### Document

```Fourth Year Final Project - BGU
HF Electromagnetic
Vector Sensor
Students:
Roy Nevo, Yiftach Barash
Mr. Benny Almog
Prof. Reuven Shavit
E
H
θ=80˚
S
φ=157˚
17.5.2011
Department of Electrical and
1
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.
2
Project Goals
Main Goal:
 Using the Poynting theorem to produce a small antenna for
HF-DF applications
E
Objectives:
 Wideband in the HF region
H
S
 Simultaneous azimuth
and elevation finding
 RMS error < 2˚
θ=80˚
 Production of the antenna
φ=157˚
 Test environment for the HF range – The TEM Cell
3
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 1.43
Total Error RMS
Measurements - 1.98
Total Error RMS
4
Theoretical Background
The Poynting Theorem
 Propagating EM plane wave
in free space:
E-field ┴ H-field ┴ Propagation (Poynting vector).
 The Poynting Theorem
1  
S  EH
2
 From the Cartesian elements of the fields, the propagation
direction can be extracted
5
Theoretical Background
Electric and Magnetic Dipoles
Z
 Electric dipole on the Z axis
 Response related to Ez
E
Y
H
 Magnetic dipole on the Z axis
 Response related to Hz
Ez
H E
Y
X
2

ka I 0e  jkr

zˆ  k I
4r
Z
X
1 z

S x  E y H z  E z H y  k1k 2 I y _ dipole I z_ loop  I z _ dipole I y _ loop
S y  E z H x  E x H z  ...
S z  E x H y  E y H x  ...


 Sy 



  at an
,   at an
 Sx 




Sz
S x 6 S y
2
2





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).
(Eθ)
Rectangular loop far
8
Dipoles Simulation
 Slotted Dipole – far field (incident wave response).
(Eθ)
(Eφ)
9
Test Environment – The TEM cell
 The TEM-cell was matched
Ez [V/m]
to have 200Ω impedance
 The Electric field orientation
in the center is well defined
Ex [mV/m]
Ey [mV/m]
10
Combined Simulation – DF analysis
 Simulation results – 6 dipoles in the TEM CELL
Sx
Ez
Hy
|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-07
H
z
E
S
Z

E
Y
y

X
x

1 Expected
S  EH
Phi
0
2
Angle
H
Theta
Simulation
result
0.0023
0
0.34
11
Orientation Index
Polarization=30˚
Polarization=0
Theta=0
Theta=30˚
Phi=30˚
Phi=0
12
DF Results and Noise Analysis
 The slotted dipole show
better DF result in
simulation
Error in RMS
Phi
Theta
Abs
Dipole and Loop
2.0275
0.9701
2.2476
Slotted Dipole
1.3266
0.5481
1.4353
40
 For good performance,
RMSE
with no signal processing
operations, the signal
must be larger than the
noise in at least 20dB.
30
20
10
0
-20
0
20
40
60
Currents SNR [dB]
80
13
100
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
Output/
Termination
Input
0
S11 amplitude
S21 amplitude
[dB]
-10
-20
-30
0
5
10
15
20
Frequency [MHz]
25
30
14
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.
15
Sensor Element Measurement Results
 The elements
Ex amplitude
Ey amplitude
Ez amplitude
-20
directional response
is as expected !
[dB]
-40
-60
 In most of the HF
range, the signal
response in the
TEM is larger than
the noise in more
than 30dB
-80
0
10
15
20
10
15
Frequency [MHz]
20
25
30
25
30
Hx amplitude
Hy amplitude
Hz amplitude
-20
-40
[dB]
5
-60
-80
-100
0
5
16
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)
 =30 =45 =60
-40
10
Error in 
Error [degree]
Gain [dBi]
-50
-60
-70
Electric dipole Gain
Magnetic dipole Gain
-80
-90
0
5
10
15
20
Frequency [MHz]
25
30
Error in 
5
0
-5
0
5
10
15
20
Frequency [MHz] 17
25
30
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
18
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
19
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.
20
Questions ???
21
The slotted dipole
 Simulation results – current density
Electric dipole ports generator - J [A/m]
Slot ports generator - J [mA/m]
22
Project Methodology
Simulation
Production and
Measurements
Electric and magnetic
dipoles basic simulation
Production of the TEMcell and S-parameters
measurements
Detailed simulation
including feed
Production of electric and
magnetic dipole
Calculation and
simulation - TEM-cell
Measurement of the
electric and magnetic
dipole in the TEM-cell
Analysis
DF calculation
Simulation and DF
calculation
24
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