digital radio frequency memories

Winter 2015

Digital Radio Frequency Memories

Class Notes

Dave Adamy

Adamy Engineering1420 Norfolk Ave, Atwater, CA 95301

Tel(209)357-4433 Fax(209)357-4434

www.lynxpub.com

Scope of Course

• Overview of the DRFM Function

• Digitization Issues

• Modern RADAR Features

• RCS analysis issues

• How DRFMs recreate Complex Waveforms

• Extra Appendix – How to use Slide Rule

Handout Material

• Course Syllabus

– All visual aids + exercise work-sheets

• EW Pocket Guide

• Antenna & Propagation Slide Rule

Follow-up Material

When issues that require follow-up arise in class,they will be put onto the following server site:

https: //lynxpub.homeserver.com

User name: StudentPassword: !Ne3dthefile

Note that there is no www in the address. There are also full size copies of nomographs, etcthat you can download from this site.

Further Reading

The material in this course is primarily taken fromChapter 8 of the new text book EW104 (Artech House 2015)

The DRFM Function

• A DRFM digitizes an RF Signal, modifies it in a computer, and coherently rebroadcasts the modified signal– I & Q digitization is required to preserve

phase information

• A DRFM can also generate a multifaceted signal to accurately represent the RADAR return from a real (complex) target

FILTER

FILTER ADC

DAC

MEMORYLOCALOSC

COMPUTER

BASIC DRFM BLOCK DIAGRAM

SIGNALIN

SIGNALOUT

¼ λ

Independent Samples

I & Q DIGITIZATION

FILTER

FILTERWIDEBAND

ADC

DAC

MEMORYDRFML.O.

COMPUTERSYSTEML.O.

IF BandInput

IF BandOutput

WIDEBAND DRFM

WIDEBAND DRFM

PW

R D

IVC

OM

BIN

ER

DRFMLPF

VCO VCO VCO

LPF

LPF

LPF

LPF

LPF

DRFM

DRFM

SYSTEML.O.

SIGNALIN

SIGNALOUT

NARROWBAND DRFM

Velocity Cells R

an

ge C

ell

s

Determined by pulse return time

Determined by Doppler filterIn which signalIs received

PULSE-DOPPLER RADAR PROCESSINGPD RADARExpects Return withinOne filter

Angular coverageOf antenna scan

Target

AntennaBeam width

SCANNING RADAR TARGET COVERAGE

PD radar has processing gain= CPI x PRF

CPI can equal illumination time

Frequency

ChaffCloud

RadarTransmissionFrequency

ReflectedSpectrumSpread by Chaff DipoleMovement

Wind

DopplerShift from

wind

CHAFF CLOUD DIPOLE MOVEMENT

Velocity Cells

Ran

ge C

ell

s

Velocity cellsFrom Doppler FilterCorresponding toTrue relative rangeRate of target

Velocity cellsFrom Doppler FilterCorresponding toRange rate of jammingplatform

ACTUALTARGET

FALSETARGETFROMJAMMER

SEPERATING TARGETS IN PD RADARS

Frequency

RandomlyChosenPulseTransmissionFrequencies

Hopping Range

FREQUENCY HOPPING RADARS

Frequency

PulseFrequencies

NoiseJammingFrequencyRange

LEAST JAMMED FREQUENCY COVERAGE

Frequency

PulseFrequencies

JammingFrequencies

BANDWIDTH MATCHED JAMMING

Frequency

PulseFrequencies

Noise SpreadAcross HoppingRange

JAMMING

SPREADING OF JAMMING SIGNAL

Time

Pulse Width

DRFM measuresFreq. and setsJamming Freq

JAMMING at HOP FREQUENCY

FOLLOWER JAMMING WITH DRFM

TIME

ER

P

TIME

FR

EQ

UE

NC

Y

CHIRPED PULSE

RADAR RESOLUTION CELL WITHOUT COMPRESSION RADAR RESOLUTION CELL

WITH LFMOP COMPRESSION

RESOLUTION CELL WITH CHIRP

COMPRESSIVEFILTER

Received Skin ReturnWith LFMOP

Chirp CompressedSkin Return PulseReceived

JammingPulse

w/o LFMOP

UncompressedJammer Pulse

CHIRPED PULSE PROCESSING

DSPDRFM

ADC

DAC

MEMORYLO

ANALYZEFREQUENCYHISTORY

GENERATERF SEGMENTS@ DIFFERENTFREQUENCIES

ARRANGE RFSEGMENTS TOMATCH RADARCHIRP

OUTPUT STEPPED FREQ SLOPE ON SUBSEQUENT PULSES

DRFM SIMUATION OF CHIRPED PULSE

OSCILLATOR

BINARY PHASE

MODULATOR

AMPLITUDEMODULATOR

POWERAMPLIFIER

ISOLATOR

RECEIVERFRONT END

TAPPEDDELAY LINEASSEMBLY

DETECTION& ANALYSIS

PSEUDO-RANDOM

CODE

RADAR WITH BARKER CODE

is180°Phase Shift

SUMMEDOUTPUT

INPUT

TAPPED DELAY LINE

180° Phase Shift

TIME

+ + + - - + -

PULSE DURATION

BITDURATION

INPUT TO TAPPED DELAY LINE

OUTPUT FROM TAPPED

DELAY LINE BITDURATION

BARKER CODE PROCESSING

3 dB beamwidthUNCOMPRESSEDRADAR RESOLUTIONCELL

HALF PULSE DURATION(x SPEED OF LIGHT)

