T Z (f z ) is extracted from (): f z. () According to (), the f z is a function of and is the inductance of K in Fig. b. By decreasing the value of, the length of K is reduced, also. As a result, T Z approaches to higher frequencies and transition-band is drowsed, as depicted in Fig.. o to have sharp transition-

3 RADIOENGINEERING, VO. 7, NO., JUNE 8 7 band, T Z is tuned at.9 GHz frequency. The variations of f z for different values of and K are summarized in Tab... PF Design. Primitive PF Design As seen in Fig. b, the stop-band is limited by transmission poles (TPs); to achieve a wide stop-band, TPs (from to GHz) should be suppressed. For this reason, a conventional rectangular resonator with wide stop-band (seen in Fig. ) is added to the T-shaped resonator, based on Fig. a. The equivalent circuit of primitive PF is depicted in Fig. b. and represent the inductances of transmission line. apacitances of open-circuited and lowimpedance stubs are modeled by. The equivalent circuit values using the methods discussed in [] are computed as follows: = nh, =.7 nh and =.7 pf. The EM and simulations results are shown in Fig. c where a good agreement between them is seen. The stop-band of primitive PF with 8 db attenuation level is extended up to. GHz. Fig.. EM simulation of conventional rectangular resonator.. Improved PF Design To have a PF with high suppression level, high return-loss and low ripple in the pass-band, two T-shaped stubs (seen in Fig. ) are added to primitive PF, based on Fig. 7a. These stubs can provide a suitable suppression level by producing a transmission zero (T Z ) at.7 GHz. The equivalent circuit of the improved PF is demonstrated in Fig. 7b where is the inductances of high-impedance stubs and is capacitances of open-circuited and low-impedance stubs. The equivalent circuit values are as follows: = 8. nh and =. pf. The transfer function of the improved PF is presented in (7), transmission zeros can be extracted from it. The EM and simulation results and transfer function result are depicted in Fig. 7c. An acceptable agreement among them is seen, confirming the validation of the equivalent circuit and transfer function. This structure has negligible insertion-loss in the pass-band, high suppression level and sharp cut-off frequency. Magnitude (db) (c) Fig.. Primitive PF: ayout, equivalent circuit, (c) EM and simulations. Fig.. EM simulation of T-shaped stubs. where v v o i ( r r( ( )( )) c r( ) ( ), (7) )( r r ( ) ( )( b ra) ( )) r( )( ) r( b)

4 8 G. KARIMI, A. GOETANIFAR, A. GHADERI, ET A., UTRA HARP TRANITION-BAND PF WITH MINIATURIZED ( )( ) ( ) ( ( )) a, ( ) ( ) ( ( b )( ( )( ) ( )) ( ), ) c r ( )( ( ( )) ( ) a ) r ( )( ( ( )) ) r ( ) ( ( )). size reduction in comparison with previous structure. Also, the proposed filter has an ultra sharp transition-band and a high suppression level in the stopband area. The physical size of the proposed PF are: A =., A =., A =., A = 9., A = 7, A =., A 7 = 7, A 8 = 9., A 9 =.9, A =.7, A m =., H =., H =., H =., H =., H =., H =., H 7 =., H 8 =., H m =, R =, R =. (all in millimeter), θ = 9 and θ = 9. (c) Fig. 7. Improved PF: ayout, equivalent circuit, (c) EM and simulations and transfer function result.. Proposed PF The improved PF has enormous dimensions (8.9 mm. mm) and occupies a large area. o to reach a miniaturized size and high performance, this structure is bent, based on Fig. 8a. The final size of the proposed PF is only. mm. mm, which shows 9.%. imulated and Measured Results The photograph of the manufactured filter is displayed in Fig. 8b. Also, an Agilent NA network analyser is used to measure the manufactured filter. The simulated and measured results are observed in Fig. 8c. The proposed filter with -db cut-off frequency of.9 GHz has an ultra sharp transition-band ( = 88.9 db/ghz) from.9 to.987 GHz (. GHz) with suppression points of and db, respectively. The insertion-loss in passband is. db. The stop-band of the structure with high suppression level of db is expanded up to. GHz. The overall dimensions of the proposed structure are only.9 λ g.9 λ g. Finally, this filter with very small size and high FOM (97) is suitable for GM applications. Based on some specifications mentioned in [], the proposed PF and the reported papers are compared in Tab.. In this table, the sharpness of transition band is computed by = ( max min )/(f s f c ), where α min and α max are suppression points of and db, respectively. Also, f s is the frequency corresponding with α max and f c is the frequency corresponding with α min. F means suppression factor and RB is the relative stopband band-width for db suppression level. The normalized circuit size is depicted by N. AF is architecture factor and FOM is defined as figure of merit that is given by FOM = ( RB F)/(N AF). All of these parameters are defined in []. As seen from Tab., the proposed PF has the sharpest cut-off, the least size and the highest FOM in comparison with the published works.

