Adaptive pattern nulling method for multi-armed spiral antennas

Future Global Navigation Satellite System (GNSS) receiver antennas will need to operate over several bands simultaneously, while being able to adaptively reject cosite interference, multipath, or potentially hostile signals, while retaining adequate satellite reception. This paper discusses the use of the phase modes of the spiral to synthesize nulls at arbitrary angles in a spirals pattern, and is organized as follows. First, the concept of phase modes is reviewed and applied to derive a simple method for determining the arm excitations required to place arbitrary nulls. Then, a numerical study of a multiarmed spiral antenna is used to achieve independent steering of nulls across the field of view. Finally, the method is validated with measurements and simulations of a four-armed spiral.