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Fourth Year Final Project - BGU

HF Electromagnetic Vector Sensor

Students: Roy Nevo, Yiftach Barash

Advisors:Mr. Benny Almog Prof. Reuven Shavit

17.5.2011

θ=80˚

φ=157˚

E

H

S

Department of Electrical and Computer Engineering - BGU

Challenges and Motivation

Electromagnetic direction finding (DF) is of high priority, both for civilian and military needs.

In the High-Frequency (HF) range (3-30MHz) the common passive DF methods require very large aperture (tens of meters).

Thus, HF DF system is bulky to carry and to set-up.

Small aperture antenna array and elements (in terms of wavelength) that perform DF is required.

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Project GoalsMain Goal: Using the Poynting theorem to produce a small antenna for

HF-DF applications

Objectives:

Wideband in the HF region

Simultaneous azimuth and elevation finding

RMS error < 2˚

Production of the antenna

Test environment for the HF range – The TEM Cell

θ=80˚

φ=157˚

E

H

S

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Project Final Result

The sensor basic element and its feeding circuitry were simulated and produced

TEM-cell test environment was also simulated and produced

The antenna was measured inside the TEM-cell and the total RMS error of the azimuth and elevation estimation was < 2˚

Simulation -Total Error RMS

1.43

Measurements - Total Error RMS

1.98

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Theoretical BackgroundThe Poynting Theorem

Propagating EM plane wavein free space:

E-field ┴ H-field ┴ Propagation (Poynting vector).

The Poynting Theorem

From the Cartesian elements of the fields, the propagation direction can be extracted

HES

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1

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Theoretical Background Electric and Magnetic Dipoles

Electric dipole on the Z axis Response related to Ez

...

...

____21

xy

zx

yz

HEHES

HEHES

IIIIkkHEHES

yxz

xzy

loopydipolezloopzdipoleyzyx

X

E

HY

Z

X

EHY

Z

22atan , atan

yx

z

x

y

SS

S

S

S

z

jkr

z Ikzr

eIkaE 1

02

ˆ4

Magnetic dipole on the Z axis Response related to Hz

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Simulated Elements

Small Electric Dipole

Small Loop –Magnetic Dipole

Combined element – Slotted Dipole With less coupling

and thus, possibly, higher SNR 7

Dipoles Simulation

Electric and magnetic dipoles – far field (incident wave response).

Electric dipole far field radiation (Eθ)

Rectangular loop far field radiation

(Eφ)

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Dipoles Simulation

Slotted Dipole – far field (incident wave response).

Electric dipole far field radiation (Eθ)

Slot far field radiation (Eφ)

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Test Environment – The TEM cell

Ez [V/m]

Ey [mV/m]Ex [mV/m]

The TEM-cell was matched to have 200Ω impedance

The Electric field orientation in the center is well defined

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Combined Simulation – DF analysis

Simulation results – 6 dipoles in the TEM CELL

|Ex| 7.12E-06

|Ey| 5.02E-09

|Ez| 4.63E-04

|Hx| 2.35E-06

|Hy| 5.19E-02

|Hz| 1.03E-07

|Sx| 2.39E-05

|Sy| 1.09E-09

|Sz| 1.45E-07Sx

Hy

Ez

Angle ExpectedSimulation

result

Phi 0 0.0023

Theta 0 0.34X

E

HY

Z HES

2

1

11

z

x

y

S

H

E

Polarization=0

Theta=30˚

Phi=0

Polarization=0

Theta=0

Phi=30˚

Orientation Index

Polarization=0

Theta=0

Phi=0

Polarization=30˚

Theta=0

Phi=0

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DF Results and Noise Analysis

Error in RMS Phi Theta Abs

Dipole and Loop 2.0275 0.9701 2.2476

Slotted Dipole 1.3266 0.5481 1.4353

-20 0 20 40 60 80 1000

10

20

30

40

Currents SNR [dB]

RM

SE

The slotted dipole show better DF result in simulation

For good performance, with no signal processing operations, the signal must be larger than the noise in at least 20dB.

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The TEM-cell The TEM-cell was produced from

wood (EM “transparent”) and two parallel metal net (EM plate)

From S parameters measurements, the TEM-cell is well matched and perform as parallel plate transmission line

0 5 10 15 20 25 30-30

-20

-10

0

Frequency [MHz]

[dB

]

S11 amplitude

S21 amplitude

Input Output/ Termination

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Testing System Layout

The antenna is placed on special holders with different angels in the TEM-cell.

The TEM-cell is connected to port 1, the antenna to port 2 of the ENA and S21 is measured.

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Sensor Element Measurement Results

The elements directional response is as expected !

In most of the HF range, the signal response in the TEM is larger than the noise in more than 30dB

0 5 10 15 20 25 30-80

-60

-40

-20

[dB

]

Ex amplitude

Ey amplitude

Ez amplitude

0 5 10 15 20 25 30-100

-80

-60

-40

-20

Frequency [MHz]

[dB

]

Hx amplitude

Hy amplitude

Hz amplitude

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Sensor Element Measurement Results

In the HF range the antenna gain is very small –

small antenna-large bandwidth limitation

The DF result on arbitrary angle show good performance up to 20MHz (The magnetic dipole upper limitation)

0 5 10 15 20 25 30-5

0

5

10

Frequency [MHz]

Err

or [

degr

ee]

=30 =45 =60

Error in

Error in

0 5 10 15 20 25 30-90

-80

-70

-60

-50

-40

Frequency [MHz]

Gai

n [d

Bi]

Electric dipole Gain

Magnetic dipole Gain

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Measurements Results and Comparison to Simulation

α β γ φ θ Error - φ Error - θ Error – RMS

0 0 0 0 0 0.86 0.98 0.92

45 45 45 -16 58 1.86 0.8 1.43

30 45 60 -58 47 0.94 0.48 0.75

30 60 30 12 4 3.95 3 3.51

Total Error-RMS 1.98

Simulation -Total Error-RMS 1.43  

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Conclusion and Future Steps

A novel HF DF antenna was developed and produced

The antenna is very small in terms of wavelength and thus highly mobile

The DF RMS error < 2˚ as was initially specified

Continuous measurements and signal processing algorithm (MUSIC) will be applied in order to further reduce the RMS error

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References

[1] C. Balanis, Antenna theory: Wiley New York, 1997.

[2] C. Balanis, Modern Antenna Handbook: Wiley New York, 2008.

[3] A. Nehorai and E. Paldi, "Vector sensor processing for electromagnetic source localization," in Signals,

Systems and computers, 1991.

[4] C. E. Smith and R. A. Fouty, “Circular Polarization in F-M Broadcasting,” Electronics, vol. 21 (September 1948): 103– 107. Application of the slotted cylinder for a circularly

polarized omnidirectional antenna.

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Thank You For Your Attention

Questions ???

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The slotted dipole

Simulation results – current density

Electric dipole ports generator - J [A/m]

Slot ports generator - J [mA/m]

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Project Methodology

SimulationProduction and Measurements

Analysis

Electric and magnetic dipoles basic simulation

Detailed simulation including feed

Calculation and simulation - TEM-cell

Simulation and DF calculation

Production of the TEM-cell and S-parameters measurements

Production of electric and magnetic dipole

Measurement of the electric and magnetic dipole in the TEM-cell

DF calculation

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