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Jeff Thomas

Tom HolmesTerri Hightower

Learn RF Spectrum

Analysis Basics

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Agenda

Overview: Spectrum analysis and itsmeasurements

Theory of Operation: Spectrum analyzerhardware

Frequency Specifications

Questions and Answers break Amplitude Specifications

Summary Questions and Answers break

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Learning Objectives

Name the major measurement strengths of a

swept-tuned spectrum analyzer Explain the importance of frequency resolution,

sensitivity, and dynamic range in making analyzer

measurements

Outline the procedure making accurate distortion

measurements

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8563ASPECTRUM ANALYZER 9kHz -26.5GHz

Overview: What is Spectrum Analysis?

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.

Modulation

Modulation

Distortion

Distortion

Noise

Noise

Types of Tests Made

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time

Amplitude(power) freq

uency

Time domain

MeasurementsFrequency Domain

Measurements

Frequency Versus Time Domain

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f1 f2

Fourier Spectrum Analyzer

Fourier analyzer transforms a signal over time

into a frequency spectrum

Display

Amplitude

Frequency

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Agenda

Overview: Spectrum analysis and itsmeasurements

Theory of Operation: Spectrum analyzerhardware

Frequency Specifications

Questions and Answers break Amplitude Specifications

Summary Questions and Answers break

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Filter

FrequencyReference

Log

Amp

RF InputAttenuator

Mixer IFFilter Detector

VideoFilter

LocalOscillator

SweepGenerator

IFGain

Input

Display

Spectrum Analyzer Block Diagram

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MIXER

RF

LO

IF

The Mixer: Key to a Wide Frequency

Range Input

RF = Radio frequencyLO = local oscillatorIF = intermediate

frequency

fLO

fin00

0

fLO-fin fLO+finfLO

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IF FILTER

Input

Intermediate Frequency (IF) Filter

IF Bandwidth: also known as

resolution bandwidth and

RBWProvides shape of frequency

domain signalf

DisplayedActual

f

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DETECTOR

Negative detection: smallest

Positive detection: largest

Sample detection: last

Am

plitude

Input

Detector

Values Displayed

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VIDEO

FILTER

Input

Without video filtering With video filtering

Video Filter

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LCD DISPLAY

SWEEP

GEN

LO

frequency

Local Oscillator and Sweep Generator

Provides swept display

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IF GAINRF INPUT

ATTENUATOR

Input Attenuator and IF Gain

Circuits

Protects input circuits

Calibrates signal amplitude

Keeps signal display position constant

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Agenda

Overview: Spectrum analysis and itsmeasurements

Theory of Operation: Spectrum analyzerhardware

Frequency Specifications

Questions and Answers break Amplitude Specifications

Summary Questions and Answers break

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What Spectrum Analyzer

Specifications are Important?

Frequency Range Frequency and Amplitude Accuracy

Frequency Resolution

Sensitivity

Distortion

Dynamic Range

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Frequency Range

Low frequencies for

baseband and IF

High frequencies for

harmonics and beyond

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Getting the Frequency Range You Need

LO

Mixer

IF signal, fif

fin

fin

Range0

1

LO Range0

2

fLO-fin fLO+finfLO

3

fif

1

2

3

0frequency

The input signal isdisplayed when

fLO - fin = fIF

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Sweepgenerator

LO

Getting the Frequency Range You Need

0

fin

fLO-fin fLO+finfLO

fin Range0

1

LO Range

0

2

3

4Display

fif

LO Feedthrough

IF

filter

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LO

Getting the Frequency Range You Need

0

fin

fLO-fin fLO+finfLO

fif

3

4

fin

fin Range0

1

LO Range

0

2

Input signaldisplayedfLO - fin = fIF

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Getting the Frequency Range You Need

Lower frequency limited by LO feedthrough

Upper frequency limited by LO range and IF

frequency

Microwave frequency measurement uses

harmonic mixing

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Absolute

Amplitude

in dBm

Relative

Amplitude

in dB

Relative

Frequency

Frequency

Frequency and Amplitude Accuracy

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Frequency and Amplitude Accuracy

Frequency accuracy:

Internal/external frequency referenceUse of internal counter

Amplitude accuracy:Not as good as a power meter

Dependent upon measurement procedure

Excellent relative measurements

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Resolution Bandwidth Residual FM

Noise Sidebands

What Determines Resolution?

RBW Type and Selectivity

Signal Resolution

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3 dB

3 dB BW

LO

Mixer

IF Filter/

Resolution Bandwidth Filter (RBW)

Sweep

Detector

InputSpectrum

Display

RBW

IF Filter Bandwidth

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3 dB

10 kHz

10 kHz RBW

Resolving Two Equal-level Signals

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3 dB

60 dB

60 dB BW

60 dB BW

3 dB BW

3 dB BW

Selectivity =

Resolving Two Unequal-level Signals

3 dB bandwidthSelectivity (filter shape)

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10 kHz Distortion

Resolving Two Unequal-level Signals For a RBW of 1 kHz and a selectivity of 15:1,

the 60 dB bandwidth is 15 x 1 kHz = 15 kHz...

so the filter skirt is 7.5 kHz away from the filters

center frequency

7.5 kHz

60 dB

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Residual FM

"Smears" the Signal

Residual FM

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Noise Sidebands can prevent resolution of

unequal signals

Phase Noise

Noise Sidebands (Phase Noise)

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Penalty For Sweeping Too Fast

Is An Uncalibrated Display

Swept too fast

Sweep Rate

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SPAN 3 kHzRES BW 100 Hz

Typical

Selectivity

Analog 15:1Digital 5:1

Analog versus Digital Resolution

Bandwidths

Analog

Filter Digital

Filter

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Rules to Analyze By:

Use the Analyzers AutomaticSettings Whenever Possible

When using the analyzer in its presetmode, most measurements will be easy,

fast, and accurate

Automatic selection of resolutionbandwidth, video bandwidth, sweep time

and input attenuation

When manually changing the analyzer

parameters, check for uncal messages

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Are There Any Questions?

