Proposed TDR Method for Site Validation Above 1 GHz

Transcription

1 Proposed TDR Method for Site Validation Above 1 GHz ACIL CAS Meeting August 15, 2011 Long Beach, CA by Greg Kiemel, Director of Engineering gkiemel@nwemc.com Northwest EMC, Inc.

2 Overview Current Site Validation Requirements Proposed Alternate Method Description of Study that was performed Data Comparison Conclusion

3 Site Validation Above 1 GHz Amendment A1:2007 to EN 55022:2006 will be mandatory starting Oct 1, Requires testing above 1 GHz. Australia and New Zealand will also require testing above 1 GHz starting October 1, 2011 VCCI required radiated emissions testing above 1 GHz starting April 1, BSMI required radiated emissions testing above 1 GHz starting October 1, In all cases, the svswr method of CISPR is required.

4 Site Validation Above 1 GHz FCC specifies ANSI C63.4 (2003) or (2009) as acceptable test methods. The 2003 version has no site validation requirements above 1GHz. The updated 2009 version has two options: absorber on the floor that meets certain performance requirements, or compliance with CISPR In both cases, compliance with NSA requirements below 1 GHz is required. See FCC KDB : &switch=p

5 svswr Method The SVSWR is the ratio of maximum received signal to minimum received signal, caused by interference between direct (intended) and reflected signals, or

6 TDR Proposed ANSI Method The TDR method is being developed as part of a working group within ANSI ASC C63 using time domain gating to evaluate only the test environment This method requires the use of a vector network analyzer and bore-sighted horn antennas.

7 ANSI Proposed TDR Method Once in the time domain the direct path is removed numerically by a process referred to as gating The time gate allows us to evaluate only the reflected signals from the test site.

8 ANSI Proposed TDR Method Normalized Bore-site Trace in the Frequency Domain

9 ANSI Proposed TDR Method Transform of Bore Sight Without Gating in the Time Domain

10 ANSI Proposed TDR Method Transform of Bore Sight With Gating in the Time Domain

11 ANSI Proposed TDR Method Max Hold trace in the Frequency Domain. With Gating this shows only the magnitude of the reflections vs. Frequency

12 SVSWR and TDR Method How is TDR and SVSWR the same? Both measure phase change due to reflections SVSWR through changing locations of the antenna TDR through direct phase measurement (VNA) Both measurements are relative (no antenna calibrations needed) Both methods assume a fully anechoic site

13 Overview of the Study TDR vs. VSWR Multiple FCC-listed test sites were evaluated: 10m chamber 5m chamber 3m chamber 10m Open Area Test Site (OATS) Vinyl Cover 10m (OATS) Wood Geodesic Dome VSWR and TDR data taken from 1 6 GHz at all sites and additionally, 6 18 GHz at the Geodesic Dome.

14 Data Analysis VSWR and TDR data were converted to Site Error for comparison: CISPR spec of 6 db VSWR is equivalent to a site error of 2.23 db, calculated as follows: Site error = SQRT(10^(VSWR/20)^2+1) TDR spec of db is equivalent to a site error of 2.23 db, calculated as follows: Site error = 20*LOG(10^(TDR data/20)+1) Courtesy of Zhong Chen, one site was compared by converting TDR data to VSWR. Source: M Windler "Site Qualifications above 1 GHz," Compliance Engineering, March 2007 (

15 OATS with Geodesic Dome Acme Testing Co.

16 OATS with Geodesic Dome Acme Testing Co.

17 Comparison by converting TDR data to VSWR Zhong Chen of ETS reviewed the TDR and VSWR data and proposed the following: The TDR_data is in essence the reflection coefficient (gamma), or Vref/Vdirect. The reflection coefficient is related to the VSWR by: VSWR=(1+ gamma )/(1- gamma ), or gamma =(VSWR-1)/(VSWR+1).

18 Horizontal (1 6 GHz) svswr and TDR Comparison Worst Case (Hor) WorstCase H TDR 4.0 VSWR db Frequency (MHz)

19 Horizontal (6 18 GHz) 6 svswr and TDR Comparison 5 TDR_1.5_Horiz F-H-H1 4 VSWR Frequency (MHz)

20 Vertical (1 6 GHz) svswr and TDR Comparison Worst Case (Ver) WorstCase V TDR 4.0 VSWR db Frequency (MHz)

21 Vertical ( 6 18 GHz) 6 svswr and TDR Comparison 5 4 TDR_1.5Vert F-V-H1 VSWR Frequency (MHz)

22 Troubleshooting TDR Method is an excellent tool for troubleshooting site issues The first step is to orient the transmit horn to the azimuth that produces the highest displayed peak. Record the trace for both frequency and time domains

23 Worst-Case Azimuth, Failing Data Frequency Domain 2.54 GHz, -8.5 db Time Domain 21.5 ns = 6.45 m db

24 Troubleshooting in the Time Domain The distance displayed on the screen is the round-trip distance that the pulse traveled from the transmit antenna to the reflecting object and back. In this case, the reflecting object was 3.2 meters from where the transmit antenna was pointing. (Propagation is 1ns/ft) A large flat piece of metal (e.g. 2 x 3 ft) can be used to confirm the reflection location. Simply hold the metal in the suspect location and confirm the peak of interest changes in amplitude.

25 Wall(s) of Absorber can be Placed at the Suspect Location(s)

26 Worst-Case Azimuth, Passing Data with Additional Absorber in Place Frequency Domain 1.92 GHz, db Time Domain 11.3 ns = 3.39 m db

27 Conclusions Both methods correlate in determining compliance. Absorber type, coverage area, and chamber volume are factors in meeting site validation requirements. svswr method is more labor intensive and utilizes more of the existing lab equipment. TDR method is an excellent tool in identifying the source of non-compliance and is much faster.