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.

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1 INTRODUCTION 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      

     

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-­‐‑

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———————————————— • The authors are with the Electrical and Electronic Engineering depart-ment at Shahed University, Tehran, IRAN.  

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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

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

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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   L1   L2   L3  Value  (mm)   33   30   20  Parameter   L3   32   W2  Value  (degree)   16   53   2  Parameter   W3   S1    Value  (mm)   16   .2    

                                   

  (a) (b)

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

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(a) (b)

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

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

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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.  

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[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 engineer-ing from Isfahan University of Technology, Isfahan, Iran, in 1999 and the M.S. degree in electrical engineering from Iran University of Sci-ence and Technology, Tehran, in 2001, and the Ph.D. degree in electrical engineering from Iran University of Science and Technolo-gy, 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 fabricat-ing 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 leaky-wave structures, slotted waveguide antennas and multiband radia-tors.