fit 2011

Reconfigurable Reflectarray Antennas: An

Alternative Novel Solutions for Satellite

Communication SystemsM. Y. Ismail, M. H. Dahri, M. I. Abbasi, N.H.

Sulaiman, A.F. M. Zain

Head of Wireless and Radio Science Center (WARAS),Universiti Tun Hussein Onn Malaysia, Johor, Malaysia

9th International Conference on Frontiers of Information Technology (FIT 2011), Islamabad, Pakistan.

Outline of Presentation Introduction to Reflectarrays Material Properties Motivations Objectives Research Methodology Results and Discussions

Isotropic and AnisotropiMaterials Tunability Performance of Reflectarray Cells

Conclusions Future Works

9th International Conference on Frontiers of Information Technology FIT 2011), Islamabad, Pakistan.

Introduction to Reflectarrays


Principle of Operation

Microstrip Patch element

Dielectric Substrate Planar

WavefrontGround Plane

Figure 2: Reflectarray operation

Reflectarray consists of array of microstrip patches. Printed on thin dielectric substrate backed by a ground plane illuminated by a feed. The individual elements of the array are designed to scatter the incident field with a

proper phase required to form a planner phase surface in front of the aperture.

Figure 1: Parabolic reflector

Curved Reflecting Surface

Planar Wavefront

Feed HornFeed Horn


Remote Sensing Satellites (Earth Observation)

Earth is the most interesting planet in the Solar System. Its diverse weather and atmospheric systems allow a multitude of lifeto thrive differently Microwave instruments are used for;

•Weather prediction•Atmospheric chemistry studies•Crop studies, deforestation detection•Observation of natural/man-made disasters

MeteoSat 2 image

Hurricane Katrina over Florida

Depletion of the ozone layer

Advantages and Disadvantages

There are some significant advantages of microstrip reflectarrays: Lighter weight and smaller volume Easily deployable because of flat structure Lower cost Scannable beam Integratable with solar arrays Good efficiency as a large array antenna

Following are some distinct disadvantages of reflectarray antennas: Narrower bandwidth with limited phase range Higher losses


Applications

Potential applications of reflectarray antenna are in the following fields: Mobile communication systems Direct Broadcast Satellite (DBS) systems High gain satellite antennas Radar and defense systems

Mobile Communications DBS

Satellite Communications

Defense Systems


Material Properties


Dielectric Isotropic Materials

The materials that does not change their properties. Dielectric isotropic materials have linear dielectric properties. Their dielectric permittivity “ε” has a constant value.

Table 1: Different dielectric isotropic materials

Material Dielectric Constant Tangent Loss

Teflon 2.1 0.0002

Mica 5 0.0003

Alumina 99.5% 9.5 0.0003

Silicon 11.9 0.005

GaAs 12.94 0.006


Dielectric Anisotropic Materials

Dielectric anisotropic materials have non-linear dielectric properties where dielectric permittivity ε can attain a range of values.

Difference between maximum and minimum values of ε is called dielectric anisotropy of the material.

Δ = ║ -

These values are considered according to the alignment of molecules of the material with respect to incident electric field.

Figure 3: Perpendicular and parallel alignment of molecules of anisotropic material with respect to incident

electric field

Electric Field

Materials ε┴ ε║ Dielectric Anisotropy (∆ε)

K-15 Nematic 2.1 2.27 0.17

BL006 2.2 2.38 0.18

BL037 2.25 2.45 0.2

ABS 2.9 3.4 0.5

LC-B1 2.6 3.05 0.45

Table 2: Different dielectric anisotropic materials


Motivations


1. Parabolic antenna requires mechanical movement for beam scanning.

2. A change in electrical behavior could also vary the static and dynamic phase distributions of reflectarrays.

3. A new design of electronically tunable reflectarray antenna has been proposed by employing dielectric anisotropic properties of materials.


