JOURNAL OF TELECOMMUNICATIONS, VOLUME 14, ISSUE 1, MAY 2012 1

Design of Dual Feed Dual Polarization Printed Slot Antenna A.R. Mallahzadeh and M.H. Amini Abstract— A dual polarized printed slot antenna is proposed. By means of dual feed one in the form of coplanar waveguide (CPW) and another microstrip transmission line, dual orthogonal linear polarizations are achieved. The radiator consists of a square ring patch located on the upper surface of a substrate. The patch is electromagnetically exited through the microstrip feed line for vertical polarization and CPW feed for horizontal one. To have a bidirectional radiation pattern, the ground plane is defected by a square slot. The antenna is designed to cover 2.4 GHz band that is suitable for wireless local area network. The reflection coefficient of the proposed antenna is simulated and good results is achieved. Far field radiation pattern of the antenna is also simulated and symmetrical radiation patterns is obtained through this design. The simulation results are carried out by commercially available software package HFSS. Index Terms— Coplanar waveguide, Orthogonal, Polarization, Ring slot, Bidirectional.

—————————— u ——————————

1 INTRODUCTION

P  

rinted   antennas   with   Polarization   diversity   have   attracted  many  attentions  over  the  past  few  years.  A   phenomenon  every  communication  system  may  deal  with   is   multipath   fading.   Through   polarization   diversity   this   fading  can  be  improved.  Dual  polarized  antennas  can  also   increase   the   channel   capacity.   A   quadric-­‐‑polarization   switchable  microstrip  antenna  is  reported  in  [1],  where  by   two   PIN   diodes,   the   polarization   is   switched   among   LHCP,  RHCP,  and  two  orthogonal  linear  polarizations.  In   [2]  a  compact  U-­‐‑slot  microstrip  patch  antenna  with  recon-­‐‑ figurable   polarization   is   proposed.   PIN   diodes   are   properly   positioned   to   change   the   length   of   the   U-­‐‑slot   arms,   which   causes   polarization   diversity.   A   CPW-­‐‑fed   square  slot  antenna  is  also  proposed  in  [3].  By  using  two   PIN  diodes  the  polarization  is  switchable  between  LHCP   and  RHCP.  Several  dual  feed  designs  providing  polariza-­‐‑ tion   diversity   have   been   designed,   and   their   characteris-­‐‑ tics   were   published   in   recent   papers   [4]–[11].   In   [4]   by   means   of   two   folded   dipoles,   two   orthogonal   polariza-­‐‑ tions   is   provided.   However   the   antenna   has   a   wide   bandwidth  but  it  has  a  large  dimensions.  By  means  of  two   orthogonal   feeds   with   spacial   structures,   The   sense   of   polarization   is   varied   between   circular   and   linear   polari-­‐‑ zations   [5].   But   the   feeding   mechanism   are   somewhat   complex.  A  tripolarization  antenna  was       ————————————————

• The authors are with the Electrical and Electronic Engineering department at Shahed University, Tehran, IRAN.  

     

Fig 1. The geometry of the proposed antenna.

proposed   in   [6],   but   isolations   between   some   ports   were   not   sufficient   and   were   hence   unacceptable   in   high-­‐‑ performance   applications.   In   resent   research,   several   techniques  have  been  published  in  [7]–[9]  to  improve  iso-­‐‑ lations   in   similar   antenna   applications.   Square   patch   an-­‐‑ tennas  fed  by  a  pair  of  coupled  microstrip  lines  through  a   pair   of   crossed   slots   to   excite   two   orthogonal   modes   for   dual  polarization  were  reported  [7].  An  air  bridge,  which   is  utilized  in  the  cross  part  of  two  feedings  for  high  isola-­‐‑ tion,   was   also   proposed   in   [7],   [8].   Different   feed   mecha-­‐‑ nisms  were  used  in  [9]  for  high  input  isolation.  It  should   be   emphasized   that   in   much   of   the   earlier   work   [7]–[9],   dual   feeding   structures   were   used   to   excite   dual-­‐‑ polarization,   thus   making   the   feed   structure   quite   com-­‐‑

2

Fig. 2. The current distribution over surface of the square ring. (a) feed #1 is active (b) feed #2 is active.

