Birth of FEMU 2.0

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.

Setting up FEMU 2.0 before flight FEMU 2.0 during measurement

 

RF Propogation measurements over a berm with the use of a Multicopter

The RF shielding effect of a berm was measured using a Multi-copter as part of my PhD program. LS of SA from LS telecom generously helped us with these measurements with their own Multi-copter measurement platform. The measurements were done with a transmitter located on the far side of the berm transmitting 9 vertically polarized frequencies in a horizontal direction, from 60m, directly at the berm. Below is a photo of the Multi-copter measuring in the vicinity of the berm.

Wessel, the Multi-copter pilot, landing the measurement vehicle

Wessel, the Multi-copter pilot, landing the measurement vehicle

Far side of berm, opposite side than transmitter

Far side of berm, opposite side than transmitter

Front side of berm, same side as transmitter

Front side of berm, same side as transmitter

The data was then processed and compiled together from a total of 7 10 min flights at different heights and configurations. The processed data was plotted and interpolated with python on a 2D grid with an overlay of the berm. The next 3 clips shows animations of the interpolated data over different frequencies and heights.

Final Word

I would just like to thank the measurement team and especially LS of SA for the great collaboration.

group photo

From the left:
Mathew Groch: Responsible for broadband loaded dipole antenna used in these measurements
Jan (crouching) from LS of SA
Nardus Mathyssen responsible for developing a pulse generator which will be used in future measurements
Wessel from LS of SA
Myself Hardie Pienaar
Brian from LS of SA