A radio frequency system package may include waveguides and loading blocks. The loading blocks may include dielectric material having a high dielectric constant between 13 and 20. Additionally, the loading blocks may be made of mold, epoxy, or the like material, and the loading blocks may fit into a region cut out of the waveguides. Moreover, the loading blocks may lower the cut-off frequency for wireless communication otherwise provided by the waveguides without the loading blocks (e.g., 28 GHz). In particular, the loading blocks may facilitate communication in low mmWave frequencies, such as 24 GHz.