Simulation helps reduce the risk of interference between aircraft radio systems

A French company specializing in maintenance and modification services for civil and military aircraft (MRO) called on NEXIO’s engineering services to study the possible impact of a new SATCOM system on an Airbus A330 on the aircraft’s other radio systems.

The problem :

Adding a new radio system and its antenna to an aircraft requires an interference analysis to ensure that it will not interfere with other systems (VHF, radionavigation, altimetry, radio-communication, etc.) which are also connected to antennas.
According to the standard procedure, analyses and then tests on aircraft are necessary to verify the absence of interference with the various existing equipment.
However, these operations come up against several problems when it comes to carrying out the measurements:
– The aircraft has to be immobilized on the ground during the tests
– The number of systems to be tested can be very large, and the tests can therefore be very cumbersome
– The difficulty of changing the antenna position during the tests.

NEXIO therefore proposed to use electromagnetic simulation for this study.

1. Carrying out the study

It was carried out in 4 stages:
– Modeling of antennas
– Digital model of the aircraft
– Simulation of decoupling between antennas
– Calculation of the interference matrix.

The first step is to model the existing antennas, as well as the new one we want to install on the aircraft. However, antenna manufacturers provide very little information. In this case, either a radiation pattern is used, or an approximate CAD model of the antenna is recreated. This model is validated with the technical data supplied by the manufacturer or by measurements of the antenna.
One of the difficulties is to reproduce the behavior of the antenna in its operating frequency band, but also outside its band. In fact, a VHF antenna operating at around 130 MHz can interfere with a GPS antenna that normally operates at 1575 MHz.

The second step is to create a digital model of the aircraft. To achieve this, a mesh is generated from the aircraft CAD.

The simulation is carried out using electromagnetic simulation software. The choice of solver depends on antenna operating frequency, model size and complexity (e.g. materials). For this study, we used a so-called “asymptotic” method, Optique Physique (OP), adapted to the size of the problem. The simulation then allows us to determine the coupling between each antenna.

Finally, the interference matrix uses the coupling data calculated above and integrates the power and sensitivity of each system to highlight the margin between sensitivity and spurious signal level.

2. Result

Simulation-based interference analysis can be used to determine the risk of interference between radio systems on an aircraft with a high degree of accuracy.
The quality of the results obtained can be used to decide whether or not installation is feasible, without incurring the high costs associated with an extensive measurement campaign.
Once the numerical model is available, it is possible to vary the antenna position on the aircraft to find the best compromise, which is impossible during aircraft testing.

Although some tests are essential for final certification, simulation helps to reduce the number of tests and thus the time the aircraft is on the ground.

Such a study clearly shows the contribution of simulation in terms of cost and time reduction for the implementation of a new antenna on an aircraft.

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