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Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Antenna EngineeringRelevance – Practical issues – Current research
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
1. Wireless technologiesBrief introduction and example applicationsPropagation of electromagnetic waves: Free space vs multipathRequirements for antennas (receive and transmit)
Antenna Engineering Lecture: Content
Content
2. Fundamentals of antenna engineeringElectrodynamic foundations and theoretical approachBasic radiating elementsExamples of practical radiating elements
3. Antenna arraysDisplacement principlePerformance figures of linear arraysBeam forming and spatial signal processing
4. Practical aspects of antenna engineeringPackaging and protectionDesign and numerical simulationAntenna measurements
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Seminar topics50% tutorial, 50% revision: See homework topics
• Loop antennas• Patch antennas• Broadband antennas• Tracking antennas• Antenna measurements (anechoic chamber)
Homework topicsPartly to be solved during the seminar, partly by yourself in a small group or at home
See current internet version: www.tu-ilmenau.de/hmt Education
Content
Further interactive formats
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Literature (selection)S. Drabowitch, A. Papiernik, H. Griffiths, J. Encinas, B.L. Smith, "Modern antennas",2nd edition, Springer, 2005 (1st edition: Chapman & Hill, 1998).Signature: ELT ZN 6440 D756(2)C.A. Balanis, “Antenna theory: analysis and design”, Wiley, 1997.Signature: ELT ZN 6440 B171(3)J. Volakis Ed., “Antenna Engineering Handbook”, 4th edition, New York, McGraw-Hill,2007.Signature: ELT ZN 6440 A627(4)Rothammels Antennenbuch (in German), 12th edition, DARC Verlag Baunatal, 2001.J.D. Kraus und R.J. Marhefka, "Antennas for all applications", McGraw-Hill, 2002.K. Fujimoto and J.R. James Eds., “Mobile Antenna Systems Handbook”, 2nd edition,Artech House, 2001.T. Weiland, M. Timm, and I. Munteanu: A Practical Guide to 3-D Simulation, IEEEMicrowave Magazine, Dezember 2008, pp.62-75; DOI10.1109/MMM.2008.929772D.G. Swanson, Jr., W.J.R. Hoefer: Microwave Circuit Modeling Using ElectromagneticField Simulation, 2003 ARTECH HOUSE, Norwood, MA , ISBN 1-58053-308-6
Literature
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Antenna = Part of a system
Mobile antenna system
s handbook, K. Fujimoto and J. R
. James Eds, Artech H
ouse, 2001
• „Air interface“• Transmitter or receiver
or transceiver• Combination of analog
RF and IF with digital baseband
• Function convolved with radio wave transmission (wireless channel)
• Antenna parameters enter link budget calculations
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Functions: Antennas ...
... convert the mode of propagation
... select spectrum and spaceTime frequencies: Single resonance – multi-
resonant – ultra-widebandSpatial frequencies: Omnidirectional – directive –
multi-beam
Antenna arrays for diversity (multipath propagation, MIMO)Phased-arrays (electronic beam-steering, radar)Adaptive arrays (tracking, reconfigurability, multi-user systems)
Antennas
Radiated wave guided-wave (RX/TX, omnidirectional / directive)Matching: Power (TX), noise (RX), bandwidth
... are (analog) signal processors
AntennaWaveguide
RX
AntennaWaveguide
TX
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Frequency f (MHz)
Wavelength (m)
Designation Propagation loss (dB) (4r/)2 at r = 10 km
< 0.003 > 100,000 ELF < 0 – 200.003...0.03 100,000...10,000 VLF 0 – 20 ... 0
0.03...0.3 10,000...1,000 LF 0 + 0 ... 200.3...3.0 1,000...100 MF 0 + 20 ... 403.0...30 100...10 HF 0 + 40 ... 6030...300 10...1 VHF 0 + 60 ... 80300...3,000 1...0.1 UHF 0 + 80 ... 1003,000...30,000 0.1...0.01 SHF 0 + 100 ... 12030,000...300,000 0.01...0.001 EHF 0 + 120 ... 1400.3-3 THz 1-0.1 mm Sub-mm-waves3-400 THz 100-0.75 mm Infrared400-750 THz 400-750 nm Visible light
Frequency ranges
RF
micro-waves
mm
0 20log(4 ) 22 dB
Multitude of services allocated to wide frequency range; inter/national regulation
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Research and development of antennasFrequency: High centre frequencies, broad bandwidthsSpectral efficiency, data rates, range, mobility (communications, multimedia, localisation, radar, hybrid)
Design and numerical simulationOptimal results: Radiation pattern, efficiency, frequency, bandwidth, sizeOptimal methods: Geometric and electromagnetic boundary conditions, CPU time and efficiencyMiniaturisation, integration (on-chip, packaging)
Added performanceSelective / Diversity (space, mode, and polarisation)Adaptive (beam steering, smart antennas, ad-hoc networks)Cognitive (spectral and spatial adaptation, RX and TX)
Antennas
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Specular and diffuse reflectionSpecular reflectionRegion of reflection is perfectly flat on scale of wavelengths (h /16)Reflection law applies (geometrical optics)One well-defined directed reflected beam exists (depending on angle of incidence)
Diffuse reflectionRegion of reflection is uneven on scale of wavelength (Rayleigh, h > /16)Huygens‘ priniciple: Superposition of point sources; incident wave is scattered in many directions (tendentially independent of angle of incidence)Ideal diffuse surface: Lambert‘s law
Mixed reflection
0P( ) P cos
specular directive diffuse Wave propagation
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Fresnel reflection
Statement of problemContinuity conditions for E- and H- fields across interfaces depend on • Angle-of-incidence• Material• Polarisation
2r
h 2r
sin cos
sin cos
2r r
v 2r r
sin cos
sin cos
Propagation scenarioTwo-path model (applies often)Line-of-sight (air) plus single reflection (ground)
ApproximationFlat geometry ( 0)|r| 1 (e.g., water)Asymptotically for 0: v = h –1 (180o phase jump)
sin Csin C
br
b 1 for V polC with
b 1 for H pol
h1 h2
r1 r2
r = r1+ r2
Wave propagation
LOS
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Atmospheric attenuation
Resonant absorptionDominated by oxygen and water at microwave frequencies55 and 118 GHz (O2)22 and 180 GHz (H2O)
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Fresnel zone – or „how thick is a ray?"
