A steerable antenna comprising an array of T-shaped slots. The location of the slots is moved to define an array of ring- or spiral-patterned phase constant regions. Distortions or contractions of the pattern occur by repositioning some or all of the slots forming the array. The antenna also comprises an intermediate insulating layer and a lower plate. The insulating layer is formed by a deformable dielectric medium. Deformation of the dielectric medium allows the beam angle to be altered.