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Data link antennas for use in air-to-air and air-to-ground communications of data at extremely high data rates have traditionally been X-Band and Ku-band dish antennas. These antennas are low-cost and provide efficient operation for the required application. Nine to 12 inch antennas are sufficiently large enough to support the required link margin at the data rates and with the associated RF power amplifiers. To increase the data transfer capacity would require more RF transmit power and/or larger antennas. RF power amplifiers are not very efficient and any increase in transmit power would result in a significant increase in power consumptions and would significantly increase the cost. In addition, any increase in antenna size would require larger radomes and this would impact aircraft performance and also increase the cost. An alternative would be to integrate an optical capability into to the RF system to augment the existing RF data link system and use a shared aperture (combined RF and optical) for the transmit/receive antenna for the optical and RF communication systems. With careful design the traditional dish antenna could be designed to accommodate the optical capability with little change in the form of the dish antenna. This would allow a retrofit to include the combined capability of RF and optical with minimal impact on the existing form of the dish antenna. This would also require a new radome design to include the transmit/receive of the optical signals in addition to the RF signals. This paper discusses several design options for the antenna, including coating designs to support simultaneous operation of RF and optical signals, feed systems for simultaneous operation, techniques for low-loss combining/splitting the RF and optical signals, and antenna configurations for simultaneous operation for RF and optical communications operation.
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