  Conventional multi-beam forming with fixed-position antenna (FPA) arrays
needs to trade-off between maximizing the beamforming gain over desired
directions and minimizing the interference power over undesired directions. In
this letter, we study the enhanced multi-beam forming with a linear
movable-antenna (MA) array by exploiting the new degrees of freedom (DoFs) via
antennas' position optimization. Specifically, we jointly optimize the antenna
position vector (APV) and antenna weight vector (AWV) to maximize the minimum
beamforming gain over multiple desired directions, subject to a given
constraint on the maximum interference power over undesired directions. We
propose an efficient alternating optimization algorithm to find a suboptimal
solution by iteratively optimizing one of the APV and AWV with the other being
fixed. Numerical results show that the proposed multi-beam forming design with
MA arrays can significantly outperform that with the traditional FPA arrays and
other benchmark schemes in terms of both beamforming gain and interference
suppression.
