Active and semi-active array antennas for mobile communications satellites

The latest generation of mobile link antennas for mobile communication satellites are characterised by the requirement to generate a lattice of similar pencil beams with good mutual isolation. To satisfy this requirement complex antennas with distributed amplification are necessary. The optimum antenna solution in any particular case may be either a direct radiating array or a reflector system, depending on various system characteristics. The paper focuses on direct radiating arrays for the mobile link transmit function and examines the application to such antennas of the latest developments in semi-active architectures. Some fundamental issues concerning beamforming, frequency reuse and grating lobe structure are addressed. A typical active antenna design is introduced for comparison, a semi-active solution for the same example is derived, and preliminary pattern plots are given.