The solid state procedure was used to produce bulk ceramics of BTO (BaTiO₃), CCTO (CaCu₃Ti₄O₁₂) and BTO_0.5–CCTO_0.5 that were studied in the medium-frequency (MF) range (100 Hz–1 MHz) and in the microwave range of frequencies. The presence of BTO is decreasing the dielectric constant (ε_r) of the BTO–CCTO composite. The CCTO and BTO samples present a strong tendency to the increase of the loss with frequency. The BTO substrates are presenting higher values of the ε_r in the range of 1–4 GHz (around 140). For pure CCTO the dielectric constant is around 37.6. Similar behaviour observed at the MF range, that the higher dielectric constant is also associated to the higher loss is also present in the microwave region. The study of a planar microstrip antenna, that uses the BTO _X –CCTO_(1−X) ceramic as a high ε_r substrate was done. Therefore, these measurements confirm the potential use of such materials for small high dielectric planar antennas (HDA). These materials are also very promising for capacitor applications and certainly for microelectronics, microwave devices (cell mobile phones for example), where the miniaturization of the devices is crucial.