Undisturbed transmissionCertain space between transmitter S and receiver E free of obstacles (otherwise direct and reflected or diffracted wave portions may interfer)Of special relevance: Region around line-of-sight (LOS) with additional path lengths up to /2 (NLOS): First Fresnel zone
GeometryRotational ellipsoid with focal points S and E, path difference /2 along edge reflections compared to LOS
http://ww
w.radartutorial.de, http://de.wikipedia.org/w
iki/FresnelzoneS E
S E
S E
S Ed1
rF,1
d2
dF,1 er d 1 1 1e 1 2d d d
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
0 F F
E 1 1 j h hC jSE 2 2 r r
F
0
rE(P) 1E 2 | h |
Asymptotic for v2 1 (“shadow”)
Asymptotic for v > 1 (“light”)21 1C(v) sin v
2 v 2
21 1S(v) cos v2 v 2
Wave propagation
Shadow Light
x2
2o
C(x) cos( u )du x
22
o
S(x) sin( u )du
F er d rF = Fresnel radius
0
0.2
0.4
0.6
0.8
1
1.2
-3 -2 -1 0 1 2 3
E/E0
h/rF
Fresnel integrals
asymptotic, h>0asymptotic, h<0
Diffraction: analytical results
Nearly undisturbed “beam” for h > rF/2Height of antenna mounting is relevant
h = distance beam – diffracting edge
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Two-path model (LOS and specular reflection off ground)
Analytical result(flat geometry, plane waves)
ges 1 2
0
| E | h h2 sin 2
E (r) r
Case 1: Variation with distanceAt given antenna heights
Case 2: Variation with heightAt given distance and height h1
0
1
2
0 2 4 6 8 10
Rel
ativ
e fie
ld s
treng
th |E
ges|/E
0
Normalised distance r/rref
0
0.5
1
1.5
2
0 0.5 1 1.5 2 2.5 3 3.5 4
Rel
ativ
e fie
ld s
treng
th |E
ges|/E
0Normalised height h
2/h
2,ref
ges 21E (r)r
Pathloss exponent nTPM = 4
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Constituents of multipath propagation
A. Paulraj, R. Nabar, D. Gore, “Introduction to Space-Time Wireless Communications,” 2003.
n(r) r
Average behaviour r = 3…300 m ( ) r = 0.3…0.6 m ( )
Wave propagation
Path loss exponent nLine-of-sight (LOS) 2
Single specular reflection
2
LOS + single specular reflection
4
Diffraction 1
Diffraction + reflection (obstacle gain)
5
Scattering (radar eq.) 4
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Radiation pattern
Wave propagation
G (dB)
(or )
-60-50-40-30-20-10
0
0
30
60
90
120
210
240270
300
330
Isotropic radiator (hypothetic, d )
Patch (d)
Rectangular aperture (d )
Normalised angular distribution of radiation parameters, e.g.
• Gain or directivity• Field amplitude• Phase of field
Distinguish between • Main lobe• Side lobes• Backward radiation
Normalisation of G0 lin (dBi)
Isotropic radiator 1 0
Rectangular patch (TM100) 6 7.8
Rectangular aperture (10 ×10 , homogeneous) 1200 30.8
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Effective area of an antenna Aeff
2eff
0
AG 4
The effective area Aeff describes the capability of collecting power from a power density (Poynting vector).
1. Hertzian dipole (lossless, HD)
Two examples
Definition and constituing equation
The ratio of effective area Aeff tomax. antenna gain G0 is constant(thus equal for every antenna).