Objectives


1. To design a reflectarray antenna based on dielectric anisotropic properties of materials.

2. To investigate the feasibility of realizing a reconfigurable antenna system electronically based on tunability capability.

3. To demonstrate the functionality of an active reflectarray antenna for beam shaping antenna


Passive and Active Antennas

Figure 4: (a) Parabolic antenna (b) Active reflectarray antenna

Anisotropic Material

(a) Mechanical movement (b) Electronic tunability

0 v + v

DC voltage source


Research Methodology


Start of work

Investigation of Material Properties

CST simulations based on Tunabilty

Design of an Algorithm based on MoM Measurements based on

Network Analyzer

Comparison of measured results

with validated results?

End of Work

Yes

Literature Studies and Validation work

Dynamic Phase Range validation

from Simulations?

Algorithm validation and comparison with

simulations?

Fabrication of Antenna

No

No

YesYes

No


Design Considerations

A rectangular patch reflectarray element has been designed in the frequency range of 2 to 20 GHz using commercially available CST MWS computer model.

Printed on 1mm thick different isotropic and anisotropic materials, resonating at 10 GHz.

Series of simulations based on passive and active reflectarray elements have been carried out to observe the performance of reflection loss and phase range with respect to the electrical properties.


Design of Reflectarray unit cell in CST MWS

Port excitation distance (λg/4)

Magnetic (Ht=0) Boundaries

Electric (Et=0) Boundaries

Figure 5: Design of reflectarray unit cell in CST MWS with (a) Proper port excitation distance and (b) Proper boundary conditions


Results and Discussions for Isotropic Materials


Electrical Behavior at ResonantFrequency

An incident electric field over a reflectarray element generates current density and electric flux density.

These fields are maximum at the resonant frequency because at that level the reflectivity of a reflectarray is maximum.

Figure 6: Electric field intensity and reflection loss with respect to frequency

1000

10000

100000

1000000

10000000

2 4 6 8 10 12 14 16 18 20

Frequency (GHz)

Ele

ctr

ic In

ten

sit

y[l

og

] (V

/m)

-14

-12

-10

-8

-6

-4

-2

0

Re

fle

cti

on

Lo

ss

(d

B)

Teflon

Mica

Alumina

Silicon

GaAs

TeflonLossMica Loss

AluminaLossSiliconLossGaAs Loss


Static Phase Range Analysis The range at which reflection phase curve shows linearity is called static phase

range. A higher value of electric flux density causes more multiple bounces of incident

energy in the substrate region. Therefore more dissipation in the dielectric layer occurs which causes degradation in

the reflectivity and an improvement in the phase range.

MaterialDielectric Constant

Electric Flux Density (C/m2)

Static Phase

Range (°)

Teflon 2.1 116197 128

Mica 5 909605 153

Alumina 99.5%

9.5 1310800 165

Silicon 11.9 3079184 167

GaAs 12.94 8101772 18510000

100000

1000000

10000000

2 4 6 8 10 12

Dielectric Constant

Ele

ctr

ic F

lux

De

ns

ity

(C

/m^

2)

120

130

140

150

160

170

180

190

Sta

tic

Ph

as

e R

an

ge

(D

eg

ree

)

Table 4: Electric flux density at 10 GHz and static phase ranges of isotropic materials

Figure 8: Relation with dielectric constant


Dynamic Phase Range Analysis

Dynamic phase range can be an efficient measure for the realization of frequency tunability of reflectarray antennas.

For dielectric anisotropic materials dynamic phase range can be obtained as;

Δ = (║) - ()

Figure 12: Dynamic phase range of anisotropic materials

Δ Range (║)

()


Tunability Performance

Anisotropic materials have frequency tunability characteristics.

Because of dielectric anisotropy every anisotropic material holds a range of reflection loss values.

Dielectric permittivity of an anisotropic material can be changed by simply applying a DC voltage across it.

