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Balun) • Archimedean Spiral PCB • Absorber Loaded Cavity 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 o RHCP G {φθ,90= } 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.
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