Designing and Tuning RF Filters to a Prescribed Specification

Transcription

1 Desigig ad Tuig RF Filters to a Prescribed ecificatio Oe for Busiess Day 8 th August 03 Dr. Richard Parry Radio Desig Ltd, hiley, West Yorkshire

2 Radio Desig Radio Desig is becomig recogised as the world leader i the desig ad maufacture of custom filter systems for cellular etworks Hardware Reair ervices ca reair 3 rd arty roducts global resece We suly filter systems to leadig cellular ifrastructure OEMs ad cellular etwork oeratig comaies worldwide Our roducts are used i some of the worlds biggest shared cellular etworks

3 What is a RF Filter? A device for isolatig a defied bad of frequecies from withi the radio sectrum We are cocered maily with mobile commuicatios chaels i the UHF bad We eed to isert or extract frequecies withi this bad without geeratig iterferece i, or receivig iterferece from systems i adjacet bads (TV, WiFi, Radio etc.)

4 Filters i ystems I a mobile commuicatios basestatio, filters are used To combie sigals from differet systems so that they ca use the same atea structure ANT f ystem Badass ystem Badass ystem ystem f f

5 Filters i ystems I a mobile commuicatios basestatio, filters are used To combie sigals from differet systems so that they ca use the same atea structure ANT f UMT Tx Badass UMT Tx Badsto UMT Rx Badass UMT Rx Badsto UMT GM f f

6 Ideal Trasfer Fuctio H j Passbad Trasmit all the ower with ero distortio Zero loss Uity gai Flat amlitude Zero hase distortio Liear hase Flat grou delay (Phase gradiet) tobad - Prevet trasmissio of all ower i the uwated bad(s) Zero gai Abrut trasitio from assbad to stobad (electivity) 0 - c 0 + c 0 H j 0 - c 0 + c Ideally we wat All or Nothig This is ot ossible!! o what is ossible?? H j V out Vi V i V out

7 Real Trasfer Fuctio H j Passbad Trasmit the maximum ossible ower with low distortio Low loss Gai close to uity Low amlitude rile Low hase distortio Liear hase over most of the bad Flat grou delay (Phase gradiet) tobad - Prevet trasmissio of as much ower as ossible i the uwated bad(s) High atteuatio tee trasitio from assbad to stobad (electivity) 0 - c 0 + c 0 H j 0 - c 0 + c igle Resoator Low loss at the cetre frequecy High Q Good hase resose close to cetre Gradual trasitio to stobad Poor electivity V i H j V out Vi L V out H ( j) + jk 0 0 K L L

8 Real Trasfer Fuctio H j Passbad Trasmit the maximum ower with low distortio Low loss Gai close to uity Low amlitude rile Low hase distortio Liear hase over most of the bad Flat grou delay (Phase gradiet) tobad - Prevet trasmissio of as much ower as ossible i the uwated bad(s) High atteuatio tee trasitio from assbad to stobad (electivity) 0 - c 0 + c 0 H j 0 - c 0 + c ouled resoators Flatter assbad (low rile) Q deeds o degree Better hase resose Better selectivity V i H j V out Vi V out

9 Real Trasfer Fuctio H j Passbad Trasmit the maximum ower with low distortio Low loss Gai close to uity Low amlitude rile Low hase distortio Liear hase over most of the bad Flat grou delay (Phase gradiet) tobad - Prevet trasmissio of as much ower as ossible i the uwated bad(s) High atteuatio tee trasitio from assbad to stobad (electivity) 0 - c 0 + c 0 H j 0 - c 0 + c No adjacet coulig Trasmissio eros Imrove selectivity Target atteuatio H j V out Vi V i V out

10 Real Trasfer Fuctio H j Passbad Trasmit the maximum ower with low distortio Low loss Gai close to uity Low amlitude rile Low hase distortio Liear hase over most of the bad Flat grou delay (Phase gradiet) tobad - Prevet trasmissio of as much ower as ossible i the uwated bad(s) High atteuatio tee trasitio from assbad to stobad (electivity) 0 - c 0 + c 0 H j 0 - c 0 + c No adjacet coulig Trasmissio eros Imrove selectivity Target atteuatio H j V out Vi V i V out

