Dual Linear Polarized UWB Imbedded Section for Tapered Chambers

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Dual Linear Polarized UWB Imbedded Section for
Tapered Chambers
By Ryan Chilton Supervisor Dr. Chi-Chih Chen
The ElectroScience Laboratory Department of
Electrical Engineering The Ohio State University
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Table of Contents
Tapered chamber operation. Embedded Feed
Concept. Numerical Modeling Investigations. Near
Field Probe. Installation and Chamber
Imaging. Additional Information Sources.
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Tapered chamber operation.
Key Features
Off the shelf antenna.
Near field range.
Redesigned elements.
lt than compact range.
Single polarization.
Complete tapered chamber systems are commercially
available.
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Prior OSU Tapered Chamber Feed 3
E-plane aperture field magnitude, dB
Prototype geometry.
Design Concepts
Conical shield matches taper.
TSA Launcher Arms
E Field Lines
Metal plates form slot antenna.
Absorber suppresses multipath.
Endfiring towards you.
Near field probing setup.
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Proposed imbedded wave launcher.
Vivaldi-style TSA is a natural endfire UWB
radiator 2.
Printed single-pol TSA.
Reflection Coefficient
E-Plane Pattern
-15dB
1GHz 18GHz
Dual orthogonal polarization achieved without
manual rotation.
High f
Low f
H-Plane Beamwidth
Widening
Image (Balance) Plane
1GHz 18GHz
Cutoff limit anticipated as operating frequency
decreases.
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FDTD modeling of launcher section.
Large problem to model, regardless of numerical
method.
Moment method far too many unknowns for dense
solve.
FE many runs required to sample UWB frequency
response.
FDTD staircasing of curved features, dispersion
of UWB signals.
FDTD selected for simplicity concerns (single
machine execution)
User Sketch
Simulation
1 pixel 1 Yee cell. ?L0.5cm (?/20 _at_ 3GHz)
Relative Ey intensity, dB
Rapid evaluation of many geometry and absorber
permutations.
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Absorber layout design tradeoff.
Transducer Gain 20 log10 (Eaperture / Jexcite)
Too little absorber yields multipath interference
in G(?)
Compromise designs.
Too much absorber yields low frequency rolloff.
Carbon loaded foam.
Ferrite flexible tile.
Absorber placement must balance low-f performance
ringing effects.
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Lower limit cylindrical guide cutoff.
Transducer Gain 20 log10 (Eaperture / Jexcite)
Low f
High f
Longer cans have worse cutoff behavior, but cant
make it too short.
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Feed construction steps.
VelcroSpray90
Autocad sketch for mech. subcontractor.
Wedge absorber w/ velcro.
Pyramidal and wedge absorber placement.
Shaped and friction fit block absorber
Tapered block absorber placement.
Completed absorber layout and support cradle.
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Additional mechanical considerations.
Laminated Blade Construction
Nylon Throat Spacers Plexiglass Collar
Aluminum provides strength.
Can slide to tune slot impedance.
Variable slotline width, tightened by countersunk
machine screws.
Oversized sliding holes.
Mechanical rigidity for feed bonds.
Brass solderable shapeable.
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Near field probe prior to installation.
20 log10 (Ecopol / 1V/m)
20 log10 (Ecrosspol / 1V/m)
Slide position, inches.
Slide position, inches.
Good (-20dB) isolation between near field co-pol.
and cross-pol cuts.
Ecopol Phase
Small dipole.
High order modes at 2 GHz and up.
Slide position, inches.
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Blade insert modifications.
Throat Region
0 dB
f2 GHz
Gradual taper(new).
20 log10 E(?) / E(0)
Approx. 18
24 circular fillet (old)
Observation angle.
80
-80
Approx. 24
-30 dB
0 dB
f4 GHz
0 dB
f6 GHz
20 log10 E(?) / E(0)
20 log10 E(?) / E(0)
Observation angle.
-80
80
80
Observation angle.
-80
-30 dB
-30 dB
No evidence of strong higher order modes at 2GHz
and higher.
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Feed transport installation.
Margarita validation.
Empty
(They passed).
Prepared to ship out.
Bowtie test antenna and positioner.
Boom
Support fixture.
Pre-existing conical feed section
(no feed boom or source antenna shown).
New embedded feed section replacement.
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S11 after installation.
20 log10 S11(t)
Time (ns)
Feed apex (coax-slotline junction) dominant
reflection mechanism.
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Test zone size purity evaluation.
Magnitude taper.
Phase taper.
Vivaldi beamwidth narrows.
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Transfer function feed to receiving horn.
Good X-pol isolation, persists until we hit the
noise floor.
Cutoff knee horn not effective aperture
receiver here.

k
Variable frequency.
Excellent isolation and flat response (small
multipath effects)
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Measuring polarization mismatch.
Blades are correctly aligned w.r.t. rest of the
chamber.
Point 1
Copol max 180
Copol max 90
Copol max 270
Crosspol notch 90
Copol max 180
Crosspol notch 270
Crosspol notch 270
Variable receiver polarization.
Point 2
Blades are correctly aligned w.r.t. each other.
(subtle)
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Near field focusing (imaging).
Coherent summation for true sources.
Definition
Random phasor summation elsewhere.
Copol field probe.
Probe integral spatial diversity improves SNR.
Image intensity function.
Spectral integral UWB diversity improves SNR.
0.1-2 GHz Bowtie
Feed location
Feed location
Phase Center
Phase Centers
Y, feet.
Y, feet.
f6-10GHz
f0.5-6GHz
2-18 GHz Ridged Horn
Probe Cut
Probe Cut
Test Antenna
X, feet.
X, feet.
Single source behavior lt6GHz, interference
problems appear gt6GHz.
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Abridged Bibliography
H.E. King, F.I. Shimaburuko, and J.L. Wong,
Characteristics of a Tapered anechoic Chamber,
IEEE Trans Antennas Propag. (Commun.), vol. 15,
pp. 488-490, 1967.
Gazit, Ehud. Improved design of the Vivaldi
antenna, Microwaves, Antennas and Propagation,
IEE Proceedings H , vol. 135, no.2 pp. 89- 92,
Apr 1988
Lee, Kwan-Ho. Development of Four Novel UWB
Antennas Assisted by FDTD Method, Ph.D.
Dissertation , OSU Electroscience Library.
Lai, A.K.Y. Sinopoli, A.L. Burnside, W.D., "A
novel antenna for ultra-wide-band applications,"
Antennas and Propagation, IEEE Transactions on ,
vol.40, no.7 pp.755-760, Jul 1992
W.D. Burnside, S.J. Essman, and W.H. Theunissen,
Enhanced Tapered Chamber Design, Tech. Rep.
737025-1, The Ohio State University
Electroscience Laboratory, Dec. 1999.
Relevant Vendor Contacts
http//www.orbitfr.com/?ItemID179
http//www.satcomweb.com/TAPER.htm
http//www.ets-lindgren.com/productpage.cfm
/model/AMS-8600/producttype/Chambers