ADVANCED ELECTROMAGNETICS, VOL. 6, NO. 1, MARCH 2017 Highly Selective Dual-Mode Micostip Bandpass Filtes Using Tiangula Patch Resonatos K.G. Avinash, I. Sinivasa Rao School of Electonics Engineeing, VIT Univesity, Velloe, India E-mail: avinashk.ng2013@vit.ac.in Abstact In this pape, highly selective dual-mode micostip bandpass filtes ae poposed using hoizontal and vetical slots fomed on the suface of a tiangula patch. Slots ae esponsible fo splitting and coupling of dual degeneate modes and also facilitate in contolling thei esonant fequencies by vaying the dimensions of the slots. Hoizontal and vetical slots eoute the diection of the flow of cuent on the suface of the patch, which esults in switching of tansmission zeos. Two 2-pole and one 4-pole dual-mode filtes ae designed, simulated and fabicated. Two-pole filtes have tansmission zeos on side of the passband and fou-pole filte have tansmission zeos on both sides of the passband. The designed filtes exhibit a factional bandwidth of less than 7 % and thee is a good ageement between simulated and measued esults. 1. Intoduction Micostip filtes with asymmetic fequency esponse on eithe side of the passband ae needed in moden mobile and wieless communication systems. These filtes have bette selectivity, sensitivity and theeby impove the efficiency of the spectum utilization. The filtes of this kind find specific applications in duplexes and multiplexes. Geneally, asymmetic filtes ae ealized by using coss-coupled filte configuations [1-3]. Single mode HTS thin film filtes using pseudo-intedigital coupled lines ae employed to achieve asymmetical ejection pefomance [1]. Micostip squae open loop esonatos [2] ae used to intoduce eithe positive o negative coss coupling. This causes finite attenuation pole to appea eithe in lowe o uppe side of the passband. In [3] closed squae loop esonato with vaied petubation is used to achieve asymmetic fequency esponse utilizing dual degeneate modes. Dual-mode esonatos ae pefeed as the numbe of esonatos equied will become half fo a given degee which futhe educes the size of the filte. The basic geometies used fo the ealization of dual-mode filtes ae loop [4-7] and patch esonatos. Patch esonatos employing cicula, squae and tiangula shapes ae epoted [1], [8-9]. Patch esonatos have many inteesting featues such as high powe handling capability, lowe conducting losses and ease of fabication at millimete waves. Highly selective bandpass filtes wee ealized by using two diffeent esonant modes of tiangula patch with cascading topology [8]. Dual-mode opeation of equilateal tiangula patch esonato was theoetically studied in [10], and they poved that dual degeneate mode is obtained by otation and supeposition of fundamental mode. A tiangula patch bandpass filte with multi-mode opeation employing highe ode modes that utilized factal defection is ealized [11-12]. An isosceles tiangula patch esonato (ITPR) is pesented in [13] with cone s cut and slits to ealize wideband bandpass filte opeating in X-band. A ightangled tiangula patch esonato with factal hole is used to achieve single and dual-band bandpass esponses [14]. Diffeent types of DGS esonatos ae also used to ealize selective and tunable bandpass filtes as detailed in [15-18]. Vey few asymmetic filtes ae designed due to difficulties in contolling and aanging coss couplings in plana configuation and still thee is a scope to ealize such high selectivity filtes. In this pape, two-pole and fou-pole filtes ae designed using micostip tiangula patch employing hoizontal and vetical slots. These slots ae used to excite dual degeneate modes and also to contol the position of tansmission zeos on eithe side of the pass band. These slots will change the diection of the cuent flowing on the suface of the patch esulting in tansmission zeo switching fom lowe passband to uppe passband. The est of the pape is oganized as