Gupta, Sanjeev

Nath, Pankaj Kanti

Sarkar, B K

IACS Institutional Repository

Indian J  Phys- 75B (3), 171-173 (2001)U P  ®— an international JournalMicrostrip miniaturised antennasS a n je e v  G u p ta * . P an k a j K an ti N a th  an d  B K  S a rk a r Society for Applied Microwave Electronics Engineering and Research, III Campus, Powai, Mumbai-400 076, IndiaE-mail sanjecv@samcer emel.inAbstract This paper deals with the various techniques for reduction in the size of the antennas A small microstrip patch antenna is presented The probe-fed microstrip patch incorporates a single shorting post which significantly reduces the overall si/c ofthe antenna Theoretical impedance behaviour and radiation characteristics of the modified patch arc given.keywords Microstrip antennas, design and simulation resultsPACS No. 84.40 Ba1. In t ro d u c tio nIn the p resen t s c e n a r io  o f  in c re a se  in  d e m a n d  b y  th e  sy s tem  designers fo r th e  im p le m e n ta t io n  o f  m o re  c o m p le x  fu n c tio n s  in reduced sp a c e , th e re  is an  in c re a se  in  th e  d e m a n d  fo r  the  active in teg ra ted  m ic ro s t r ip  p a tc h  a n te n n a s  w ith  lo w e r size  and w eight. T h is  p a p e r  a d d re s se s  th e se  d e m a n d s  b y  d e sc r ib in g  various te c h n iq u e s  to  s a t is fy  th e  s e v e re  c o n s tra in ts  on  th e  physical d im e n s io n s , th e  n e e d  fo r  “ m in ia tu r is a tio n ” o f  th e  patch an ten n as. S u c h  lig h t w e ig h t  a n d  lo w  v o lu m e  a n te n n a s  could find  a p p l ic a t io n s  in  la n d , m o b i le  a n d  p e rs o n a l com m unication  s y s te m s  a n d  a irb o rn e  a n te n n a  sy s tem s .The h a lf-w a v e le n g th  (A /2 )  o p e n -c irc u ite d  m ic ro s tr ip  pa tch  antenna is u se d  b e c a u s e  o f  b o th  its  c o n v e n tio n a l p ro p e r ty  and  relative ease  to  m a n u fa c tu re .  M in ia tu r is a tio n  o f  th e  re s o n a n t nuciLstrip p a tch  a n te n n a s  c a n  b e  a c c o m p lis h e d  b y  lo ad in g . Loading can  ta k e  v a r io u s  fo rm s , n a m e ly  ( i)  u se  o f  su b s tra te s  and/or su p e rs tra te s  o f  h ig h e r  p e rm it tiv ity , ( i i)  m o d if ic a tio n  of basic p a tch  g e o m e try  a n d  ( i i i )  u se  o f  sh o r t-c irc u itin g  posts T hese  a re  b r ie f ly  d e s c r ib e d  b e lo w .Loading th e  re s o n a n t  a n te n n a  w ith  th e  h ig h  p e rm ittiv ity  dielectric m a te r ia l  r e d u c e s  th e  s iz e  o f  th e  a n te n n a  [1]. Although th e  re d u c t io n  o f  a n te n n a  d im e n s io n s  b y  d ie le c tr ic  loading has b e e n  c a r r ie d  o u t  s in c e  a n te n n a s  w e re  f irs t u sed , practical im p le m e n ta t io n  h a s  b e e n  c lo s e ly  t ie d  to  th e  availability a n d  c o m p e t i t iv e  a n d  e c o n o m ic a l c o s t o f  d ie le c tr icm a te ria ls  in industry . O n one h an d  h ig h  p e rm ittiv ity  su b stra tes  can  im p ro v e  so m e a n te n n a  c h a ra c te r is tic s , th e y  a re , on the  o th e r  h a n d , in v a r ia b ly  c e r a m ic - b a s e d  w h ic h  re q u ir e  sp ec ia lized  m ach in in g  eq u ip m en t as c o m p ared  to  th a t req u ired  fo r p la s tic  substcates .T o  ach ie v e  sm a lle r  p la n a r  a n