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Copyright 2001 Agilent Technologies, Inc.
GET10B
Radar Measurement Basics-
Spectrum Analysis of
Pulsed Signals
Page 2
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
Page 4
Hi….. I’m John Wineman, and I’ll be
presenting the demonstrations for today’s
seminar.
Page 5
…we are going to measure CW and then
pulsed power from the new PSG signal
generator.
Page 6
I’ll set the center frequency of the
generator to 20GHz and the output power
to +10dBm.
Page 7
We’ll use a high quality microwave cable
with a 10dB pad at the output to insure a
good VSWR.
Page 8
The first thing we must do to make a good
measurement is to calibrate the power
head.
Page 9
The first step in calibration is to zero the
power meter. This corrects for DC offsets
in the meter.
Page 10
Once the zero is complete, we need to run
the power cal. Note the precision 50MHz
source.
Page 11
After the cal is complete, we must enter
the frequency of the signal to be
measured… 20GHz.
Page 12
Now that the meter has been zeroed and
calibrated, we will connect the sensor to
the PSG.
Page 13
The CW power of the PSG is set to
+10dBm, and through the 10dB pad, we
measure -0.89dBm.
Page 14
Now turn on a the pulse modulator with a
1usec PW and 10usec PRI and measure -
10.79dBm….
Page 15
….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.
Page 16
Q and A
Agilent Restricted
Page 17
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
Page 18
Spectrum Analyzer Block Diagram
IF
IF
PeakDetector
Sweep
LO
Mixer
RF Input
Smoothing
Animation
(Animation)
Page 19
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Page 21
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Page 23
Q and A
Agilent Restricted
Page 24
VSA Block Diagram
Page 25
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)
Page 26
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Page 34
Page 35
Q and A
Agilent Restricted
Page 36
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
Page 37
How the Spectrum Changes With PRF
Same PRF
t
PRFSame t PRF
Same t
Same PRF
t
Page 38
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
Page 39
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
Page 40
Demo: Band Power Measurement Using a Spectrum Analyzer
See Demo
Page 41
We will now use the spectrum analyzer to
take a closer look at our pulsed signal.
Page 42
First, we will do a preset. This defaults to
a reference level of 0dBm…. Our peak
signal level.
Don’t let the smoke out!!
Page 43
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
Page 44
Now turn on the pulse modulation. The
power of the central line drops as
20*log(duty cycle).The marker now reads
-20.79dBm.
Page 45
Now integrate the power in the central
three lobes using band power markers.
The band power (average
power) is -11.12dBm.
Page 46
Q and A
Agilent Restricted
Page 47
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)
Page 48
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
Page 49
Demo: Zero Span Pulse MeasurementsUsing a Spectrum Analyzer
See Demo
Page 50
Now we will use the spectrum analyzer as
a fixed tuned receiver and see the pulse
power vs time.
Page 51
Set the Span to 0Hz, RBW to 8MHz, and
the Sweep time to 10sec, and trigger
externally.
Page 52
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.
Page 53
Q and A
Agilent Restricted
Thanks for Attending!
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