Executive Summary : | Antenna is an important element of any wireless communication system. The antenna used for tactical satellite communication systems on military vehicles needs to have a scannable beam, so that it always points towards the satellite with which it has established communication. As the vehicle moves, the beam also needs to reorient, so that the communication is not disrupted. This can be achieved by using a mechanically steerable antenna or an electronically steerable one. Typically, the antenna is mounted horizontally on the roof of a vehicle, and the main beam points towards the zenith. The system should be able to steer the beam from 90° down to about 20° in the elevation plane and by 360° in the azimuth. Therefore, with this system, the vehicle is able to communicate with any satellite that is in a cone angel of 70°. As the vehicle is mobile, it is desirable to have an antenna that has low profile. Ku and Ka band satcom-on-the-move terminals offer broadband satellite communications to military and civilian users, on land, air and sea. Single Ku-Ka band antenna system will allow seamless connectivity to mobile platforms travelling on routes where one single network is not available continuously like the transoceanic regions. Also, these systems need to be ultra-low profile, light weight and electronic beam forming flat panel antennas to provide benefits such as reduced drag in airborne operations, working under higher velocity, acceleration and shock specifications for given tracking accuracy, easier installation, easier manoeuvrability and so on. The antenna beam can be steered mechanically or electronically. Mechanical steering does not alter the beam characteristics, such as width of the main beam, side lobe level, gain of the antenna, and appearance of the grating lobe, etc. However, the mechanically steered antenna is complicated, more susceptible to angular acceleration, shocks while tracking, bulky and high in profile. Electronic beam steering, on the other hand, does not require any moving parts and can be designed to be ultra-low profile, however, as the direction of the beam changes, the pattern characteristics degrade. When the look angle goes below 45°, the performance of the antenna significantly deteriorates. Some of this is due to fundamental limitations associated with beam steering achieved by introducing phase shift in the excitation. The effect of electronic beam steering on the performance of generic antennas have been studied. However, how it manifests in the context of antennas used for OTM tactical antennas needs to be investigated. It is also important to study the effect of various array parameters on the performance vis-à-vis the electronic beam steering. The main challenges to be addressed are development of dual-band shared aperture antenna for wide-angle beam steering and the array electronics packaging within the limited space available. |