Professional Pilot, March 2018

Astronics AeroSat FliteStream T Series system is a tail mounted internet and live tv connectivity solution ideal for business aircraft FliteStream T Series is composed of an antenna GAU transceiver LPT PAU and satellite modem antenna controller ACMU PROFESSIONAL PILOT March 2018 63 and correspondingly costly to do the same on an aircraft The enormous cost of certification for aviation use is a big driver when it comes to price And the technological challenges of installing and then keeping airborne antenna aligned with satellites while moving in 3 dimensions and also crossing satellite boundaries are other salient factors Nearly all communication satellites which include voice data and entertainment are parked in orbit over the equator By definition a satellite over the equator that remains over the same geographical location is known as geostationary Line of sight has to be maintained for signal reception to be continuous However unlike a ground receiver that can remain stationary and locked at a specific azimuth aircraft receivers must have the ability to constantly track the satellite as the aircraft moves Additionally physics plays an important role in designing an antenna The home satellite system previously mentioned consists of a parabolic dish connected to a protrusion that extends outward from the center or an attachment that wraps up from underneath In either case the hardware known in industry parlance as a feed horn serves an important purpose When receiving a signal the curved parabolic dish reflects radio waves inward to the feed horn much like the concave mirror behind a flashlight bulb focuses light into a concentrated beam And when transmitting the controller 1st sends a signal to the feed horn which bounces the signal off the dish transforming it into a narrow outgoing beam A side effect of a traditional open ended feed horn is that by the nature of its placement it blocks a portion of the incoming satellite signal much like an umbrella blocks overhead sun One solution to increase gain and efficiency is to just make the parabolic antenna enormous which is not a problem if the corporate aircraft happens to be an 800 ft long Zeppelin with a top speed of 75 knots But for a midsized business jet flying at 80 of the speed of sound theres a finite limitation contingent on fuselage space and willingness to accept parasitic drag The Astronics AeroSat approach Astronics AeroSat has developed a novel approach to the feed horn issue AeroSat which was acquired by Astronics in 2013 was founded in 1997 with the purpose of creating satellite connectivity for aircraft The company rapidly excelled in the field of antenna performance so it wasnt long before it developed and patented a lens horn technology The gist is that in lieu of a using a traditional feed horn to serve as the radio wave focal point for transmission and reception the lens covering the antenna performs that function The lens itself is composed of Rexolite an extremely lightweight 15 lighter than acrylic cross linked polystyrene plastic with superior properties that make it an excellent choice for satellite dishes and other antennas The lens material is important but the key to it functioning like a traditional feed horn is in the way the lens is engineered If the word Fresnel sounds familiar its probably because it brings back memories of 8th grade science class A Fresnel lens named after French mathematician and physicist Augustin Fresnel in 1822 is made of concentric rings with each groove cut at a different angle so that it focuses light towards the center Its the principle behind a magnifying glass lens which is thick in the middle and thinner towards the outside This ability of a Fresnel lens to take a weak light source and magnify it was the reason it was used in lighthouses An example of this exists today In Florida the original 9 ft tall Fresnel lens hand blown in Paris France still sits atop the St Augustine lighthouse Although the original low powered light source has since been replaced with a 1000 watt bulb the Fresnel lens still directs the beam Fresnel lens horn design Astronics AeroSats Fresnel lenshorn design enables the antenna to capture RF energy at greater incident angles This efficiency makes it especially advantageous when flying in latitudes above 75 degrees Again think back to that home satellite system The dish points towards the satellite on the equator If your house was located on the equator the dish