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Aircraft can be equipped with a number of radios which need to be operated simultaneously and in the full-duplex mode. To prevent interference required a combination of antenna separation, frequency separation, transmitter power control, and specific design considerations. Interference cancellation systems often use a common antenna, a common Low Noise Amplifier, and signal splitting to each receiver. Onboard transmitter signal would be sampled, delayed, adjusted in amplitude equal to the unwanted received signal (the transmitted signal), adjusted to 180 degrees out of phase with the unwanted received signal; and injected prior to the LNA, thus canceling the unwanted transmitter signal. The time delay can be accomplished by using coaxial cable or by digitizing the transmit signal spectrum. An optical alternative would convert the RF spectrum to the optical domain, use fiber or polymeric waveguide for time delay, and then convert back to the RF domain for injection into the receiver system to accomplish the cancellation. The optical system would have to process the RF signal(s) without creating distortion, and provide sufficient flexibility to allow the system to be readily adjusted to optimize performance. The optical system, installed at the receiver, would consist of a transmitter, a programmable delay line and a receiver. An attractive implementation would be a single chip to incorporate the optical generation and switching functions to redirect the optical signal into a selected optical path. The optical paths might be polymer waveguides patterned onto a PCB. With newly developed optoelectronic integration technologies, the combination of sources, detectors, waveguide switches and amplifiers becomes a realistic possibility. The result is a rugged system with low cost and high performance. This paper describes these optical technologies and the optical interference cancellation implementation approach.
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