follows. Section II explains with design chaacteistics of dual-mode tiangula patch and its suface cuent distibution. Pototype filtes ae designed and simulated, in section III, with fist filte exhibiting tansmission zeo on lowe side of the passband, second filte showing tansmission zeo on uppe side of the passband and thid filte displays tansmission zeos on both sides of the passband. Expeimental esults ae pesented in section IV. Finally, conclusions ae given in section V. 2. Dual-mode Resonato Accoding to Wheele s cavity model, suounded by magnetic walls, thee ae no electomagnetic field vaiations along the thickness of the substate diection. Electic field E Z satisfies Helmholtz wave equation [19],
2 + + k 2 2 m, n, l EZ = 0 (1) x y 4 2 2 km, n, l m mn n (2) 3a Whee E Z is given as Am, n, lt x, y, A m, n, l is constant based on the magnetic bounday conditions, k denotes m, n, l wave-numbe constant and T x, y is given as 2 x 2 2 m n y T x, y cos l.cos 3a 3 3a 2x 2 2 n l y + cos m.cos 3a 3 + 3a 2x 2 2 l m y cos n.cos (3) 3a 3 3a j Ez Ez Am, nt ( x, y), H x y o Figue 1: Coupling aangement between dual degeneate modes of a tiangula patch. H y j Ez, x E E H 0 (4) o x y z The esonant fequencies of dominant mode and highe ode modes of the tiangula patch ae given by 2c f 1,0, 1 (5) a 3 2c fm, n, l m mn n 3a 2 2 (6) Whee c is the velocity of light, is the elative dielectic constant of the substate, and a is the side dimension of the tiangle. We have chosen a as 12mm, which gives the fundamental esonant fequency of 5.16 GHz fo dominant mode with m = 1, n = 0. The equilateal tiangula patch is known to exhibit dual-mode popety [10]. In a tiangula patch esonato the coupling of two degeneated modes can be done by distubing the symmety of the esonato o by adding slot in the stuctue. The dual degeneate mode is obtained by otating the othe mode to 90 o in the coodinate system and supeposition of fundamental mode. Unlike the squae and cicula patches, these degeneate modes do not couple to each othe diectly, but couple to input and output pots by ceating two paallel paths fom input to output. The coupling aangement is shown in Figue 1. These two modes ae also efeed to as even and odd modes. A fullwave HFSS Eigen mode simulato is used fo simulating the stuctues. RT duiod substate with a dielectic constant of 10.2 and with a height of 0.635 mm is used fo simulating the stuctues. The suface cuent distibution fo even and Figue 2: Suface cuent distibution of tiangula patch odd mode, even mode. an odd mode is depicted in Figue 2. Fo even mode, cuent is concentated in the uppe pat of the patch along the slant sides of the tiangle, wheeas fo odd mode, cuent is concentated aound base of the tiangle. The suface cuent of the even mode can be eoiented by adding a hoizontal slot nea to the base of the patch esonato and similaly the odd mode cuent can be eoiented by adding a vetical slot nea to the top of the patch esonato. The oientation of suface cuents fo specified hoizontal and vetical slots is shown in Figue 3. Fom the Figue 3, it is obseved that hoizontal slot does not distub odd mode, 78
wheeas it petubs the field of even mode. Similaly a vetical slot does not distub even mode, but it will alte the field of odd mode. We can notice that the diection of the cuent flowing on the suface of the patch is evesed, when we change fom hoizontal to vetical slot. This eouting of suface cuent distibution leads to switching of tansmission zeos. edges of the tiangle. It is also achieved by incopoating slots ove the suface of the patch. The dual esonant modes unde weak coupling ae shown in Figue 4. The esonant fequencies of degeneated modes can be contolled by vaying the slot lengths. Figues 5 and 5 shows the vaiation of esonant fequencies of odd and even modes with espect to vaiation in the hoizontal and vetical slot lengths. Fom Figue 5, it is obseved that by inceasing the length