A J Gasiewski remote sensing course notes lecture24

46 Pages·01.433 MB·English

by  A J Gasiewski

ECEN 5254
Remote Sensing Signals and Systems
Professor Albin J. Gasiewski
Lecture #24 – April 12, 2012
ECOT 246
303-492-9688 (O)
[email protected]
Classes: ECCS 1B14 TR 9:30-10:45 AM
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ECEN 5254 Remote Sensing Signals & Systems Spring 2012 University of Colorado at Boulder
Administration
• Reading:
– RSSS slides
– Skolnik, Intro to Radar Systems, Chs 3-5
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ECEN 5254 Remote Sensing Signals & Systems Spring 2012 University of Colorado at Boulder
Last Lecture
• Target detection
• Radar system components
– Transmitter Sources
– Transmit/Receive Isolation
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ECEN 5254 Remote Sensing Signals & Systems Spring 2012 University of Colorado at Boulder
Today’s Lecture
• CW radar
• FMCW radar
• Monopulse tracking radar
• Conical scan tracking radar
• Moving Target Indicator (MTI)
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ECEN 5254 Remote Sensing Signals & Systems Spring 2012 University of Colorado at Boulder
Transmit/Receive Isolation
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Requirement for Isolation
• P can exceed saturation and/or maximum rated power
T
levels of receiver by 104-108, depending on system
• Isolation of this level is required to prevent damage
and/or system saturation - especially in CW systems
• Three primary means of isolation:
 Transmit/receive (T/R) switching
 Use of non-reciprocal devices (e.g., circulators)
 Bistatic isolation (e.g., bistatic radar)
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3-dB Hybrid Coupler Duplexer
1 3
~
Transmitter Antenna
Receiver
2 4
Advantage: Simple, readily integrated into MMIC form
Disadvantage: 6 dB loss, limited isolation
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Transmit Feedthrough Nulling
~
Transmitter Antenna
Aejϕ
Receiver
Compensates for residual transmit-receive coupling
Adaptable to cancel time-varying T/R coupling
Useful for CW systems, but less so for pulsed systems
where bandwidth is nonzero.
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Typical T/R Switch-Isolator Architecture
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Gas Discharge Duplexer Switches
from Eaves and Reedy
Gas T/R switch shown in transmit state
• Operation based on ionization of high-conductivity
plasma channel during transmit pulse
• High power capability (100's of kW) with ~usec
response, rugged designs
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