These ground planes include Novatel's GNSS-750 hemispherical choke ring ground plane, new types of frequency selective cut-off choke ring ground planes, Electronic Band Gap (EBG) and Artificial Magnetic Conductor (AMC) Ground planes and resistivity tapered ground planes made by the Trimble Corp. Several new types of broadband ground planes have recently been proposed to address these issues. Most prevalent are aircraft and ground based pulsed DME and TACAN beacons (1.025 to 1.150 GHz), JTIDS and MIDS (0.969 to 1.206 GHz), and ATC/ARNS interrogators, as well as harmonics of other VHF and UHF transmissions from communications antennas. Since the new L 5 signal resides in the Aeronautical Radio Navigation Service (ARNS) band it is particularly susceptible to in-band interference from non GPS signals emitted by several U.S. This is in addition to the legacy L 1 signal operating at a center frequency of 1.5754 GHz (20 MHz bandwidth). The GPS modernization program will soon require GPS antennas located on aircraft to receive the new L 5 signals operating between 1.164 GHz to 1.188 MHz with a center frequency at 1.176 GHz.
These systems also go by the name GNSS (Global Navagation Satellite Systems). The Federal Aviation Administration (FAA) is currently relying on Global GPS navigation for all commercial aircraft flying in the U.S. Microstrip antennae on aircraft are particularly prone to creating “creeping waves” since they use high dielectric constant substrates that can create creeping waves. Microstrip “patch” antennas are commonly used for building GPS antennas mounted on aircraft due to their low profile for reducing aerodynamic drag and their low cost and ease of manufacture.
All of these antennas can be potential sources of RFI (Radio Frequency Interference). These antennas may operate at other frequencies on the aircraft and could be communications antennas, aeronautical radio navigation antennas, radar antennas etc. Other signals can originate from antennas located on the aircraft itself, most likely on the lower surface of the aircraft. Some of the antennas that create interfering signals originate from radiating sources located on the ground-the most likely scenario.
Ground based interference sources are relatively much closer to the GPS antennas on the aircraft and suffer much less path loss hence they can easily overpower the GPS satellites signals and prevent them from being received. Hence they encounter a large amount of “space loss” during their long travel distances. GPS signals are very weak due to their long travel distances from GPS satellites that are located 20,000 kilometers above the earth. GPS antennas on aircraft can be either jammed or interfered with by a large number of sources. It is this radiation that creates the back-lobes in the radiation pattern of the antenna that make these GPS antennas very vulnerable to interference from strong radiating sources located on the ground. This diffracted energy then propagates or “creeps” around the surface fuselage continuously shedding energy as it propagates until it dies out. A portion of the RF energy radiated by the GPS antenna is diffracted around the smooth cylindrical surface of the fuselage of the aircraft. This radiation is primarily caused by what is known as “creeping waves” generated by curved surface diffraction. Global Positioning System (GPS) antennas used for navigation on aircraft generate considerable backward radiation which is directed downwards towards the ground. This disclosure relates to antenna based systems and methods for aircraft navigation.
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