MasterMaster ThesisThesis DevelopmentDevelopment ofof aa BroadbandBroadband CircularCircular PolarisedPolarised AntennaAntenna forfor OverOver--TheThe--AirAir PerformancePerformance TestTest ApplicationsApplications
Saeed Arafat Universität Duisburg-Essen Hochfrequenztechnik Prof. Dr.-Ing. K. Solbach IMST GmbH : Dipl.-Ing. A. Winkelmann
Arafat Jan 2008 1 Outline • Motivation • Introduction • Frequency Independent Antenna • Planar Spiral Antenna • Simulation Results • Measurement Results • Conclusion • Future Work
Arafat Jan 2008 2 Motivation • Over The Air (OTA) Test
• Characterize the air interference of a mobile device. • Need a measurement system that can collect data on a spherical surface enclosing the DUT.
• Broadband antenna GSM,UMTS & Higher order modes
• Circular Polarized Unknown DUT Polarization
• Planar Spiral Antenna Balance feeding • Conical Spiral Antenna • Cross Log-periodic Antenna Unidirectional pattern Arafat Jan 2008 3 Introduction •Frequency Independent Antenna The antenna characteristics are invariant to change of the physical size of antenna. •Frequency Independent Antenna Principles:
•Angle principle
•Truncation principle Z1
•Periodic principle Z2
•Self-Complementary Structure 2 ⎛⎞ ⎜⎟Z Z = Z =Ω188.5 ⎜⎟0 = 188.5 2 ()Ω 12 ZZ12* = ⎜⎟() ⎜⎟2 ⎝⎠ Arafat Jan 2008 4 Selection Process
Arafat Jan 2008 5 Selection Process (Cont.)
Arafat Jan 2008 6 Planar Spiral How Radiation happen Archimedean Spiral
Self-Complementary when δ =π /2 rr− sw==10 4N
sw+ 2w a == π π rr=+(1 aφ) Lr= π = λ /2 First 1 0 QP′ Arm rr2 =+−0(1 a(φδ)) Under Antiphase feeding rr=+−(1 a(φπ)) at points A and B Second 3 0 Arm Radiation happen when rr4 =+−0(1 a(φ πδ−)) 2πλr =
Arafat Jan 2008 7 Circular Polarized Radiation
I x,I y with 90o phase shift
Circumference=λ RHCP Rule
RHCP OR LHCP depend on IIx ≅ yx & I⊥ Iy
o Rotation sense I xy,I 90phase different
Arafat Jan 2008 8 Spiral Antenna System
Consist from 3 Units • Feeding circuit (Balun) • Archimedean Spiral PCB • Absorber loaded Cavity
Arafat Jan 2008 9 Feeding Circuit (Balun) Balun will provide • Balanced feeding • Impedance transformation Baluns type • Linear Tapered Balun Marchand Balun • Infinite Balun • Marchand balun
Linear Tapered Balun Infinite Balun Arafat Jan 2008 10 Balun Simulation and Measurement
Measurement and Simulation Measurement and Simulation results for Single balun results for B2B balun
Arafat Jan 2008 11 Measurement Verification
SS11==22 , S21 S12 ⇐ Symmetry
aa12= − ⇐ Balanced feed
Γ=−SS11 21
1+Γ 1+ SS11 − 21 ZZin ==210 00 11−Γ −SS11 + 21
Arafat Jan 2008 12 Antenna Parameters and Simulation
1: Spiral rate of growth (a) 2: Conductor spacing (w)
Improved in AR for tight Self-Complementary or No Self- spiral growth of rate (small Complementary control the value of a) impedance of antenna
3:Feed structure 4: Spiral diameter
Dmax >λ /π Dmax <λ /π rw0 = will provide flat Activate High Reduced Gain resistance and close to order modes zero reactance Increased AR Pattern distortion
Arafat Jan 2008 13 3D Far-Field pattern Simulation
RHCP far field radiation pattern (Simulation)
Arafat Jan 2008 14 Current Distribution Simulation
Current Density Distribution (Simulation)
Active Region Concept
Arafat Jan 2008 15 Antenna Measurement
Return losses better than 15 dB
Antenna impedance using two ports measurement.
Arafat Jan 2008 16 Cavity •Unloaded cavity •When high gain need •Narrow bandwidth •Absorber loaded cavity •Gain reduction not critical •Wide bandwidth •Cavity Dimension •Depthλ/4 at lower frequency •Diameter 1.05 spiral diameter •Absorber material
μr=−μμr′ jjrrr′′ =ε=ε′ −εr′′
μ μ μμ Z = ==0 rr377 =377ΩArafat εεε ε Jan 2008 0 rr 17 Antenna Measurement In Anechoic Chamber
L/H/W=12/5.5/8 m
From 0.4 up to 64 GHz
Gain Measurement Polarization Measurement
Gain Transfer method Polarization Pattern Method
1 2
H V
Arafat Jan 2008 18 Sp5 and Sp7 Measurement Results
Sp5 Axial Ratio
G {φθ,90= o } RHCP Gain LHCP
Sp7
Arafat Jan 2008 19 Measurement with Cavity
Empty & loaded Cavity Diff. Absorber length
Arafat Jan 2008 20 Measurement with Resistance Termination
Termination improved Axial Ratio With and Without Low Frequency range Impedance Termination
Arafat Jan 2008 21 Far-Field Measurement For Final Version
G {φθ,90= o} RHCP Arafat LHCP Jan 2008 22 Cross-Polarization Omnidirectional Pattern
⎧ ⎫ G ⎨φ=0,θ ⎬ ⎩⎭
Cross-Polarization Omnidirectional pattern in the better than 20dB spiral plane
Arafat Jan 2008 23 3D Far-Field Radiation Pattern Measurement
RHCP far field radiation pattern (Measurement)
Arafat Jan 2008 24 Conclusion • RHCP antenna worked (0.6 < f/GHz < 13) • Two arms Archimedean spiral antenna was shown many desirable characteristic. • Microstrip tapered balun provides a balance feeding and impedance transformation • An unidirectional pattern achieved using absorber loaded cavity. • The numerical results were confirmed by measurements. • As a result the developed antenna worked well for OTA measurement test.
Arafat Jan 2008 25 Future Work • Reduce the spiral size using slow wave techniques or absorber painting at the open end of spiral.
• Improve and reduce balun size.
• Decrease the cavity depth by thinner absorber loading
• Benefit of the new MetaFerrite material for reducing the antenna size.
Arafat Jan 2008 26 ThankThank YouYou forfor YourYour AttentionAttention
Arafat Jan 2008 27 Questions
Arafat Jan 2008 28 Questions
Arafat Jan 2008 29