Desgn and Optmzaton of a New Power Montor wth Small Sze ABBAS ALI LOTFI NEYESTANAK ALI HOMAII MASOOD KHOSROSHAHY MOHAMMAD MIRHOSAINI Eletral Engneerng Eletral Engneerng Eletral Engneerng Eletral Engneerng Islam Azad Un ve r s t y- Branh of Ray Ghom Hghway, Islam Azad Unversty- Branh of Ray Ghom Hghway, Iran Unversty of Sene & Tehnology Narmak, Islam Azad Un ve r s t y- Branh of Ray Ghom Hghway, I.R.IRAN I.R.IRAN I.R.IRAN I.R.IRAN Abstrat: -Ths paper desrbes the theory of the operaton of dretonal oupler and presents some nformaton about desgnng a very flat oeffent ouplng. A power montor s desgned and then optmzed for UHF band usng genet algorthm wth fratal odng. In ths paper, a transformer element s used to obtan a very flat ouplng fator and then t s fabrated and ompared wth expermental results. Usng two elements and genet algorthm optmzaton, an outstandng result n sze and ouplng fator has been aheved. The measured results of the optmzed power montor valdate a hgh ompatblty between the smulaton and the real experene. Key-Words: - Power Montor, Dretonal Coupler, Genet Algorthm, Fratal Codng, Wde Band, UHF. 1 Introduton Dretonal ouplers have found numerous applatons n mrowave networks and systems. They perform a varety of funtons suh as splttng and ombnng power n mxers, hybrd power samplng of soures for level ontrol, separatng ndent and refleted sgnals n network analyzers, and dvdng power among a number of loads. In ths paper, a dretonal oupler wll be desrbed and t s shown that the orrespondng desgn has a wdeband oeffent whh s useful for AGC unt n transmtter. As mpled n the paper s ttle, all of the networks wll be transmsson lne, TEM network strp lne or mrostrp lne based. Dretonal ouplers have the speal property of ouplng energy from a spef dreton nto a ouple of ports. The oupled lne ouplers make use of the bakward wave ouplng prnple: odd and even modes of the wave on the par of the oupled lnes travel at the same veloty wth dfferent haraterst mpedanes. The haraterst of a dretonal oupler an be expressed n terms of ts ouplng fator and dretvty. There are a lot of ways to desgn a wdeband dretonal oupler, alulatons of whh are very dffult; but n ths paper, wth the nformaton found n other papers about dretonal ouplers, a dretonal oupler wth mult element s desgned to obtan a flat oupled fator and a weak ouplng fator. Some methods whh have been reognzed n the past years by a number of authors have been employed [1], [2], [3]. Usng genet algorthm wth fratal odng, a ouplng fator of -4dB wth ±.5dB tolerane s obtaned. HP-HFSS software has also been used for smulaton and desgn. Due to the measureless number of varables and large number of output haratersts related to the antenna struture, antennas annot be optmzed by onventonal tehnques, whh use gradent methods. Applatons of genet algorthms for optmzaton problems are wdely known [4]. Ther advantages and dsadvantages n omparson wth lassal numeral methods are also known. The performane of the genet algorthm s determned by the nvestgaton and utlzaton of relatonshps throughout the run. Ths balane between the
utlzaton of the whole soluton spae and the detaled searhng of some parts an be modfed to hange the genet algorthm operators (.e. seleton, rossover and mutaton). Fratal odng of parameters n genet algorthm offers a hoe to follow extremely omplex strutures n optmzaton [5, 6]. Maybe the largest obstruton n the way of usng GA n eletromagnet, s the sze of the jobs they try to attempt. In [6], a method of redung the sze of the parameter gene through a ompressed fratal odng s dsussed. In [7], a very flat dretonal oupler s reported. In ths paper, a small dmenson wth very flat ouplng and good mathng s presented. 2 Dretonal Coupler A round ondutor s used to desgn ths dretonal oupler. Ths s partularly good for weak ouplng and hgh power applaton. Mult seton oupler formulas are very dffult so even-and-odd mode s the best way to analyze ths problem. It means that mpedane of one s the admttane of the other. In ths desgnng, we have two elements wth round ondutors. 12 4b e + =.ln ε πd r (1) 12 πs e = ln ot an ε 2b Couplng fator C s as shown: C = e e 1 + 1 r (2) Where e and o are the even and odd modes mpedanes and are dsussed below. In order for the oupler to perfetly math to ts termnatng transmsson lne of haraterst mpedane, t's neessary that: = e. (3) The even mode mpedane, e, s the haraterst mpedane of a sngle oupled lne to ground when equal urrents are flowng n the two lnes whle the odd mode mpedane, o, s the haraterst mpedane wth urrents flowng n the opposte dreton n the two lnes. Values of e and o for a number of ross setons presented are gven by: =. (4) e o =. 1 (5) Physal dmenson neessary to produe the requred even and odd mode mpedane, e and o, ould be obtaned from (1). When three setons of elements to obtan wdeband oeffent exst, the followng equatons are employed: ( e ) =. = 1, 2 (6) ( o ) =. = 1, 2 (7) and o are the mpedanes of the even and odd modes n the oupled lne normalzed to the mpedane of the nput lnes, and are related by: 1 (8) e. = and o are obtaned for eah element and then the oupled lne for the ntended applaton ould be desgned. 3 Smulaton and measurement Results In ths seton, smulaton results for more dretonal oupler samples wth dfferent dmensons are studed and then the best sample between the smulated sample and optmzed sample s onsdered and at the end, these methods have been ompared wth eah other. In ths dretonal oupler, two elements are used, alulatons of whh are n the related seton. Dmensons of ths dretonal oupler are related aordng to the mpedanes of eah element and alulatons of odd and even mode mpedanes whh are renormalzed wth 5 Ω. Radus and dstane of lnes (man lne and the oupled lne) and the dmenson of avty of oupler are shown n fgure 1. In ths fgure, a dretonal oupler wth three elements s desgned usng transformer theory and the ouplng fator of ths struture s shown n fgure 2. Ths fator s flat wth.25 db tolerane but the dmenson of ths struture s very large so two small-lengthed elements have been used. In fgure 3, a power montor wth two elements s shown whh s used for smulaton as well.
