DEFINITION:
It includes:

• RF Systems, Payloads and Technologies : Covers all technologies and techniques operating in the RF domain related to satellite systems and networks, spacecraft payloads, instruments and specific ground equipment (Technologies for control centres, TT&C and Earth Observation Payload Data Transmission Ground Stations and Ground Station Networks are covered in 1 K), for telecommunication, TT&C, Earth observation and space science, including security aspects. Radio navigation systems and subsystems are included in 1 H).
• Electromagnetic Technologies and Techniques : Covers antennas and related technologies, wave interaction and propagation, and electromagnetic compatibility.
• Optoelectronics: Covers the development and application of technologies combining photonics (i.e. circuits handling photons) with electronics to achieve given functions.
• Optical Communications: Covers techniques and technologies for the design, manufacture and testing of optical equipment/subsystems and terminals for optical communications between satellites and between spacecraft and ground stations (e.g. feeder links, deep space communications); includes specific technologies like quantum communications for secure links, cryptography and global key distribution.

(Source: ESA TD 6A, 6C, 6D and 6E (6B is included into 1 G 6), TD7, TD17 and TD16C-VI)