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Agenda

Overview: Spectrum analysis and itsmeasurements

Theory of Operation: Spectrum analyzerhardware

Frequency Specifications

Questions and Answers break Amplitude Specifications

Summary

Questions and Answers break

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Sweep

LO

MixerRF

Input

RES BWFilter

Detector

A spectrum analyzer generates and

amplifies noise just like any active circuit.

Sensitivity and Displayed Average

Noise Level

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10 dB

Attenuation = 10 dB Attenuation = 20 dB

signal level

Displayed noise is a function of RF input

attenuation

Signal-to-noise ratio decreases as

RF input attenuation is increased

RF Input Attenuator Effects

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Decreased BW = Decreased Noise

100 kHz RBW10 dB

Displayed noise is a function of IF filter bandwidth

IF Filter (Resolution Bandwidth)

Effects

10 kHz RBW

1 kHz RBW10 dB

Best sensitivity = narrowest RBW

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Video BW smoothes noise for easieridentification and measurement of low-

level signals

Video Bandwidth Effects

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Signalequals

noise

~2.2 dB

Sensitivity - the smallest signal that

can be measured

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Rules to Analyze By:

Getting the Best Sensitivity RequiresThree Settings

Narrowest resolution bandwidth

Minimum RF attenuation Sufficient video filter to smooth noise

(VBW < 0.01 Resolution BW)

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Resulting

signal

Mixers Generate Distortion

Where is Distortion Generated?

Signal to be

measured

Frequency

translated signals

Mixer-generated

distortion

M I fl i l Di i i h

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Most Influential Distortion is the

Second and Third Order

Two-Toned Intermod Harmonic Distortion

< -50 dBc< -50 dBc< -40 dBc

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f 2f 3f

Power

in dB

Distortion Increases as a Function of

the Fundamentals Power

=1 dB

=2 dB =3 dB

Fundamental2nd

Harmonic

3rd

Harmonic

For every dB fundamental level change,

the 2nd changes 2 dB and the 3rd changes 3 dB.

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How Distortion Amplitudes Change

Since distortion changes relative to the

fundamental, a graphical solution is practical.

f 2f 3f

1 dB/dBfund 2 dB/dBfund

=1 dB

=2 dB =3 dB

Plotting Distortion as a Function of

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0

-20

-40

-60

-80

-100-60 -30 0 +30

.

Third Order

Intercept - TOI

SecondOrder

Third

Order

Plotting Distortion as a Function of

Mixer Level

+5

Distortion,dB

c

Power at the mixer =Input level minus the attenuator setting, dBm

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Dynamic

Range

Dynamic Range -

Optimum Amplitude DifferenceBetween Large and Small Signals

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.

Displayed Noise Limits

Dynamic Range

Distortion,dB

c

0

-20

-40

-60

-80

-100 -60 -30 0 +30

Noise at 10 kHz

RBW

Displayed average

noise level can be

plotted like distortion.

1 kHz

RBW

Power at the mixer =Input level minus the attenuator setting, dBm

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..

Maximum 2nd

Order DynamicRange

Maximum 3rd

Order DynamicRange

Dynamic Range as a Function of

Distortion and Noise Level

Di

stortion

andSignal-

to-Noise,

dBc

0

-20

-40

-60

-80

-100

Power at the mixer =Input level minus the attenuator setting, dBm

-60 -30 0 +30

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R l t A l b

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Rules to Analyze by:

Determining Dynamic Range

Internal second and/or third order

distortion

Displayed noise level

Noise sidebands when close to

large signals

Your spectrum analyzers dynamic range

is dependent upon:

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Summary

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Summary

The RF spectrum analyzer is a heterodyne receiver Offers a narrow resolution capability over a wide

frequency range

Measures small signals in presence of large signals

Remember to:

Adjust the measurement procedure for specificapplication

Test for internal distortion

Take sideband noise into account

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Agilent Vector Signal Analyzer Product Families

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g g y

89600 Series

Multi-Format & Flexible vector signal analysis DC 6.0 GHz

Bandwidth: 36 MHz RF, 40 MHz Baseband

RF and modulation quality of digital

communications signals including WLAN.

Spectrum & Time (FFT) Analysis

OFDM Analysis (802.11a)

Links to design software (ADS)

PC Based for the Ultimate in Connectivity

Analysis software links to PSA, ESA, E4406A signal

analyzers.

E4406A

Multi-Format wireless

capabilities

7 MHz - 4 GHz

Fast & Accurate

Simple User Interface

Base-band IQ

inputs

89400 Series

Flexible Signal Analysis

DC to 2.65 GHz

10 MHz Signal Bandwidth

Block Digital demodulation

Integral Signal Source

Spectrum & Time waveform

Analysis Complex time varying signals

Color LCD Display

89600 Ultra-wide bandwidth

500+ MHz Signal Bandwidth!

89600 Analysis Capability

Low Cost Oscilloscope Front-end for

RF Scope measurements

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