Introduction to Satellite Systems

1
Introduction to Satellite Systems Technical
University of Denmark June 2002 Antennas

• Contents
• Antenna definition and examples
• Antenna radiation
• Hertzian dipole and linear antenna
• Antenna impedance
• Directivity, gain, and effective area
• Transmission between antennas
• Antenna specifications
• Bibliography
• Exercises and assignments

Contact Olav Breinbjerg ØrstedDTU,
Electromagnetic Systems Technical University of
Denmark Building 348, Ørsteds Plads DK-2800 Kgs.
Lyngby, Denmark Phone [phone] Email
ob_at_oersted.dtu.dk½
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Radio Communication System
Transmitting antenna
Receiving antenna
Receiver
Transmitter
Available signal power
Received signal power
3
Antenna Definition and Examples
IEEE Standard Definitions of Terms for
Antennas (IEEE Std 145-1993)
Nokia mobile phone model 3210 with internal
antenna
Antenna. That part of a transmitting or
receiving system that is designed to radiate or
receive electromagnetic waves
Arecibo radio astronomy antenna
4
Danish Satellite Antenna Examples
Rømer Two 2GHz cavity-backed crossed-slot
antennas flush-mounted for hemispherical coverage
with each.
Ørsted A 2GHz crossed-dipole antenna mounted on
the Earth-facing side for directive coverage.
DTUSat A 435MHz canted-turnstile antenna for
spherical coverage.
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Antenna Radiation I
Arbitrary point of observation
V
Vector potential
O
Magnetic field
Time-harmonic case
Electric field
Phasor-notation
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Antenna Radiation II
Far-field point of observation
V
Electric field
O
Time-harmonic case
Magnetic field
Phasor-notation
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Hertzian Dipole Radiation
Electric far-field
Magnetic far-field
8
Linear Antenna Radiation
Electric far-field
L/2
Radiation patterns
-L/2
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Interference from Antenna Support Structure
Antenna
Support structure
Hertzian dipole above infinite ground
z
h
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Antenna Impedance I
Example
Generator
Transmission line
Antenna
Voltage reflection coefficient
Power transfer
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Antenna Impedance II
Resistance
Reactance
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Directivity
Power density
Directivity
Average power density of radiated power
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Gain and Efficiency
Power density
Gain
Average power density of accepted power
Efficiency
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Effective Area
Impedance match
Polarization match
Effective area is not necessarily equal to
physical area!
Reciprocity principle
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Transmission between Antennas
R
Impedance and polarisation match
Impedance and polarisation mis-match
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Antenna Specifications

• General Rømer
• Frequency (up- and downlink) 2.0258-2.1087 /
  2.20-2.29 (GHz)
• Gain gt -12dBi everywhere
• Polarisation Left-hand circular
• Impedance 50 Ohm
• Reflection coefficient 0.2
• Bandwidth 8

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Bibliography
D.K.Cheng, Field and Wave Electromagnetics,
Addison-Wesly Publishing Company, 1992. C.A.
Balanis, Antenna Theory Analysis and Design,
John Wiley Sons, 1997. J.D. Kraus and R.J.
Marhefka, Antennas for all Applications,
McGraw-Hill 2002. J.E. Kadish, T.W.R. East,
Satellite Communications Fundamentals, Artech
House, 2000. O. Breinbjerg, Satellitantenner
aktiviteter ved Danmarks Tekniske Universitet,
Dansk Rumfart, no. 47, Oct.-Dec. 2000. See
also http//www.oersted.dtu.dk/PR/popular_science
_articles/Satellitantenner/satellitantenner.html.
Antenna and Electromagnetics Group homepage,
see http//www.emi.dtu.dk/research/afg/index.html.

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Exercises and Assignments
Exercises
Assignments
A1. For a satellite communication ground
station Design a 10 element end-fire antenna
array consisting of horizontally polarized
Hertzian dipoles by proper selection of spacing
and excitation. Determine the directivity and
plot the radiation patterns. Determine, by use
of image theory, the influence of the ground on
the directivity and radiation patterns for
varying elevation angles. Compare the results to
those from assignment A2. A2. For a satellite
communication ground station Design a 10
element end-fire antenna array consisting of
vertically polarized Hertzian dipoles by proper
selection of spacing and excitation. Determine
the directivity and plot the radiation patterns.
Determine, by use of image theory, the influence
of the ground on the directivity and radiation
patterns for varying elevation angles. Compare
the results to those from assignment A1.

• E1. Derive the expression for the z-directed
  Hertzian dipole electric far-field. Plot the
  field amplitude as a function of the angle q.
• E2. Plot the linear antenna current for the
  length L being equal to l/2, l, 5 l /4, and 3 l
  /2. Plot the z-directed linear antenna field
  amplitude as a function of the angle q in a
  rectangular plot.
• E3. Determine the G0.2 bandwidth and the G0.33
  bandwidth for the antenna example on Antenna
  Impedance I page.
• E4. Determine the directivity D of the Hertzian
  dipole.
• E5. Determine the directivity D of the l/2
  linear antenna.
• E6. A satellite communication system has the
  following parameters f 2.15GHz, Gt 5dB, Gr
  30dB, Pav 5dB, and R 1.000km. Determine PL.