In the future, civilian drones will travel ever greater distances and in many cases even fly out of sight of the pilot, as military drones do now. During the entire flight, there must be stable radio contact with the aircraft. Satellite communication is a solution for this. However, this requires special antennas that are a lot larger than the usual radio antennas. The Royal Aerospace Center (NLR) is therefore working with Orange Aerospace on an antenna system that is fully integrated into the design of a drone.

Long Distance Signal Transmission

Most drones that are now used for civilian applications such as inspections or aerial photography fly not too far from the pilot. This is the result of the regulations, which states that a drone must always be in sight during the flight. But in the future there is increasing demand for drones that travel longer distances, for example, to inspect miles of power lines or pipelines during an uninterrupted flight. The regulations for (BVLOS) flights make this increasingly possible, but the technology must also be ready.

The problem with BVLOS flights is that traditional radio connections are no longer possible at some point. With current technology, it is perfectly possible to fly a drone a few kilometers away from the ground station, but in the built-up environment or at greater distances, the stability of the radio link quickly becomes problematic. For more serious BVLOS operations, the operator must therefore choose a different solution for the signal transmission.


A solution can be to stop radio communication taking place directly between pilot and drone, but to enable satellite communication (SATCOM) for this purpose. After all, more and more telecommunications satellites are hanging in space, in order to provide coverage in all corners of the world. Control signals from the pilot (and vice versa the downlink with, for example, the live video image and telemetry) then first go to a satellite in space, which then sends the signal back to the drone or the ground station, whether or not via another satellite. This way, the control signal and the downlink can bridge hundreds or even thousands of kilometers.

In daily life, you already have to deal with SATCOM regularly, for example if you connect to the internet in a passenger plane via the onboard Wi-Fi network. In that case, the data communication between the aircraft and the Internet is also via satellites. To make this possible, the aircraft is equipped with a special antenna, which is in continuous contact with a satellite during the flight. This can be a mechanically controlled antenna or an electrically controlled antenna. Hybrid antennas (mechanical/electric) are also used.


The main disadvantage of satellite communication is that the radio signals from space are many times weaker than the signal of a transmitter on the ground. This not only means that the required antenna on board the drone must be a lot larger, but that directional sensitivity also becomes an issue: the radio signal must be sent from the plane or drone exactly in the right direction to provide sufficient signal strength to the receiving side care.

To achieve that, a so-called phased array or beamforming antenna is needed, which consists of separate patch antennas and a beamformer. A beamformer is an electronic circuit that ensures that the radio signal can be directed at the receiver, without the antenna having to physically change its direction. Additional advantages are that beamforming antennas require less maintenance and are less vulnerable than mechanically targeted antennas.

Antenna in the wing

Researchers associated with NLR are now working on an antenna array based on multiple patch antennas under the project name ISABELLE (shortly before). The special thing is that the array is part of the mechanical design of the drone. This has the advantage that there is no protruding parts, which would adversely affect aerodynamics. However, the electromagnetic interaction between the integrated antenna and the aircraft must be taken into account.

For the ISABEL project, the antenna is processed into a component that is not normally used for this purpose: the wings of a fixed-wing drone. “The challenge here is to make the antenna and beamforming more compact, so that the antenna system takes up less space and is less vulnerable, but is also more reliable and cheaper,” said Senior R&D Engineer Jaco Verpoorte.


The mechanical integration of the antenna presents the necessary challenges. For example, the wing skin applied over the antenna should not weaken the radio signal. Glass fiber reinforced composites are in the advantage. The distance between antenna and wing surface also plays a role. This means that the antenna properties must be included in the wing design from the start.

A trial version of the array antenna has now been integrated into a fixed-wing drone from the Dutch company Orange Aerospace B.V. It concerns the OA-60 platform, with a wingspan of four meters and a maximum take-off weight of 60 kg. internal combustion engine and can fly on fifteen liters of fuel for about six hours. The hull and wings are made of carbon composite material.

Each wing incorporates an antenna array consisting of 2×4 patch antennas. In one wing an antenna for transmitting, in the other wing an antenna for reception.

Initial test results

The properties of the antennas integrated into the wings were first measured on NLR’s Antenna Test Range (ATR). Then static tests were carried out with the plane on the ground. The quality of the satellite link could be determined here. Ultimately, some flight tests were also carried out in which the dynamic behavior of the antennas could be determined.

The initial test results with the antenna system are encouraging. It turns out that the radio signal can indeed be sent to the satellite (beamforming). To determine the correct direction of the antenna beam, the drone is equipped with an Inertial Measurement Unit (IMU), which continuously measures the position and position of the device.

Verpoorte: “From the results of the first flight tests, it can be concluded that the antenna system is functioning correctly in the sense that it follows the satellite accurately during all maneuvers. The antenna control unit correctly directs the beam to the satellite based on the input of the position and position sensor.”

Next steps

The next step is to further improve the antenna system, as the stability of the connection is not yet optimal. “As a result, reliable data transfer is not yet possible,” says Verpoorte. “The relative signal strength is still too dependent on the orientation of the drone.”

After optimizing the antenna system, testing for NLR’s ATR, soil tests and flight tests will be carried out again. The aim is to give a demonstration of a live video link via satellite with the camera on board the drone. The ultimate goal is that the business community will develop products that will find their way in the market based on this innovative technology.