A planar, metamaterial-based, one-dimensional periodic structure that can be switched between multiple states is numerically investigated. It can be fabricated at low cost in gallium-arsenide (GaAs) technology for antenna-on-chip and system-on-chip millimeterwave applications. The device radiates in the leaky wave region and its radiation pattern can be changed by switching between states in addition to changing the frequency, over a wide bandwidth. It can also be employed to obtain nearly identical radiation patterns at different frequencies due to its reconfigurability. This digitally programmable device presents dynamic shifting of the band-gap by as much as 80 GHz. Tunability is obtained by externally controlled FET switches, directly integrated into the device in the GaAs substrate. The switches dynamically change reactive loads imposed by N rectangular patches in each unit cell, positioned below a microstrip line, allowing the device to switch between 2N states. A representative CAD model is presented, giving closer attention towards the requirements of commercial GaAs monolithic MMIC fabrication processes. Interesting radiation characteristics of this leaky wave antenna are presented and discussed.