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Francesco Alessio Dicandia, Simone Genovesi, Agostino Monorchio

Characteristic Modes Analysis for Pattern Shaping of Handheld Platforms

Forum for Electromagnetic Research Methods and Application Technologies (FERMAT)


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Abstract

The effects of introducing a phase–shift in the characteristic modes (CMs) of arectangular conductive plane have been investigated. More in detail, a carefulcharacteristic modes analysis (CMA) has been carried out in the aforementionedconditions to verify the possibility of significantly altering the shape of theoverall radiated pattern. Among all the CMs, only two radiating modes (Jn) havebeen selected to achieve a pattern-reconfiguration ability. In particular, by aweighting linear superposition of only these two radiating modes over theconductive sheet, it is possible to realize a null-steering antenna in a principalplane. As proof of concept, a prototype of the proposed antenna has beenrealized and measured. The obtained results present a good agreement with thesimulations and prove that the proposed design guidelines are reliable and alsoapplicable to other kinds of structures.

Key Words: Characteristic Modes; pattern reconfigurable; null-steering.


Biography

Francesco Alessio Dicandia received the Bachelor’s and Master’s degrees intelecommunications engineering from the University of Pisa, Pisa, Italy, in 2012 and 2014,respectively, where he is currently pursuing the Ph.D. degree. His current research interestsinclude reconfigurable antennas, multiple-input and multiple-output antennas, non-Fostermatching network, and characteristic modes analysis.

Simone Genovesi is an Assistant Professor at University of Pisa. From 2004 to 2006 he hasbeen a research associate at the ISTI institute of the National Research Council of Italy (ISTI-CNR) in Pisa. Current research topics focus on metamaterials, radio frequency identification(RFID) systems, optimization algorithms and reconfigurable antennas. He was the recipientof a grant from the Massachusetts Institute of Technology in the framework of the MITInternational Science and Technology Initiatives (MISTI).

Agostino Monorchio is a Professor at the University of Pisa and IEEE Fellow. He is active in anumber of areas including computational electromagnetics, microwave metamaterials,radio propagation and wireless systems, design and miniaturization of antennas andelectromagnetic compatibility, biomedical microwaves applications.The activity is mainly carried out at the Microwave and Radiation Laboratory(www.mrlab.it) of the Dept. of Information Engineering, University of Pisa, Italy. Hisresearch results have been published in more than 120 journal papers and book chapters,and more than 250 communications at international and national conferences.


Outline

Characteristic Modes Theory (CMT)

Null-Steering Antenna design by exploiting phase-shiftedCharacteristic Modes

CMA of the antenna Feeding network Prototype and comparison between simulations and

measurements

Conclusions and future activities



• Characteristic Modes Theory (CMT) represents a powerful electromagnetic toolwhich gives useful information about the radiative characteristics of theinvestigated structure. They are obtained by solving the eigenvalue equation:

n n nX J R J

o n Eigenvalueso Jn Eigenvectors (nth Characteristic Modes)

* *

* *

* *

1 1,

2 2

1 1,

2 2

1 1, 1

2 2

m n m n mn

S

m n m n n mn

S

m n m n n mn

S

J RJ J RJ ds

J XJ J XJ ds

J ZJ J ZJ ds j

• The orthogonality properties of characteristic modes can be summarized as:



• Characteristic Modes Theory (CMT) allows obtaining a physical interpretation ofthe radiation phenomena. According to the CMT, the total current distributionover the antenna (Jtot) can be decomposed as a weighted linear superposition ofinfinite current modes (Jn):

1 1

i in n

tot n n tot n n

n n n

E J ds VJ J J J J

j j

Modal Weighting Coefficient (MWC)

• The magnitude, phase, the position and the kind of the external exciters (Ei)affect the modes excitation degree (n) over the structure.

Modal Excitation Coefficient (MEC)

, 1

1

i i

n n

i

n n

V E J ds

V MSMS

j

External Source


CM of a Ship (Example)

Mode 1 Mode 2 Mode 3


44.6 mf = 6 MHz

• First six Current Modes distribution (Jn) of a ship.


CM of a Ship (Example)



44.6 mf = 6 MHz

• First six Current Modes distribution (Jn) of a ship.



• The usefulness of the CMT has been highlighted in different kind of antenna andapplications.

H. Li, Z. T. Miers, and B. K. Lau, “Design ofOrthogonal MIMO Handset Antennas Based onCharacteristic Mode Manipulation at FrequencyBands Below 1 GHz,” IEEE Transactions onAntennas and Propagation, vol. 62, no. 5, pp.2756–2766, May 2014.

