Spherical array antenna using digital beamforming techniques for mobile satellite communications

Problems arise in providing excitation phases and amplitudes to individual antenna elements for wide-angle scanning by applying spherical array antennas for mobile satellite communications for ships, automobiles, and aircraft. These antennas do not have many antenna elements. Thus, emphasis is on obtaining the maximum gain rather than realizing the characteristics of low sidelobe levels. This paper considers the application of spherical arrays for antennas of mobile satellite communications. An adoption of a control method is assumed which regulates the phases and amplitudes freely and accurately for individual antenna elements for the beamforming circuits of digital beamforming antennas. A beamforming method is examined for spherical arrays. First, a selection of necessary antenna elements is proposed utilizing the received signals and an adjustment of their phases and amplitudes. This method is applied to a 16-element spherical array which had circular micro-strip antennas. Their radiation characteristics are calculated. As a result, it was clarified that the maximum directive gain could be obtained almost without being influenced by the properties of individual antenna elements. Next, circuits are designed for the reception of binary PSK signals of constant envelope modulated waves. Carrier recovery circuits are established for individual antenna elements for spherical arrays, and a method is used to detect their phases and amplitudes. The method shows the effectiveness in obtaining the amount of gain reduction due to the detected phase and amplitude errors.