1 ft/nsec

COMPRESSEDRADAR RESOLUTIONCELL

RESOLUTION CELL WITH BARKER CODE

Skin Return PulseWith MatchedBarker Code

TAPPEDDELAYLINE

Jamming Pulsewithout

Matched Barker Code

PROCESSINGWINDOW

BARKER CODE IMPACT ON JAMMING

DRFM PROCESSOR

RFPULSESFROM

RADAR

COHERENTRFJAMMING PULSESTORADAR

DigitizedRadarPulses

Determine bit duration and code from 1st pulse

Generate digital “one” & “zero” code bits

Assemble correct bitsto reproduce radar code

Modify pulse amplitude, frequency and timing for jamming modulation

DigitizedJamming

Pulses

DRFM HANDLING OF BARKER CODE

COMPLEX RCS

RADAR

TURN TABLE

RADIOABSORPTIVEMATERIAL

RADIOTRANSPARENTSUPPORT

TARGET

RCS MEASUREMENT IN CHAMBER

CONECONICALSECTION

CONICALSECTION

CURVEDPLATES

COMPLEXCURVEDSHAPE

INTERSECTIONOF TWO CURVEDSURFACES

CYLINDER

RCS COMPONENTS

Realistic Return Pulses

SIMPLE PULSE

REALISTIC RETURN PULSE

TARGET RETURNS

Modern RADAR may reject simple pulse

EXTRACTIMPORTANTFEATURES

RCS DATA

FROM CHAMBER ORCOMPUTER ANALYSIS

Feature 1 Phase, amplitude & position GENERATE

COMPOSITEDATA BASE

FOR ALL SIGNIFICANTFEATURES OF TARGET

COMPUTER MODEL OF TARGET

TOXMTR

DOPPLER MODULATORA/D MEMORY D/A

CONTROL


CONTROL


CONTROL

X

COMBINER

X

LO

FROMRCVR

COMPLEX RCS IN OLDER SYSTEMS

FROMRCVR

A/D

DOPPLERGENERATOR

MODULATOR RANGEDELAY

QUADRATUREGENERATION

COMBINER

DOPPLERGENERATOR


DOPPLERGENERATOR


DOPPLERGENERATOR


D/ATO

XMTR

SINGLE DRFM WITH FPGAs

DRFM Based Decoy

This is an expendable radar decoy (called Bright Star) from SELEX. It inclues multiple DRFMs.

An issue is that it is the size of a beer can and thus needs a specialDispenser

ReceivedWaveform

TransmittedWaveform

PulseWidth

Maximum ProcessLatency

TIMING OF PULSE CAPTURE

Pulse Width

Analysis Increments

ReceivedFrequencyModulation

TransmittedFrequencyModulation

DRFM CAPTURE OF CHIRP

Pulse Width

BPSK code clock

Transmitted BPSKModulation

On subsequent pulses

Received BPSKModulation

On first pulse

DRFM CAPTURE OF BARKER CODE

ReceivedWaveform

TransmittedWaveform

ProcessLatencyTime

Pulse Width

Rebroadcast Pulse Width

CAPTURE OF UNIQUE PULSES

Doppler Frequency Cells

Non-coherentJamming

signal

CoherentSkin

Return

COHERENT PULSE vs NON-COHERENT JAMMING

in PD RADAR

Radar Pulses

Radar tracks on leading edge

LEADING EDGE TRACKINGvs RGPO

DRFM captures frequency

Fre

qu

en

cy

Radar Pulse

JammerPulse


Radar Pulse

JammerPulse


Radar Pulse

JammerPulse

Time

DRFM CAPTURE of FREQUENCY HOPPED PULSES

DRFM captures PulseCompression modulation parameters

Radar pulses

Pulses have matched pulse compression modulation

Jammer Pulses

DRFM CAPTURE OF PC RADAR PULSES

Radar pulses

Jammer Pulses

PIPE-LINING DRFM OPERATION

Consider high-prf PD Radar

CURRENT DRFM SPECS

• Bandwidth – 1 to 2 GHz

• Number of bits – up to about 5

• Latency – less than 50 nsec.

