Beam-steering Antenna Array Based on a Butler Matrix Feed Network with CP Capability for Satellite Application

In this paper, a broadband circularly polarized (CP) antenna array for beam-steering applications is presented. The antenna consists of a 2 x 2 antenna array of substrate integrated waveguide (SIW) CP slot elements fed by a Butler matrix network. Each SIW element is rotated sequentially with respect to each other to improve the array CP purity. To validate the performance of the proposed structure, a prototype is fabricated and measured. The measured results show an impedance bandwidth of 18% (9.15-10.92 GHz) for vertical bar S11 vertical bar <= -10 dB and a minimum 3-dB axial ratio bandwidth from 9.4 to 10.1 GHz. The beam-steering antenna has about 25-degree scan angle with the peak gain of 14 dBi at 10 GHz.