plex.  Even  the  use  of  the  air  bridge  in  [7]  and  [8]  brought   insertion   loss   and   occupied   more   space.   In   order   to   sim-­‐‑ plify   the   feeding   structure   and   save   space,   a   coplanar   waveguide  (CPW)  approach,  which  supports  two  orthog-­‐‑ onal  modes,  was  adopted  in  [10].  Two  different  radiators   were  utilized,  one  was  a  monopole  and  the  other  was  an   equivalent   dipole.   The   isolation   reported   in   this   paper   was  -­‐‑15  dB,  which  is  sufficiently  acceptable  in  some  prac-­‐‑ tical  applications.  In[11]  the  authors  were  proposed  a  du-­‐‑ al   polarized   loop   antenna.   Two   orthogonal   linear   polari-­‐‑ zations   were   excited   by   one   CPW   feed   structure,   but   the   overall  size  of  the  antenna  is  40×53  mm2  that  is  large.  It  is   well-­‐‑known  that    antennas  with  dual  polarizations,  wide   bandwidth,   good   port   isolation,   and   compact   dimension   are   highly   desirable   for   modern   wireless   communication   applications.  All  above  technics  are  somewhat  complicat-­‐‑ ed   and   makes   their   dimentions   relatively   large.   In   this   paper   we   introduce   a   dual   polarized   antenna   with   an   easy   structure   which   provides   good   isolation   and   small   dimentions.   The   antenna   consists   of   a   square   ring   patch   electromagnetically   fed   through   two   orthogonal   feeds:   CPW  and  transmission  line.  The  CPW  structure  provides   horizontal   polarization   while   the   microstrip   line   can   ex-­‐‑ cite   vertical   polarization.   The   antenna   operates   over   2.4-­‐‑ 2.44  GHz  that  is  suitable  for  wireless  local  area  networks   (WLANs).   The   simulation   results   are   carried   out   by   commercially  available  software  package  HFSS.  

2 ANTENNA DESIGN          Fig.  1  shows  the  geometry  of  the  proposed  dual  polar-­‐‑ ized   antenna.   The   antenna   is   printed   on   FR4   substrate   with   a   size   of   32×33   mm2,   thickness   of   1mm   and   relative   permitivity  of  4.4  with  loss  tangent  of  0.02.  The  radiating   element   consists   of   a   square   ring-­‐‑patch   located   on   the  

upper   surface   of   the   substrate.   The   ring   is   fed   through   two   orthogonal   feeds,   one   is   microstrip   line   and   another   coplanar   waveguide   (CPW).   The   transmission   line   can   excite  vertical  polarization  while  with  CPW  feed  horizon-­‐‑ tal   polarization   can   be   achieved.   In   order   to   assess   the   performance  of  antenna,  we  initially  assume  that  the  feed   #1   is   active.   Microstrip   feed   line   is   able   to   transmit   the   energy   from   the   feeding   point   to   the   line’s   end   without   approximately   any   losses.   As   we   know,   a   microstrip   transmission   line   has   fringe   fields  at  its  edges.   The  effect   of  these  fringe  fields  on  the  square-­‐‑ring  would  excite  two   vertical  arms.  In  effect,  the  square-­‐‑ring  is  fed  electromag-­‐‑ netically  from  transmission  line.  Fig.  2a,  in  which  the  ex-­‐‑ citement  of  two  vertical  arms  is  obvious,  shows  the  distri-­‐‑ bution   of   current   flow   on   the   ring’s   surface.   This   type   of   current  flow  causes  vertical  polarization  to  be  created.  To   excite  the  ring  effectively,  we  must  have:  

                                                 Lpatch=  

!!""

                                                                                               (1)   ! where  Lpatch   is  the  total  length  of  the  ring  and    λeff  is  effec-­‐‑ tive  wavelength  of  the  structure.            Another   polarization   is   excited   as   the   ring   is   fed   through  CPW.  In  this  case,  similar  to  what  was  said  about   microstrip  feed  line,  the  effects  of  fringe  fields  of  the  feed   line   on   the   square-­‐‑ring   results   that   this   polarization   gets   excited.  In  this  situation,  by  generation  of  a  strong  current   flow   in   two   horizontal   arms,   the   vertical   polarization   is   obtained.   In   order   to   excite   horizontal   polarization   ap-­‐‑ propriately,  as  mentioned  above,  the  length  for  the  patch   must  be  in  accordance  with  equation  (1).  Fig.  2b  indicates   the  current  distribution  over  surface  of  the  ring.  It  can  be   found   from   this   figure   that   the   horizontal   polarization   is   excited   carefully.   In   order   to   create   a   bi-­‐‑directional   pat-­‐‑ tern,  a  square  slot  should  be  created  in  the  ground  plane.   The   absence   of   this   slot   would   lead   radiation   pattern   be-­‐‑ comes   uni-­‐‑directional.   It   is   worth   mentioning   that   over   expansion   of   the   surface   of   this   slot   would   weaken   the   current  flow  over  vertical  arms  as  well  as  horizontal  arms  

