2011-08-13 - Testing CPA v4 at NW EMC

We tested our linearly-polarized cylindrical patch antennas (CPAs) version 4 in NW EMC's 3m anechoic chamber in Hillsboro today.

Many thanks to NW EMC for sponsoring these tests!

VNA Testing of Resonant Frequency

First thing we did was verify our measurements of the CPA's resonant frequency. We already measured these antennas at PSU using their Agilent VNA, but we weren't convinced we had sane results. In NW EMC's anechoic chamber and amazing VNA, we were dang sure we got good results.

ATV

Design frequency: 2.430 GHz
Actual response: 2.349 GHz (-3.3 % / 81 MHz too low)

GPS

Design frequency: 1.575 GHz
Measured frequency: 1.523 GHz (-3.3% / 52 MHz too low)

WiFi

Design frequency: 5.785 GHz
Measured frequency: 5.629 GHz (-2.7% / 156 MHz to low) and 6.010 GHz (+3.9% / 225 MHz too high)

Conclusion

Off by ~ 3%!! Not terrible, really, given all the changes to the CPAs in the last build and the new batch of UHMW PE dieletric.

Notes

Between test setups, Glenn gave an excellent explanation of Smith charts (part of the VNA results), then we found a nice poster tacked up on a wall, which we liked. A copy (pdf) of the poster is on Agilent's site:

http://cp.literature.agilent.com/litweb/pdf/5989-6924EN.pdf

Watching the results change on the VNA as Glenn alternated between placing his hands on the Al shell of the rocket below the antennas and letting go was a dramatic demonstration of how easy it was to affect the results. In this case, by changing the (effective?) dielectric constant of the antenna system. (Longer, more accurate explanations may be available.)

As it turned out the VNA results at NW EMC were consistent with measurements at a PSU lab with a different VNA, in what was a higher RFI environment.