2HD 2eff
3 1A2 4 8
PR 2eff physA A d
4
2 2
20
d dG 10
2. Parabolic reflector antenna (diameter d, PR)
Wave propagation
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Radio links: Friis equation
Customised version (matched antennas)
System-oriented version (max. gains G0) • EIRP = PTX·GTX0 defined bystandards
• SNR determined by BER• Range rmax determined by
mobility and data rate
22 0max TX
min B RX
G 1r EIRP4 T SNR k B F
RX
TX2
2TX RX TX RX
P 1P ( , )
G ( , ) G ( , ) e e4 r
• Path loss FS
• Matching (orientation, polarization, impedance)
• Antenna gain → link budget• Antenna Frontend
Wave propagationTX RX
TX RX(dB) 92.4 20 logf(GHz) 20 logr(km) 10 logG 10 logG
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Parameter space of wireless data transmission
Wave propagation
Stat
iona
ryN
omad
icM
obile
22max Tx
sys B min Rx
G 1r EIRP4 T k BW SNR
User data rate (bps)
Mobility / Range
TX RX
Bluetooth
DECT
GSMGPRS
EDGE
WLAN802.11x
3G
UMTSHSDPA
.16x
WMAN
4G LTE
PersonRoom
Noma-dic
Pedes-trian
Urban
High-way
Rural
100k 1M 10M 100M 1G 10G 100G
WiGigWLAN802.11ad
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Antenna noise temperatureBlack body radiationEvery object emits radiation (T > 0 K)
(emissivity)B physT ( , ) ( , ) T
Example values (radiometry)• Dark sky (average background): 3 K• Earth (on average): 290 K• Human body: 310 K
Advancing Pahoehoe toe, Kilauea Hawaii 2003
Images obtained with a THz scanner
2
B0 0
A 2
0 0
T ( , ) G( , )sin d dT
G( , )sin d d
http://hvo.wr.usgs.gov/kilauea/update/archive/2003/May/main.html
Antenna noise temperatureMean environmental temperature, weighted by antenna gain pattern
http://www.tsa.gov/graphics/images/approach/mmw_large.jpg
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Electromagnetic foundations
E j H (Faraday 's law)
H j E (Ampere's law)
E H 0 (Sourcelessness, free space)
dJdt
Constituing vector fields Sources of electromagnetic fields
Maxwell‘s equations (f-domain)Free space (no sources)Harmonic time-varying fieldsLinear isotropic media
Fundamentals
Electrical field EElectrical displacement DMagnetic field HMagnetic flux density BComplex material parameters: permittivity , permeability
Stationary: Charge density Moving: Current density J
Conservation of charge
Electromagnetic potentialsMagnetic vector potential AElectric scalar potential
A B
A j
j A E
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Electromagnetic properties of matter
Medium Material Propagation Wave impedance
Free space(Vacuum, air)
= 0
= 0
= 0
Perfect(lossless)dielectric
= 0r real = 0 r real = 0
Dielectricwith losses
= ‘ - j ‘‘ = ||e-j
= 0 r real
= 0
Good metallicconductor
arbitrary = 0 r real ||
0 0 0k / c
0 0v c 1/
k / v
r rv c /
k ' | | cos 2 /
r rv c / cos | |
k '' | | sin 1/
k ' k '' 2 / 1/
2/
0 0 0Z /120377
Z /
j / 2Z / | | e
s sZ R (1 j)
sR 1/2
propagation cons tant j jk k '' jk '
Fundamentals
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Why do antennas radiate?Cases to be distinguished1. Static fields 2. Stationary fields 3. Time varying fields
Double curl coupling: Equivalent to charges being accelerated
H
Et
E
Ht
J(t) 0
E(t),H(t) const.
J(t) const.
E(t) H(t) 0t t
J(t) 0t
E(t) H(t)0, 0t t
H
E
Et
Ht
FundamentalsAccelerated charges cause electromagnetic radiation
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Derivation of radiation parametersFull electrodynamic solution
Fundamentals
Far-field approximation
Radiated power density and total radiated power
Antenna parameterse.g., G, D, SLL
Electromagneticpotentials
Wave equations, Lorenz gauge
Electric andmagnetic fields
Near fields andfar fields
Electromagneticsources
Time-varyingcharge and current
densities
Radiated power density and total radiated power
Antenna parameterse.g., G, D, SLL
Distribution of electric or magneticfields across radiating aperture
Aperture illumination
Electric andmagneticfar fields2D Fourier
transformation
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Fourier transform between real domain and image domainFourier transformationTime – frequency domain
j t1G(t) G( )e d2
Radiation source in (x,y)-planeSpatial – image domain (k-space)
Wave vector
jk( x y)2
1G( , ) G(x,y)e dxdy
Tk | k | ( , , )
Time domain – frequency domain Spatial domain – spectral domain (2-dim)
t x, y kx, ky
Phase t Phase kxNormalisation 2/ = T Normalisation 2/|k| = t·c = |r|, ·c = k |r| / c = t, |k| / c =
Fundamentals
j t1G( ) G(t)e dtT
Corresponding terms
jk( x y)G(x,y) G( , )e d d
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Determination of radiation field by tangential components in aperture
Follows from Maxwell‘s equations and absence of sources in propagation region (Verification: see homework)
z x y1divE 0 E E E
2x x y
1H E 1 EZ
2y x y
1H 1 E EZ
z x y1H E EZ
z x y1divH 0 H H H
2x x y
ZE H 1 H
2y x y
ZE 1 H H
z x yE Z H H
E-field given H-field given(electrical antenna) (magnetic antenna)
Fundamentals
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Four key rules of antenna theory
Every field component is fully determined by its value in the aperture plane (free space: no sources)
Far field = Superposition of plane waves along direction of propagation, weighted by the field distribution in aperture plane G(,,0+)
Far field determined by tangential field components in aperture plane
Far field proportional toFourier transform of aperture illumination
jkr
FF 0 0t 0eE (x,y,z) j 2 k E ( , ,0 ) zkr
jk( x y z)G(x,y,z) G( , ,0 ) e d d
Fundamentals
1.
2.
3.
4.
FF 0 FF1H (x,y,z) k E (x,y,z)Z
(No information about near-field through 2D-FT; accessible through em potentials)
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Radiation fields
Fourier transform
jk( x y)
21G( , ) G(x,y)e dxdy z
Aperture plane
Radiating area or aperturein (x,y)-plane (at z = 0)
y
x
Q1(x,y,0)
Q2(x,y,0)
Q3(x,y,0)
M(x,y,z)
Distribution of sources Qi
Function G(x,y)
Example2
1 for x a,y b ab sin(k a / 2) sin(k b / 2)G(x,y) G( , )0 for | x | a,| y | b k a / 2 k b / 2
Fundamentals
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Fourier transformation: Trade-off between D and SLL
Solution: Adjust aperture distribution (amplitude tapering)
0
0.2
0.4
0.6
0.8
1
-4 -2 0 2 4
Nor
mal
ised
ape
rture
fiel
d di
strib
utio
n
Position along aperture (a.u.)
