Applying a Composite Pattern Scheme to Clutter Cancellation with the Airborne POLARIS Ice Sounder
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Applying a Composite Pattern Scheme to Clutter Cancellation with the Airborne POLARIS Ice Sounder Keith Morrison 1 , John Bennett 2 , Rolf Scheiber 3 [email protected] 1 Department of Informatics & Systems Engineering Cranfield University, Shrivenham, UK. 2 Private Consultant, UK. 3 Microwaves and Radar Institute German Aerospace Research Center , Wessling, Germany.
description
Applying a Composite Pattern Scheme to Clutter Cancellation with the Airborne POLARIS Ice Sounder Keith Morrison 1 , John Bennett 2 , Rolf Scheiber 3 [email protected] 1 Department of Informatics & Systems Engineering Cranfield University, Shrivenham , UK. - PowerPoint PPT Presentation
Transcript of Applying a Composite Pattern Scheme to Clutter Cancellation with the Airborne POLARIS Ice Sounder
Applying a Composite Pattern Scheme to Clutter Cancellation with the Airborne POLARIS Ice
Sounder
Keith Morrison1, John Bennett2, Rolf Scheiber3
1Department of Informatics & Systems EngineeringCranfield University, Shrivenham, UK.
2Private Consultant, UK.
3Microwaves and Radar InstituteGerman Aerospace Research Center , Wessling, Germany.
COLLABORATORS
Matteo Nannini - DLR Pau Prats - DLR Michelangelo Villano - DLR Hugh Corr - BAS
ESA-ESTEC Contract: 104671/11/NL/CT Nico Gebert Chung-Chi Lin Florence Heliere
PRESENTATION
• Problem• Composite Pattern
- convolution - array polynomial
• Application• Results
H
dhr
ice
bedrock
air
RR
z
POLARIS
PROBLEM
Geometric alignment and dimensions of the 4 independent receive apertures of the POLARIS antenna
ANTENNA ARRAY
Test-ID Bandwidth
[MHz]
Remarks
p110219_m155222_jsew1
85 & 30 MHz From east: grounded ice, then crossing the glacier tongue, frozen grounded ice in the
middle, ice shelf in the westp110219_m155222_jswe1 85 & 30 MHzp110219_m155222_jsns1 85 & 30 MHz cross-track slopes with
grounded icep110219_m180339_jsns2 85 & 6 MHz profile along the glacier
tongue
ICEGRAV 2011
PROCESSING SCHEME
Rx Pattern
Rx Array & Element Pattern
• Phased-array nulling traditionally optimizes performance by utilising available array elements to steer a single null in the required direction.
• However, here we exploit the principle of pattern multiplication.
• With different element excitations, nulls in differing angular directions are generated.
• Composite array is produced by the convolution of two sub-arrays.
• The angular response of the composite array is the product of those generated by the individual sub-arrays.
COMPOSITE ARRAY
CONVOLUTIONThe building block is the 2-element array.
To generate a null at angle θA the excitation of the array is required to be:
Similarly to generate a null at angle θB the excitation of the array is required to be:
1.0
1.0
3-ELEMENT : 2-Null
To preserve these nulls we must generate the product of the two patterns and this is achieved by convolving the two distributions to give the following 3-element distribution:
1 a+b ab
where: a = -exp[jkdsinϴA] b = -exp[jkdsinϴB]
4-ELEMENT : 2-Null
1 a b0 ab0
where: a = -exp[jkdsinϴA] b = -exp[jkdsinϴB] b0=-exp[jk2dsinϴB]
4-ELEMENT : 3-Null
To generate a third null at angle, θC, requires convolution of the result from the 3-element, 2-null case with an additional 2-element array, with the distribution:
1.0
SIMULATIONWavelengthRange bandwidth Noise powerChirp duration Clutter
attenuationRange sampling frequency
150m
300m
500m
0m
700m
1000m
H=3000m
COMPOSITE – 3 NULL
Double-null with 2° separation centred at left-hand clutter angle
COMPOSITE – 2 NULL
-75
-50
-25
0
25
-2000 -1500 -1000 -500 0
Ground height [m]
Am
plitu
de [d
B]
• This is done using Schelkunoff scheme.
• Array excitation represented by the array polynomial and its representation as zeros on the unit circle.
• Computationally straightforward because there are only three zeros for the four element array.
ARRAY POLYNOMIAL
Array factor:
dkdjnCFN
nn
cosexp0
If substitute (where αd is a linear phase term to account for beam steering)
dkdjz cosexp
nN
nn zCF
0
then
θ
Factorizing
NN zzzzzzCF .......21
For the 4-element case factorizes to (z-a) (z-b) (z-c)Providing coefficients 1, -(a+b+c), (ab+ac+bc), (-abc)
ARRAY POLY. – ALT. 3-NULL
• Ensured maximum amplitude contribution from this zero in the nadir direction.
• Remaining two zeros were used to position the pair of nulls at the clutter angles.
-75
-50
-25
0
25
-1000 -500 0
Ground height [m]
Ampl
itude
[dB]
0
2
4
6
8
-2000 -1500 -1000 -500 0
Three null approachTwo element composite array designTwo null with constrained third zero
Ground height [m]
Ampl
itude
NADIR RESPONSE
-75
-50
-25
0
25
-1000 -500 0
Ground height [m]
Am
plitu
de [d
B]
-75
-50
-25
0
25
-1000 -500 0
Ground height [m]
Ampl
itude
[dB]
-75
-50
-25
0
25
-2000 -1500 -1000 -500 0
Ground height [m]
Ampl
itude
[dB]
FINAL RECOMMEDATION
1 a + b + 1 ab + (a+b) ab
h𝑤 𝑒𝑟𝑒 a=−𝑒𝑥𝑝 [ 𝑗𝑘𝑑𝑠𝑖𝑛𝜃 𝐴 ]b
c
a+b+1
RESULTS
COUNTERACTING NADIR NULLS
0
2
4
6
8
-2000 -1500 -1000 -500 0
Zeros on unit circleZeros gradually leave unit ciclefor angles greater than 1.75
Ground height (m)
Am
plitu
de
Two null with constrained third zero
-75
-50
-25
0
25
-1500 -1000 -500 0
Ground height (m)
Am
plitu
de (d
B)
-75
-50
-25
0
25
-1500 -1000 -500 0
Ground height (m)
Am
plitu
de (d
B)
• Considered two and three-nulling scenarios using convolution.
• “Best Result” obtained from a modified 3-null approach:» Array Polynomial: third null located 180° on the unit circle.
• Nadir null can be avoided by allowing points to move off the unit circle.
CONCLUSIONS
