In this study, dielectric properties of Acrylonitrile butadiene styrene (ABS) thermoplastic material with different fill-densities are investigated. Three separate sets of samples with dimensions of 25 mm × 25 mm × 5 mm were created at three different machine preset porosities using a LulzBot 3D printer. To understand the actual porosities of the samples, a 3D X-ray computed tomography microscope was used. The great advantage of this 3D microscopy is that it is fully non-destructive and requires no specimen preparation. Hence, the manufacturing defects and lattice variations can be quantified from image data. It is observed that the experimental pore densities are different from the factory preset values. This provides insight to further understand pore distribution-property relationships in these dielectric materials. Micro-strip patch antennas were then created on the 3D printed ABS substrates. The samples were then tested using a vector network analyzer (VNA) and resonant frequencies were measured. It is observed that the resonant frequency increases with an increase in porosity. These results clearly demonstrate the ability to control the dielectric constant of the 3D printed material based on prescribed fill density. Copyright © 2016 by ASME