RectangleTriangleGaussian
-60
-50
-40
-30
-20
-10
0
-4 -2 0 2 4
Dire
ctiv
ity p
atte
rn ~
|E|2
(dB
)
Image domain (k-space) (a.u.)
RectangleTriangleGaussian
-13 dB
-26 dB
Fundamentals
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Example
Important consequences
Horn antenna (nearly homogenous aperture illumination)
Principles of antenna theory
The far field of an antenna is determined by the 2D Fourier transform of the field distribution in the aperture plane.
Fundamentals
1. Electrical size of an antenna ↔ Capability of spatial focusing (Least focusing antenna: Hertzian dipole)
2. Homogeneous illumination Maximal directivity3. Side lobe level varies in an opposite way as directivity (SLL↑ ↔ D↓)
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Elementary dipole: Geometry
x
y
z
r
k0
r0
0
0
Electrical dipole (Hertzian dipole)Straight wire element in originConstant current, length
Electrical dipole moment Current density
jkr
0 0t 0eH(x,y,z) j 2 k H ( , ,0 ) xkr
0t 0 02
1H ( , ,0 ) I y const.2
jkr
0jk eH (r, , ) I sin4 r
0I z
0 0 0 0k r r
Fundamentals
Dq u
DJ I (x) (y) (z) u
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Field components of the Hertzian dipoleDistinguish between contributions in the near field and the far field (stored energy, reactive power vs effective power)
Radially directed power flow (radiation)
Tangential power flow (near field) Fundamentals
jkr0I e 1H j sin 12 r jkr
jkr0
2
I e 1 1E jZ sin 12 r jkr (kr)
jkr0
r 2
I e 1 1E jZ cosr jkr (kr)
rH H 0
E 0
Zero Near field Far field
×
××
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Antenna dPrad(,)/dS Prad Directivity D(,) Dmax
Hertzian (electrical) dipole
Fitzgerald (magnetic) dipole
Homogeneously illuminated aperture S 2
Rectangular, aperture ab 2
[cos] radiation into half-sphere
Power-based antenna parameters
2 2
21 I sinZ8 r
2IZ3
23 sin( )
23 (1.76dB)2
22 2
2 24 IS sinZ8 r
22
2IS4 Z
3
21A cos ,r 2
2A
1
2 ( 1) cos
22
2
1 | E( , ) |2Z r
22| E | d d
2Z
jk( x y) 2
S2 22
S
| E(x,y)e dxdy |4 4 S
| E(x,y) | dxdy
24 ab
0 2
ab sin( a / ) sin( b / )E Ea / b /
Fundamentals
sin cossin sin
=1: 4 (6 dBi) =2: 6 (7.8 dBi)
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
The size of antennas
• Radius, length• Limited by specific
application (e.g., mobile handset)
Physical size (m)
• Directivity and beamwidth• Input matching • Radiation quality factor
and matched bandwidth• Radiation efficiency• Realised gain
Electrical size /(1)determines:
Electrically small large
-40
-30
-20
-10
0
10
20
-2 -1.5 -1 -0.5 0 0.5 1N
orm
alis
ed a
nten
na p
aram
eter
(dB
)
Electrical size of antenna, log(/)
Radiation quality factor Q
rad ~1/BW
Input matching ||
Maximum directivity D
max Efficiency
Realised gain Geff
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Dipole antennas
FeaturesCurrent varies along lengthRequires symmetric feedDiameter neglected (slim wire)
0I(z ) I sin k | z |2
Far fieldLinear phase-correct superposition of the field contributions from elementary dipoles along current axis
J.D. K
raus, R.J. M
arhefka, Antennas for all applications,
McG
raw-H
ill 2002
Fundamentals
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Electrical dipole: Radiation patterns
n
n ncos cos cos2 2( )
sin
Fundamentals
• Radiation pattern n() for n = n/2• n 2: Nulls along dipole axis at
cos0 = ± 1• n > 2: Additional nulls at n
n
1 31, , n oddn n
ncos 1, 0 even2
1 n1, oddn 2
H.D.n=1/2 n=1 n=3/2 n=2
n=2n=5/2n=3
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
C.A. Balanis, „Antenna theory“, John Wiley, 1982.