of the hoizontal slot, the esonant fequencies of even mode ae shifting fom 5.05 GHz to 5.25 GHz while the odd mode is unchanged. Fom Figue 5, it is found that vaiation of vetical slot affecting the odd mode fequencies wheeas even mode fequencies ae hadly affected. Figue 3: Suface cuent distibution of tiangula patch afte adding slots hoizontal slot vetical slot. Figue 5: Sepaation of dual esonant fequencies with hoizontal slot and vetical slot. Figue 4: Splitting of dual modes of the patch esonato. The splitting of dual modes can be done by defoming the equilateal tiangle to isosceles o cutting the 3. Bandpass Filte Design Based on the above discussions and simulations, two dualmode and one quaduple-mode filtes ae designed. All the filtes ae fed by 50 Ω feed lines at the bottom of the tiangula patch with paallel coupling. Ealie epoted wok [9] uses cascading of tiangula patch esonatos with changing the position of feed lines to achieve selective filtes. In contast to slant line feed, the poposed design utilizes hemline feed, and also slots ae used to position the tansmission zeos on eithe side of the cente fequency using a single equilateal tiangula patch, without changing 79
the position of feed lines. Figue 6 shows the fist dualmode filte (Filte A), which uses hoizontal slot placed at the bottom side of patch. Figue 6 depicts second dualmode filte (Filte B), which employs vetical slot placed at the top side of the patch. Figue 6(c) illustates quaduplemode filte which utilizes both hoizontal and vetical slots. The stuctual paametes of all the designed filtes ae given in Table 1. The side dimension of the tiangula patch a is chosen as 12 mm. All the thee filtes ae designed using commecially available full-wave EM simulato High Fequency Stuctue Simulato. Figue 6: Two-pole bandpass filte using hoizontal slot (Filte A), two-pole bandpass filte using vetical slot (Filte B), (c) fou-pole filte using both hoizontal and vetical slots (Filte C). Filte A Figue 7: Simulation esults fo vaious positions (slot_pos) of hoizontal slot fo a slot length (slot_ho) of 5.8 mm. Filte B Figue 8: Simulation esults fo vaious positions (slot_pos) of vetical slot fo a slot length (slot_ve) of 5.7 mm. (c) Filte C The length and position of both hoizontal and vetical slots is optimized by using full wave EM simulato. The lengths of slots ae appoximately aound λ/10. The position of slots affects both insetion and etun loss esponse of the filte. Figue 7 shows the simulated esults fo vaious slot positions of hoizontal slot, vaied above with espect to the slot position shown in Figue 6, keeping length of the hoizontal slot fixed at 5.8 mm in steps of 0.2 mm. Similaly Figue 8 depicts the simulation esults fo vaious positions of vetical slot, vaied above with espect to the slot position shown in Figue 6, keeping length of vetical slot constant by 5.7 mm in steps of 0.2 mm. The slot positions ae chosen in such way that both insetion and etun loss behave well, and the coesponding slot positions ae given in Table 1. 80
Table 1: Dimensions of the filte stuctues (mm). Filte type stip_wid slot_wid slot_ho slot_ve Gap len slot_pos slot_pos_h slot_pos_v A 0.59 0.2 5.8 ---- 0.2 1.2 0.86 ---- ---- B 0.59 0.2 ---- 5.7 0.2 0.8 3.46 ---- ---- C 0.59 0.2 6.0 6.0 0.2 1.2 ---- 2.31 3.17 4. Results The filtes descibed above ae fabicated using RT Duiod substate with dielectic constant of 10.2 and substate height of 0.635 mm. Coppe cladding is used with a thickness of 0.035 mm. The photogaphs of the fabicated Filte A (c) Filte C Figue 9: Photogaphs of the fabicated two pole and fou pole filtes. filtes ae shown in Figue 9. Agilent s N99181A seies vecto netwok analyze is used to measue the esults. Figue 9 shows the dual-mode filte (Filte A) with hoizontal slot and the filte is esonating at 5.06 GHz. The simulated and measued esults of etun loss and insetion loss ae shown in Figue 10. Fom Figue 10 it is obseved that thee is a tansmission zeo at the lowe passband of the filte which is at a fequency of 4.91 GHz. The simulation esults indicate an insetion loss of 1.93 db and etun loss of 20.58 db with a factional bandwidth of 4.94 %. The measued insetion and etun loss ae at 2.27 db and 20.58 db espectively. Filte B 81
