Measurements using a GTEM cell above 1GHz

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







Introduction: What’s GTEM?

• GTEM cell – Giga-Hertz Transverse Electromagnetic cell.• Tapered Coaxial Transmission Line with 50 termination

at both ends.


• Designed for use as EMC radiated emission and radiated immunity test facility without impact of the ambient electromagnetic environment.


• 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


• 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.







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.







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.


• 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.


• Small EUT (SEUT): [ (L:W:H) = 23cm 20cm 11cm ]

Side 5

Side 2Side 1

Side 5

Side 3 Side 2


• Large EUT with complicated slots (LEUTC):

[ (L:W:H) = 12.5cm 48.5cm 48.5cm ]

Side 1

Side 2

Side 3







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







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) ]


• 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) ]


• 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


• 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?

Measurements using a GTEM cell above 1GHz

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