Measurement of Electrically Small Antennas
Electrically Small Antennas
Measurement Concepts
Dipl.-Ing. Rainer Wansch
http://www.antennen.fraunhofer.de mailto:[email protected] Introduction
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Fraunhofer-Society in Germany
Leading Organisation doing applied research in Europe 56 Instituts on 40 locations 12 700 employees, 1.2 billion € turnaround Combination of Institute Competencies in Technology Clusters and Alliances − Microelectronics − Information and Communication Technology − Defense and Security Research − Materials, Components; Production; Life Sciences; Surface Technology and Photonics
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Fraunhofer-Institute for Integrated Circuits IIS
Founded: 1985 Locations: Erlangen, Fürth, Nürnberg, Dresden Employess: about 520 Turnaround: € 60 Mio.
Financing > 80% Projects < 20% basic founding
www.iis.fraunhofer.de Seite 4
Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Overview
Parameters – Pattern – Polarisation – Efficiency – Matching – Noise Parameters – Sensitivity / Radiated Power (CTIA) Methods – Far-Field – Near-Field – Reverberation Chamber – GTEM Cell – Wheeler Cap
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Some Definitions
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Gain and Directivity
Directivity and Gain are S(θ,ϕ) angular dependent D(),ϕθ= functions S()sin, dd ϕθθϕθ Relation between gain and ∫∫ directivity gives the efficiency By measuring the pattern of the antenna and peak gain of the antenna one (θ ϕ)= η⋅ (θ,D,G ϕ) can determine the efficiency
G max = η⋅Dmax
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Radiation Regions
Reactive Near- λ R = Fraunhofer-Zone Field 2π Radiating Near- Field (Fresnel D3 Region) R1 = 62.0 λ λ R1 R = D 1 2π Far-Field, R2 Fraunhofer- 2D2 Region R2 = λ Fresnel-Zone Region of plane waves
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 How is the Far-Field Region for Antenna Measurements defined?
1 1 RR 16 ϕλ °=Δ+= )5,22( 22 D 2 1 RR += ()2 2D2 R =→ λ
AUT (Antenna under Test) has to be in Far-Field Region! This distance is only defined by the AUT and not by the probe
antenna! Seite 9
Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 How is the Far-Field Region defined?
Let‘s assume an electrically small antenna being smaller than the halfwavelength dipole. This means, we are always in the far-field with respect to the measurement definition. So, near- and far-field approaches lead to the same results and no transformation would be necessary – except for a better angular resolution.
1 D = λ 1 = RR + 16 λ Δϕ = °)5,22( 2 2 22 D 2 2D λ 1 RR += ()2 R ==→ λ 2 2D2 R =→ λ Seite 10
Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Antenna Noise Temperature
T T a TA +TAP U Environ- TR Line of length l TP mental noise Receiver T0 of line
2π π Antenna noise temperature T : θ,T ,G ϕϕ⋅⋅ sin θθ dd ϕθ A ∫∫ U ()() Integration of environmental noise weighted T = 0 0 with antenna gain A 2π π ∫∫ (),G ϕ ⋅ sin θθ dd ϕθ 0 0 Antenna noise temperature due to physical ⎛ 1 ⎞ TAP = ⎜ − 1⎟ TP eA ≈ 0,9-1 temperature TP of antenna: ⎜ e ⎟ ⎝ A ⎠
Cumulative noise temperature at receiver −2α l −2α l −2αl Ta = TAe + TAPe + T0 (1 − e ) input: Seite 11
Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 CTIA Measurements
CTIA acceptance tests include Over-the-Air measurement in a reflection and interference-free environment. Key aspects included: − Shielded Anechoic chamber – Controlled environment − Over-the-Air tests include − Base Station Simulator interface − Radiated power pattern − Sensitivity pattern (Bit-error-rate, for GSM BER=2.44%) − Intermediate channel test − Fixed spherical grids: Theta-Phi: − Radiated power: Every 15 degrees in theta and phi, excluding 0 and 180, 2-pols − Sensitivity: Every 30 degrees in theta and phi, excluding 0 and 180, 2-pols CTIA - Cellular Telecommunications & Internet Association Seite 12
Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 CTIA Measurements: Radiated Power
Total Radiated Power (TRP) 1 2π π TRP = ()()θ,EIRP ϕ + EIRP ,ϕ ()⋅sinθθ dd ϕθ Integration over the complete 4π ∫∫ θ ϕ sphere 0 0
Near-Horizon Partially 3π 1 2π 4 Radiated Power NHPRP45 = ()()θ,EIRP ϕ + EIRP ,ϕ ()⋅sinθθ dd ϕθ ∫∫ θ ϕ 4π 0 π Integration ±30° or ±45° from 4 horizon
2π 1 2π 3 NHPRP30 = ()()θ,EIRP ϕ + EIRP ,ϕ ()⋅sinθθ dd ϕθ ∫∫ θ ϕ 4π 0 π 3
