The extension of the operational frequencies of communication antennas to optical frequencies allows the transmission of very high data rates far beyond that of usual radio bands. The required optical communication antennas (OCAs) have at first glance some similarities to optical telescopes as used for astronomy, but their operational scenarios are very different. The biggest challenge from the system design point of view is the requested operation during daytime for communication with probes for deep space missions. They must allow communication with probes at very small SEP (Sun-Earth-Probe angle), where different strategies for tackling the solar irradiance are essential. The paper presents system design concepts for OCAs of very large (4m-8m) and extreme large (12m) clear aperture. Main subjects of discussion are the influence of alternate optical arrangements on heat rejection, seeing, stray light and caustic issues and the related degradation of the communication detector/receiver performance. Link budgets will be established for different aperture sizes. The paper concludes with a comparison of enclosure concepts and their influence on the design of the large optical components and the related cost aspects.