[TowerTalk] Antenna measurements from UAV was Re: Tips for Modelling swaged antenna tubing sections

[jimlux]

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.
>