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 CTIA Measurements: Sensitivity
Total Isotropic Sensitivity 4π TIS = (TIS) 2π π ⎛ 1 1 ⎞ ⎜ + ⎟ ⋅ sin θ dd ϕθ Integration over the ∫∫⎜ EIS θ, ϕ EIS θ, ϕ ⎟ 0 0 ⎝ θ () ϕ ()⎠ complete sphere
Near-Horizon Partial Isotropic Sensitivity 4π NHPIS30 = 2π Integration ±30° from 2π 3 ⎛ 1 1 ⎞ ⎜ ⎟ sinθ dd horizon ∫∫⎜ + ⎟ ⋅ ϕθ 0 π EISθ ()θ,ϕ EISϕ ()θ,ϕ 3 ⎝ ⎠
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Methods not Needing an Anechoic Chamber
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Input Impedance: Wireless Transmitter in Water Metering System
Measurement of Matching Properties at CH1 S11 ↑ 1 U 1: 16.15 mU -j106.5 mU 1 868.5 MHz 2: 260.4 mU j164.0 mU Vector Network Analyzer 0.5 2 844 MHz 3: -293.1 mU -j146.5 mU 889.5 MHz 5 Simulated environment with water pipe 2 0 1 segment and porous concrete brick 3 1
-5
CA L
-0.5 -2 OF S -1 CH2 S11 dB MAG 2.5 dB/ REF 0 dB 1: -19.36 dB 0 dB 868.51.5〈 0GHz MHzdB 2: -10.24 dB 844 MHz CP L 3: -9.690 dB 889.5 MHz 2 3
2.5 dB/
FI L 1100k 1
-25 dB START 200 MHz 100 MHz/ STOP 1.6 GHz Date: 8.FEB.08 16:12:59 Seite 16
Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Wheeler Cap
Only applicable for determining the efficiency of an antenna Comparison between free space operation and operation in a small resonator
Equivalent circuit of an ZA = Rv + Rs + jXA antenna
R Efficiency definition based η= S R + R on network elements S V
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Wheeler Cap
Measurement of Z using Z FreeSpace = + LS + jXRR VNA in free space Wheeler L += jXRZ Real part related to Re( Z − Z )Re() radiation and loss resistance η = FreeSpace Wheeler Measurement of Z with Re( Z FreeSpace ) Wheeler Cap Real part related to loss resistance only Radius of Wheeler Cap should be smaller than λ/2π
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 GTEM Cell Measurement
Coaxial Line
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 GTEM Cell Measurement
Antenna placed in the homogenous field region of the GTEM cell Rotation around y-axis of cell Power measured using VNA Comparison with anechoic chamber measurement shows a good agreement for a λ/4 patch @ 1.92 GHz Efficiency also possible
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Reverberation Chamber
Picture Source: http://www.bluetest.se Seite 21
Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Reverberation Chamber
Mode stirring chamber Rayleigh-Fading channel can be simulated as S21 has complex Gaussian distribution and a Rayleigh envelope
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Reverberation Chamber: Determination of Antenna Parameters
Avaraging over N stirring Free Space N 1 n)( positions Reflection S22 = ∑ S22 Coefficient of AUT N n=1
Relative received n )( 2 N S power of AUT 1 21 PAUT = ∑ 2 2 N n =1 ( 11 )(11 −− SS 22 )
P 2 Radiation efficiency η AUT (1−= S ) is related to a well 22 Pref known reference antenna
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Antenna Noise Temperature
– Outdoor Method – Measurement in an electromagnetically quiet environment – Possible for low gain antennas with D > 4-5 dBi – Adaptation of method for measurements in house in process – For directivities below 3 dBi a direct method is required which can evaluate the received power level
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Antenna Noise Temperature
Y-Factor Method: – Compare the received power when antenna is pointing to cold sky with a black radiator at environment temperature
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Anechoic Chamber Methods
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Near-field Scan Types
Planar Planar Near-field − Directional antennas − Gain > 15 dBi Cylindrical − Max angle < ± 70 º Cylindrical Near-field Spherical − Fan beam antennas − Wide side/ backlobes Spherical Near-field − Low gain antennas − Wide or omni-directional patterns on any antennas
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Spherical Coordinate System and Spherical Scanner for Spherical Far- or Near-Field Methods
Small antennas need to be measured on spherical scanners as they can collect the complete radiation
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Combined Far-/Near-Field Antenna Test Range at Fraunhofer IIS
– Size: 6mx6mx15m – Frequency range: 0.5 GHz - 40 GHz – Max. probe – AUT distance: 7.5m – Spherical Scanner (NSI 700S-60)
