The Basics of Aircraft Antennas
Across the body of a typical commercial airliner, one may find various antennas spread out in different locations. Each of these antennas serves a specific role in standard flight operations, some implemented for the means of communication while others are for navigation. To help you better understand the various features of aircraft, we will provide a brief overview of common antenna types.
Communications antennas are crucial for flight operations, allowing for pilots to relay information to air traffic control and other personnel. Generally, these antennas may be found on the top or bottom of the aircraft, placed in an area where they are not shadowed by the fuselage. It is important that placement is strategic, promoting an optimal range and coverage for the means of optimal communication. Typically, an antenna placed atop the fuselage is useful for when the plane is still on the ground, while an antenna on the bottom facilitates communication while in the air.
GPS systems are highly beneficial for navigation, and their antenna is typically placed at the top portion of the aircraft fuselage. Due to the weak signals that such antennas produce, they utilize a built-in amplifier antenna accessory for boosting signals. As GPS and communications antennas tend to interfere with one another, they are placed far apart.
Long-range navigation (Loran) antennas have a similar external appearance to communications antennas, their placement being on top or on the bottom of the fuselage. Such antennas may either feature an amplifier built into their base or a small amplifier may be placed just under the skin of the fuselage. Loran systems are often sensitive to P-static, that of which is generated from electrical charge buildups from flight through heavy dust or rain. To mitigate such issues, airframe structures and antennas should be bonded correctly.
Loop antennas are true to their name, coming in the form of loops that are capable of determining the direction that a signal is sent from. Loop antennas are generally constructed from two to three coils that receive signals at different strengths. Loop antennas may be placed atop or below the fuselage, though the most common placement is on the bottom.
Marker Beacon Antennas
Marker beacon antennas are placed on the bottom of the fuselage, allowing them to establish communication with the transmitting ground station. Marker beacons may come in a wide variety of types, common ones being around 10 inches long.
Nav antennas regularly find implementation on the vertical tail of the fuselage, and they come in three different types. The cat whisker antenna extends outwards from the stabilizer at a 45-degree angle, benefiting pilots while flying low. The dual blade is the second antenna that comes outwards from each side of the tail. The towel bar is the final type, coming in the form of a balanced loop antenna that is placed on both sides of the airplane tail.
Radio altimeters utilize antennas which are installed at the bottom of the aircraft, coming in the form of either a single- or dual-antenna system. Bouncing radar signals off of the ground, radio altimeters may be used to determine the height of an aircraft over the terrain below it.
UHF antennas are often used for distance-measuring equipment (DME) and transponders, the two main types being blade and spike antennas. Generally, the spike antenna is best suited for transponders, while the blade antenna works well with DMEs. Due to their placement, UHF antennas can be shadowed by deployed landing gear.
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