mediciones agilent radar - tecnm

Copyright 2001 Agilent Technologies, Inc.

GET10B

Radar Measurement Basics-

Spectrum Analysis of

Pulsed Signals

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

Demo: Power Meter Measurement

See Demo

C:/TEMP/video/agi003a.mpg

Hi….. I’m John Wineman, and I’ll be

presenting the demonstrations for today’s

seminar.

…we are going to measure CW and then

pulsed power from the new PSG signal

generator.

I’ll set the center frequency of the

generator to 20GHz and the output power

to +10dBm.

We’ll use a high quality microwave cable

with a 10dB pad at the output to insure a

good VSWR.

The first thing we must do to make a good

measurement is to calibrate the power

head.

The first step in calibration is to zero the

power meter. This corrects for DC offsets

in the meter.

Once the zero is complete, we need to run

the power cal. Note the precision 50MHz

source.

After the cal is complete, we must enter

the frequency of the signal to be

measured… 20GHz.

Now that the meter has been zeroed and

calibrated, we will connect the sensor to

the PSG.

The CW power of the PSG is set to

+10dBm, and through the 10dB pad, we

measure -0.89dBm.

Now turn on a the pulse modulator with a

1usec PW and 10usec PRI and measure -

10.79dBm….

….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.

Q and A

Agilent Restricted

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

Spectrum Analyzer Block Diagram

IF

IF

PeakDetector

Sweep

LO

Mixer

RF Input

Smoothing

Animation

(Animation)

Espectrum/SPECAN1.EXE

Q and A

Agilent Restricted

VSA Block Diagram

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)

Q and A

Agilent Restricted

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

How the Spectrum Changes With PRF

Same PRF

t

PRFSame t PRF

Same t

Same PRF

t

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

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

Demo: Band Power Measurement Using a Spectrum Analyzer

See Demo

C:/TEMP/video/agi003b.mpg

C:/Archive/video/agi003b.mpg

We will now use the spectrum analyzer to

take a closer look at our pulsed signal.

First, we will do a preset. This defaults to

a reference level of 0dBm…. Our peak

signal level.

Don’t let the smoke out!!

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

Now turn on the pulse modulation. The

power of the central line drops as

20*log(duty cycle).The marker now reads

-20.79dBm.

Now integrate the power in the central

three lobes using band power markers.

The band power (average

power) is -11.12dBm.

Q and A

Agilent Restricted

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)

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

Demo: Zero Span Pulse MeasurementsUsing a Spectrum Analyzer

See Demo

C:/TEMP/video/agi003c.mpg

Now we will use the spectrum analyzer as

a fixed tuned receiver and see the pulse

power vs time.

Set the Span to 0Hz, RBW to 8MHz, and

the Sweep time to 10sec, and trigger

externally.

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.

Q and A

Agilent Restricted

Thanks for Attending!

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