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Digital Radio Frequency Memories
Transcript of 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
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
Time
Pulse Width
DRFM measuresFreq. and setsJamming Freq
JAMMING at HOP FREQUENCY
FOLLOWER JAMMING WITH DRFM
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
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
DOPPLER MODULATORA/D MEMORY D/A
CONTROL
DOPPLER MODULATORA/D MEMORY D/A
CONTROL
X
COMBINER
X
LO
FROMRCVR
COMPLEX RCS IN OLDER SYSTEMS
FROMRCVR
A/D
DOPPLERGENERATOR
MODULATOR RANGEDELAY
QUADRATUREGENERATION
COMBINER
DOPPLERGENERATOR
MODULATOR RANGEDELAY
DOPPLERGENERATOR
MODULATOR RANGEDELAY
DOPPLERGENERATOR
MODULATOR RANGEDELAY
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
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
DRFM captures frequency
Fre
qu
en
cy
Radar Pulse
JammerPulse
DRFM captures frequency
Radar Pulse
JammerPulse
DRFM captures frequency
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
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
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 & 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
Antenna Gain & Beamwidth (cont)
Read Boresight Gain at Efficiency
Note 55% efficiency for Narrow Bandwidth antennas
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)
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Antenna & Propagation Calculator
Ant. Gain reduction vs surface
Fresnel Zone
2 Ray Attenuation
Antenna Calculations
Free Space Attenuation
Calculate dB
sm = 1.6 kmnm = 1.15 sm
1
2
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
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Antenna & Propagation Calculator
Ant. Gain reduction vs surface
Fresnel Zone
2 Ray Attenuation
Antenna Calculations
Free Space Attenuation
Calculate dB
1
2
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
Antenna & Propagation Calculator
Ant. Gain reduction vs surface
Fresnel Zone
2 Ray Attenuation
Antenna Calculations
Free Space Attenuation
Calculate dB
1
2