l/ 3dB(o)
D0(dBi)
Rrad()
1 90 1.76 0
1/4 87 1.9 < 10
1/2 78 2.14 73.2
3/4 64 2.8 200
1 47.8 3.82 200
Dipole antennas: Radiated power and directivity
2
rad
120D( ) ( )R ( )
Fundamentals
/2-dipole -dipole
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Antenna design for manufacturabilityApplicationBroadcast, P2P, communications, radar, sensing, navigation, direction-finding, tracking, ...EnvironmentLand, sea, air, spaceNearfield, far fieldFree space, implanted, embeddedPerformanceSpectral f0, BW, ...Spatial Pattern, G, 3dB, SLL, ...Polarisation Linear, dual, circular, ellipticFunction fixed, switched, phased-
array, adaptive, ...Operation stationary, nomadic, mobile
ImplementationRadiator Elements, arrays,
geometry, homo-geneous, periodic
Feed Active, passive, hybrid
Assembly Geometry, materials, interfaces
Package Shape, volume, mass, integration, stability
CostManufacture, installation, power consumption maintenance,
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Antennas: Geometries and shapes (categories)
Quasi-planar Volumetric, conformal
Aperture antennas (fields)
PatchSlotSurface wave Leaky traveling waves, coupled elements
Waveguide Aperture and leaky waveReflector Single, multipleDielectric lens
Wire antennas
(currents)
Linear Straight, folded
Loop Elliptical, rectangular
Circular symmetric Bi-conical, discone, ...Helix, ferrite
Hybrid Multitude of combinations / variations
Fundamentals
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Aperture antennas
Radiating elements
Horn, lens, reflector, surface wave (leaky waves)
J.D
. Kra
us a
nd R
. J. M
arhe
fka,
Ant
enna
s fo
r all
appl
icat
ions
, M
cGra
w H
ill (2
002)
Fundamentals
Radiation pattern
Aperture distribution E(,)
Far field E(x,y)
Homogeneous aperture distribution Maximal directivity Pronounced sidelobes
Reduced sidelobes Inhomogeneous aperture
distribution (amplitude taper)
~
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2014
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
ww
w.2cool4u.ch/microw
ave/rifu_anforderungen/rifu_anforderungen.pdf
1 – Main reflector (Rotational paraboloid, Focus F, Apex S)
2 – Sub-reflector (Focal widths f1 and f2)
3 – Focal point of main reflector
4 – Focal point of sub-reflector
5 – Feed horn
Direct feed Indirect feed (Cassegrain)
Rotational paraboloids
Shell antenna
Reflector antennas
Horn parabol
Direct feed Indirect feed (Gregory)
Fundamentals
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Parabolic reflector antenna
Gain
3-dB beamwidth
G(dBi) 20.4 10log 20log D(m) f(GHz)
3dB D G
2 22 D DG 10
3dB0.12
D(m) f(GHz)
Rule-of-thumb (simplification)
Fundamentals
After http://commons.wikimedia.org/wiki/File:Parabel-def-p.png
Q
Relevant geometry parameters
| FS | f| PQ | D
15
20
25
30
35
40
45
50
55
1 10 100
D=0.6mD=1.2mD=1.8mD=2.4mD=3.0mD=3.7mD=4.5m
frequency f (GHz)G
ain
G (d
Bi)
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
H-sector horn antenna
Aperture distribution corresponds to waveguide mode, e.g., TE10:Ey(x) = E0x·cos(x/A), Ey(y) = E0y
E
x
y
z
Fundamentals
Gain
Rule-of-thumb (simplification, fundamental mode)Geometry
b
a
AR
HRG 3
b 0.25
optA R1.73
HRG (dBi) 7.4 5log
H,3dB0.125
R
3-dB beamwidth http://www.feko.info/applications/white-papers/naval-radar-analysis-with-utd30. May 2012
a 0.5
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Microstrip patch antennaDielectric resonator (modes: standing waves)Field distribution and radiation pattern
2 2 2
mnpr
c m n pfa b h2
TM100 TM020
Fundamentals
h p 0
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Patch antenna
Fundamental modeEz(y) = E0
Ez(x) = E0·cos (x/a), a g/2Virtual magnetic dipole sources:
Two narrow slits constructiveConstant field distributionTwo-element array pattern
Two long slits destructiveIn (y,z)-plane as well as in opposing (x,z)-plane.
z
y
x
b
a
h
Fundamentals
E
H
M
E
M 2n E
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
10-4
10-3
10-2
10-1
100
0
30
6090
120
210
240270
300
330
E-planeH-plane
Patch antenna: radiation patternC
.A. B
alanis, „Antenna theory“, John W
iley, 1982.
Broad beam perpendicular to surface of patch (array pattern)
E|E|
aC cos sin
bH|E| b
sin sinC cos
sin
Fundamentals
E-plane
H-plane
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Patch antenna: Directivity
1. Estimated from radiation mechanismTwo elementary dipoles: 1.76 dBi + 3 dBReflection from groundplane: + 3 dB
2e 3
4 4D 6 (7.8 dBi)
D 7.8 dBi (factor 6)
2. Estimation from radiation patternEffective aperture angle about 120 deg
Fundamentals
3. Analytical approximationTwo-slit array
b/ D D (dBi)1 6.6 8.2
1 8·b/ 9+10·log (b/)
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Polarisation of patch antennasLinear polarisationPolarisation determined by surface currents on patch controlled by feed point
Circular polarisationSuperposition of two linear polarised fields in quadrature (either dual-feed or mode mixing)
x
y
Fundamentals
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
http
://en
.wik
iped
ia.o
rg/w
iki/F
ile:G
SM
_bas
e_st
atio
n_2.
