Art of Comparing Rfid Reader Power Outputs Isotropic Circular Polarized Antenna | Radio Technology | Antenna (Radio)

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  Art of comparing RFID reader power outputs 19 September 2011 Mirva SaarijärviA white paper describing how to compare RFID reader power otpts!I have recent # tmb ed into $ew RF%&s and RF'&s where RFID readers radiating power $igres are as(ed! And at the same time in some cstomer discssions it became obvios that it is not a wa#s c ear how to compare $igres o$ di$$erent $ormats! )e co ected this  paper together with one o$ *ordic ID&s RF grs +Mr! ,oni -eijari! .r goa is to e/p ain inan eas# wa# what the di$$erent RFID power $igres mean and how the# can be sed!RFID radiating power is an essentia $igre describing the per$ormance a thogh it mst benoted that it is not the on # one! ,o pt it simp # + more power ot $rom antenna mean that tags $rther awa# hear the reader + it is a good thing i$ ong reading distance is the goa ! t power otpt does not describe a aspects o$ the reader per$ormance! It does not describe receiver sensitivit# + $rom how $ar can a reader hear the tag it does not describe readers speed or abi it# to read tags withot orientation sensitivit# etc!,here are two common wa#s to show radiating power mi iwatt 3m)4 and some $orm o$ decibe s 3d4! 5omp e/it# arises when di$$erent t#pes o$ decibe $igres are compared + $ine i$ it is done correct # bt mista(es are easi # done! An e/amp e .ther things e6a + which reader has onger reading distance a reader with 70dm 31!0)4 8R' or a reader with 72dm 31!)4 8IR': )e wi give the answer ater in this artic e!Decibe s 3d4 describe re ations o$ two $igres in ogarithmic sca e!0d /;1<#7d /;2<#d /;=<#10d /;10<#20d /;100<#and+7d /;#>2+10d /;#>10)hen RFID readers power is discssed d is not jst a p ain d bt dm di etc! the part a$ter d describes into which the $igre is compared to! For e/amp e an antenna with gain 7di emits to the main direction 2 times the power o$ an isotropic re$erence antenna! ,he ?i? in di stands $or the isotropic re$erence antenna!RFID readers power otpt depends on 2 components! 'ower otpt going into the antennaand antenna gain! 'ower going into the antenna 3RF power4 is sa # given as mi iwatt  3m)4 or in dm! In this case dm describes the power compared to 1m)! In tab e one  be ow the dm to m) re ation is described!.ther component + antenna gain + is given as compared to some re$erence antenna!di describes gain compared to isotropic re$erence antennadd describes gain compared to re$erence dipo e antennadic describes gain compared to re$erence isotropic circ ar po ari@ed antenna)e have seen a so di being sed it re$ers to re$erence inear po ari@ed antenna bt the re ation to di is not c ear<4 and we don&t recommend se o$ di!,here is a c ear re ation between the estab ished re$erence antennas+ dipo e antenna radiates more to directions in 90 degree ang e to the antenna dipo e than idea isotropic antenna 0dd ; 2!1= di  3sorce www!ti!com4+ Isotropic circ ar po ari@ed antenna ? ooses? some o$ the radiation power in the circ ating po ari@ation de to po ari@ation mismatch when tag antenna is inear! As a res t0dic ; +7 di'ictre I stration o$ inear and circ ar po ari@ation! 3www!ti!com4In 8ropean egis ation radiating power imits are described in re ation to dipo e antenna and 8R' 38$$icient Radiating 'ower4 is sed as a measre! An e/amp e RF power is 2Bdm 3C00m)4 and antenna has gain o$ Cdi! 8R' ; 2Bdm  Cdi +2!1C ; ca! 70dm 31!0)4In ES egis ation 8IR' 386iva ent Isotropica Radiated 'ower4 is sed! 'ower is comparedto isotropic re$erence antenna! )ith same reader and antenna as above 3RF power is 2Bdm3C00m)4 and antenna has gain o$ Cdi4 8IR' ; 2Bdm  Cdi ; 72 dm 31!)4Answer to the 6estion posted above reader with radiating power o$ 1) 8R' same as reader with radiating power o$ 1!) 8IR'!Form as8R' in dm ; 3RF power in dm4  3antenna gain in di4 +2!1Cd this can be converted to m) sing tab e above8IR' in dm ; 3RF power in dm4  3antenna gain in di4 this can be converted to m) sing tab e abovedi ; dic + 7d 3in RFID se4di ; dd 2!1CdMore e/amp esreader with C00m) RF power antenna with dic gain+ C00m) ; 2Bdm+ 8R' ;2B dm  3dic +7d4 +2!1Cd ; ca! 2dm 370m)4+ 8IR' ;2B dm  3dic+7d4 ; 70 dm 31)4  reader with =00m) RF power antenna with C di gain+ =00m) ; ca 2dm+ 8R' ; 2 dm  =di +2!1Cd ; ca! 2 dm 370m)4+ 8IR' ; 2dm  =di ;70 dm 31)4Athors ,eem Ainasoja and ,oni -eijariFor more in$ormation p ease contact spportGnordicid!com<4 http>>www!nitehaw(!com>rasmit>ve7ont!htm ! In the re$erence ca c ation o$ di is done b# sbstracting 7d $rom dic which in $act means that di wo d be same as di! From antenna per$ormance point o$ view inear antenna is sa # a dipo e antenna!,his entr# was written b# Mirva Saarijärvi posted on 19 September 2011 oo(mar( the  perma in( ! Ho can  post a comment! 11 3 comments  on “Art of comparing RFID reader power outputs” 1!)od@imier@ 'aJ'osted 20 September 2011 at 1=0CB' se send me white paper abot crrent in antenna2!Steve )right'osted 21 September 2011 at 0CB70,his artic e is a bit mis eading as the power measrements described are on # app icab e in the $ar $ie d 3where the antenna beam has $ormed4! In the near $ie d 3where a ot o$ RFID ta(es p ace4 It is not certain the the power $ / densit# 3power on m) or Dbm4 is an accrate represenation o$ acta power eve ! ,he correct wa#to measre in the 8 and - $ie ds and ca c ate the power! I earned this when measring RF power eve s at aviation navigation aids $rom F 3100 K-@ *D4 to S band 37 L-@ A,5 Radar4 7!,eem Ainasoja'osted 22 September 2011 at 111C70
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