Andersen, J. Bach

Schjær-Jacobsen, Hans

Online Research Database In Technology

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Bach; Schjær-Jacobsen, HansPublished in:Antennas and Propagation Society International SymposiumPublication date:1972Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Andersen, J. B., & Schjær-Jacobsen, H. (1972). Optimization of antenna properties. In Antennas andPropagation Society International Symposium (Vol. Volume 10, pp. 115-118). IEEE.S E S S I O N  V - COMPUTER A I D E D  ANTENNA DESIGN 1 : 4 5 - 3 : 3 0  P.M., Monday, Room B Pape r  N o .  1 OPTII4IZATIO?J OF A I f E i R A  PROPERTIES J. Bach Andersen  and €i, SchjcrJacobsen Laboratory of Electromagnetic Theory The Technical University of Denmark Wnpby , Dennark. Antenna pat tern synthesis  i s  in  gene ra l  a  d i f f i cu l t  sub jec t  fo r  two reasons.  First ,  only fo r  r e l a t ive ly  s imple  cases  do t h e  synthesis  problem have a so lu t ion ,  and i f  o r a c t i c a l  c o n s t r a i n t s  l i k e  bandwidth and low s ide lobes  for  cer ta in  spec i f ic  angles  a re  included the problems are more or  less  inso lvable .  Second, i n  the cases  where t h e  problem has been solved, the result i s  usual- 4 the cur ren t  d i s t r ibu t ion ,  which may only be realizable with g r e a t  p r a c t i c a l  d i f f i c u l t i e s .  The theme of th i s  pape r  is how t o  get around both of t h e s e  d i f f i c u l t i e s  by a d i r e c t  numerical a p  proach, using non-linear optimization techniques. The general  problem (which w i l l  be exemolified later)  considered here  i s  t h a t  of an antenna or antenna system which may be model- l e d  by the network equations where the  vol tage  vec tor  V i s  given. The impedance matrix i s  a funct ion of t h e  independeFt variables E , and the  cur ren t  vec tor  I i s  d e s i r e d  i n  o r d e r  t o  compute some performance  index  PI which i s  a non-linear function of 2 , Further  SOEE cons t ra in ts  may be defined: Now the t ask  i s  t o  maximize PI  defined by ( 3 )  subjec t  t o  t h e  constraints defined by ( h ) .  It is vorth n o t i n e  t h a t  t h i s  de- &ription covers a g r e a t  nany antenna types such as wire anten- nas, loaded or unloaded, variable reactance antennas, Yagi-Uda arrays, e tc .  Meny problems of numerical neture arise when solving an optimi- zat ion problem l i k e  t h i s ,  t h e  main one being computing tine. Since a complete antenna analysis has t o  be carried out hundreds of t imes during the opt imizat ion,  a  casidereble  amount af time 115 Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on June 30,2010 at 11:32:07 UTC from IEEE Xplore.  Restrictions apply. sur face  with s u f f i c i e n t  accuracy. h o f h e r  p o s s i b i l i t y  which (up t o  708) m e y  be saved by nodellint .  7. by a nul t id inens iona l  arises due t o  t h e  f a c t  t h a t  x often chaoges very slowly, is t o  so lve  eq. (1) by some perturi;ationd technique. In the talk, a comparison of d i f f e r e n t  s t t e m p t s  t o  c u t  down conputin(. time Wil be reaorted. PS au exemplification of  the Eeneral nodel out l ined  above, con- technique  fails   completely.  It can t e l l  us, s ~ ,  the opt inun a ider  the  Yagi-Uda array. In th i s  ca se  the  c l c s s i ca l  syn thes i s -  cu r ren t  d i s t r ibu t ion  on e driven array of half-wave dipoles, b u t  t h i s  c u r r e n t  d i s t r i b u t i o n  i s  in  r ene ra l  no t  r ea l i zab le  w i t h  n p a r a s i t i c  array. 116 Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on June 30,2010 at 11:32:07 UTC from IEEE Xplore.  Restrictions apply. To s t a r t  w i t h  a very simple model of t h e  Yagi-Uda array,  an equi- d i s t an t  a r r ay  of in f in i t e ly  th in  loaded  half-wave dipoles  is con- sidered, the reactivc loadings being the independent variables.  Results fron! t h i s  model a r e  r epor t ed  in  111. Vie now t u r n   t o   t h e  more complicated problem, namely t o  end up with a rea l izable  an tenna  tha t  has  maximun kain with constraints  imposed upon the  +value.   In   f ig .  1 sone  r e su l t s  a r e  shown, a l l  opt i rLzat ion [2]. The curves are t h e  mwinum obtainable   gain as of which have been obtained by means of Rosenbrock's method of tennas,  (4,2) b e i q  a 4 eleizent entenna with element no. 2 ex- as a funct ion of  the maximun d l o w a b l e  !&value f o r  d i f f e r e n t  an- c i t e d   e t c .  '?ne same nethod has been a?plied t o  o b t a i n  naximum Eein Yaci-Uda ar reys  wi th  cons t ra in t  on the  front-to-back  ratio.  Fig. 2 shows r e s u l t s  f o r  a s p e c i f i c  e q u i d i s t a n t  array together  wi th  meas- Gain (dB) 1 1  10 f 60 50 40 30  20 10 0 FTB (dB) Fig. 2 !laxinun  gain  with  constraint  on FTB. (6,3), d = 0.3451, r = 0.01X - Theory. e---. Zxperinent. 117 Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on June 30,2010 at 11:32:07 UTC from IEEE Xplore.  Restrictions apply. Other examples of p a t t e r n  s y n t h e s i s  f o r  Yagi-Uda ar rays  us ing  t h i s  method w i l l  be giPen i n  t h e  t a l k .  The results have been ex tens ive ly  ver i f ied  by experiments carried out in The Radio- anechoic Chamber a t  this laboratory.  REFERENCES: 1. J.H. Bojsen, H. Schjer-Jacobsen, E. Nilsson and J. Bach Andersen (1971 Electronics  Let ters  L, D. 531). 2. H.B. Rosenbrock (1960 Computer Journal 3, p. 175). 118 Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on June 30,2010 at 11:32:07 UTC from IEEE Xplore.  Restrictions apply. 

Optimization of antenna properties

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Optimization of antenna properties

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