JPG
Examples of array antennas
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Displacement principle
Two identical sources O and O'Distant observation point in far field
00
jkr
0
jkk djkr jkrjkk d
0 00
jkd
eE f (k )kr
e e eE f(k ) f (k ) ekrk(r k d)
E E e
Arrays
Simplifying assumptions
Displacement in spatial domain (x,y,z) corresponds to phase shift in spectral domain (kx,ky,kz)
0
0
| r | | r | k d
k d d cos
r,k
r
d
O
O
y
x
0k d
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
nk0
θ d
A0 A1 A2 An
0
nAdAsinθ
an
f()
L = Nd
a0
1 n
Line
ar a
rray
(pha
sed
arra
y)
Uniform linear arrangement of N identical radiation elements
Arrays
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Normalised array factor RN'(,0)
Arrays
0
0.2
0.4
0.6
0.8
1
-1.5 -1 -0.5 0 0.5 1 1.5
Mag
nitu
de p
atte
rn |R
'()|
Direction = sin
real(visible) region
virtual(invisible)
virtual(invisible)
=/d
0
Auxiliary parametersAngular direction = sinElectrical element separation = d/
0N 0
0
sin[N ( / 2)]R ( , )N sin( / 2])
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Array pattern RN'(,0)
• Determined by electrical element spacing and phase gradient 0
• Main beam direction: 0 = 2·0
• Main lobes periodic: = 1/• Unambiguity: ≥ 2 ( 1/2)• Beamwidth: R'N (1/2) = 1/2• Beamwidth varies with steering:
Scan loss (broadfire – endfire)• Scan range max: < (1+sinmax)–1
Arrays
0
0.2
0.4
0.6
0.8
1
-1.5 -1 -0.5 0 0.5 1 1.5
Mag
nitu
de p
atte
rn |R
'()|
Direction = sin
real(visible) region
virtual(invisible)
virtual(invisible)
=/d
0
0N 0
0
sin[N ( / 2)]R ( , )N sin( / 2])
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Linear phased-arrays
Feed networkPower distribution, matching, de/coupling (angle-dependent reflections)
Phase shiftersElectronic beam steering (as opposed to mechanical)
Antenna elementsSuperposition of the field-patterns (amplitudes and phases) of the individual radiation elements in a certain array configurationAntennas potentially complemented by focusingreflector or lens
Arrays
nu
θ d
A0An AN-1
Array
Phaseshifters
a0
b0
an
bn
aN-1 bN-1
Feed and distribution network
Driver
ProcessorTransceiver
...
.........
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Active arrays
Transmit (TX)Compensate attenuation between feed and radiatorDistributed power control (high total power, e.g., tube amplifier required for full array)Improved reliability (drop-out of single elements, graceful degradation)Improved phase accurady (small-signal operation before amplifier)
Receive (RX)Adaptive amplitude and phase control for each individual radiating elementPhase → direction of main beam. Amplitude: Beam forming and null steering
TX-RX switching (duplex)Speed, power, circuit technology, MMIC solutions (Si, GaAs or SiGe)
Each radiating element equipped with its own amplifiers (RX and TX) → Maximal variability Maximal complexity
Arrays
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Beam forming: Switched-beam N-element arrayArray provides set of M ≤ N predefined beams (e.g. sectorial antenna) Simple implementation (single frontend for entire array) Limited adaptivity (no beam forming)
Arrays
C.A. Balanis, „Antenna theory“, John Wiley, 1982.
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Beam forming: Adaptive N-element array
Arrays
C.A
. Balanis, „A
ntenna theory“, John Wiley, 1982.
Frontend
Frontend
N complete frontends (RF to baseband),1 beamformerDigital signal processing (direction estimation, complex-weight pattern adaptation)
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Beam forming: Spatial division multiple access (SDMA)
Arrays
C.A
. Balanis, „A
ntenna theory“, John Wiley, 1982.
N complete frontends (RF to baseband),M N beamformers Ultimate adaptivity (multiple adaptive subsystems) Ultimate complexity (signal processing, power consumption, size & weight)
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Analog beam forming networks
vv
v
12
3
A
B• Provides amplitudes and phase gradients
for M N patterns• Low-loss. Matched. Wideband or selective.
Power transfer from feed into far field• Excites “independent” beams
No exchange of power, “orthogonality”• Analog HW implementation of a linear set of
equations (N+M) (N+M) matrix, function can be implemented in the digital domain
A1 A2 A3
B1 B2 B3
A1 B1
A2 B2
A3 B3
0 0 a a a0 0 a a a
a a 0 0 0a a 0 0 0a a 0 0 0
A B 1 2 3AB123
N-element antenna array → N different beams or N-1 different nulls
M-port beam forming network
Arrays
Losslessness: Orthogonality:N 2
ipi 1
S 1
N
*ni pi np
i 1S S
A Ba a 1 *
A Ba a 0
A lossless reciprocal network is orthogonal.
aAbA
a3b3
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Fading minima depend strongly on antenna position:• Multiple displaced receive antennas beneficial (antenna arrays)• Risk of all antennas undergoing a deep fade simultaneously reduced• Signal optimised by coherent combination (e.g., maximum ratio combining)
Mitigating fading by spatial diversity with antenna arrays
CombinedAntenna 1 Antenna 2
Time or receiver position
SNR
(dB
)
Enhanced stability and reliability of the link
Arrays
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
No signal-strength fluctuationDistribution function: unit step
Diversity antennas: Statistical description of fading
Line-of-sight transmission (LOS)
Received power “fades” (fluctuates) upon movement of mobile stationRayleigh distribution function
Non-line-of-sight (NLOS)
Deep fades are less likelyRice-factor KDistribution functions "intermediate"
Combined LOS and NLOS fading
Arrays
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Diversity antennas (Rayleigh fading)
Array size: N elements• SNR improves with N (link budget)• Probability for deep fades decreases
with N (link reliability and quality)Arrays
N 1 r
0
1CDF( ) r e dr(N 1)!
