Quarter-Wavelength Stub Bandpass Filter with T-type Inverter for Harmonic Suppressed Application

Transcription

1 Iteratioal oural of Cotrol ad Automatio Vol. 6 No. April 03 Quarter-Wavelegth Stub Badpass Filter with T-tpe Iverter for Harmoic Suppressed Applicatio Su-Ku Noh ad Tae-Soo Yu * Dept. of Photoelectroics Iformatio Chosu College of Sciece & Techolog Gwagju Korea Dept. of Radio Mobile Commuicatio Eg. Hoam Uiv. 330 Eodeugo Gwagsa-gu Gwagju Korea Tel) Fax) s7078@hamail.et easteru@gmail.com Abstract I this paper the desig method of stub badpass filter (BPF) is suggested b equatios of the tapped-lie geometr ad the λ g /4 stub BPF with T-tpe iverter is implemeted for the harmoic suppressig for ISM bad. Desig parameters for the tapped-lie geometr are obtaied usig the equivalet circuit of the -iverter for the filter prototpes ad the T-tpe iverter is realized b the equivalet circuit of the quarter wavelegth trasmissio-lie. The harmoic suppressed λ g /4 stub BPF is fabricated o Teflo substrate ad its harmoics of the λ g /4 stub BPF are suppressed over 30 db up to 0 GHz. Kewords: badpass filter (BPF) short-stub harmoic tapped-lie iverter. Itroductio I the micrstrip filter a tapped feedig method has bee applied to various filter tpes such as a comblie filter a iterdigital filter a edge coupled filter a square rig filter ad so o [-8]. For the desig of a filter usig tapped-lie a ope-wire-lie equivalet circuit approach has bee suggested [ 3] ad the the desig method with the couplig coefficiet ad the exteral qualit factor Q e has bee geerall used whe eeded for complicated electro-magetic (EM) field aalsis [4-9]. The tapped feedig method is realized such that the -iverter of filters is replaced with tapped feed-lie. Especiall i our previous wor tapped-lie is realized o the ope-stub ad additioal trasmissio-lie which has egative electrical legth [7-9]. Otherwise the stub badpass filter (BPF) has bee widel used because of its simplicit i implemetatio ad eas coectivit with other compoets although the stub BPF has a relativel broad badwidth [5]. Also i order to obtai high selectivit of BPFs more resoators are used or the ellipticfuctio respose is used such as ope-loop resoators ad rig resoators. The ellipticfuctio BPFs have trasmissio zeros ad show high selectivit b usig smaller umber of the resoator [5]. As usig tapped-lie geometr the trasmissio zero ca be obtaied b the ope-stub ad BPFs ca be realized with high selectivit. I this paper a harmoics suppressed λ g /4 short-stub BPF is suggested ad realized b isertig the T-tpe equivalet circuit for the λ g /4 trasmissio-lie as the iverter. This filter provides compact desig sharp sirt characteristic ad secod ad third harmoics suppressed characteristic. 93

2 Iteratioal oural of Cotrol ad Automatio Vol. 6 No. April 03. Aalsis of Tapped-lie Method for λ g /4 Stub BPF I our previous wor the -iverter ca be alterated as the ope-stub ad additioal trasmissio-lie ad their electrical legths are as followed [7]: a ta () 0 a 0 a 0 0 ta. () 0 0 where θ 0 ad θ 0 are the electrical legth of the ope-stub ad trasmissio-lie respectivel ad ad a are the ormalized admittace of the lie ad source respectivel. i 0 ' λg/4 ' +' λg/4 a jbr jbr jbr (a) + i' θ λg/4 a jbr jbr + θ O.C. (b) Figure. Cofiguratio of the filter with (a) divided -iverter ad ier tapped-lie (b) a equivalet circuit For the tapped-lie method i the stub BPF each -iverter of the ier sectio is divided ito three sectios as show i Figure (a) ad ABCD parameters are used for the cascaded etwor because the overall parameters are computed b simpl multiplig the matrices of the idividual etwor. Here is the ormalized admittace of the λ g /4 lie as show i Figure (a). Figure (a) shows the circuit cofiguratio of a filter with divided -iverters. I Figure (a) because B r is 0 at the resoat frequec the admittace toward source i the th resoator is give b 94

