Single phase, (100) oriented Ba0.5Sr0.5TiO3 (BST) thin films have been deposited onto (100) LaAlO3, SrTiO3, and MgO substrates using pulsed laser deposition (PLD). Interdigitated capacitors patterned on top of the ferroelectric film have been used to measure the dielectric constant and dissipation factor of these films as a function of DC bias and temperature at 1 MHz and as a function of DC bias and frequency (1 to 20 GHz) at room temperature. At room temperature, the capacitance can be reduced by as much as a factor of 4 using an electric field of ≤ 80 kV/cm. The dielectric properties (% tuning and dielectric loss) of the ferroelectric film is sensitive to both the deposition and post processing conditions. Optical imaging of the ferroelectric films using confocal scanning optical microscopy (CSOM) shows reproducible polarization fluctuations over sub-micrometer length scales. Dielectric loss in the ferroelectric film is reduced through a combination of post deposition processing and donor/acceptor doping of the films. A zero field tan5 = 0.01 - 0.005 has been measured for BST films which show significant tuning at microwave frequencies.