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
• Radiation matrix [H] = [1] – [S]H[S]• Efficiency
• Depends on feed vector (array element excitation, "illumination")• Determined by radiation matrix (S-parameters, radiation patterns)• Enables quantitative comparison of different arrays
Generalised efficiency
H
r adH
avail
P a [H]a(a)P a a
C. Volmer, Dissertation, Ilmenau 2009 Arrays
Radiation matrix of a lossless N-element antenna array
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Diversity gain Gdiv• Given outage probability tolerated
by the radio link (e.g., 1%)• SNR-difference between N-element
array and single radiator at same probability (e.g., Gdiv,3(1%) = 16.3 dB for N = 3)
Gdiv,N(p) = Power that could be saved by spatial diversity – without affecting reliability nor coverage
16.3 dB • Approximationp
1
div,N
tr [H]qG (p) 1 qp N N 1
Nq N! p det [H]
C. Volm
er, Dissertation, Ilm
enau 2009
Arrays
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Diversity loss Ldiv
• Accounts for radiation coupling
• Marks the SNR-difference between coupled diversity antenna (real) and fully decoupled version (ideal)
Mutual element coupling always reduces diversity gain
• Approximation
Ldiv
div,N10L (dB) log det [H] 0N
Arrays
C. Volm
er, Dissertation, Ilm
enau 2009
div,Ndiv,N
1L !G
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Packaging issues of antennas
Transmission lineDefined by geometrical dimensions and material parameters (, , )Propagating modes: TEM (broadband), TE vs TM vs hybrid (low-/high-pass)
Practical aspects
Matching networkMatching of impedance, effective power, propagating modeLumped vs distributed vs hybrid (affects frequency, bandwidth, losses, size)
RadomeMechanical and environmental ruggedness, affects electrical properties
Example: Transmit antenna
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Types of transmission lines (selection)
Strip transmission linesMicrostrip, slotline, coplanar waveguide, coplanar slot (Principle of duality, characteristic impedance, field concentration, power handling)
Hollow-tube waveguidesDifferent contours (e.g., rectangular, circular)Different cross-sections (e.g., ridged, fin-line)Different environments (substrate-integrated waveguides, via fences)
Coaxial linesPower handlingFlexibility vs dissipation losses
Wire transmission linesOpen and shielded geometries (simplicity vs performance)
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Impedance matching using transmission line elements
Practical aspects
0 Lin L
L 0
Z cos jZ sinZ Z
Z cos jZ sin
/ Z0 = 0 (short circuit) Z0 → (open circuit)
< /2 < 1/4
= /2 = 1/4
< < 1/2
= = 1/2
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Baluns: NecessityR
othamm
els Antennenbuch, 12. A
uflage (in Germ
an)http://de.w
ikipedia.org/wiki/B
aluneven mode
odd mode
Current distribution at unbalanced-balanced transition
Dipole radiation pattern with (top) and without balun (bottom)
Mode matching and/or suppression of ground currents required
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Baluns: Types and example implementations
1 Differential transformers
2 Half-wave line baluns
3 Quarter-wave baluns (loop, collinear: Marchand)
4 Reactance networks (lumped elements, distributed line elements)
5 Radials, bazooka, coil baluns (suppress sheath currents)
6 Absorbers (ferrites)
Practical aspects
1 2 5
3 3
4 4 6
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Antenna radomesFunction• Protective enclosure• Minimal impact on performance
Implementation• Sandwich, space frame,
dielectric, solid laminate• Ceramic and organic materials
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Simulated influence of a radome (direction finding antenna at 950 MHz) on electromagnetic fields
Direction of propagation (plane wave)
Courtesy R
ohde & S
chwarz, D
r. M. P
auli, Nov. 2010
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Radome materials (selection)
Practical aspects
MaterialMass density (g/cm3)
Dielectric permittivity r
Loss tangent103·tan
Al2O3/AlN 3.69 9.28 0.3
Aluminum oxide 3.32 7.85 0.5
Beryllium oxide 2.88 6.62 1
Boron nitride 2.13 4.87 0.5
Silica-fiber composite 1.63 2.90 4
Silicon nitride 2.45 5.50 3
Ceramics
Material (g/cm3) r 103·tanLexan 1.2 2.86 6
Teflon 2.2 2.10 0.5
Epoxy-E glass cloth 1.9 4.40 16
Polyester-quartz cloth 3.70 7
Quartz-reinforced polyimide 1.3 3.2 8
Duroid 5650 2.2 2.65 3
Organics and composites
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Circuit analysis versus field simulation
Practical aspects
Circuit elements of uniform cross-section can be modeled by conventional circuit analysis (transmission line models), including simple types of discontinuities (steps, vias, ...)
Engineered transformations of field distributions and/or radiation effects require numerical field simulation
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Classification of field problems
Practical aspects
Keyword Description
Electrical size Number of variables
DomainTime domain (broadband, switching)Frequency domain (resonant, high-Q)Related by FT in linear systems
BoundariesElectric (PEC, E, H||) Magnetic (PMC, H, E||) Space (matched, absorptive)
Dimensionality1d (transmission lines)2/2.5d (PCB, symmetric 3d problems)3d full complexity
3minN ~ /
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Classification of simulation methods
Practical aspects
Keyword Description
General Procedure
Wave equations potentials fields parameters like impedance, gain/directivity/efficiency, radiation pattern, ...
Boundary conditions
Geometry Material(s)Ports (position, type)Excitation (current/voltage, E/H fields, modes)
Solver
Analytical: Closed form, simple problems, reference solution (e.g., Hertzian dipole)Semi-analytical: Integral expression numerical computation high computational efficiency(specific problems, limited validity, e.g., /2-dipole)Numerical: Wave equation @ discrete lattice, local interpolation
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Finite-element method
Practical aspects
Complex and inhomogeneous field problems are split into homogeneous simple sub-structures with known solutions
Discretisation of a planar problem using a triangular mesh
Example for an Ansoft HFSS microstrip mesh
11 11 1
2 2 2 2
3 33 3
c 1 x yc 1 x y
1 x yc
212
V
| | dV min
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Finite-difference time domain models
Practical aspects
Example FDTD grid, formed by brick-shaped hexahedral cells
Solution of wave equations on a discrete lattice (mesh)
2 2 2
2 2 2 0x y z
l 1,m,n l 1,m,n1
x 2h
l,m,n l 1,m,n l 1,m,n
l,m 1,n l,m 1,n
l,m,n 1 l,m,n 1
6 ...