D. Manteuffel and R. Martens, “Compact MultimodeMultielement Antenna for Indoor UWB Massive MIMO,” IEEETransactions on Antennas and Propagation, vol. 64, no. 7, pp.2689–2697, Jul. 2016.

T.-Y. Shih and N. Behdad, “Bandwidth Enhancement of Platform-Mounted HF Antennas Using theCharacteristic Mode Theory,” IEEE Transactions on Antennas and Propagation, vol. 64, no. 7, pp.2648–2659, Jul. 2016.

MIMO

Massive MIMO

Complex Platform

• These attractive features of the CM can be also useful in terms of the designs ofreconfigurable antenna systems.


Design Guidelines for Pattern Control

I. Evaluate the Characteristic Modes and their related radiationpatterns of the investigated platform,

II. Select the radiation patterns of the current-modes (Jn) that, onceoverlapped, satisfy the desired requirement,

III. Find the optimum feeding position and the kind of the exciters inorder to efficiently excite these desired Characteristic Modes,

IV. Introduce a phase difference between the sources in order toasymmetrically excite the modes and realize the phase-shiftedCharacteristic Modes to generate a pattern reconfigurable antenna.


Null-Steering Antenna Design

• Goal: Pattern Reconfigurable antenna by exploiting the CMT.

L = 150 mmW = 75 mm

(2.45 GHz)

• Characteristic Modes of a rectangular conductive plane.



Mode 4

Mode 8

• Two current modes (Jn) that we want excite to realize a pattern reconfigurableantenna.

Capacitive Coupling Exciter (CCE)



-180

-150

-120

-90

-60

-30

0

30

60

90

120

150

180

1 2 3 4 5 6 7 8 9 10

CCE-1 Only

CCE-2 Only

MW

C P

ha

se

(d

eg

.)

Mode #

71.58°

-108.42°

180°

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1 2 3 4 5 6 7 8 9 10

CCE-1 Only

CCE-2 Only

MW

C A

mp

litu

de

Mode #

• Modal Weighting Coefficient (MWC) when the exciters (CCE) are individuallyexcited.

1 1

K Nk

tot n n n n

n k n

J J J

K = number of ExcitersN = number of Excited Modes


Asymmetric Excitation Concept

8

2 2

4

1 1

1 1

4 81 1

tot

K Nk

n n

k n

j jJ e J e JJ

• By introducing a phase difference () between the exciters, the total currentdistribution (Jtot) becomes:

,4 4 8 8

2 2

4 8

1 1

4 82 2

2 cos 2 sini i

totJ J Je e



0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1 2 3 4 5 6 7 8 9 10

0°

30°

60°

90°

120°

150°

180°

MW

C (

n)

Mode #

Modes Correlation r

2 2

4 8

1 1

4 82 2

2 cos 2 sini i

totJ J Je e




Simulated Pattern (y-z plane)

2 2

4 8

1 1

4 82 2

2 cos 2 sini i

totJ J Je e


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1 2 3 4 5 6 7 8 9 10

0°

30°

60°

90°

120°

150°

180°

MW

C (

n)

Mode #


Power Balance

• Due to the orthogonality of the modes (Jn), the total radiated power is the sumof the power of each mode:

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 30 60 90 120 150 180

Mode 4 (Theory)

Mode 8 (Theory)

Mode 4

Mode 8

Pe

rcen

tag

e P

ow

er

Ex

cit

ati

on

Delta-Phase (deg.)

*

2 22*

0 0 0

1 1 1, 1,2,...,

2 2 2m m n n n n n

m n n nS S S

P E E ds E E ds E ds n NZ Z Z

1

2 2

4 8

1 1

4 82 2

2 cos 2 sini i

totJ J Je e



0

30

60

90

120

150

180

• Total current distribution (Jtot) over the antenna as a function of the phasedifference ().

Mode 4

Mode 8


Feeding Network

Diodo: BAR 50-02V

Anode Cathode

Inductance (L)

L = 33uH

• Model: 495-1836-1-ND• Dim: 1.6x0.8 mm

Resistance (R)

R = 500Ω

• Model: 541-1905-2-ND• Dim: 1.07x0.56 mm

• Discrete Phase-Shifter implemented by using several PIN diodes to generate thephase-difference between the CCEs.


Feeding Network

Anode Cathode

• Discrete Phase-Shifter implemented by using several PIN diodes to generate thephase-difference between the CCEs.

0

30

60

90

120

150

180

210

2.3 2.35 2.4 2.45 2.5 2.55 2.6

30° (Sim.)

60° (Sim.)

90° (Sim.)

120° (Sim.)

150° (Sim.)

180° (Sim.)

30° (Meas.)

60° (Meas.)

90° (Meas.)

120° (Meas.)

150° (Meas.)

