Transcript Preliminary Design Review Presentation: Calibration

Overview
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Exciter
Receiver
Oscillators
High-Powered Amplifier
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Calibration
Calibration: Requirements
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Able to retrieve calibrated reflectivity (Phase A)
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Transmitted power
Receiver gain
System noise floor
Must be extendable to retrieve calibrated polarimetric variables (Phase B)
Must accommodate pulse compression (Phase B)
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Measurement of the transmitted pulse desirable
Calibration: Requirements
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Absolute Calibration
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Laboratory measurements using noise and signal sources to measure gain and
dynamic range of the receiver
Ground corner reflector for periodic reflectivity calibration
Other techniques in flight, e.g. sea surface (Li, 2003)
Dynamic Calibration
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Transmitted signal continuously switched into the receiver during operation while
the radar is “blind”
Blue sky noise measurement possible periodically during aircraft turns, etc.
Calibration Network: Dynamic Calibration
• Transmitted signal is coupled into the into the receiver through a well-calibrated
path, GCAL
RX
CAL
• Reflectivity can be calculated from the ratio of PADC and PADC
RX
G CAL
1 PADC
η
CAL
G REC1G TX r 2 κ PADC
PEIKA
GCAL
PADC
GREC2
GTX
PRX
GREC1
Calibration Network: Dynamic Calibration
• Therefore, need to know GCAL, GREC1, and GTX
• Need to temperature stabilize front-end electronics
• Move calibration coupler to after T/R circulator to minimize GTX
GTX
GCAL
GREC1
Calibration Network: Isolation
• T/R isolation required between calibration channel signal, and transmit signal
reflected from the antenna
• Given antenna return loss of −14 dB, and maximum linear-range input signal to the
LNA of −30 dBm, 114.1 dB of isolation is required between transmit and receive (5
latching circulators at 25 dB/circulator) to achieve > 0.1 dB amplitude distortion on
calibration signal
114 dB isolation