Aircraft antennas

By any measure – design, function, operation – it’d be impossible to overstate the importance of today’s aircraft antennas, since they’re the only link an aircraft has to its outside environment.

The Aircraft Owners and Pilots Association describes these discrete but indispensable pieces of equipment as being among the most overlooked parts of an aircraft’s avionics system. This is ironic since antennas are crucial to nearly all flight systems, including communications with air traffic control while flying through highly congested airspace, downloading diagnostic information from onboard sensors, maintaining the correct heading while cruising over the ocean thousands of miles from land, and detecting hostile aircraft in military operations. They’re also a vital element in receiving and broadcasting data from passengers’ own digital devices. For reference, though there can be variation between commercial and defense aircraft; Boeing’s 787 has more than 20 antennas.

Location

Antenna size, purpose, and placement on an aircraft are generally determined by their directional qualities and the electromagnetic frequencies at which they operate. Additionally, the volume of data broadcast and received via antennas is growing dramatically, and the more microwave and radio frequency (RF) systems adorning an aircraft, the greater potential for interference.

For example, seams around aircraft panels and doors can allow electromagnetic fields to pass through, or cause resonances that reradiate fields that could lead to interference problems. Then there are the technical issues tied to the increased use of composite materials in place of traditional metals; they have unusual electrical properties determined by the exact arrangement of their individual carbon fibers. The invisible nature of electromagnetic waves at these frequencies makes the task of identifying the source of such issues difficult. Traditional testing and measurement will often produce only a pass or fail outcome, providing little or no insight into the failure mechanisms.

The design and optimum placement of antennas is critical to reliable performance and aviation safety. Moreover, adherence to strict functional and safety regulations set by aviation authorities is basic to achieving aircraft certification. These certifications are for electrical compatibility of the antenna with other antennas as well as electrical systems, and an antenna’s safe continued operations in the electrical environment during events such as lightning strikes.

Exacerbating original equipment manufacturers’ (OEMs) challenge of where to position antennas is the fact that many components are supplied by multiple outside contractors who in turn must source components from their vendors. Fundamental to integrating these parts to produce a perfectly operating product is a reliable, secure way for team members to collaborate seamlessly, while maintaining careful control over commercially sensitive intellectual property, or classified information.

As with any complex piece of hardware under development, engineering problems identified late in the testing phase can be expensive to fix, may require significant redesign, and could even delay an entire aircraft-development program, causing it to fall behind schedule and over budget.

Modeling, simulation

To help reduce development costs, time, and risks early, more OEMs and their suppliers are using digital engineering – in particular, modeling and simulation (MODSIM) – to perform design studies on a virtual prototype.

Simulation yields more information than measurements alone. For example, full 3D results show the complete radiation patterns of antennas in all directions, avoiding unintended blockage from the airframe. Conversely, it reveals exactly how fields and currents may propagate around and through the aircraft, illuminating potential interference scenarios.

MODSIM can be accomplished using any one of a variety of software platforms, but the best engineering approach is to select one offering an integrated solution for every stage of product development. In this way, an OEM can be sure of fulfilling quality requirements at each step and providing engineers with access to accurate and validated simulation results early to verify all certification standards have been met.

In the final stages of development, components sourced from many different suppliers are assembled into a single system for simulation. When sharing data with all team members, sensitive parts can be hidden using encrypted black-box models capturing components’ behavior without revealing their structure. Data from other simulations and various field measurements also can be incorporated.

Engineers have the option of researching a library of antenna types for the application they have in mind, each fully documented and tagged according to their design and application. Once a suitable candidate is found, users can import the antenna model or its simulated or measured radiation pattern onto the aircraft body to model and then simulate whether the equipment works as intended when attached to the airframe. In addition, engineers must determine how the different radio systems interact with one another, requiring full product simulation. Since the placement of antennas will affect airflow around the aircraft, aerodynamic and electromagnetic simulation will be equally useful for considering possible tradeoffs.

Summary

Aerospace industry professionals occasionally quip that an aircraft in flight is actually millions of components flying in formation. Of all those parts, antennas are among the most flight-critical and whose placement is as important as their design. Compared to pure physical prototyping, introducing simulation for antenna design has been observed to reduce major airframe OEMs’ design cost by 50%. Other antenna analysis should have similar or even more reduction through introduction of simulation. The use of simulation in the design process may be the best tool for determining where antennas should be positioned, allowing their performance to be analyzed early, reducing the number of physical tests required and the risk of discovering performance issues late in development.

Dassault Systèmes

About the author: Ian Wood is aerospace and defense industry process expert, Dassault Systèmes. He can be reached at simulia.cst.us.support@3ds.com.