Planar Antennas for Satellite Communications

Abstract

Modern Satellite Communications requires the development of very small size, low-cost, lowprofile, high gain and high directivity antennas. Antennas form the link between transmitting and receiving equipment and the space propagation path. Even the general principles may apply to satellite communications antennas, imposed limitations of gain, field pattern and mainly the physical environment lead to design requirements which should be taken in account. Most satellite antennas are designed to give coverage over a specified restricted area defining restrictions over antenna gain; on the other hand payload restrictions of weight and size lead to small size and weight antennas. Especially for these characteristics, planar antennas could have wide application on communications satellites. Since the late 1970s, the international antenna community has devoted much effort to the theoretical and experimental research on microstrip and printed antennas, which offer the advantages of low profile, compatibility with integrated circuit technology and conformability to a shaped surface. The results of this research have contributed to the success of these antennas not only in military applications such as aircraft, missiles, and rockets but also in commercial areas such as mobile satellite communications, the Direct Broadcast Satellite (DBS) system, global position system (GPS) and remote sensing but their main applications are on ground transceivers. Last two decades have been especially worthwhile on planar antennas development, mainly for mobile communications, but its applications should be extended to satellite systems. Particularly for the first Mexican satellite system (Morelos I and II), primary array receiving Ku band , was a planar array to produce an elliptical footprint over Mexican territory. For the second generation of Mexican satellites, was introduced the L band circular polarization array, formed by 16 parabolic reflectors feed by crossed short dipoles producing the needed circular polarization and also an elliptical footprint. It is clear that if there were used a planar array, as those that technology has developed in the last two decades, the cost and the weight would be reduced to a fourth part. This chapter of the Satellite Communications book, is devoted to planar antennas, not only for that already in use but proposing other kind that could be applied for satellite communications. It starts with a brief description of planar antennas, their characteristics, and their applications as antenna arrays. The next part will describe actual planar antennas used in satellite communications systems and will finish with a proposal of new developments of planar antennas that could be used in the near future.