0 v + v ║

Dielectric Permittivity

DC voltage source

Anisotropic Material

Electric Field

Figure 10: Alignment of molecules of anisotropic material in presence of a DC voltage source

Reflection Loss (dB)

Reflection Phase(°)

Frequency (GHz)


Reflection Phase Analysis

An algorithm based on Method of Moments for obtaining the required reflection phase from the individual elements of reflectarray has been developed.

In the absence of a microstrip patch element,the resulting electric field will be:

And in presence of microstrip patch elements,the resulting electric field will be:

Where, is the total electric field vector, is the incident electric field, is the electric field vector for ground plane reflection and is the scattered electric field by the patch elements.

tot inc refE E E

tot inc ref scatE E E E totE

incE refE

scatE


Algorithm of Phase Distribution

The phase for individual reflectarray elements has to be determined in order to obtain a plane wavefront

Due to the limited bandwidth performance the effect of differential patch length has to be taken into account.


Algorithm of Phase Distribution

The required phase distribution across the periodic reflectarray antenna can be calculated by employing trigonometric ratios.

1

1

tan ;....... 0

tan ;....... 0

p

l

ie

p

r

ie

dk n

nd

dk n

nd

Where:

dp is the port distance

die is the distance between two consecutive elements kr and kl are angle in degrees for the patch elements on right and left of the central patch


EXPERIMENTAL SET UP


X –Band Experimental WorkSyringe filling

5KHz Triangle Wave10V peak to peak

Mounting structuresSyringe


Waveguide Simulator

Adapter

Functiongenerator

Network Analyzer

Fig. 9: Scattering parameter measurement set up


X –Band Experimental Work

Results and Discussions for Anisotropic Materials


Electrical Behavior at ResonantFrequency

Due to dielectric anisotropic nature of anisotropic material it generates ranges of current density and electric flux density.

It is because anisotropic materials contain a range of dielectric permittivity values. These fields are maximum at the resonant frequency.

Figure 11: Current density Vs frequency for different anisotropic materials

0

500

1000

1500

2000

2500

3000

3500

2 4 6 8 10 12 14 16 18 20

Frequency (GHz)

Cu

rren

t Den

sity

(A/m

^2)

ABS

K-15

BL006

BL037

LC-B1


Experimental & Simulated Results

Fig. 13: Measured and simulated performance of periodic cell using K15 and BL006 TLC = 500 μm TS = 125 μm

Ts = 125 um

LC Mixtures

(a) (b)


LC MIXTURES

Fig.14 : Measured and simulated performance of periodic cell using K15 and BL037 TLC = 200 μm TS = 250 μm

(a) (b)

Experimental & Simulated Results


Performance Comparison

Performance Parameter

Planar Reflector)Proposed

Product(

Parabolic Reflector

)Existing Product(

Phased Array (Existing Product)

GainHigh

35 dBHigh

30-40 dBHigh

30-40 dB

BandwidthModerate

<15%High

<40%Moderate

<25%

Beam SteeringElectronicFast, 360°

MechanicalSlow, <360°

ElectronicFast, 360°

CostRM 25000

)Low(RM50,000

)Moderate (RM100,000

)High(

DesignComplexity

Low High High

StructureLight weight ,

PlanarBulky,

ParaboloidComplex,Planar


Conclusions


Reflection loss and phase range of reflectarray can be optimized by the selection of a proper dielectric material.

Dielectric anisotropy of anisotropic materials are shown to offer rapid dynamic phase change behavior for designing a tunable reflectarray antenna.

Different electrical properties including electric flux density are shown to be a crucial factor to achieve an enhanced phase characteristics.

Anisotropic materials are used to design an active reflectarray antenna system where dynamic phase range and electronic frequency tunability is required.


Future Works


Complete Reflectarrays

Based on the measured and simulated results, complete reflectarrays with different slot configurations have been proposed for performance improvement.