5 RADIOENGINEERING, VO. 7, NO., JUNE 8 9 Hm A H H A H8 H7 A H H A H A8 A7 R, θ A A Am A A9 R, θ H Refs fc RB F N AF FOM [] [] [] [] [7] [8]..8 [] [] [] [] [8] (Filter) [8] (Filter) [9] This work Tab.. omparison among reported works and the proposed filter. Magnitude (db) Measurement imulation Frequency (GHz) (c) Fig. 8. The proposed filter: ayout, photograph of the fabricated filter, (c) simulated and measured results.. onclusion An ultra-sharp transition-band PF with very small dimensions and very high FOM (97) has been simulated, manufactured and tested. In this filter, to reach a sharp transition-band and wide stop-band, T-shaped and conventional rectangular resonators are employed. The designed PF has a -db cut-off frequency of.9 GHz, which it is appropriate for GM communications. The other properties of the proposed PF are: simple structure, high return-loss and wide rejection band. The final dimensions of the presented PF are only.9 λ g.9 λ g. References [] HONG, J.-., ANATER, M. J. Microstrip Filters for RF/Microwave Applications. John Wiley & ons, Inc.,. DOI:./79 [] KARIMI, G., IAHKAMARI, H., HAMEDANI, F. K., et al. Design of modified Z-shaped and T-shaped microstrip filter based on transfer function analysis. Wireless Personal ommunications,, vol. 8, no., p.. DOI:.7/s z [] ZHANG, Y., JIN,., I,. Design of PF using Hi-o interdigital DG slot. IEIE Electronics Express,, vol., no. 9, p.. DOI:.87/elex..7 [] YANG, R. Y., IN, Y.., HUNG,. Y., et al. Design of a compact and sharp-rejection low-pass filter with a wide stopband. Journal of Electromagnetic Waves and Applications,, vol., no. 7-8, p DOI:.8/ [] RAPHIKA, P. M., ABDUA, P., JAMINE, P. M. Planar elliptic function lowpass filter with sharp roll off and wide stopband. Microwave and Optical Technology etters,, vol. 8, no., p.. DOI:./mop.9 [] RAPHIKA, P. M., ABDUA, P., JAMINE, P. M. ompact lowpass filter with a sharp roll off using patch resonators. Microwave and Optical Technology etters,, vol., no., p.. DOI:./mop.8 [7] AADBEIGI, H., VIRDEE, B.. ompact notch filter design using stepped impedance resonators for sharp roll off and large wideband rejection. International Journal of RF and Microwave omputer Aided Engineering,, vol., no., p DOI:./mmce.88 [8] AFZAI, B., KARKHANEHHI, M. M., KARIMI, G. Design of compact microstrip lowpass filter with ultra-wide stopband using modified T-shaped resonator. International Journal of Microwave and Wireless Technologies,, vol. 7, no., p DOI:.7/79787X [9] KUFA, M., RAIDA, Z. owpass filter with reduced fractal defected ground structure. Electronics etters,, vol. 9, no., p. 99. DOI:.9/el..7 [] MOUAVI,. M. H., MAKKI,. V. A. D., IAHKAMARI, H. Design of microstrip lowpass filter using bend configuration with

