Master Thesis. Development of a Broadband Circular Polarised Antenna for Over-The Performance Test Applications

Transcription

1 Master Thesis Development of a Broadband Circular Polarised Antenna for Over-The The-Air Performance Test Applications Saeed Universität t Duisburg-Essen Hochfrequenztechnik IMST GmbH : Prof. Dr.-Ing. K. Solbach Dipl.-Ing. A. Winkelmann 1

2 Outline Motivation Introduction Frequency Independent Antenna Planar Spiral Antenna Simulation Results Measurement Results Conclusion Future Work 2

3 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 Circular Polarized GSM,UMTS & Higher order modes Unknown DUT Polarization Planar Spiral Antenna Conical Spiral Antenna Cross Log-periodic Antenna Balance feeding Unidirectional pattern 3

4 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 Periodic principle Z 1 Z 2 Self-Complementary Structure Z * Z 1 2 = Z ( ) 2 = ( Ω) Z Z 1 = 2 = 188.5Ω 4

5 Selection Process 5

6 Selection Process (Cont.) 6

7 Planar Spiral Archimedean Spiral How Radiation happen Self-Complementary when s δ = π /2 = w = r r 4N s+ w 2w a = = π π First Arm Second Arm 1 0 r = r (1 + aφ) 1 0 r = r (1 + a( φ δ)) 2 0 r = r (1 + a( φ π)) 3 0 r = r (1 + a( φ π δ)) 4 0 L QP = π r = λ /2 Under Antiphase feeding at points A and B Radiation happen when 2πr = λ 7

8 Circular Polarized Radiation I x, I y with 90o phase shift Circumference= λ I I & I I x y x y o I, I 90 phase different x y RHCP Rule RHCP OR LHCP depend on Rotation sense 8

9 Spiral Antenna System Consist from 3 Units Feeding circuit (Balun) Archimedean Spiral PCB Absorber loaded Cavity 9

10 Feeding Circuit (Balun) Balun will provide Balanced feeding Impedance transformation Baluns type Linear Tapered Balun Infinite Balun Marchand balun Marchand Balun Infinite Balun Linear Tapered Balun 10

11 Balun Simulation and Measurement Measurement and Simulation results for Single balun Measurement and Simulation results for B2B balun 11

12 Measurement Verification S = S, S = S Z a in = a 1 2 Γ= S S Symmetry Balanced feed 1+Γ 1+ S S = 2Z 0 = Γ 1 S + S

13 Antenna Parameters and Simulation 1: Spiral rate of growth (a) Improved in AR for tight spiral growth of rate (small value of a) 3:Feed structure 2: Conductor spacing (w) Self-Complementary or No Self- Complementary control the impedance of antenna 4: Spiral diameter r0 = w will provide flat resistance and close to zero reactance D max > / λ π Activate High order modes Pattern distortion D max < / λ π Reduced Gain Increased AR 13

14 3D Far-Field pattern Simulation RHCP far field radiation pattern (Simulation) 14

15 Current Distribution Simulation Current Density Distribution (Simulation) Active Region Concept 15

16 Antenna Measurement Return losses better than 15 db Antenna impedance using two ports measurement. 16

17 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 μ = μ jμ = ε = ε jε r r r r r r Z μ μ μ μ ε ε ε ε 0 r r = = = 377 = 377Ω 0 r r 17

18 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 18

19 Sp5 and Sp7 Measurement Results Axial Ratio Sp5 Gain o {, 90 } G φ θ = RHCP LHCP Sp7 19

20 Measurement with Cavity Empty & loaded Cavity Diff. Absorber length 20

21 Measurement with Resistance Termination Termination improved Low Frequency range Axial Ratio With and Without Impedance Termination 21

22 Far-Field Measurement For Final Version o {, 90 } G φθ= RHCP LHCP 22

23 Cross-Polarization Omnidirectional Pattern G φ 0, θ = Cross-Polarization better than 20dB Omnidirectional pattern in the spiral plane 23

24 3D Far-Field Radiation Pattern Measurement RHCP far field radiation pattern (Measurement) 24

25 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. 25

26 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. 26

27 Thank You for Your Attention 27

28 Questions 28

29 Questions 29