measurements using a gtem cell above 1ghz dr tian hong loh
TRANSCRIPT
Measurements using a GTEM cell above 1GHz
Dr Tian Hong LOH
Overview of the Presentation
• Introduction to GTEM cell
• Reason for GTEM measurement above 1GHz
• Equipment under test (EUT)
• Experimental Setup
• Experimental Results
Overview of the Presentation
• Introduction to GTEM cell
• Reason for GTEM measurement above 1GHz
• Equipment under test (EUT)
• Experimental Setup
• Experimental Results
Introduction: What’s GTEM?
• GTEM cell – Giga-Hertz Transverse Electromagnetic cell.• Tapered Coaxial Transmission Line with 50 termination
at both ends.
Introduction: What’s GTEM?
• Designed for use as EMC radiated emission and radiated immunity test facility without impact of the ambient electromagnetic environment.
Introduction: What’s GTEM?
• At the input, a normal 50 coaxial line is physically transformed to a rectangular cross section.
• The cross sectional dimensions are a ratio of 3:2 horizontal to vertical cross sectional dimensions.
a
b
b/a = 3/2
Introduction: What’s GTEM?
• The centre conductor – septum, is a flat and wide conductor that will produce a uniform electrical field distribution underneath it which form a test volume for testing the EUT.
Overview of the Presentation
• Introduction to GTEM cell
• Reason for GTEM measurement above 1GHz
• Equipment under test (EUT)
• Experimental Setup
• Experimental Results
Reason for GTEM measurement above 1GHz
• The use of GTEM cell above 1GHz is still novel to product manufacturers.
• Increasing clock speed of computer processors.
• The need to measure the wave structure and to understand potential limitations in the use of the cell at higher frequencies.
Overview of the Presentation
• Introduction to GTEM cell
• Reason for GTEM measurement above 1GHz
• Equipment under test (EUT)
• Experimental Setup
• Experimental Results
Equipment under test (EUT)
• Dummy device that is commissioned resembling typical products.
• Consists of monocone antenna as radiating source mounted on the inside of a metal box.
Equipment under test (EUT)
• Power by a battery operated York EMC Services CGE01 comb generator with 100MHz harmonic spacing.
• Fundamental signal of 100MHz.• Measurable E-field from EUT up to 15GHz.
Equipment under test (EUT)
• Small EUT (SEUT): [ (L:W:H) = 23cm 20cm 11cm ]
Side 5
Side 2Side 1
Side 5
Side 3 Side 2
Equipment under test (EUT)
• Large EUT with complicated slots (LEUTC):
[ (L:W:H) = 12.5cm 48.5cm 48.5cm ]
Side 1
Side 2
Side 3
Overview of the Presentation
• Introduction to GTEM cell
• Reason for GTEM measurement above 1GHz
• Equipment under test (EUT)
• Experimental Setup
• Experimental Results
Experimental Setup
• Instrumentation used:
1. Spectrum Analyser (PSA)
2. Microwave Amplifier
3. Cables
4. Computer System
5. GTEM cell
6. Foam Table
7. EUT
12
3
4
5
Experimental Setup
Ver
tica
l P
olar
isat
ion
75
• Instrumentation used:
1. Spectrum Analyser (PSA)
2. Microwave Amplifier
3. Cables
4. Computer System
5. GTEM cell
6. Foam Table
7. EUT 6
Experimental Setup
• SEUT:
1750mm1620mm
450mm535mm590mm
645mm
1
Experimental Setup
• SEUT:
1750mm1620mm
450mm535mm590mm
645mm
1120mm
3mm483mm
538mm
12
Experimental Setup
• SEUT:
1750mm1620mm
450mm535mm590mm
645mm
1120mm
3mm483mm
538mm
820mm
255mm
60mm370mm
425mm
12
3
Experimental Setup
• LEUTC:
1750mm
1620mm
450mm
85mm
485mm
535mm
777.5mm
125mm
Overview of the Presentation
• Introduction to GTEM cell
• Reason for GTEM measurement above 1GHz
• Equipment under test (EUT)
• Experimental Setup
• Experimental Results
Experimental Results
• SEUT: Sensitivity --- Transverse displacement
0 1 2 3 4 5 6 7 8
x 109
-100
-90
-80
-70
-60
-50
-40
-30
Frequency (Hz)
Pe
ak
sea
rch
on
ha
rmo
nic
s (d
Bm
)
Emission Sensitivity Measurement - Transverse displacement (Side1 face apex)
centreL.H.S. 50mmL.H.S. 100mmR.H.S. 50mmR.H.S. 100mm
0 1 2 3 4 5 6 7 8
x 109
0
2
4
6
8
10
12
14
Frequency (Hz)
Co
mp
ari
son
(d
B)
Emission Sensitivity Measurement - Transverse displacement (Side1 face apex)
abs[ (L.H.S. 50mm) - (centre) ]abs[ (L.H.S. 100mm) - (centre) ]abs[ (R.H.S. 50mm) - (centre) ]abs[ (R.H.S. 100mm) - (centre) ]
Experimental Results
• SEUT: Sensitivity --- Vertical displacement
0 1 2 3 4 5 6 7 8
x 109
-100
-90
-80
-70
-60
-50
-40
-30
Frequency (Hz)
Pe
ak
sea
rch
on
ha
rmo
nic
s (d
Bm
)
Emission Sensitivity Measurement - Vertical displacement (Side1 face apex)
0 1 2 3 4 5 6 7 8
x 109
0
5
10
15
20
Frequency (Hz)
Co
mp
ari
son
(d
B)
Emission Sensitivity Measurement - Vertical displacement (Side1 face apex)
620mm720mm820mm
abs[ (720mm) - (620mm) ]abs[ (820mm) - (620mm) ]
Experimental Results
• SEUT: E-field comparison between GTEM & FAR
1 2 3 4 5 6 7 8
x 109
65
70
75
80
85
90
95
Frequency (Hz)
E f
ield
Str
en
gth
[d
B(u
V/m
)]
Comparison between Emission measurement of SEUT in GTEM and FAR
GTEM 2m E-field at 1620mm septem heightGTEM 2m E-field at 1120mm septem heightGTEM 2m E-field at 820mm septem heightFAR 2m E-field, Ant. VP, 2m away from SEUT
Experimental Results
• LEUTC: E-field comparison between GTEM & FAR
2 4 6 8 10 12 14
x 109
40
45
50
55
60
65
70
75
80
85
90
95
Frequency (Hz)
E f
ield
Str
en
gth
[d
B(u
V/m
)]Comparison between Emission measurement of Vertically Polarised LEUTC in GTEM and FAR
GTEM, NORMAL detectorFAR, PEAK detector, Antenna Vertically Polarised, 3m away from LEUTC for all antenna heights
Modified Experimental Setup
• LEUTC:
1750mm
1620mm
450mm85mm
485mm
535mm
777.5mm
125mm
Stepper Motor
Experimental results
• LEUTC: E-field comparison between GTEM & FAR
2 4 6 8 10 12 14
x 109
40
45
50
55
60
65
70
75
80
85
90
95
Frequency (Hz)
E f
ield
Str
en
gth
[d
B(u
V/m
)]Comparison between Emission measurement of Vertically Polarised LEUTC in GTEM and FAR
GTEM, MAX E-field in azimuth cutGTEM, E-field obtained from three position RSS algorithmFAR, MAX E-field, VP Ant., 3m away from LEUT for all antenna heights
Experimental results: Radiation Pattern
• Radiation pattern of LEUTC in GTEM:
Thank you for your attention.
Any Questions?