ADC OVERSAMPLING

• The Problem– Need very high sampling rate for Bandwidth

– Need multiple Bits to Avoid Spurs

– ADCs trade off speed vs # of Bits

• The Solution Approaches– Tapped Delay Line

– Shift Registers with 1 bit Digitizers

Series-parallel Sampling

MUX

TAPPED DELAY LINE

Δt 2Δt 3Δt 4Δt

ADC ADC ADC ADC ADC

SIGNALIN

DIGITALOUTPUT

(Clock rate)

Clock/5

Digitizes at 5 x max ADC rate

1 bit DRFM• Hard Limit signal

• Really Fast (much faster than A/D Conv)

• Capture zero crossings

• Spurs a problem

• This captures the frequency of signal only

• Requires no A/D converter

Shift Register Series-parallel Conv.

HARDLIMITER

SHIFT REGISTER

SHIFT REGISTER

RANDOM ACCESS MEMORY

SIGNALIN

SIGNALOUT

WRITE

DELAYEDREAD

CLOCK

CLOCK/8

CLOCK

COMPUTER

Appendix

Extra SlidesHow to Use Slide Rule

Antenna & Propagation Calculator

Ant. Gain reduction vs surface

Fresnel Zone

2 Ray Attenuation

Antenna Calculations

Free Space Attenuation

Calculate dB

1 m = 3.3 ft 1ft = .3m

1

2

Antenna Amplitude Pattern



Fresnel Zone

2 Ray Attenuation



Calculate dB

1 m = 3.3 ft 1ft = .3m

Antenna Scales

Antenna Scales

Antenna Gain & Beamwidth

Set Antenna Diameter (in ft) at Frequency (in GHz)

Antenna Gain & Beamwidth (cont)

Read Boresight Gain at Efficiency

Note 55% efficiency for Narrow Bandwidth antennas


Read 3 dB Beamwidth at 3 dB line


Read 10 dB Beamwidth at 10 dB line

First Null

First Null and Sidelobe

FirstSidelobe

Gain reduction vs. Surface Tolerance

Frequency

Gain reduction vs Surface Tolerance

Gain Reduction

Frequency

Surface Tolerance

Gain Reduction

Free Space Attenuation from Formula

LS = 32.44 + 20 Log(d) + 20 Log(f)

LS = Spreading loss between isotropic antennas (in dB)d = distance in kmf = frequency in MHz32 is a fudge factor

Warning: This equation only works if exactly

the right units are input

Some Extra Information, not in book:

If Distance in kilometers: round 32.44 to 32 for 1 dB calculationsIf Distance in staturte miles: replace 32.44 with 36.52 (round to 37)

If Distance is in nautical miles: replace 32.44 with 37.74 (round to 38)

15



Fresnel Zone

2 Ray Attenuation



Calculate dB

sm = 1.6 kmnm = 1.15 sm

1

2

Front of Antenna/Propagation slide rule with line of sight attenuation scales highlighted

1

Free Space Attenuation from Slide Rule

Set Frequency


Read Attenuation at Range


Also notice short range scale (in meters)

Two Ray Attenuation

Also called: 40 Log d attenuationdistance4 attenuation

Determined from: FormulaNomographSlide Rule

Applicable when: One primary reflectorFrequency lowAntennas wide

Direct and Reflected Rays close to the ground

XMTR RCVR

GROUND

TransmitAntennaHeight

ReceiveAntennaHeight

16

Two Ray Attenuation from Formula

LS = 120 + 40 Log(d) - 20 Log(hT) - 20 Log(hR)

LS = Spreading loss between isotropic antennas (in dB)d = distance in kmhT = height of transmit antenna in metershR = height of receiving antenna in meters

Warning: This equation only works if exactly

the right units are input

Note:There is no frequency termMinimum antenna heights may apply

30 MHz over good soil 10 meters(to 3 meters at 60 MHz & 1 meter at 200 MHz)

Higher over salt waterUse higher of actual or minimum antenna height

16



Fresnel Zone

2 Ray Attenuation



Calculate dB

1

2

Back of slide rulewith two-ray calculation scales highlighted

2

Two Ray Attenuation from Slide Rule

Set Transmit antenna height at link distance

Two Ray Attenuation from Slide Rule

Read attenuation at receiving antenna height

Propagation mode vs. Fresnel zone distance

XMTR

RCVR

Fresnel Zone Distance

RCVR

13

Fresnel Zone Calculation

FZ = [hT x hR x F] / 24,000

Where: FZ = Fresnel Zone in kmhT = Transmit antenna height in metershR = Receiving antenna height in metersF = frequency in MHz

13



Fresnel Zone

2 Ray Attenuation



Calculate dB

1

2

Back of slide rule with Fresnel zone scales highlighted

2

Fresnel Zone from Slide Rule

Align transmit and receive antenna heights(both in meters)

Fresnel Zone from Slide Rule

Read Fresnel Zone (in km) at Frequency (in MHz)

digital radio frequency memories

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