11 Lowass Prototye ythesisig a lowass is easier tha sythesisig a badass A lowass filter serves as a temlate for other filter tyes We trasform its elemets to rovide the other filter tyes calig elemet values to give lowass filters with differet cut-off frequecies Traslatio ad badwidth scalig for a badass filter resose calig ad frequecy iversio for highass filters Traslatio, badwidth scalig ad frequecy iversio for badsto filters Imedace scalig L L4 Lowass Prototye Amlitude - c =- 0 + c =+ Frequecy Badass 0 0 Frequecy BP Elemet LP Prototye W 3 5 R L W P out P i () L3 ource Load Power I Power Out

12 Equirile Trasfer Fuctio Trasfer Fuctio oservatio of Eergy P P + P + P For low loss dissiated reflected Zero Loss -> Uitary oditio We use the lossless reflected ower fuctio to fid the iut imedace ad carry out the sythesis i ( j) + ( ) It s easier to measure ad alig a filter usig the reflected ower out P out + P P i reflected T N

13 Trasfer Fuctio The ratio of two olyomials ( ) K N( ) K ( )( ) ( k D( ) ( )( ) ( ) The deomiator Poles of the trasfer fuctio are ormally comlex ad ot o the imagiary axis There are the same umber of oles as there are filter elemets Numerator Fiite frequecy trasmissio eros There are the same umber of factors i the umerator as there are trasmissio ero roducig elemets Normally they occur at frequecies we ca see o a trace o the imagiary axis Trasmissio eros A filter without fiite frequecy trasmissio eros has a umerator of degree 0 ad is called a All Pole trasfer fuctio If we have oles we ca have a max eros Toology iflueces the umber of ossible eros ythesis Fid the elemet values from the trasfer fuctio Magitude <= Passive & Lossless ) W ource Power I P out L P 3 L3 i L4 5 () R L W Load Power Out

14 Poles Zeros Zeros Pole Zero Plot () & () Im j db 0-5 lowass : Grah : Mag db / Mag db 0 db e-0 e-0 3e-0 5e-0 GH Re j i d j ~ i ~ j j ~ i ~ i ji i j j ~ d j ~ i ~ j i ~ i ji

15 Poles Zeros Zeros Pole Zero Plot () & () Im j db 0-5 lowass : Grah : Mag db / Mag db 0 db e-0 e-0 3e-0 5e-0 GH Re j i d j ~ i ~ j j ~ i ~ i ji i j j ~ d j ~ i ~ j i ~ i ji

16 Poles Zeros Zeros Pole Zero Plot () & () Im j db 0-5 lowass : Grah : Mag db / Mag db 0 db e-0 e-0 3e-0 5e-0 GH Re j i d j ~ i ~ j j ~ i ~ i ji i j j ~ d j ~ i ~ j i ~ i ji

17 Poles Zeros Zeros Pole Zero Plot () & () Im j db 0-5 lowass : Grah : Mag db / Mag db 0 db e-0 e-0 3e-0 5e-0 GH Re j i d j ~ i ~ j j ~ i ~ i ji i j j ~ d j ~ i ~ j i ~ i ji

18 Poles Zeros Zeros Pole Zero Plot () & () Im j db 0-5 lowass : Grah : Mag db / Mag db 0 db e-0 e-0 3e-0 5e-0 GH Re j i d j ~ i ~ j j ~ i ~ i ji i j j ~ d j ~ i ~ j i ~ i ji

19 Poles Zeros Zeros Pole Zero Plot () & () Im j db 0-5 lowass : Grah : Mag db / Mag db 0 db e-0 e-0 3e-0 5e-0 GH Re j i d j ~ i ~ j j ~ i ~ i ji i j j ~ d j ~ i ~ j i ~ i ji

20 Poles Zeros Zeros Pole Zero Plot () & () Im j db 0-5 lowass : Grah : Mag db / Mag db 0 db e-0 e-0 3e-0 5e-0 GH Re j i d j ~ i ~ j j ~ i ~ i ji i j j ~ d j ~ i ~ j i ~ i ji

21 Poles Zeros Zeros Pole Zero Plot () & () Im j db 0-5 lowass : Grah : Mag db / Mag db 0 db e-0 e-0 3e-0 5e-0 GH Re j i d j ~ i ~ j j ~ i ~ i ji i j j ~ d j ~ i ~ j i ~ i ji

22 Poles Zeros Zeros Pole Zero Plot () & () Im j db 0-5 lowass : Grah : Mag db / Mag db 0 db e-0 e-0 3e-0 5e-0 GH Re j i d j ~ i ~ j j ~ i ~ i ji i j j ~ d j ~ i ~ j i ~ i ji

