Antennas for Aeronautical Broadband Services

Abstract

The most challenging aspect of building an aeronautical broadband service is the antenna. Being mounted on the outside of an aircraft subjects them to some of the most extreme environmental conditions experienced by any satellite antennas: temperatures that may vary from nearly +50°C on the tarmac to -60°C at altitude less than 20 minutes later, lightning, icing, and the ability to withstand the impact of birds at speeds in excess of 670 km/hr. Above all, aeronautical antennas and their accompanying radomes must be lightweight and aerodynamic so they can operate at near transonic airspeeds while minimizing the drag and consequential fuel burn impacts on their host aircraft. Aerodynamic considerations place extreme limits on the dimension and particularly the height of aeronautical antennas. These size constraints, in turn, make it extremely challenging to operate these antennas within the interference limits and environment in the Fixed Satellite Service (FSS) frequency bands. Panasonic Avionics Corporation (Panasonic) is keenly aware of the challenges posed by aeronautical antennas due to its efforts in building the eXConnect global aeronautical broadband network. The eXConnect network provides data, voice (eXPhone), video (eXTV) over a service area that covers 99.6% of all flight hours globally and has been authorized in 209 countries. Panasonic operates two antenna types currently: a mechanically steered elliptic reflector made by Mitsubishi Electronics Company (MELCO) and inherited from the earlier Connexion by Boeing program, and a dual panel mechanically steered, planar array antenna that is manufactured by Panasonic. Panasonic is also currently introducing a new single panel, mechanically steered antenna and an ultra-low profile electronically steered phased array antenna, which will significantly reduce the drag penalty. This paper will describe the environmental and regulatory constraints that apply to aeronautical antennas, the various types of antennas used by Panasonic and others have used including reflectors, mechanically and electronically steered arrays, and novel antenna technologies that are entering the market. The paper will also cover the performance trades that occur between antenna height, aerodynamics, and performance as a function of elevation, azimuthal and skew angle and their effect on coverage area. Finally, this paper will show that different antenna types are suited to different segments of the aeronautical market. As an example, long-haul aircraft that fly trans-Atlantic and trans-Pacific routes often fly through regions where the elevation angle to geostationary satellites is as low as 5°. These aircraft require antennas that physically stick up off the crown of the aircraft so that they can view satellites that are near the local horizon, which has led to the development of antennas like the MELCO antenna and Panasonic’s dual and single panel antennas. These antennas tend to be wide horizontally and relatively short vertically for aerodynamic reasons, which in turn create challenges when these antennas are operated at high skew angles near the equator. Alternatively, there has been great interest in low profile phased array antennas. Panasonic intends to introduce a low profile antenna in the future. These antennas are light with low drag and are ideal for operation on short-haul aircraft that operate in the mid-latitudes and near the equator. The only downside with these antennas is that their performance decreases with decreasing elevation angle so they become difficult or impossible to use on long-haul trans-Atlantic and trans-Pacific routes. No single antenna type is likely to be ideal for every segment in the aeronautical broadband market. This paper will help clarify the tradeoffs between different types of antennas and different market segments for both service providers and their customers.