Figue 10: Simulated and measued esults of bandpass filte using hoizontal slot (Filte A) etun loss, insetion loss. A tansmission zeo at the uppe passband can be intoduced by eplacing the hoizontal slot with a vetical slot. Figue 9 shows the second dual-mode filte (Filte B) with a vetical slot and the filte poduces tansmission zeo at the uppe passband. Figue 11 and 11, shows the simulated and measued etun loss and insetion loss esponse of the Filte B. Simulation esults show that the cente fequency of the filte B is at 4.95 GHz with an insetion loss of 1.67 db and etun loss of 21.78 db. The factional bandwidth of the filte is 4.84 %. The measued insetion and etun loss ae at 2.48 db and 12.69 db espectively. The geneation of tansmission zeos on eithe side of the cente fequency i.e. uppe o lowe passband will poduce vey high selectivity on the espective passband which is a majo equiement fo many applications like diplexes and multiplexes. Bandpass filte with tansmission zeos on both sides of the passband esembles the ideal filte esponse which esults in high attenuation on both sides of the stopband. A fou-pole filte with tansmission zeos on both sides of the passband is shown in Figue 9(c). Hee we have combined the two patch Figue 11: Simulated and measued esults of bandpass filte using vetical slot (Filte B) etun loss, insetion loss. 82
Figue 12: Simulated and measued esults of bandpass filte using both hoizontal and vetical slots (Filte C) etun loss, insetion loss. exhibits a minimum stopband attenuation level of 10 db on both sides of stopband. The midband fequency of the filte is at 4.82 GHz and factional bandwidth is aound 6.43 %. The simulated and measued insetion losses ae 1.5 db and 2.40 db espectively. Similaly, simulated and measued etun losses of the filte ae 21.2 db and 20.2 db espectively. The small diffeences between simulated and measued esults may be due to dielectic and conducto losses, and as well as filte housing effect, since we have not enclosed the filte in metal box fo measuement. The designed filtes ae compaed with existing filte designs, and pefomance analysis is shown in Table 2. The poposed filtes can be used to ealize both symmetic and asymmetic filte esponses. esonatos with hoizontal and vetical slots to obtain tansmission zeos on both sides of passband. Fom the simulated the measued esults shown in Figue 12, the filte Table 2. Pefomance analysis of the designed filtes with ealie epoted patch esonato filtes. Refeence No. Patch Topology Side dimen sions (mm) Cente fequency (GHz) Insetion Loss (db) Factional Bandwidth (FBW) Fequency Response [20] Squae 20 1.62 3.4 1.6 Symmetic [9] Tiangula [I] Tiangula [II] 15 4.1 ------ ------ Asymmetic [21] Sta type [I] 2.98 2 4.99 15 Sta type [II] 2.98 2 4.69 Asymmetic [22] Cicula 36 1.58 1.41 20.25 Symmetic [14] Tiangula 5.7 10.36 2.08 55 Symmetic This wok Tiangula [I] Tiangula [II] Tiangula [III] 12 5.06 4.95 4.82 2.27 2.48 2.40 4.94 4.84 6.43 Asymmetic & Symmetic 5. Conclusion Thee highly selective bandpass filtes ae designed using dual-mode tiangula patch esonatos. Hoizontal and vetical slots ae used to poduce tansmission zeos on eithe side of passband. Degeneated modes ae coupled by vaying the slot positions and dimensions. Two-pole filtes have tansmission zeos on one side of the passband wheeas quaduple-mode filte is moe selective with tansmission zeos on both sides of the passband. Fom the measued esults, it is obseved that insetion loss and etun loss esponse of all filtes ae close to bandwidth of less than 7 % associated with high selectivity and high powe handling capability. 83