23 Poles Zeros Zeros Pole Zero Plot () & () Im j db 0-5 lowass : Grah : Mag db / Mag db 0 db e-0 e-0 3e-0 5e-0 GH Re j i d j ~ i ~ j j ~ i ~ i ji i j j ~ d j ~ i ~ j i ~ i ji

24 ythesis ythesise a lowass rototye from the trasfer fuctio Uitary coditio Lossless etwork Factorise hoose LHP oles (stability) ( j) ( ) + ( j) ( ) + ( ) ( ) Poles of are the same as oles of P iut Lossless -Port P reflected Network P trasmitted L L4 Y( ) + ( ) ( ) W 3 5 R L W L3 ource Load Power I Power Out

25 ythesis Trasform the rototye ito a badass structure of resoators ad couligs Evaluatio of circuit losses Loss does ot ecessarily eed to be uiformly distributed over the resoators everal alterative toologies ca be used to realise the same trasfer fuctio Differet toologies will have differet assbad loss variatio P iut P reflected ( j) ( ) + ( j) ( ) + ( ) Lossless -Port Network ( ) P trasmitted Y( ) + ( ) ( ) P i P out

26 ythesis Trasform the rototye ito a badass structure of resoators ad couligs Evaluatio of circuit losses Loss does ot ecessarily eed to be uiformly distributed over the resoators everal alterative toologies ca be used to realise the same trasfer fuctio Differet toologies will have differet assbad loss variatio Aroximatios to ideal elemets require otimisatio to restore trasfer fuctio P iut P reflected ( j) ( ) + ( j) ( ) + ( ) Lossless -Port Network ( ) P trasmitted Y( ) + ( ) ( ) P i P out

27 Practical Badass Filter Resoators hort circuit trasmissio lies resoated by caacitive ed loadig urface resistivity adds loss Larger resoators, smaller loss Distributed loss Passbad width affects loss Larger badwidths give smaller losses Highest loss is ormally at badedge Trasfer fuctio degree affects loss Higher degree trasfer fuctios (more resoators) result i larger losses K i K K 3 K 3 3 K 34 4 K 45 5 K 5o

28 Determie The Trasfer Fuctio (Maual Otimisatio) Passbad Isertio Loss Iut ad Outut Retur Loss tobad Frequecy/MH D Temerature Rage ystem Imedace MH 0.5 db (max) 5 db (mi) Atteuatio/dB (mi) -0 to W Fid a trasfer fuctio that fits the required assbad ad stobad temlates efficietly Determie the degree (oles) Determie the umber of trasmissio eros ad their frequecies to miimise the umber of oles Determie the uloaded Q of the resoators from the ermitted loss (ultimately determies sie) Accout for shiftig of the resose due to temerature chages Is it ossible at all!! All of this is doe maually by a exerieced desiger ie?? How do we kow that we have distributed the losses ad adjusted the trasfer fuctio to give the smallest sie With distributed sies (losses) differet etwork toologies have differet assbad loss characteristics

29 ie omariso Degree 5 Badwidth 36.0MH ( ) Tx 98.6MH Resoator Model Diam Qu Uiform Qu Qu=69 Footrit 786 mm sq K i K K 3 K 3 3 K 34 4 K 45 5 K 5o

30 ie omariso Degree 5 Badwidth 37.4MH ( ) Tx 980.0MH Resoator Model Diam Qu Uiform Qu Qu=34 Footrit 569 mm sq 7% K i K K 3 K 3 3 K 34 4 K 45 5 K 5o

31 ie omariso Degree 5 Badwidth 37.4MH ( ) Tx 980.0MH Resoator Model Diam Qu Distributed Qu Qu=73, 706, 488, 98, 73 Footrit 54 mm sq 65% K i K K 3 K 3 3 K 34 4 K 45 5 K 5o

32 ie omariso Degree 5 Badwidth 37.4MH ( ) Tx 980.0MH Resoator Model Diam Qu Distributed Qu Qu=76, 74, 87, 74, 76 Footrit 503 mm sq 64% K i K 3 3 K 34 K K 4 K K 5o

33 ie omariso Degree 5 Badwidth 38.6MH ( ) Tx 978.0, 990.6MH Resoator Model Diam Qu Distributed Qu Qu=665, 378, 35, 450, 66 Footrit 453 mm sq 57% Is this otimum?? ometimes a icrease i degree is better K i K 4 K K 34 3 K 45 K 3 K K 5o

