Avionics News March 2023 - 31

also called phased array antennas because of their working
principle.
Satcom Frequency Bands: Internationally, frequencies
are divided into well-defined bands. For satellites, the
relevant bands are:
* L-Band - The range of radio spectrum frequencies
from 1 to 2 GHz as defined by the Institute of Electrical
and Electronics Engineers. It's at the top of the ultrahigh-frequency
band and the lower end of the microwave
range. L-band is used for mobile satellite services
and offers good penetration through adverse weather
conditions and foliage.
* Ku-Band - The frequency range from 11.7 to 14.5
GHz. Ku-band has higher power than C-band, allowing
smaller dishes to be used. However, the higher frequency
of the Ku-band makes it more susceptible to adverse
weather conditions. Applications include VSAT, satellite
news gathering, videoconferencing and multimedia.
* Ka-Band - The frequency range from 17.7 to 21.2
GHz, higher than the Ku-band. Smaller dishes can be
used for high-bandwidth interactive services such as
high-speed internet, videoconferencing and multimedia
applications. Ka-band transmissions are more sensitive
to poor weather conditions than Ku-band.
Geosynchronous Earth Orbit Satellite: Satellites
orbit at 35,786 kilometers (22,282 miles) above the equator in
the same direction and speed as the Earth rotates on its axis,
making them appear fixed in the sky.
Interference: Any signal that interferes with the reception
of radio waves. Interference can be caused by transmissions
within the same satellite system, other satellite systems using
the same frequencies, or ground-based sources.
Internet of Things (IoT): It describes the increasing
combination of multiple machines - or electronic components
and sensors on a business aircraft - all sharing information
simultaneously and sending it to a dedicated receiving party
via the internet.
Kilobits per Second (Kbps): This refers to 1,000 bits
per second transmission speed. One kilohertz is the equivalent
of 1,000 hertz or 1,000 cycles per second. Kilohertz is used to
measure frequency and bandwidth.
Latency (Signal Latency): Typically measured
in round-trip time, this is the time the communications
network needs to transport data from the sender to the receiver.
Short latency times are critical for voice, email and
delivering smooth video streaming connections.
Because ATG connections are so relatively short (relatively
speaking, the terrestrial towers are close to the aircraft), latency
isn't much of an issue here (see air-to-ground networks).
Nor is it too much of a problem with low Earth orbit satellites
because they are relatively close to the Earth (see LEO satellites).
Since
a geosynchronous satellite orbits the Earth approximately
22,000 miles above the equator, a signal must travel
44,000 miles: 22,000 miles from the aircraft to the satellite and
another 22,000 miles from the satellite to the ground. If the internet
sends a reply, this requires another 44,000-mile trip back
to the aircraft. That's 88,000 miles round trip for each signal.
Even traveling at the speed of light, a radio wave traveling
at the speed of light takes about 0.6 seconds for this total
88,000-mile round trip.
Licensed Spectrum: This is a spectrum of frequencies
that is owned by a specific company or is dedicated for a
particular use such as broadcast radio or television. Unlicensed
spectrum is readily available to anyone and is typically associated
with " open " connections such as Wi-Fi and Bluetooth.
Local Aera Network (LAN): This is a wireless network
covering a limited area such as an office, home or cabin
of a private aircraft.
Low Earth Orbit (LEO) Satellite: LEO satellites orbit
from 100 to 1,243 miles above the Earth and take approximately
1.5 hours for a complete orbit. Because individual LEO
satellites cover only a tiny portion of the Earth's surface at any
time, a LEO satellite constellation can consist of hundreds or
even thousands of satellites.
LRU (Line Replaceable Unit): This is an onboard
component that can be readily changed on an aircraft during
routine line maintenance operations.
Medium Earth Orbit (MEO) Satellite: Satellites
located above LEO and below GEO satellites, which typically
travel in an elliptical orbit over the North and South pole or
in an equatorial orbit. MEOs are not currently used by any
business aviation connectivity providers.
Multi-Band Antenna: It's an antenna that is capable
of sending and receiving signals in different radio frequency
bands.
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Avionics News March 2023

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