1 fourth year final project - bgu hf electromagnetic vector sensor students: roy nevo, yiftach...
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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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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
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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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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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