... ...
... 0
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Numerical simulation tools: summary
Practical aspects
FDTD FEM
ExampleCST Microwave Studio Many other codes available
Ansoft HFSSMany other codes available
Domain Time FrequencySolution Iterative time steps Matrix equationCell geometry Rectangular / cubic Triangular / tetrahedral
Advantages
Low memory requirementsEfficient for broadband problems and physical transitionsElectrically large geometries
Adaptive discretisation of complex structuresRapid computation for single frequency points (e.g. high-Q devices) and multi-port devices
Dis-advantages
Less efficient for curved structuresEach port requires separate simulation
Electrically small geometriesHigh memory requirementsCPU time increases with number of frequency points
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Port modeling and mode matching
Practical aspects
Port parameters (mode specific) define incident power flowCurrents and voltages (circuit design) must be related to field parameters requires a reference path 1 for integration
cond
portI Hd
1 2 pathA
Ed j BdA 0
1
port
2
port 12
A
( Ed )Z
(E H*)dA
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Input matchingReflection coefficient
Standing wave ratio
Return loss
Matching (Reciprocity)Voltage ratio
1 | |S1 | |
RL 20log | |
0
0
Z / Z 1Z / Z 1
1 1 2 2
1 1 2 2
RxFS AUT2 2
Tx T SA AUT R
V e et (1 )V 1 e 1 e
Practical aspects
0
5
10
15
20
25
30
0 2 4 6 8 10
Ret
urn
loss
RL
(dB)
Standing wave ratio S
S ~ 5.8
S ~ 1.9
S ~ 1.2
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
• Known reflections or none• Natural or artificial environment• Defined methods
(e.g., far/near field; frequency/time domain)
• Calibrated precision measurements (distances, power levels, phase centres, …)
Radiation measurements
Free space www.orbitfr.comAnechoic chamber (HMT)
"Virtual road" antenna and channel measurements (HMT)
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Rad
iatio
n m
easu
rem
ent s
chem
es
http://ww
w.cuminglehm
an.com/pdf/m
ag.pdf (12.07.2017)
Rectangular anechoic chamber Compact antenna test range
Outdoor elevated range Ground reflection range
Planar near-field Cylindrical near-field Spherical near-fieldPractical aspects
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Anechoic chamber measurementsReflections damped by absorbers (-30 ... -50 dB)Absorber: Height reflects wavelength, shape matches impedance (free space – metal shield)Chanber size: Far field conditions, constant amplitude under rotation Specific adaptations w.r.t. frequency ranges and test specs
Practical aspects
http://ww
w.m
vg-world.com
/en/products/field_product_family/absorber-6 12.07.2017
ECCOSORB® HHP-60-NRL
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
From near field to far field
Near field: reactive (stored energy)Far field: plane waves (E H z)
Rayleigh Fresnel Fraunhofer
Electrically small antennas:rff / < 1
Given value of D/ 1/2: rff / ≈ 1
High gain:rff / 1
Example: parabolic reflector antenna
2ffr D2
22
parabolDG
ffparabol2
r 2 G
Practical aspects
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Radiation measurement uncertaintiesMajor influencesMeasurement setup Quiet zone, electrical distance, calibration, dynamic range, e.g. for high frequenciesNear field Region ≈ , environmental effects, e.g. SARNon-idealities Phase centre variation upon rotation, parasitic radiation from cables, shadowing from positioner, calibration
Require careful adjustment and critical analysisPractical aspects
H. Eder, A. Wiedenhofer, http://www.mobilfunkundschule.bayern.de, 2012
After Jeffrey A. Fordham, Microwave Instrumentation Technologies, LLC
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Examples of measured radiation patterns
Commercial GNSS antennaTallysmanTM TW3870
Graphical display of measured data: AUT Studio, www.lisa-analytics.de
Polar
Cartesian
Elevation Azimuth
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Doppelsteg-Hornantenne (im Prinzip für große Bandbreiten geeignet)
Examples of measured radiation patterns (UWB)U
. Schw
arz, TU Ilm
enau, Dissertation in Vorbereitung (2008)
Practical aspects
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
Dispersion: frequency dependent impulse responsesRadiation patterns in time domain
W. W
iesbeck, „Ultrabreitbandantennen“, KIT, 2008
Non-resonant(Vivaldi)
Resonant(Log-periodic)
E-plane H-plane
time(ns)
Azimuth (deg)Practical aspects
Antenna EngineeringProf. Dr. M. Hein
Summer semester 2018
RF & Microwave Research Labwww.tu-ilmenau.de/hmtSince 1961
G/T-measurements
G – Antenna gainTsys – System noise temperature – Power flux1 sfu = 10-22 W/m2Hz
N,B2
sys N,0
PkG 4 1T P
Data (Sun)Power flux of the sunData updated on daily basisFrequency specific analysis
Other astronomic radiating sources:Cassiopeia A, 3Cxyz, Cygnus A, ... Practical aspects
http://www.ips.gov.au/Solar/3/4 (12.07.2017)
101
102
103
102 103 104Sol
ar fl
ux
S(f)
in "s
olar
flux
uni
ts"
Frequency f (MHz)
Steady contribution (quiet solar)Learmonth /Australia
22.01.200427.01.200626.01.200710.07.200809.07.200903.04.201029.06.201012.07.201110.07.201208.07.201304.07.201413.07.201511.07.201612.07.2017
burst?
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