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