design of a concept planar array for the biomass space mission
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Design of a concept Planar Array for
the Biomass Space Mission
Relatore:Prof. Gaetano Marrocco
Guido Casati
Correlatore:Ing. Marco Sabbadini
BIOMASS Mission
Earth Explorer 7 Mission
Biomass Mapping
Enhancement of carbon cycle model
P-band (435 MHz)
SAR quad-POL (HH, VV, VH, HV)
External calibration through active ground Transponder
Operating Frequency: 435 MHz (λ=69 cm) Dual-Pol
Bandwidth: 10 MHz (2.3 %)
About 4 m diameter to get required RCS
High Directivity: ~25 dBi Broadside
Very low Back-Radiation and Side Lobe levels: SL< -45
dB
Negligible Cross-Talk: XPD > 40 dB
Calibration Transponder Requirements of a concept Planar Array
Solution: Planar ArrayGeometry:
HexagonalSpacing: 0.48 m
Illumination law: Tukey
Process Flow
Prototyping:Measurements
Advanced array:Enhancement of the radiating element
Enhancement of the array design
Preliminary DesignDesign and assessment of the radiating
elementPerformance of different array layouts
61 dual polarised Sub-Array
4 linearly polarised elements per Sub-Array
244 linearly polarised radiating elements
7 excitation levels, 26 dB dynamic range
Preliminary Design
Central area:Uniform
Illumination
Tukey Illumination Law 5% tapering
fo = 435 MHz
L = λo\4
Do = 3 dBi
B(Γ=-10dB) = 4.5 %
Preliminary design: PIFAPlanar Inverted-F Antenna
ADF-EMS/3DAM
hL
z
yx
PEC
w
Preliminary design: PIFAsub-array
ADF-EMS/3DAM
L=166 mm, W=172 mm h = 20 mm
Preliminary design: Array
Spacing: 535 mm (~480mm)
Diameter: >5m (~4 m)
SL < -40 dB at the horizon (<-45dB)
XPD > 25 dB (>40dB)
SL SL
Improvement of performance
Critical points:
Radiation Pattern
Coupling among active and passive elements
Spacing
Array size
Solution:
Reduce the volume of the Radiating Element
Advanced Design: Folded PIFA
λ/8λ/4
from “Development and Analysis of a Folded Shorted-Patch Antenna With Reduced Size”
di M. M. Tentzeris
Do = 4 dBi
Advanced Design: Folded PIFA
L = W = 86 mm, h = 22 mm
Lg = Wg = 220 mm
Inductive Zin (Xin>0)
Γ = -17 dB
B(Γ=-10dB) = 6.5 MHz (1.5 %)
Tukey Illumination Law with 5% tapering
Spacing: 480 mm
Diameter of Sub-array: 330 mm
Overall Diameter: 4.16 m (~4 m)
Advanced Design: Array
x
y
SL < - 45 dB ( < 45 dB )
XPD > 45 dB ( > 40 dB )
Do = 23 dBi
BW3db = 13°
B(Γ = -20 dB)= 3 MHz
Advanced Design: ArrayV-POL
H-POL
91 sub-array (364 radiating elements)
Diameter: 5 m (~4 m)
Tukey Illumination Law with2.5 % tapering (9 levels, DR=32 dB)
Do = 25 dBi
SL < -55 dB (<-45 dB)
XPD > 50 dB (>40 dB)
Optimisations: 5 Rings Array
Optimisations: spacing
d=440 mm d=480 mm
θ=90°
Optimum for d=440 mm
Analytically:
Copper patch (height 0.25 mm)
Copper ground plane filled with duroid (height 2 mm)
Copper pin (diameter 2 mm) welded to SMA connector
Prototyping
ESTEC's CATR: 4 – 110 GHz 300 – 500 MHz, 250 KHz step Γ = -13 dB a f = 411 MHz StarLab: Γ = -19 dB a f = 417.5 MHz B(Γ = -10 dB) = 7 MHz
Measurements: Return Loss
IFFT Filtering FFT
Sensitivity analysisTilt angle
High sensitivity to small changes of the tilt angle of the patches
+-
+-
Lower patch
Upper patch
MVI's StarLab: 800 MHz - 18 GHz NF / FF method Do = 4.3 dBi, Go = 3.9 dB (e=98.7%) BW = 120° (H-cut) / 110° (E-cut)
Measurements: radiation pattern
Directivity
H-Cut E-Cut
Outcome: Design of a Planar Array that meet the requirements. Data about several assessed layouts Design and prototype of a miniaturised radiating
element
Critical points: Sensitivity of the radiating element Bandwidth Complexity of the feeding network
Evolution: Array-Metasurface solution
Conclusions
THANK YOU FOR YOUR ATTENTION.
Info: Guido.casati89 [at] gmail.com
Q&A
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