introduction to space systems and spacecraft design space systems design communications - antennas...
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Introduction to Space Systems and Spacecraft DesignSpace Systems Design
Communications - AntennasRef: SMAD Sections – 13 Communications Architecture
Introduction to Space Systems and Spacecraft DesignUniversity of Idaho
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Communications I
How do these antennas work?
RF – radio frequency
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Ground Antennas
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Ground Antennas
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Ground Antennas
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Spacecraft Antennas
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Spacecraft Antennas
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Ground Antennas
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Ground Antennas
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Ground Antennas
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Ground Antennas
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Ground Antennas
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Ground Antennas
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Spacecraft Antennas
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Spacecraft Antennas
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Spacecraft Antennas
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Spacecraft Antennas
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Spacecraft Antennas
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Spacecraft Antennas
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Spacecraft Antennas
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Spacecraft Antennas
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Spacecraft Antennas
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Spacecraft Antennas
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Spacecraft Antennas
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W = Power Density – W/M2
S = distance from antenna to a point in space
La = atmospheric loss
EIRP = effective isotropic radiated power
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Communications - Antennas
Antenna gain for a parabolic antenna
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( )2
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What is the affect on the gain of antennas with frequency?
When perfect impedance match – get 100% transfer to antenna
100%
Perfect impedance match – get VSWR = 1.0
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What is the affect on the gain of antennas with frequency?
What happens when VSWR > 1.0?
<100% forward wave
Output power of antenna (gain) is less off resonant frequency.
Reflected wave
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What is the affect on the gain of antennas with frequency?
The gain on all antennas are frequency sensitive.
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¼ wavelength antenna above a ground plane
Center fed ½ wavelength
~
~
Antenna Polarization
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Communications - Antennas
Electric field lines froma ½ wave antenna
Generated vertical electric field lines
Vertically polarized antenna
Antenna Polarization
Ground
(B) (A)
(C)
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Communications - Antennas
(C) Electric field lines from
a ½ wave antenna
Horizontal electric field lines
Horizontal polarized antenna
(A) (B)
Antenna Polarization
Ground
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Communications - Antennas Antenna Polarization
Circular Polarization Helical Antenna
Spiraling electric field
Introduction to Space Systems and Spacecraft DesignSpace Systems Design
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Communications - Antennas Antenna Polarization
Circular Polarized Helical Antenna
Rotating electric field
Counter clockwiserotating
Looking to forward end of antenna
LHP – left hand polarization
Clockwiserotating
Looking to forward end of antenna
RHP – left hand polarization
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Communications - Antennas Antenna Polarization
Polarized Antenna Coupling
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What type of antenna polarization should be used on satellites and ground stations?
V polarization?H polarization?LH circular?RH circular?
V polarization?H polarization?LH circular?RH circular?
What about when satellite is coming toward you?
What about when satellite is going away from you?
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Communications - Antennas Antenna Polarization
Didn’t answer the question of polarization on the ground and on the satellite???
Something tricky happens to the polarization as the RF passes through the atmosphere to and from the satellite.
We will find out when we look further at the link equations.
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Questions?