Mediciones Agilent Radar - TecNM
Transcript of Mediciones Agilent Radar - TecNM
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Copyright 2001 Agilent Technologies, Inc.
GET10B
Radar Measurement Basics-
Spectrum Analysis of
Pulsed Signals
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Agenda: Power Measurements
• Module #1: Introduction
• Module #2: Power Measurements
• Module #3: Time Domain Measurements
• Module #4: Noise Measurements
• Module #5: Evaluating I/Q Demodulator Errors
• Module #6: Pulsed Component Measurements
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Hi….. I’m John Wineman, and I’ll be
presenting the demonstrations for today’s
seminar.
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…we are going to measure CW and then
pulsed power from the new PSG signal
generator.
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I’ll set the center frequency of the
generator to 20GHz and the output power
to +10dBm.
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We’ll use a high quality microwave cable
with a 10dB pad at the output to insure a
good VSWR.
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The first thing we must do to make a good
measurement is to calibrate the power
head.
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The first step in calibration is to zero the
power meter. This corrects for DC offsets
in the meter.
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Once the zero is complete, we need to run
the power cal. Note the precision 50MHz
source.
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After the cal is complete, we must enter
the frequency of the signal to be
measured… 20GHz.
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Now that the meter has been zeroed and
calibrated, we will connect the sensor to
the PSG.
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The CW power of the PSG is set to
+10dBm, and through the 10dB pad, we
measure -0.89dBm.
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Now turn on a the pulse modulator with a
1usec PW and 10usec PRI and measure -
10.79dBm….
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….and so with a 1 sec pulse width and a
10 sec pulse repetition interval, we have
a 10% duty cycle. The average power of
this signal is
-10.79dBm. Note that the pulsed power
dropped from our CW power (which is
also our peak power in this instance)
= 10log(PW/PRI)
= 10*log(1sec/10 sec)
= -10dB
This agrees nicely with our measured
results.
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Q and A
Agilent Restricted
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Why Measure Power Spectrum?
}}A
F
Unintentional Radiation
Wastes expensive Peak Power
Increases vulnerability (creates a signature for
the particular transmitter)
Desired
Radiation
Out of Band
Radiation
In band spurs
Interferes with other electronic signals
Unintentional radiation
• Wastes expensive peak power
• Increases vulnerability
(creates a signature for the particular transmitter)
• Interferes with other electronic signals
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Spectrum Analyzer Block Diagram
IF
IF
PeakDetector
Sweep
LO
Mixer
RF Input
Smoothing
Animation
(Animation)
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Q and A
Agilent Restricted
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VSA Block Diagram
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Measuring Pulsed Power with a Spectrum Analyzer
Pulsing RF Desensitizes Measurement
Measured:
PRI = 1 ms
P = -30 dBm
P = 30 dBmpeak
Calculated:
Example
= 1 sPW
= -60 dB
meas•
•
•
•
•
Measured Power
-30dBm
Peak Pulse PowerPulse Desensitization
= 20 log (PW/PRI){
1
PW
PRF
Line Spectrum
= 60dB
Animation
(Animation)
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Q and A
Agilent Restricted
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Pulse ParametersP
ow
er
Pavg = Ppk * t /T
Frequency2/t
PRF=1/TThe frequency
domain
representation
of a pulse.
Po
wer
Time
PRF=1/T T
PulseWidth
t
Peak
Power
Average
Power
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How the Spectrum Changes With PRF
Same PRF
t
PRFSame t PRF
Same t
Same PRF
t
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Measuring with a Spectrum Analyzer
Advantages
• Wide frequency range
• Wide dynamic range
• Zero span (time domain)
• Relative power measurement
• Band Power
Considerations
• Identification of narrowband
vs. broadband signals
• Absolute amplitude accuracy
• Dealing with noise like
measurements
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Spectrum Measurements
FREQUENCY
PULSEPRF
MODULATOR
AGILE L.O.
RECEIVER
PROTECTIONGENERATOR
ADC S/H LPFVIDEO
AMP
COHO LIMITER LPF
ADC S/H LPF VIDEO
AMP
90o
0
SPLITTER
o
2nd
IFAIF
BPF
2nd
L.O.
1st
IFAIF
BPF
LNA
STALO
COHO BPF AMPRF
BPF
Doppler
and
Range
FFT
Processor
PREDRIVER
AMP
PULSED
POWER
TRANSMITTER
DUPLEXER
Transmitter/Exciter
Receiver/Signal Processor
Antenna
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Demo: Band Power Measurement Using a Spectrum Analyzer
See Demo
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We will now use the spectrum analyzer to
take a closer look at our pulsed signal.
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First, we will do a preset. This defaults to
a reference level of 0dBm…. Our peak
signal level.
Don’t let the smoke out!!
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Connect the PSG to the spectrum
analyzer, set the CF to 20GHz and Span to
5MHz.
Observe the -.79dBm CW
signal near the ref level
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Now turn on the pulse modulation. The
power of the central line drops as
20*log(duty cycle).The marker now reads
-20.79dBm.
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Now integrate the power in the central
three lobes using band power markers.
The band power (average
power) is -11.12dBm.
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Q and A
Agilent Restricted
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Frequency Selective Time Domain Measurement
Swept tuned spectrum analyzer in zero span
• Using a fast internal digitizer
• Look at the spectrum analyzer’s detected video
Vector signal analyzer
• Faster than a swept tuned analyzer
• Can make complex measurements (phase,
group delay, etc)
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Pulsed Power Measurements
FREQUENCY
PULSEPRF
MODULATOR
AGILE L.O.
RECEIVER
PROTECTIONGENERATOR
ADC S/H LPFVIDEO
AMP
COHO LIMITER LPF
ADC S/H LPF VIDEO
AMP
90o
0
SPLITTER
o
2nd
IFAIF
BPF
2nd
L.O.
1st
IFAIF
BPF
LNA
STALO
COHO BPF AMPRF
BPF
Doppler
and
Range
FFT
Processor
PREDRIVER
AMP
PULSED
POWER
TRANSMITTER
DUPLEXER
Transmitter/Exciter
Receiver/Signal Processor
Antenna
PM SA
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Demo: Zero Span Pulse MeasurementsUsing a Spectrum Analyzer
See Demo
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Now we will use the spectrum analyzer as
a fixed tuned receiver and see the pulse
power vs time.
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Set the Span to 0Hz, RBW to 8MHz, and
the Sweep time to 10sec, and trigger
externally.
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Now we can use the marker to measure
the peak power of our signal in an 8MHz
bandwidth.
The marker reads a
peak pulse power of
+ 0.25dBm.
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Q and A
Agilent Restricted
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Thanks for Attending!