Oneof lastapplications forUVWBtechnology is breasttumordetection [2].Inthis detectionsystem,the antenna has to work infrequencies ranging from 3 to 9GHz.. The behavior of this antenna in
Trang 1UWB SLOTANTENNA INTHIE3-9GHZBAND
JoseManuel PidreMosquera*, Maria Vera Isasa Dpto Teoria de la Sefial y
Comunicaciones Universidad deVigo Spain.http://www.grp.tsc.uvigo.es
Introduction Recently anemergingultra-wide band(UWB) technologyison development It
requires harddesign specifications forantennas over averywide bandwidth
U.S Federal Communication Commission (FCC) defines UWB as higher than
20%fractional instantaneous bandwidth Short-pulseUWBtechnology is applied
incommunication,radar andprecisionradiolocation [I ]
Oneof lastapplications forUVWBtechnology is breasttumordetection [2].Inthis
detectionsystem,the antenna has to work infrequencies ranging from 3 to 9GHz
Inaddition, theimpulseresponsehastobeshort,constantradiation pattem over
the band and low return losses
Oneof themostpromisingantennasthatcan meet thesedesign goals is the
ultra-widebandmagnetic antenna [3] [4] The behavior of this antenna in the 3-9 GHz
rangeispresented in thispaper AnV-model and theuseofaback-absorberlayer
in order toimproveitsperformance isanalyzed A prototype has been builtand
measured
UWBMagneticslot antenna The antennaconsists ofaleaf-shaped slot, excitedacross thegapas can be seen in
figure 1 The radiated fields are orthogonally polarized to the longitudinal slot
axis
Figure 1 UWB Magnetic slot antenna Original flat configuration (right ) and proposed
configuration (intheleft)
Trang 2In [3]is defined thewidth of the slotwas we moveacrosslongitudinalslot axis
1:
whereXois thewavelength in the center frequency A deeper analysis of equation
1,reveals this ratio between maximumslotwidthWand slotlengthL:
L 16
Theantenna wasevaluatedusingthe software packages IE3D andXFDTD.IE3D
is a commercial method ofmoments code [5] XFDTD is acommercial code
based on FDTD algorithm [6] Both can deliver radiated fields and input
impedance of simulated devices IE3Disveryfastevaluating planar slots So we
haveemployed ittostudy how the slot input impedancechanges with dimensions
XFDTD is apowerful tool to simulate 3Ddevices in time domain It was very
usefultoanalyze the antenna with differentbending angles
Starting with slot dimensions obtained from (1) for 6GHz, several simulations
weremade changingthe W/L ratio We found thatincreasing slot dimensionsthe
matching bandwidth increases and the frequency band where radiation pattem
does notchangedecreases
Inordertoget anultra-widematching bandmaintaining the broadside maximum
radiation,alonger slot bent acrossH-plane isproposed,asfigure I shows After
studyingseveralangles, wehave found anoptimal bending of58°whenL=2X0
andW=X/2 (W/L=1/4,Xo=50mm).Figures2and3show the simulatedradiation
pattern of this configuration inE-plane and H-plane The pattern still needssome
corrections: sidelobes andback radiation can besuppressedwithabsorber sheets
13Ghz-4 Ghz -5 Ghz 6 Ghz-7 Ghz-6 Ghz*9 Ghz I
9= \- - - -T -I- - - I- - -
-7 - 5- -L -\-, -i -/ -
Theta[Grados]para Phi = 0°
Figure 2 Simulated E-plane Gain Magnitude
Trang 37 i- - - ,
-Ii
~0
0 20 40 60 80 100 120 140 160
Theta[Gradosipata Phi - 900
Figure 3 Simulated H-plane Gain Magnitude
Results and Discussion
A prototype with the mentioned dimensions was built and measured The
prototype was built in0.5mmbrass,andasheet of eccosorb [7]wasemployedas
absorber
Figure4showsthe measured and simulatedinputimpedance Themeasurementis
comparable to the simulation result Therefore, ifwe feed the antennawith a
suitable matching network the antenna would be well matchedoverthe entire
desiredfrequency band Measuredand simulated gainin broadside direction is
plotted infigure5
Measurement '4 SirTulation
Figure 4.Inputimpedancefrom3GHzto6GHz.Simulation and Measurernent.
Ga.in i Bmdrdd dheti
385 485 585 6885 75
Frr.qu0ny (G3I)
Figure 5 Gain in broadside direction Simulation and Measurement
Trang 4Conclusions andFuture Work TheUWB magneticslot antenna canbe designed in order to meet challenging
specifications over a very wide frequency band The patented design of [3] was
analyzed, and some changes are proposed in order to get better return losses
without radiation pattern deterioration We built a prototype increasing the
dimensionspublishedin[3]andbendingtheantenna580 Anabsorber sheetwas
addedinordertocorrectundesiredsidelobes and back radiation
Measurements were very similar to simulation results, and both comply with
proposed objectives
Acknowledgment This work was supported by Xunta de Galicia (PGDITOITIC32201PR) and
FEDER-CYCIT(TIC2003-01432)
References:
[1] R.J Fontana "Recent System Applications of Short-Pulse Ultra-Wideband
(UWB) Technology".IEEE Trans.MicrowaveTheory and Techniques Vol.52 N
9.September2004 Pp.2087-2104
[2] E.J Bond, X Li, S.C Hagness, "Microwave Imaging via space-time
beamforming for early detection of breastcancer".IEEE Trans on Antennasand
Prop.Vol 51.N°8.August 2003.Pp 1690-1705
[3] M Barnes "Ultra-Wideband Magnetic Antenna" US Patent 6091374 July
2000
[4]H.G Schantz, M.Barnes "TheCOTAB-UWB magnetic slotantenna".IEEE
APS Int Symposium 2001,Vol.4, July2001.Pp 104-107
[5] Zeland SoftwareInc "IE3D User'sManual".January 2001
[6]"XFDTD Reference Manual.Version 6.0" Remcom Inc 2003
[7]Emerson&CumingMicrowaveProducts.http://www.eccosorb.com