3 Iteratioal oural of Cotrol ad Automatio Vol. 6 No. April 03 0 a a ; odd ; eve. (3) The divided -iverter ca be represeted b the equivalet circuit of the tapped-lie as show i Figure (b). The ier tapped-lie is composed of the trasmissio-lie ad the ope-stub with the ormalized admittace +. The electrical legths of the stub (θ ) ad lie (θ ) for the ier tapped-lie ca be determied b the iput admittace such as the case i tapped-lie feedig. The iput admittace toward source i ' as show i figure (b) ca be obtaied as j ta. (4) i ' j ta j ta O the other had the ormalized iput admittace prior to the th iverter is give b i ( ' ). (5) If the electrical legth of the trasmissio-lie is assumed to be egative such as the case i tapped-lie feedig [8] the electrical legths of the trasmissio-lie ad the ope-stub i the th resoator ca be give as equatio (6) ad (7) respectivel which are derived from equatio (4) ad (5). ' ' ta. (6) ( ') ta. (7) ( ') θ Θ- θ Θ θ λg/4 Θ- θ + Θ λg/ r r r r θ0 θ Θ-+ Θ0 θ0 θ Θ-+ 0 st Reso. d Reso. 'th Reso. Θ0 + 'th Reso. (a) 95

4 Iteratioal oural of Cotrol ad Automatio Vol. 6 No. April (b) Figure. Schematic of (a) the λ g / stub BPF ad (b) λ g /4 stub BPF usig tapped-lie geometr A λ g /4 stub BPF is suggested usig tapped-lie geometr as show i Figure (a). I Figure the resoators are coected b the λ g /4 trasmissio-lie. Also + is the admittace of the λ g /4 lie betwee resoators ad θ 0 θ ad θ are the electrical legths of the ope-stubs which are determied b equatio () ad (6) ad θ 0 θ ad θ are the electrical legths of the trasmissio-lies with egative values which are determied b equatio () ad (7). Also Θ 0 Θ ad Θ -+ are the electrical legths of the ope-stubs ad Θ 0 Θ ad Θ -+ are the electrical legths of the trasmissio-lies which are determied b the -iverter ad the output admittace toward load. The parameters for toward load ca be obtaied b substitutig admittace toward load - for oe toward source. The ormalized admittace toward load i the th resoator - is defied as eve odd b b ; ) ( ; ) ( 3 3 (8) where b is the ormalized load admittace. I case of a smmetric structure such that a filter has a odd order ad the same iput ad output admittace Θ has the same value with θ -+. The λ g /4 stub BPF ca be desiged as show i Figure (b) where r is the admittace of the th resoator. Because the admittace of each λ g /4 resoator becomes twice as large as that of a λ g / resoator the λ g /4 stub BPF ca be desiged usig a λ g /4 resoator with a double resoator admittace or with a half fractioal badwidth of a desired oe. The electrical legths of a ope-stub ad short-stub ca be defied as follows [8]: s o s o s o (9)

5 Iteratioal oural of Cotrol ad Automatio Vol. 6 No. April 03 s. s. s. s. g 4 g 4 0 s. s. g 4 ad the electrical legth of each resoator is almost quarter wavelegth. 3. Desig of Harmoic Suppressed λ g /4 Stub BPF 0 (0) (a) (b) Figure 3. Schematic of (a) the λ g /4 lie as the th iverter ad (b) the T-tpe iverter as alteratig b the T-tpe equivalet circuit for the λ g /4 lie For the tapped-lie geometr the -iverter ca be alterated as the ope-stub short-stub ad additioal trasmissio-lie. Also their electrical legths ad impedaces are demostrated. Figure 3(a) ad (b) are the λ g /4 lie as the th iverter for the λ g /4 stub filter ad the T-tpe iverter as alteratig b the T-tpe equivalet circuit for the λ g /4 lie respectivel where Z i is the characteristic impedace ad θ i is the electrical legth of the 97

