On 10/1/20 10:53 AM, Curt Mills wrote:
I don't have an answer for you, but since you asked such a general
question I'll generalize it a bit more and suggest you do a search on:
measuring antennas with drones
I read one such article a few weeks back and thought it a neat idea,
but for the one I read it was evident they were only checking
near-field and had more work to do to even get that right.
Having an antenna range, a UAV/drone, and appropriate data collection
/ data reduction could simplify a lot of this in the future. Should be
much cheaper to do too. Reading more articles should give you a
feeling for what the state-of-the-art currently is. I don't have a
handle on that yet having only read one article.
this has been around a while - they used to use a pod suspended by a
nonconductive cable from a helicopter (see RELEDOP or XELEDOP).
I have a 1/3 scale powered paraglider from more than 10 years ago that I
was going to fly a test transmitter on. I found the technology wasn't
quite mature enough yet.
I know some folks using drones to try and measure HF antennas for a
spacecraft at Univ of Iowa(?) but it's been pretty dicey. Likewise,
folks trying to measure patterns for radio telescope arrays (EDGES, I think)
https://iopscience.iop.org/article/10.1086/683467
https://ieeexplore.ieee.org/document/7297261
https://dial.uclouvain.be/memoire/ucl/fr/object/thesis%3A14813
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6864538/
https://link.springer.com/article/10.1007/s10686-017-9566-x
The ones looking at SKA and LOFAR are probably most relevant for amateur
radio - they're big arrays at 100 MHz and below.
We've been considering it for the OVRO-LWA (30-90 MHz) too.
For the low frequency arrays - the pattern is basically a big blob
pointing up (e.g. LWA is crossed dipoles over a ground screen). The
interest is in knowing if there are funny lobes anywhere else (if you
are imaging a source overhead, and there's a bright source that's 30dB
brighter on the horizon, will it leak in?)
Turns out there's a LOT of factors to consider.
I think it *is* the way to go in the future.
Things to think about:
How accurately do you know the UAV position (better than "meters"
requires some form of differential GPS)
Do you measure fairly close to the antenna under test (say, 100m) but
you're sort of in the near field. Or do you get well away (>1km) and
have to deal with terrain effects.
How accurately do you know the antenna pattern of the probe? (most folks
use a very short dipole or monopole which makes the antenna pattern
easy, but not necessarily the "pattern on the UAV" easy. So you have
to calibrate the sensor's pattern.
How accurately do you know the gain of the receiver or transmitter on
the probe (and is it stable over the duration of the measurement).
For these kinds of things, 10% accuracy (0.4dB) on any one of them isn't
too tough, 1% (0.04 dB) is pretty hard.
I think though, that even with all these problems if you wanted to do
precision metrology, you could get really decent data on null and main
lobe positions and approximate relative gain. Consider a 4-square
array, or wondering if you're getting some interaction between antennas
in a multiband stack? The UAV measurement gives you another cross
check, and one that has been hard up until now.
Good luck in your quest.
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