Fgure1: Three-seton dretonal oupler Fgure 4: Flow hart of the optmzaton algorthm Fgure2: Couplng fator of the three-seton element Fgure 4 shows the flowhart of the optmzaton algorthm. Now the best oeffents of ths oupler smulated n omputer are presented and ompared wth expermental sample made n the lab. The frst oeffent s the return loss of the nput whh s equal to the output. Ths fator s very good n the omputer smulaton and s shown n fgure5. Fgure3: Two-element power montor In ths struture, two elements ould be used to aheve best result usng genet algorthm optmzaton. The fratal odng method works by usng a odng proess, whh desrbes the number of teratons, generator, randomness, and so on [5]. Fgure5: Return loss of the two-element power montor
Ths fator s presented to explan the refleted and forwardng powers n eah struture. It has been used n all of the strutures to ompute the value of the forwardng and refleted powers whh are related to eah other wth VSWR (voltage standng wave rato). The seond parameter s the ouplng fator and s shown n fgure 6. analyzer for omparson wth smulated results. Fgure 8 shows the fabrated sample wth two elements. Fgure8: Expermental power montor Varous parameters suh as ouplng fator, return loss of ths struture have been measured and depted n the followng fgures. Couplng fator s shown n fgure 9. Fgure 6: Couplng fator of ths struture Then the nserton loss of ths struture s shown n Fgure7. A brass has been used as ondutor. Fgure9: Couplng fator of the expermental power montor Fgure7: Inserton loss of the two-element dretonal oupler 4 Test results In ths seton, the testng and the measurement of the dretonal oupler have been desrbed and ompared wth smulaton results. The dretonal oupler whh s made n the lab s shown and ts varous parameters have been measured wth network Return loss of ths struture s shown n fgure 1. Ths fator s almost equal to the smulated parameter. The sample measurement results have been ompared wth smulaton results n table 1. It s apparent that the expermental sample whh s tested n the lab and the smulated one have lose values. Although the dmensons of the expermental sample were hosen equal to the smulated struture dmensons but return and nserton losses are not lose to the expeted smulated sample losses and depend on the knd of brass and platng used and the varatons of the dmensons. The advantage of ths optmzaton s the fxed struture to fx the ouplng fator for all of the UHF frequeny bands.
Fgure1: Return loss of the power montor When the fxed ouplng fator s aheved for all of the frequeny bands, there s not any hange of ths fator resultng from other hanges for example movng the oupler or hangng the frequeny. Power output of the antenna an be measured wthout turnng off the transmtter. [2] B.M. Olver, "Dretonal eletromagnet ouplers," Pro IRE, vol.42, November 1954, pp.1688-1692. [3] G. L Matthae, L. Young, and E. M. T. Jones, "Mrowave Flters, Impedane- Mathng Networks and Couplng Strutures". New York: MGraw Hll, 1988. [4] Y. Rahmat-Sam and E. Mhelssen, "Eletromagnet Optmzaton by Genet Algorthms", New York, NY: Wley, 1999. [5] Cohen, N., 1997, Genet Antenna Optmzaton wth Fratal Chromosomes, Proeedngs of ACES, 1997, pp. 35-38. [6] Cohen, N., Fratal Codng n Genet Algorthm (GA) Antenna Optmzaton, Proeedngs of IEEE- APS/URSI, 1997, pp. 113-117. [7] G. P Rblet, A dretonal oupler wth very flat ouplng, IEEE Trans. Mrowave Theory Teh., vol. MTT-26, Feb. 1978, pp. 7 74. Table 1: Comparson of the smulated and expermental sample values Inserton loss Return loss Varaton Couplng fator -.15dB -45dB ±.5dB -4dB Smulaton -.3dB 36dB ±.35dB -4dB Measurement 5 Conluson In ths paper, a dretonal oupler wth wde bandwdth and small sze was presented and optmzed. In ths oupler two elements ould be used to get the best result usng genet algorthm optmzaton wth fratal odng. The ouplng fator and return loss of ths struture have been measured. The measured results of the optmzed dretonal oupler onfrm a hgh ompatblty between the smulaton and the atual experene. Referenes: [1] R. Levy, "General synthess of asymmetr multelement oupled-transmsson-lne dretonal oupler," IEEE Trans.on Mrowave Theory and Tehnques, vol.mtt -11, July 1963, pp. 226-237.