34 Desig Process ummary (Maual Otimisatio) Re-sythesise ad evaluate ew etwork No Trasfer Fuctio Degree Badwidth Trasmissio Zero Locatios ythesis Resoator & ouligs ircuit Trasformatios Aroximatios Otimisatio Evaluatio Iclude Loss omare with ecificatio Distributio of Loss alculate ie ecificatio Met? ie Mi? Determie dimesios Verify 3D model Yes

35 3D EM imulatios/physical Device Dimesios for hysical device The Ls ad s of the circuit simulator model are ot measureable i the hysical device Resoat frequecies, coulig badwidths ad exteral Qs are measureable quatities that defie the trasfer fuctio Poles ad eros are maiulated idirectly by tuig resoat frequecies ad badwidths orrect values for these will esure correct locatio of oles ad eros ad hece the required trasfer fuctio Iitial dimesios come from these values Res Frequecy (MH) oulig Badwidth (MH) ig ve ve ve ve ve K i K 3 3 K 34 K K 4 K K 5o Ideedat Variables oles + eros + 5Resoators + 6Mai K + ross K

36 3D EM imulatios/physical Device EM Model Provides a accurate full 3D EM simulatio of the filter Relaces the eed for hackig at a rototye The EM model icludes the facility to tue resoators ad couligs as we would i reality Poles ad eros are maiulated idirectly by tuig resoat frequecies ad badwidths We tue the EM model s dimesios to a tolerace that is withi the tuig rage of the available hysical adjustmet (crews) Eables a hybrid maual/automated otimisatio techique Res Frequecy (MH) oulig Badwidth (MH) ig ve ve ve ve ve K i K 3 3 K 34 K K 4 K K 5o Ideedat Variables oles + eros + 5Resoators + 6Mai K + ross K

37 Utued Res D Frequecy (MH) oulig D Badwidth (MH) This resose is tyical of a first cut 3D EM model or ractical device Poles are ot i the required locatio Reflectio eros have moved off the imagiary axis Fiite, trasmissio eros are ot located correctly ad may actually be i-bad or off the imagiary axis This still reresets a trasfer fuctio which is a ratioal olyomial of essetially the same degree as the theoretical oe ad ca be tued to restore the desired trasfer fuctio Resoat frequecies, coulig badwidths, ad exteral Q s Measuremets ca be made (with some difficulty) Give a clue to which dimesios should be modified ad by how much

38 Pre-tued Res D Frequecy (MH) Ideedat Variables + + oulig D Badwidth (MH) oles oles eros Refl Zero Refl Rile + BE 5 Resoators + 6 Mai K + ross K This resose is tyical after iitial tuig usig resoat frequecy ad coulig badwidth iformatio Reflectio eros are all visible (rile levels) Trasmissio eros are roughly laced EM Model I this state the EM model ca be tued by mathematically otimisig the aroriate tuig elemets to give the equirile reflectio with the correct badwidth ad atteuatio riles Real Filter Withi the tuig rage of the mechaical adjusters Tued by exerieced techicia

39 Tued Res D Frequecy (MH) Ideedat Variables + + oulig D Badwidth (MH) oles oles eros Refl Zero Refl Rile + BE 5 Resoators + 6 Mai K + ross K After tuig/otimisatio All reflectio eros are visible ad the rile levels correct Badwidth is correct Trasmissio eros ositioed to give correct atteuatio rile levels Mixed distributed ad lumed elemets The oles, reflectio ad trasmissio eros locatios are ot recisely the same as the origial rototye Rile levels are more imortat Reflectio miima are ket close to ero

40 Automated Aligmet Res D Frequecy (MH) oulig D Badwidth (MH) reate the ratioal olyomial fuctios that fit the measured data,,? ythesise the etwork? Fid the resoat frequecies ad badwidths? Provide tuig guidace?

41 Fially Desig ie eeds to be miimised Distributed loss adds to desig comlexity Evaluated loss is deedat uo the etwork toology Loss caot be icluded util after sythesis Evaluated loss is a fuctio of Degree Badwidth Trasmissio ero locatios ie Loss distributio How ca we esure that the fial desig has the smallest sie Aligmet Poles ad Zeros are ot where we require Measurig resoat frequecies ad coulig badwidths is slow ad difficult i ractice The utued resose essetially still has the correct degree of umerator ad deomiator We ought to be able to fit a ratioal olyomial to measured results Higher order terms may be eeded for the fit (mixed lumed ad distributed variables) a we use the fitted olyomial to derive resoat frequecies ad coulig badwidths