6 Iteratioal oural of Cotrol ad Automatio Vol. 6 No. April 03 stub ad lie (i = T L S ad = 3). The T-tpe equivalet circuit of the λ g /4 lie ca be obtaied b usig the ABCD matrix. Geeral equatios for Z L ad Z S are derived as follows: Z Z Z T L () ta L Z ta T S S. () ta L where Z T is the impedace of the λ g /4 lie as the th iverter ad Z L Z S θ L ad θ S are impedaces ad electrical legths of the th lie ad stub respectivel. Also the λ g /4 short-stub BPF usig the tapped-lie geometr ca be desiged as show i Figure 4(a). The impedace ad electrical legths for the lie ad ope/short-stub ca be calculated from equatio (9) ad (0). Especiall the electrical legth of the trasmissio-lie as the th iverter θ T is 90. For compariso the stub ad trasmissio-lie as the iverter for the λ g /4 stub BPF is desiged 50 Ω i.e. Z OS = Z SS = Z T = 50 Ω. To demostrate the feasibilit ad usefuless of the desig the short-stub BPF usig the tapped-lie geometr is desiged the 5th order chebschev prototpe filter with 0.0dB ripple ad 0% badwidth at the ceter frequec of.4 GHz. (a) (b) Figure 4. Structure of (a) the λ g /4 stub BPF with 5 th order ad (b) the proposed harmoic suppressed stub BPF with the T-tpe iverter 98

7 Iteratioal oural of Cotrol ad Automatio Vol. 6 No. April 03 Table. Parameters of the proposed harmoic suppressed λ g /4 stub BPF λ g /4 short-stub BPF with T-tpe iverter θ OS = θ OS θ S = θ S4 5.6 θ SS = θ SS θ L = θ L4 3.0 θ OS = θ OS θ S = θ S θ SS = θ OS θ L = θ L θ OS Z S = Z S4 07.7Ω θ SS Z L = Z L4 87.0Ω Z S = Z S3 6.3Ω Z L = Z L4 7.0Ω Figure 4(b) shows the structure of the suggested harmoic suppressed stub BPF. Each λ g /4 trasmissio-lie i figure 4(a) is alterated the T-tpe iverter. I order to suppress the secod ad third-mode harmoics two differet T-tpe iverters with differet electrical legths of the ope-stub are desiged as show i Figure 4(b). Parameters i Figure 4(b) ca be obtaied b usig equatio () ad (). The the parameters of two tpes of stub BPFs are summarized i Table. I Table θ OS ad θ SS are the electrical legths of the th opestub ad short-stub respectivel. Also θ S ad θ L is the electrical legths of the th stub ad lie respectivel for the T-tpe iverter. As BPFs with odd order are smmetric parameters of the BPF with 5th order are smmetric. Also Z S ad Z L are the impedace of the th stub ad lie respectivel. 4. Maufacturig ad Results of Harmoic Suppressed Short-Stub Badpass Filter Figure 5. Fabricated harmoic suppressed λ g /4 stub BPF with T-tpe iverter I this paper the harmoic suppressed stub BPF with the T-tpe iverter is desig with the badwidth of 0% at the ceter frequec of.4 GHz for ISM bad usig EM simulator. To validate the desig cocept two filters are built o a copper coated tefro substrate with a dielectric costat of.54 a height of 0.54 mm ad a metal s thicess of 0.07 mm. I the experimet the measuremet has bee doe with a Agilet 850C etwor aalzer usig 99