6 G. KARIMI, A. GOETANIFAR, A. GHADERI, ET A., UTRA HARP TRANITION-BAND PF WITH MINIATURIZED excellent sharpness in transition band. Frequenz,, vol. 7, no. -, p. 7. DOI:./freq--9 [] HAYATI, M., VAZIRI, H.. ompact microstrip low-pass filter with wide stop-band and sharp roll-off. Frequenz,, vol. 7, no. 9-, p. 9. DOI:./freq-- [] KUMAR, A., VERMA, A. K. Design of Bessel low-pass filter using DG for RF/microwave applications. International Journal of Electronics,, vol., no. 9, p. 7. DOI:.8/77..8 [] UHA, D., AKHMI,. R., RINIVAA RAO, Z., et al. A systematic implementation of elliptic low-pass filters using defected ground structures. Journal of Electromagnetic Waves and Applications,, vol. 9, no., p.. DOI:.8/97..7 [] KUMAR, D., DE, A. Design of compact low pass microstrip filter for wireless communication system. Frequenz,, vol., no. -, p. 7. DOI:./freq.. [] ZHANG, P., I, M. A novel sharp roll off microstrip lowpass filter with improved stopband and compact size using dual plane structure. Microwave and Optical Technology etters,, vol. 8, no., p DOI:./mop.97 [] XIAO, M., UN, G., I, X. A lowpass filter with compact size and sharp roll-off. IEEE Microwave and Wireless omponents etters,, vol., no., p DOI:.9/MW..98 [7] IU,., XU, J., XU, Z. harp roll-off lowpass filter using interdigital DG slot. Electronics etters,, vol., no. 7, p.. DOI..9/el..7 [8] DURAN-INDREU, M., BONAHE, J., MARTIN, F. ompact elliptic-function coplanar waveguide low-pass filters using backside metallic patterns. IEEE Microwave and Wireless omponents etters,, vol., no., p.. DOI:.9/MW..9 [9] WANG, J., XU,. J., ZHAO,., GUO, Y. X., WU, W. ompact quasi-elliptic microstrip lowpass filter with wide stopband. Electronics etters,, vol., no., p DOI:.9/el..9 About the Authors... Gholamreza KARIMI received his B.c., M.c., and Ph.D. degrees in Electrical Engineering from the Iran University of cience and Technology, Tehran, Iran, in 999,, and, respectively. ince 7, he has been with the Electrical Department, Razi University, Kermanshah, Iran, where he is now an Associate Professor. His main research interests are low power analog and digital I design; RF I design; and modeling and simulation of RF/mixed signal I. He is also interested in microwave devices and artificial intelligence systems. Alireza GOETANIFAR was born in Kermanshah, Iran in 99. He received his B.c. and M.c. degrees in Electronics Engineering from the Islamic Azad University, Kermanshah, Iran in and 7, respectively. He is member of the Applied omputational Electromagnetics ociety (AE). His current research includes microwave passive circuits and RF integrated circuit design. Amirhossein GHADERI was born in Kermanshah, Iran in 99. He received his B.c. and M.c. degrees in Electronics Engineering from the Islamic Azad University, Kermanshah, Iran in and 7, respectively (Honor). He has been selected as the best student in the Electronics Engineering Department and awarded by the university president in. He is now member of the Young Researchers and Elite lub. His current research includes microwave passive circuits and RF integrated circuit design. Navid AIMPOUR was born in Kermanshah, Iran in 99. He received his B.c. degree in Electronics Engineering in from the Islamic Azad University, Kermanshah, Iran. He is member of the Islamic Azad University Kermanshah Branch, Young Researches lub. His current research includes RF/microwave circuit and digital integrated circuit design.