As part of my PhD research, characterizing the propagation environment of the SKA Karoo site, a multi-copter RF metrology vehicle was developed. A dramatic autopilot failure in our early prototype caused us to lose the entire vehicle. This gave us a clean slate to do a full redesign upon what we have learned. The main problems with RF metrology using a multi-copter is the effect of the multi-copter itself on the measurement which at this point has not been properly addressed in research. Therefore, we set out to design a vehicle that could be properly de-embedded from a measurement.
The performance of antennas on-board these vehicles are in most cases unknown or assumed. These antennas have a certain characteristic pattern which could cause significant fluctuations in the measured signal, depending on its orientation. Even if the orientations were kept constant, the antenna patterns are sensitive to changes in metallic structures of the vehicle. A good example of this is the replacement of a battery after flight. The replacement battery might have slightly different dimensions, position and will most certainly perturb some of the large power cabling.
Our approach was to shield all of the subsystems of the vehicle in a metallic enclosure. This gave us a vehicle which had a predictable antenna pattern over time. Also, by closing the complex metallic environment, accurate antenna simulations have been made possible. A paper will be published on this shortly. Additionally, FEMU 2.0 also boasts a quasi-isotropic antenna pattern and a bandwidth of 260 MHz to 960MHz (See the paper for more information on this).
Hopefully this will pave the way for RF metrology using multi-copters. If done correctly this could significantly speed up measurement time and deliver measurements that are spatially continuous. The entire vehicle has been constructed from 3D printed parts and local hardware supplies. The electronics, receiver and antenna systems can all be made available if another research group is interested in further developing the project.
Below are 2 images showing FEMU 2.0 during setup and measurement.