© 2012 JOT www.journaloftelecommunications.co.uk

3

  (a)

(b)

Fig. 3. (a) The impact of parameter S1 on isolation and reflection coefficient and (b) that for parameter L4.

of   the   ring;   thereby,   the   performance   of   the   antenna   would  be  diminished.  Matching  of  port  1  depends  on  the   value   of   parameter   S1.   In   fact,   the   smaller   this   parameter   is,   the   bigger   the   energy   amount   coupled   from   transmis-­‐‑ sion  line  to  the  patch  will  be  which  is  followed  by  the  in-­‐‑ tensification   of   current   flow   on   the   vertical   arms   of   the   patch.   Moreover,   this   parameter   determines   the   isolation   between   two   ports   so   as   its   increase   causes   the   isolation   improvement.   Accordingly,   in   order   to   achieve   a   good   reflection  coefficient  as  well  as  a  reasonable  isolation,  it  is   required   to   decide   an   optimal   amount   for   the   parameter   S1.   Matching   of   port   2   is   also   possible   by   means   of   L4   length.   Fig.   3   shows   the   impact   of   parameters   L4   and   S1   changes.   The   optimum   amounts   of   these   parameters   are   listed   in   Table   1.   Fig.   4   depicted   the   reflection   coefficient   of  the  structure.  As  shown  in  this  figure,  the  antenna  has   reflection   coefficient   of   about   -­‐‑24   dB   and-­‐‑27   dB   at   center   frequency  of  2.44  GHZ  for  port  #1  and#2  respectively.  It  is   necessary   to   mention   that   the   length   of   horizontal   and   vertical   arms   of   the   patch   are   optimal   for   the   desirable   resonance  frequency  for  both  ports,  thus  the  length  of  the   vertical  arms  has  become  slightly  more  than  the  horizon-­‐‑ tal   one   and   the   mentioned   loop   looks   rather   rectangular.   In  Fig.  5  the  normalized  simulated  far  field  radiation  pat-­‐‑ terns   of   the   antenna   are   shown.   The   half   power   beam   widths  for  each  feed  are  about  70  degrees  and  88  degrees   in  the  E-­‐‑plane  (feed  #1)  and  H-­‐‑plane  (feed  #2)  respective-­‐‑ ly.   It   is   apparently   that   good   omnidirectional   patterns   is   obtained  through  this  design.        

  TABLE 1 DESIGN SIZE OF THE PROPOSED ANTENNA  

Parameter   Value  (mm)   Parameter   Value  (degree)   Parameter   Value  (mm)      

                               

L1   33   L3   16   W3   16  

L2   30   32   53   S1   .2  

L3   20   W2   2      

4

 

Fig. 4. Reflection coefficient of the proposed dual feed antenna.

(a) Fig. 5. Far field radiation pattern of the antenna. (a) vertical pol. and (b) horizontal pol.

(b)

5

3

CONCLUSION

         A  dual  feed,  dual  polarization  printed  antenna  is  pro-­‐‑ posed.   The   radiator   element   consists   of   a   square   ring-­‐‑ patch   located   on   the   upper   surface   of   FR4   substrate.   The   ring  is  fed  by  two  orthogonal  feeds:  CPW  and  microstrip   transmission  line.  Two  orthogonal  linear  polarizations  are   excited   and   agreeable   radiation   patterns   are   obtained   through   this   design.   The   isolation   between   two   ports   is   about  -­‐‑19  dB  at  2.44  GHz.  The  antenna  has  the  reflection   coefficient  of  about  -­‐‑24  dB  and  -­‐‑27  dB  at  center  frequency   for  vertical  and  horizontal  polarizations  respectively.    