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Near-Field: Stargate / Starlab by Satimo
Switched multiple probe approach lead to fast measurement times and reduced shadowing by absorbers
Picture Source: http://www.satimo.fr/eng/index.php?categoryid=171&p2008_sectionid=5 Seite 30
Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Near-Field: RAMS by TKK
Multi-arch architecture Measurement times should reduce to some ten ms, so it can be used to characterise the radiation properties of mobile handsets for all relevant communications systems, with the possibility to perform tens of full 3-D measurements within a second
Picture Source: http://www.hut.fi/Units/Radio/research/RAMS.html Seite 31
Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 CTIA Measurements
Picture Source: http://www.nearfield.com/Sales/datasheets/NSI-700S-90-CTIA.htm Seite 32
Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Measurement Impairments
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Sources of Errors
Cabling jacket currents on cables Exact positioning and fixture of cables Mismatch BALUNs and impedance transformation at antenna footpoint
Fixture Reflective Fixtures Size of fixture Repeatability of mounting antenna to fixture Scanner Shadowing effects Reflection on metallic interface Misalignment
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Shadowing Caused by Positioner and Absorber
Theta Scan range is limited to positioner and Absorber nearby AUT – reduction of about 30° for a half sphere
60° Y-Achse
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Detailed Measurement Setups
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Setup for Pattern and Gain Measurement in Near-Field Mode (same for Far-Field Mode) W4, 4.60m, AUT
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Setup of Measurement Example
AUT size: 20mm x 30mm x 10mm Fixture size: 200mm x 200mm Absorber: 40 cm pyramidal absorber – Different cabling – Different absorber position
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Measurement Results: Cables With and Without Ferrites to Suppress Jacket Currents
Far-field amplitude of PIFAprt-oewg430-ferrit-absnorm-Pos1.nsi Far-field amplitude of PIFAprt-oewg430-ferrit-absnorm-Pos1.nsi
Ferrit ohne Ferrit Ferrit ohne Ferrit 0.0 0.0
-2.5 -2.5
-5.0 -5.0
-7.5 -7.5
-10.0 -10.0
Amplitude (dB) -12.5 Amplitude (dB) -12.5
-15.0 -15.0
-17.5 -17.5
-20.0 -20.0 -100 -50 0 50 100 -100 -50 0 50 100 Theta (deg) Theta (deg) Seite 39
Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Measurement Results: Different Absorber Positions Behind Antenna, Absorber moved λ/4 towards antenna
Far-field amplitude of PIFAprt-oewg430-ferrit-absnorm-Pos1.nsi Far-field amplitude of PIFAprt-oewg430-ferrit-absnorm-Pos1.nsi
Absorber_Pos1 Absorber_Pos1 + lambda/4 Asorber_Pos1 Absorber_Pos1 + lambda/4 0.0 0.0
-2.5 -2.5
-5.0 -5.0
-7.5 -7.5
-10.0 -10.0
Amplitude (dB) -12.5 Amplitude (dB) -12.5
-15.0 -15.0
-17.5 -17.5
-20.0 -20.0 -100 -50 0 50 100 -100 -50 0 50 100 Theta (deg) Theta (deg) Seite 40
Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Measurement Results: Combination of two FF Data Sets Near-field amplitude of PIFAprt-oewg430-ferrit-absnorm-Pos2.nsi Far-field amplitude of PIFAprt-oewg430-ferrit-absnorm-Pos2.nsi Far-field amplitude of PIFAprt-oewg430-ferrit-absnorm-Pos1.nsi
80.00 80.00 80.00
60.00 60.00 60.00
40.00 40.00 40.00
20.00 20.00 20.00
0.00 0.00 0.00 Phi (deg) Phi (deg) Phi (deg) -20.00 -20.00 -20.00
-40.00 -40.00 -40.00
-60.00 -60.00 -60.00
-80.00 -80.00 -80.00
-150.00 -100.00 -50.00 0.00 50.00 100.00 150.00 -80.00 -60.00 -40.00 -20.00 0.00 20.00 40.00 60.00 80.00 -80.00 -60.00 -40.00 -20.00 0.00 20.00 40.00 60.00 80.00 Theta (deg) Theta (deg) Theta (deg)
Near-field amplitude of PIFAprt-oewg430-ferrit-absnorm-Pos2.nsi Far-field amplitude of PIFAprt-oewg430-ferrit-absnorm-Pos2.nsi Far-field amplitude of PIFAprt-oewg430-ferrit-absnorm-Pos1.nsi
80.00 80.00 80.00
60.00 60.00 60.00
40.00 40.00 40.00
20.00 20.00 20.00
0.00 0.00 0.00 Phi (deg) Phi (deg) Phi (deg) -20.00 -20.00 -20.00
-40.00 -40.00 -40.00
-60.00 -60.00 -60.00
-80.00 -80.00 -80.00
-150.00 -100.00 -50.00 0.00 50.00 100.00 150.00 -80.00 -60.00 -40.00 -20.00 0.00 20.00 40.00 60.00 80.00 -80.00 -60.00 -40.00 -20.00 0.00 20.00 40.00 60.00 80.00 Seite 41 Theta (deg) Theta (deg) Theta (deg)
Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Setup for Pattern Measurement in Far-Field Mode Using Spectrum Analyzer
W5, 0.50m, NF-Probe W9, 0.80m, AUT W8, 0.50m, AUT W6, 0.50m, FF-Probe
STANDARD BEAM CONTROLLER
A3 A3-1? W4, 4.60m, AUT A1
HP-IB Computer ADR=16 W2, 10m, NF Stand W10, 2.5m, NF Stand W3, 13m, FF Stand W11, 2.5m, FF Stand
W1, 6.10m, AUT
W12, 2.5m,AUT W7, 0.815m, AUT A2 M1 M2 M3 ANTENNA RANGE CONTROLLER Motor Cables A4
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Setup for Pattern Measurement in Far-Field Mode Using Spectrum Analyzer
Measurement is performed using a battery powered transmitter sending a CW signal Measurements are done in STOP mode (positioner moves to position, stops, power spectrum is measured, positioner moves to next position)
Everything is done using a script to control the positioner and the spectrum analyzer
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Measurement Example: Wireless Transmitter in Water Metering System
Pattern Measurement in Anechoic Chamber
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Measurement System for Time Delay Measurements
battery powered transmitter under test Reference (TUT) Antenna @ phi stage
SNF Probe Rotation Axis Phi RJ3 RJ2
SNF Probe Stand RJ1
Rotation Axis Theta
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Measurement System II
battery powered transmitter under test Reference (TUT) Antenna @ phi stage
SNF Probe Rotation Axis Phi RJ3 RJ2
SNF Probe Stand RJ1
Rotation Axis Theta
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Measurement System III Anechoic Chamber Windows NSI PC Measurement PC battery powered transmitter under test Reference (TUT) Antenna @ phi stage
SBC Controller ANTENNA RANGE CONTROLLER SNF Probe Rotation POWER Axis Phi OFF NSI RJ3 RJ2
SNF Probe Event Stand RJ1 Trigger
Rotation Axis Theta
Antenna Unit 1 Antenna Unit 2
RF-Cables Matlab
Clock and Trigger Generator Fiber optic cables 1 2 FPGA Boards for correlation(CB) Linux-Workstation Ethernet Network Seite 47
Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Results Transmitter with Integrated Dipole Antenna
3D directivity
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 CTIA Measurement Setup Using Communication Tester Radiated Power: Communication Tester establishs call with mobile and records the received power level @ maximum output power mode of mobile Sensitivity: SW changes power level of base station simulator and determines the BER of the received signal (mobile acts as repeater), measurements can last several hours W4, 4.60m, AUT 4.60m, W4,
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Recommendation for Measurements in Anechoic Chambers
– Construct a fixture that is small and reliable – Define the co-ordinate system properly – Be aware of Your cabling and its influences on the measurement – Always use the same absorber behind the antenna and put it as far away as possible – Measure full NF data, with two positions of the antenna – Look at the whole picture: Compare NF and FF data Then You should get repeatable measurements
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Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Summary: Comparison of the Different Methods
Parameter/ Method Pattern Polarisation Efficiency Matching CTIA
Far-Field
Near-Field
Reverberation Chamber
GTEM Cell
Wheeler Cap Seite 51
Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08 Literature
– Hiroyuki Arai: „Measurement of Mobile Antenna Systems“, Artech House, Boston, 2001 – Clemens Icheln: „Methods for Measuring RF Radiation Properties of Small Antennas“, Dissertation at Helsinki University of Technology, Report S 250, Espoo, 2001 – Gregory F. Masters: „An Introduction to Mobile Station over the Air Measurements“, NSI User Meeting, Bletchley, 2006 – Per-Simon Kildal: „Reverberation Chamber for Characterizing Antennas and Mobile Terminals under Rayleig Faindg: Efficiency, TRP, TIS, AFS, diversity, MIMO, UWB“, Shourt Course SC12 at EuCAP2007, Edinburg, 2007 – Lars Foged: „Small Antenna Measurements in Spherical Nearfield Systems“, EuCAP2007, Edinburgh, 2007 – Rainer Wansch: „Methodology for Measuring Electrically Small Antennas“, AMTA2004, Atlanta, 2004 – Rainer Wansch: „Measurement Setups Using a Theta-Phi Scanner“, NSI User Meeting, Erlangen, 2007 Seite 52
Measurement Electrically of Antennas Small Rainer Wansch, 02.06.08