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Statistical Investigation of Frequency-Stirred Reverberation Chambers. Shih-Pin Yu Charles F. Bunting. Founded by NASA Grant NCC-1-01032. Statistical Investigation of Frequency-Stirred Reverberation Chambers. What is the Reverberation Chamber ?.

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statistical investigation of frequency stirred reverberation chambers

Statistical Investigation of Frequency-Stirred Reverberation Chambers

Shih-Pin Yu

Charles F. Bunting

Founded by NASA Grant NCC-1-01032

what is the reverberation chamber

Statistical Investigation of Frequency-Stirred Reverberation Chambers

What is the Reverberation Chamber ?
  • Reverberation chamber is an electrically large cavity consisting of metal walls with a perturbation mechanism inside to obtain an uniform, isotropic and randomly polarized electromagnetic environment throughout the working volume.
  • Conventional way to perturb the field inside the chamber is by using metallic stirrer/tuner(s) to continuously change the boundary conditions in the chamber.
  • A novel way to perturb the field is by using a amplitude and frequency modulated source instead of a CW source.
mechanical stirred reverberation chambers
Mechanical-Stirred Reverberation Chambers

*RTCA/DO-160D, "Environmental Conditions and Test Procedures for Airborne Equipment (Draft #9 for the Change Notice to Section 20)," October 6,2000.

frequency stirred reverberation chambers

0

Frequency-Stirred Reverberation Chambers
  • The rotation of the mechanical stirrer has equivalent effect to frequency and amplitude modulation.

Frequency domain

Time domain

*D. I. Wu and D. C. Chang, "The Effect of an Electrically Large Stirrer in a Mode-Stirred Chamber,“1989

frequency stirred reverberation chambers1
Frequency-Stirred Reverberation Chambers

*M. L. Crawford, T. A. Loughry, M. O. Hatfield, and G. J. Freyer, "Band-limited, White Gaussian Noise Excitation for Reverberation Chambers and Applications to

Radiated Susceptibility Testing," National Institute of Standards and Technology Technical Note 1375, 1996.

why frequency stirred reverberation chambers
Why Frequency-Stirred Reverberation Chambers ?
  • Real-time homogeneous field can be achieved.
  • Test time reduced up to a factor of 200 compare with mechanical stirring.
how to achieve it
How to achieve it ?
  • There are many ways to achieve frequency stirring by using different sources, one of them is Band Limited White Gaussian Noise (BLWGN) source.
  • By given a designated source bandwidth, the frequency stirring can be applied to reverberation chambers.
hill s 2 d simulation 1994

Y

b

I0

(x0,y0)

a

X

Hill’s 2-D simulation (1994)
  • D. A. Hill performed a 2-D simulation in 1994 using a electric line source for frequency stirring and obtain a good field uniformity result.

Line source

the effects on the statistics1
The Effects on the Statistics
  • Mode structure

High number of possible modes !

the effects on the statistics2
The Effects on the Statistics
  • Line source bandwidth

Several modes exist even in 1 MHz BW !

how to improve the result
How to Improve the Result ?
  • Lower chamber Q
  • Increase the line source bandwidth

Standard derivation lower than 1 dB!

statistics with lower chamber q
Statistics with lower Chamber Q

Worse Standard derivation due to lower Q !

3 d simulation using modal mom

Y

Aperture

X

3-D Simulation using Modal_MoM
  • Modal_MoM was developed by M.D. Deshpande for the simulation of the shielding effectiveness of the lossless cavity with apertures on it.
  • A 3-D simulation of frequency stirring is performed by using the aperture as the excitation source to the chamber.
conclusion and future work
Conclusion and Future Work
  • In 2-D simulation the field uniformity dose not indicate good statistics of the field itself.
  • In 2-D simulation, in order to be analogous to mechanical stirring, the chamber Q and the line source bandwidth should be carefully choose.
conclusion and future work1
Conclusion and Future Work
  • The 3-D simulation of a lossless cavity shows poor field uniformity and field statistics indicate not enough modes existing in the frequency stirring simulation.
  • A thorough investigation should be performed for further use of the real frequency stirring in reverberation chambers.