Arizona State University

Cosite Interference

Advanced Helicopter Electromagnetics Laboratory | Comments

As the telecommunication systems become more complex and more antennas are placed on the same structure (e.g., helicopter airframe) the problem of interference becomes significant for the performance of the systems. In helicopter communication systems wire antennas, e.g., monopoles, whip elements, transmission line antennas, etc., are used to provide HF, VHF and UHF links. Also, other types of antennas, such as cavity-backed slot antennas and patch antennas are used in the UHF or higher bands. Furthermore, in specific applications very advanced communication systems are required (e.g., communication systems of helicopters or aircraft).

For example, pilots of airplanes (or helicopters) depend substantially on guidance systems that check the alignment and the position of the airplane (or helicopter) during landing especially at nights or poor visibility conditions. Consequently, in order to ensure safety, the communications instrumentation should be extremely reliable. However, when many antennas are placed on the same structure (e.g., helicopter or airplane airframe) the problem of interference and coupling between transmitting and/or receiving elements can influence the operation and integrity of the communication systems.

Interference can corrupt the signals with noise and deteriorate the quality of the communications. In addition, it can cause jamming of the systems, followed by complete interruption of already established communications.

One way to visualize areas of low or high coupling is to plot the surface current densities induced to a structure. The following two Figures illustrate two sample results of coupling analysis, one performed for the HUMVEE ground vehicle and the other for the Blackhawk helicopter.

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