REFERENCES [1]

R.-­‐‑H.  Chen  and  J.-­‐‑S.  Row,  “Single-­‐‑fed  microstrip  patch   antenna   with   switchable   polarization,”   IEEE   Trans.   Antennas   Propag.,   vol.  56,  no.  4,  pp.  922–926,  Apr.  2008.   [2] Pei-­‐‑Yuan  Qin,  Andrew  R.  Weily,  Y.  Jay  Guo,  and   Chang-­‐‑Hong   Liang,   “Polarization   Reconfigurable   U-­‐‑Slot   Patch   Antenna,”   IEEE  Trans.  Antennas  Propag.,  vol.  57,  no.  10,  Oct  2009.   [3] Y.  B.  Chen,  Y.  C.  Jiao,  and  F.  S.  Zhang,  “Polarization   reconfigu-­‐‑ rable   CPW-­‐‑fed   square   slot   antenna   using   pin   diodes,”   Microw.   Opt.  Technol.  Lett.,  vol.  49,  pp.  1233–1236,  Jun.  2007.   [4] S.   Daoyi,   J.   J.   Qian,   Y.   Hua,   and   D.   Fu,   “A   novel   broadband   polarization   diversity   antenna   using   a   cross-­‐‑pair   of   folded   di-­‐‑ poles,”  IEEEAntennas  Wireless  Propag.  Lett.,  vol.  4,  pp.  433–435,   2005.   [5] H.  Zhong,  Z.  Zhang,  W.  Chen,  Z.  Feng,  and  M.  F.  Iskander,  “A   tripolarization   antenna   fed   by   proximity   coupling   and   probe,”   IEEE  Antennas  Wireless  Propag.  Lett.,  vol.  8,  pp.  465–467,  2009.   [6] P.  Mousavi,  “Multiband  multipolarization  integrated  monopole   slots  antenna  for  vehicular  telematics  applications,”  IEEE  Trans.   Antennas  Propag.,  vol.  59,  no.  8,  pp.  3123–3127,  Aug  2011.   [7] M.   Barba,   “A   high-­‐‑isolation,   wideband   and   dual-­‐‑linear   polari-­‐‑ zation  patch  antenna,”  IEEE  Trans.  Antennas  Propag.,  vol.  56,  no.   5,  pp.  1472–1476,  May  2008.   [8] K.-­‐‑M.  Mak,  H.  Wong,  and  K.-­‐‑M.  Luk,  “A  shorted  bowtie   patch   antenna  with  a  cross  dipole  for  dual  polarization,”  IEEE  Anten-­‐‑ nas  wireless  Propag.  Lett.,  vol.  6,  pp.  126–129,  2007.   [9] Y.-­‐‑X.  Guo,  K.-­‐‑M.  Luk,  and  K.-­‐‑F.  Lee,  “Broadband  dual  polariza-­‐‑ tion   patch   element   for   cellular-­‐‑phone   base   stations,”   IEEE   Trans.  Antennas  Propag.,  vol.  50,  no.  2,  pp.  251–253,  Feb.  2002.   [10] X.   Wang,   W.   Chen,   Z.   Feng,   and   H.   Zhang,   “Compact   dual-­‐‑ polarized   antenna   combining   printed   monopole   and   half-­‐‑slot   antenna   for   MIMO   applications,”   in   Proc.   IEEE   Antennas   Propag.  Soc.  Int.  Symp.,  Charleston,  SC,  2009,  pp.  1–4.   [11] Y.  Li,  Z.  Zhang,  Z.  Feng,  and  M.  F.  Iskander,  “Dual-­‐‑mode   loop   antenna   with   compact   feed   for   polarization   diversity,”   IEEE   Antennas  Wireless  Propag.  Lett.,  vol.  10,  pp.  95–98,  2011.     A. R. Mallahzadeh received the B.S. degree in electrical engineering from Isfahan University of Technology, Isfahan, Iran, in 1999 and the M.S. degree in electrical engineering from Iran University of Science and Technology, Tehran, in 2001, and the Ph.D. degree in electrical engineering from Iran University of Science and Technology, Tehran, in 2006. He is a member of academic staff, Faculty of Engineering, Shahed University, Tehran. He has participated in many projects relative to antenna design, which resulted in fabricating different types of antennas for various companies. Also, he is interested in numerical modeling and microwaves. M. H. Amini is a student in communication engineering from Shahed University, Tehran, Iran. He also has experience as an antenna de-

signer. His research interests include printed antennas and leakywave structures, slotted waveguide antennas and multiband radiators.