te n n a s  o p e ra tin g  at th e  sam e  fre q u e n c ie s  as c o n v e n tio n a lly  c o n fig u re d  a n te n n a s  req u ire s  a m o re  co m p lex  g eo m e try . O n e  o f  th e  g e o m e try  is C -p a tch  m ic ro s tr ip  a n te n n a  fo rm ed  b y  c u ttin g  a  sm a ll a re a  in o n e  o f  th e  ra d ia tin g  e d g es  o f  th e  a n te n n a  [2]. A  s im ila r  te c h n iq u e  u ses H -sh a p e d  o r  re c ta n g u la r  r in g  m ic ro s tr ip  p a tc h , w h ich  c o n s is ts  o f  a  s trip  o f  m e ta l, H -sh a p e d  o r  re c ta n g u la r  rin g - sh a p e d  su p p o rte d  on  th e  g ro u n d e d  d ie le c tr ic  sh ee t. It h as  a size  a b o u t h a lf  th a t o f  th e  re c ta n g u la r  p a tc h , w ith  la rg e r b e am w id th  b u t sm a lle r  b a n d w id th . O th e r  m in ia tu risa tio n  sh a p e s  in c lu d e  th e  d o u b le  C -p a tch  ( tw o  s ta c k e d  C -sh ap ed  a n te n n a  e le m e n ts  c o n n e c te d  to g e th e r  w ith  a  v e rtic a l g ro u n d  p la n e ) [3 ], a n n u la r  s lo t an d  th e  a n n u la r  se c to r. S o m e  o f  th e  o th e r  sh a p e s  m a k e  in e f fic ie n t u se  o f  th e  a v a ila b le  a re a  and  an  a d e q u a te  p e rfo rm a n c e  ca n  o n ly  b e  a c h ie v e d  e ith e r  by  su p e r-c o n d u c tin g  m a te ria l o r  th ic k  lo w -lo ss  su b s tra te s .C o m m o n  te c h n iq u e  to  re d u c e  th e  o v e ra ll s iz e  o f  a m ic ro s tr ip  p a tch  an te n n a  is to  te rm in a te  o n e  o f  th e  ra d ia tin g  e d g e s  w ith  a  sh o rt c irc u it [4]. T h e  sh o r t c irc u it c an  b e  in th e  fo rm  o f  a m eta l c la m p  o r a c o p p e r  sh e e t w ra p p e d  a ro u n d  theCorresponding Author © 2001 lACS172 Sanjeev Gupta, Pankaj Kanti Nath and B K Sarkare d g e  o r  a  se r ie s  o f  sh o r tin g  p o sts  lo ca ted  n e a r  th e  feed  o f  th e  a n te n n a . T h e se  m o d if ie d  p a tch e s  a re  a p p ro x im a te ly  a q u a r te r -w a v e le n g th  in len g th  an d  g e n e ra lly  h a v e  a w id e r b e a m w id th  c o m p a re d  to  c o n v e n tio n a lly  s ized  p a tc h e s . H o w e v e r, th is  a lso  e lim in a te s  th e  m u tu a l c o u p lin g  b e tw een  th e  tw o  so u rc e s  an d  th e  b a n d w id th  is re d u c e d  by ab o u t o iic- fifth .R e d u c in g  th e  o v e ra ll len g th  o f  a  q u a rte r-w a v e le n g th  (A /4 )  sh o rte d  p a tch  to  less th an  z l/8  is p o ss ib le  b y  re p la c in g  th e  co ax  feed  by  a c a p a c itiv e  feed  [5]. I 'h e  c a p a c itiv e  load  is fo rm e d  by  fo ld in g  th e  o p e n  en d  o f  the  p a tc h  to w a rd s  th e  g ro u n d  p la n e  an d  a d d in g  a p la te  (p a ra lle l to  th e  g ro u n d  p lan e ) .2 . A n te n n a  d e s ig n  a n d  s im u la t io n  r e s u l tsA s w as e v id e n t in [4], a lth o u g h  re d u c in g  th e  n u m b e r o f  sh o r tin g  p o s ts  e f fe c tiv e ly  re d u c e s  th e  size  o f  th e  p a tch , th e  in p u t im p e d a n c e  at re so n a n c e  b e c o m e s  s ig n if ic a n tly  la rg er. T h is  is in d eed  th e  case  w h en  u s in g  a s in g le  sh o r tin g  post. It w as  ib u n d  th a t to  red u c e  th e  in p u t im p e d a n c e  at re so n a n c e  to  c lo se  to  .50 Q , v e ry  sm all c o n d u c to rs  fo r b o th  th e  c o ax ia l feed  an d  th e  sh o r tin g  p o st m us! be u sed  a n d  a lso  th ese  c o n d u c to rs  m u s t be  lo ca ted  in c lo se  p ro x im ity . In th e  d es ig n  o f  th e  p ro b e -fe d  c irc u la r  m ic ro s tr ip  p a tch  w ith  a s in g le  sh o r tin g  p o st, th e  sh o r t-c irc u it w a s  m o v e d  s lig h tly  aw ay  fro m  th e  p a tch  c o n d u c to r  e d g e  T h e  re a so n s  fo r d o in g  so w e re  to  ea se  th e  to le ra n c e s  o n  th e  e tc h in g  o f  th e  p a tc h  as w e ll as to  re d u c e  th e  l ik e lih o o d  o f  e x c itin g  h ig h e r  o rd e r  m o d e s  in th e  v ic in ity  o f  th e  post.F ig u re  1 sh o w s  th e  g e o m e try  o f  th e  p ro b e -fe d  c irc u la r  m ic ro s tr ip  p a tc h  w ith  a  s in g le  sh o r tin g  p o s t I’he ra d iu s  o fFigure I. Geometric layout of probe-fed circular microstrip patch antenna with a single shorting postc o n v e n tio n a l c irc u la r  p a tch  (m o u n te d  o n  th e  sa m e  substrate an d  d e s ig n e d  to  re so n a te  at th e  sa m e  fre q u e n c y )  w ith  the ra d iu s  o f  27.1 m m , ~ 0 .l4 A o . T o  a c c u ra te ly  p re d ic t the im p e d a n c e  b e h a v io r  an d  th e  ra d ia tio n  c h a ra c te r is tic s  o f  the m o d if ie d  p ro b e -fe d  c irc u la r  p a tc h , IE 3 D  so f tw a re  [6] was u sed . F ig u re  2  sh o w s th e  re tu rn  lo ss  c h a ra c te r is tic  o f  theFigure 2. Impedance behavior of tlie modified patch (Smith th.iriiab o v e  p a tch . T h e  th e o re tic a l im p e d a n c e  b e h a v io r  o f  the sh o rte d  p a tch  is sh o w n  in F ig u re s  3 an d  4 w hile  theirr^ ehm)Figure 3. Impedance characteristic.s of shorted microstrip patch antenna.this modified circular patch is 9.19 mm, ~0.047Ao (where ^  is the free spare wave' th). T h is compares with a Fieure 4. Return loss of shorted microstrip patch antennaMicrostrip miniaturised antennas 173la d ia t io n  characteristics of the modified patch are shown in l-iiliire 5.E thdta, phi=0. (deg)E-phi, phi««90. (deg)0.0Hgiiri' 5. Sitmiliilcd F-plane and 11-planc radiation patlcras ol'shortcd microsltip patch.3. C o n c lu s io n sA small microstrip patch antenna has been analysed. The inobc-lcd microstrip patch with a single shorting post is si!;nilic;mlly smaller in size than conventional microstrippatch antennas and is thus suitable for applications where limited antenna real estate is available.AcknowledgmentThe authors are thankful to the Armament Research Hoard, New Delhi for the sponsorship of the work described in this paper.krtcrmcc!!111 I’ I Iwany, Y V /hanp,, (i X 7hcng and t' K t '  Lo Electronics te ll 31 1710 ( I W )Dl (i koisiavas, A Papiciiuk, J I’ lluissel and M Sauvan Electronics Icii 25 25.1 (lOKO)['1 I Zaid, (i kosMavas, J A' Dauvignac and (i 1‘apicrnik Electronics icii 34 911 (1998)I'll M SanaJ I'mt IEEE Symposium on .Inlennos anil I’ropagalion p79-I (1994)[5] C R Rowell and R 11 Mnrch IEEE Vransachons on Antennas and Propof’aiion 45 817 (1997)[h| II'JI) Solmair Rclcusi’ -JO (/xlaiul SuTlwarc Inc, I rcmoiU. Ccililornia, USA)

Microstrip Miniaturised Antennas

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Microstrip Miniaturised Antennas

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