Fabricated 16 X 16 reflectarray using slots and results showing better bandwidth performance as compared to variable patch reflectarray


Radiation Pattern Measurements


Recommendations for Future Work The proposed slot configurations can be used for the design of active and

tunable reflectarray antennas if a set of electronic switches can be used to control the slot dimensions.

Electronic tuning of reflectarrays can also be employed for monopulse reflectarray antenna and phase agility of reconfigurable reflectarrays.

The investigations carried out can be useful for designing planar microwave absorbers for radar cross section reduction.

A long-range radar antenna known as ALTAIR Phased arrays used for radar applications Microwave absorber (Salisbury screen)


References Harish Rajagopalan and Yahya Rahmat-Samii “On the Reflection Characteristics

of a Reflectarray elementwith low loss and high loss substrates” IEEE Antennas and Propagation Magazine, Vol. 52, No. 4, August 2010 pp. 73- 89.

M. Y. Ismail, M. Inam and A. M. A. Zaidi (2010). “Reflectivity of Reflectarrays based on dielectric substrates” American J. of Engineering and applied Sciences 3 (1): ISSN 1941-7020, 2010, pp. 180-185.

Alexander Moessinger, Carsten Fritzsch, Saygin Bildik, Rolf Jakoby “Compact Tunable Ka-Band Phase Shifter based on Liquid Crystals” Microwave Symposium Digest (MTT), 2010 IEEE MTT-S International.

M.Y. Ismail and R. Cahill (2005). “Beam Steering Reflectarrays Using Liquid Crystal Substrate” Tenth IEEE High Frequency Postgraduate Student Colloquium, University of Leeds, pp. 62-65.

M.Y. Ismail, W. Hu, R. Cahill, V.F. Fusco, H.S. Gamble, D. Linton, R. Dickie, S.P. Rea and N. Grant “Phase agile reflectarray cells based on liquid crystals” IET Microw. Antennas Propag., 2007, 1, (4), pp. 809–814.


Acknowledgements

This work is carried out at Wireless and Radio Science Center (WARAS) UTHM and is fully funded by Fundamental Research Grant Scheme (FRGS) (VOT 0718) and Prototype Research Grant Scheme (PRGS) awarded by the Ministry of Higher Education Malaysia.


AchievementsResearch Awards

1. “Multi-Function Tunable Broadband Flat Antenna”, Gold Medal and Special Diamond Medal Award for the category “International Invention Of the year” at British Invention Show (BIS 2011), Old Spita lfields, London, United Kingdom, October 2011.

2. “Multi-function Dynamic Steerable Flat Antenna”, Gold Medal at International Conference and Exposition on Invention of institutions of Higher Learning (PECIPTA 2011), September 2011, Kuala Lumpur, Malaysia.

3. “Novel Broadband Planar Reflector for Terrestrial Systems” Silver Medal at 22nd International Invention, Innovation & Technology Exhibition (ITEX 2011), May 2011, Kuala Lumpur, Malaysia.

4. “Novel Reflectarray Antenna Design with Combined Variable Slot Configurations”. Gold Medal at 10th Malaysia Technology Expo (MTE 2011), The Invention and Innovation Awards, February 2011, Kuala Lumpur, Malaysia.

Invited Talks

1. M. Y. Ismail, M. Inam, M. H. Dahri, “Performance Optimization of Reconfigurable Reflectarray Antennas”. The 28th International Review of Progress in Applied Computational Electromagnetics (ACES 2012) April 2012, Columbus, Ohio, U.S.A.

2. M. Y. Ismail, M. Inam, A. F. M. Zain and M. A. Mughal, “Phase Agility of Reflectarray Antennas”. 2011 IEEE International Symposium on Antennas and Propagation (APS) and USNC/URSI National Radio Science Meeting, July 2011, Washington, U.S.A.


WARAS at a Glance


Thank You


fit 2011

Documents

dielectric permittivity

tunable reflectarray

dbs material properties

active reflectarray

reflectarray operation

parabolic antenna

atmospheric systems

incident field