8 Iteratioal oural of Cotrol ad Automatio Vol. 6 No. April 03 stadard SMA coector. Figure 5 shows the photograph for the proposed harmoic suppressed stub BPF. The size of the proposed stub BPF is mm. The overall simulated ad measuremet results of the harmoic suppressed λ g /4 stub BPF with iserted T-tpe iverter agree ver well as show i Figure 6. From the simulatio results of the Figure 6 the covetioal λ g /4 stub BPF has the higher mode harmoics however the proposed stub BPF with T-tpe iverter has the characteristic of the secod ad third mode harmoics suppressio up to 0 GHz. Also the proposed short-stub BPF with T- tpe iverter is simulated with a isertio loss of. db ad a retur loss of less tha 0 db at the ceter frequec.38 GHz. While the measuremet data show the isertio loss of.64 db ad retur loss of 0 db at the ceter frequec of.37 GHz with suppressed harmoics uder 30 db up to 0 GHz b the additioal ope stubs of the T-tpe iverter. Figure 6. Simulated ad measured results of frequec resposes for the harmoic suppressed λ g /4 stub BPF with T-tpe iverter 5. Coclusio I this paper a simplified desig method of the harmoic suppressed short-stub BPF for ISM applicatios is proposed b usig the covetioal short-stub BPF with iserted T-tpe iverter. The T-tpe iverter ca be desiged b the equivalet circuit of the quarter wavelegth trasmissio-lie ad ca be suppressed harmoics b the ope-stub. Proposed short-stub BPF has two differet T-tpe iverters ad the secod ad third-mode harmoics of the proposed short-stub BPF are rejected. Also the suggested short-stub BPF desig allows arrower badwidth ad suppressed the secod ad third mode harmoics implemetatio compared to the covetioal short-stub BPF which is tpicall provided. The proposed filter is easil implemeted ad itegrated with other devices ad circuits. 300

9 Iteratioal oural of Cotrol ad Automatio Vol. 6 No. April 03 Refereces [] Y. C. Yoo ad K. H. Eom Iteratioal oural of Future Geeratio Commuicatio ad Networig vol. 3 o. 4 (0). [] E. G. Cristal IEEE Tras o Microwave Theor Tech vol. o. 3 (975). [3]. L. Naraaa K. Krisha L. Redd G. V. Subrahmaam ad M. Sidhu Iteratioal oural of Future Geeratio Commuicatio ad Networig vol. o. 5 (0). [4]. S. Wog IEEE Tras o Microwave Theor Tech. vol. 6 o. 7 (979). [5]. S. Hog ad M.. Lacaster Microwave filters for RF/microwave applicatios Wile (00). [6] S. Caspi ad. Adelma IEEE Tras o Microwave Theor Tech. vol. 4 o. 36 (988). [7] T. S. Yu T. U. Hog B. Lee.. Choi. Y. Kim K. B. Kim ad. C. Lee Microwave ad Optical Tech. Lett. vol. 6 o. 49 (007). [8] T. S. Yu Y. K. Yoo B. Lee.. Choi. Y. Ki ad. C. Lee Microwave ad Optical Tech. Lett. vol. 0 o. 5 (009). 9] T. S. Yu S. K. Noh H.. Kim E. K. Oh H. M. So ad. C. Lee Microwave ad Optical Tech. Lett. vol. o. 53 (0). Authors Su-Ko Noh received his B.Sc. the M.Sc. ad the D.Sc. degrees i Electroics Egieerig from Chosu Uiversit of Gwagju Republic of Korea i ad 000 respectivel. From March 00 to August 004 he was a Research Professor i the Divisio of Electroics ad Iformatio Egieerig Chobu Natioal Uiversit Republic of Korea. From Sept. 004 to Feb. 0 he has bee a assistat professor i the Departmet of Mobile Commuicatios Egieerig Hoam Uiversit Gwagju Korea. Sice Oct. 0 he is a assistat professor i the dept. of Photoelectroics Iformatio Chosu College of Sciece & Techolog Gwagu Republic of KOREA. He is a Member of IEEE CN IEEK ad KICS. His major research iterests iclude mobile commuicatios radio propagatio DMB RFID RF devices Atea ad NFC. Tae-Soo Yu received his M.S. ad Ph.D. degrees i Radio Sciece ad Egieerig from Kwagwoo Uiversit. He spet a oe ear as a postdoctoral fellow at the SUNY at Buffalo. Sice 00 he is a full-time lecturer i the Dept. of Mobile Commuicatios Egieerig of Hoam Uiversit. His research iterests iclude CRLH-lie WPT sstem millimeter-wave devices usig micromachiig ad RF devices. 30

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