ADVANCED ELECTROMAGNETICS, VOL. X, NO. X, MONTH 20XX Acknowledgement The authos ae thankful to Bapuji Institute of Engineeing & Technology, Davangee, Kanataka, India, fo thei kind suppot and encouagement towads the successful completion of this wok. Refeences [1] R.R Mansou, Design of supeconductive multiplexes using single mode and dual mode filtes, IEEE Tans. Micowave Theoy Tech., Vol. 42, pp. 1411-1418, 1994. [2] J.S. Hong and M.J. Lancaste, Micostip coss-coupled tisection bandpass filtes with asymmetic fequency chaacteistics, IEE Poc. Micowave, Antennas Popag., Vo. 146, pp. 84-90, 1999. [3] G.M. Eylimaz, C. Kapuz and A. Gou, Dual-Mode micostip filtes with adjustable tansmission zeos, IET Micow. Antennas Popag., Vol. 2, pp. 839-847, 2008. [4] I. Wolff, Micostip bandpass filte using degeneate modes of a micostip ing esonato, Electonic Lett., Vol. 8, pp. 302 303, 1972. [5] J.S. Hong and M.J. Lancaste, Bandpass chaacteistics of new dual mode micostip squae loop esonatos, Electonics Lett., Vol. 31, pp. 891-892, 1995. [6] C. Lugo and J. Papapolymeou, Bandpass filte design using a micostip tiangula loop esonato with dual mode opeation, IEEE Micowave Wieless Compo. Lett., Vol. 15, pp. 475-477, 2005. [7] J.S. Hong and M.J. Lancaste, Micostip bandpass filte using degeneate modes of a novel meande loop esonato, IEEE Micowave Guided wave Lett., Vol. 2, pp. 371-372, 1995. [8] J.A. Cutis and S.J. Fiedziuszko, Miniatue dual mode micostip filtes, IEEE MTT-S Dig., pp. 443-446, 1991. [9] J.S. Hong and M.J. Lancaste, Micostip tiangula patch esonato filtes, IEEE MTT- S Dig., pp. 331-334, 2001. [10] J.S. Hong and Shuzhou Li, Theoy and expeiment of dual mode micostip tiangula patch esonatos and filtes, IEEE Tans. Micowave Theoy Tech., Vol. 52, pp. 1237-1243, 2004. [13] J.-K. Xiao, Q.-X. Chu and H.-F. Huang, Tiangula esonato bandpass filte with tunable opeation, Pogess in Electomagnetic Reseach, Vol. 2, pp. 167-176, 2008. [14] A.R.H. Alahwai.and A. Ismail, Compact wideband bandpass filte using single cones-cut isosceles tiangula patch esonato, Pogess in Electomagnetic Reseach C, Vol. 14, pp. 227-237, 2010. [15] A. Boutejda, A. Elshebini, A. Balalem, J. Machacand A. S. Oma, Design of new DGS haipin micostip bandpass filte using coupling matix method, Poc. PIERS'2007, Pague, pp. 261-265, 2007. [16] A. Boutejda, A.A. Ibahim, W.A.E. Ali, Design of compact size and tunable bandpass filte fo WLAN applications, Electonics Lettes, Vol. 52, No. 24, pp. 1996-1997, 2016. [17] A. Boutejda, A new appoach to design compact tunable BPF stating fom simple LPF topology using a single T-DGS-esonato and ceamic capacitos, Micowave and Optical Technology Lettes, Vol. 58, No.5, pp. 1142-1148, 2016. [18] A. Boutejda, Design of 5 GHz-compact econfiguable DGS-bandpass filte using vaacto-diode device and coupling matix technique, Micowave and Optical Technology Lettes, Vol, 58, No. 2, pp. 304-309, 2016. [19] R. Gag, P. Bhatia, I. Bahl, Micostip Antenna Design Handbook, Boston-London: Atech House, 2001. pp. 429-430. [20] Lei Zhu, P-M Wecowski and Ke Wu, New plana dual-mode filte using coss-slotted patch esonato fo simultaneous size and loss eduction, IEEE Tans. Micow. Theoy Tech., Vol. 47, No. 5, pp. 650-654, May 1999. [21] S.R. Zinka, Akhilesh Mohan and Animesh Biswas, Bandpass filte ealization using degeneate dual-modes of a new type of patch esonato fo significant size eduction, Poceedings of Asia Pacific Micowave Confeence, pp. 1-4, 2007. [22] Y.K. Singh and Ajay Chakabaty, Miniatuized dualmode cicula patch bandpass filtes with wide hamonic sepaation, IEEE Micow. Wieless Compo., Vol. 18, pp. 584-586, Sept. 2008. [11] J.-K. Xiao, Q.-X. Chu and S. Zhang, Novel micostip tiangula esonato bandpass filte with tansmission zeos and wide bands using factal-shaped defection, Pogess in Electomagnetic Reseach, Vol. 77, pp. 343-356, 2007.