180° (Meas.)P

ha

se d

iffe

re

nce

(d

eg

)

Frequency (GHz)

Diodo: BAR 50-02V


Feeding Network

Wilkinson Power Divider

Discrete phase-shifter

/4 transformer

-10

-9.5

-9

-8.5

-8

-7.5

-7

-6.5

-6

2 2.1 2.2 2.3 2.4 2.5 2.6 2.7

0°

30°

60°

90°

120°

150°

180°

0° (Sim.)

180° (Sim.)

Sij (

dB

)

Frequency (GHz)

• Complete feeding network located below the grounded substrate dielectric layer.


Prototype

Top View

Side View

Feeding Network

Substrate Layer

Conductive Plane

CCEs

Vias


Antenna Measurements

23

• Comparison between the simulated and the measured radiation pattern.

0

30

60

Delta-Phase q Null-Depth

0° 0° 33 dB

30° 11° 26 dB

60° 15° 31 dB

90° 17° 27 dB

q

y

x

z



90 120

150 180

Delta-Phase q Null-Depth

90° 17° 27 dB

120° 22° 18 dB

150° 28° 21 dB

180° 32° 21 dB

q

y

x

z

• Comparison between the simulated and the measured radiation pattern.



• Comparison between the simulated and the measured input reflectioncoefficient.

-35

-30

-25

-20

-15

-10

-5

0

2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3

0° (Meas.)

0° (Sim.)

S1

1 (

dB

)

Frequency (GHz)

-30

-25

-20

-15

-10

-5

0

2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3

30° (Meas.)

30° (Sim.)

S1

1 (

dB

)

Frequency (GHz)

-30

-25

-20

-15

-10

-5

0

2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3

60° (Meas.)

60° (Sim.)

S1

1 (

dB

)

Frequency (GHz)

-35

-30

-25

-20

-15

-10

-5

0

2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3

90° (Meas.)90° (Sim.)

S1

1 9

0°

Me

as

.

Frequency Mod

-30

-25

-20

-15

-10

-5

0

2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3

120° (Meas.)

120° (Sim.)

S1

1 1

20

° S

im.

R=

2

Frequency (GHz)

-25

-20

-15

-10

-5

0

2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3

150° (Meas.)

150° (Sim)

S1

1 (

dB

)

Frequency (GHz)


Conclusions

A novel approach based on Characteristic Modes analysis has been proposed forthe design of a pattern reconfigurable antenna.

The selective excitation of the modes over the conductive body has beenrealized by proper position of the exciters.

The phase-shifted characteristic modes is implemented by introducing anasymmetric excitation in order to steer the null.

Phase-shifted Characteristic Modes for pattern control on complex platform.


References

[1] F. A. Dicandia, S. Genovesi, and A. Monorchio, “Null-Steering Antenna Design Using Phase-Shifted CharacteristicModes,” IEEE Transactions on Antennas and Propagation, vol. 64, no. 7, pp. 2698–2706, Jul. 2016.

[2] F. A. Dicandia, S. Genovesi, and A. Monorchio, “Design guidelines for pattern reconfigurable antennas by exploitingthe characteristic modes analysis,” in 2016 46th European Microwave Conference (EuMC), 2016, pp. 441–444.

[3] S. Genovesi, F. A. Dicandia, and A. Monorchio, “Compact and low profile frequency agile antenna for multistandardwireless communication systems,” IEEE Trans. Antennas Propag., vol. 62, no. 3, pp. 1019–1026, Mar. 2014.

[4] R. J. Garbacz and R. Turpin, “A generalized expansion for radiated and scattered fields,” IEEE Trans. AntennasPropag., vol. 19, no. 3, pp. 348–358, May 1971.

[5] R. F. Harrington and J. R. Mautz, “Theory of characteristic modes for conducting bodies,” IEEE Trans. AntennasPropag., vol. 19, no. 5, pp. 622–628, Sep. 1971.

[6] E. Safin and D. Manteuffel, “Reconstruction of the characteristic modes on an antenna based on the radiated farfield,” IEEE Trans. Antennas Propag., vol. 61, no. 6, pp. 2964–2971, Jun. 2013.

[7] H. Li, Z. T. Miers, and B. K. Lau, “Design of orthogonal MIMO handset antennas based on characteristic modemanipulation at frequency bands below 1 GHz,” IEEE Trans. Antennas Propag., vol. 62, no. 5, pp. 2756–2766, May2014.

[8] Z. T. Miers, H. Li, and B. K. Lau, “Design of bandwidth-enhanced and multiband MIMO antennas usingcharacteristic modes,” IEEE Antennas Wireless Propag. Lett., vol. 12, pp. 1696–1699, 2013.

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