Titanium dioxide substrates have been synthesized by means of solid-state reactions with sintering temperatures varying from 1150 °C up to 1350 °C. X-ray diffraction and scanning electron microscopy (SEM) where employed to investigate the crystal structure, grain size and porosity of the resulting samples. The obtained ceramics are tetragonal (rutile phase) with average grain sizes varying from 2.94 µm up to 5.81 µm. The average grain size of samples increases with increasing temperature, while the porosity decreases. The effect of microstructure on the dielectric properties has been also studied. The reduction of porosity of samples significantly improves the dielectric parameters (relative dielectric permittivity and loss tangent) in comparison to those of commercial substrates, indicating that the obtained ceramic substrates could be useful in the miniaturization of telecommunication devices.

The pervasiveness of mobile internet, in conjunction to the ubiquitous computing of the internet-of-things has claimed the concept of 5G technology research to allow massive growth of machine communications. One of the main challenges is the scalability problem, which implies issues like small mobile device antennas to fit in the limited amount of space for the smartphone's design, followed by radiation control and low cost. The purpose of this paper is to develop an antenna, which meets the next generation of the mobile technology 5G as well as other resources available and desired in a smartphone (GPS-1575 MHz, WLAN-2.4 GHz, 3G-2.1 GHz, Brazilian 4G-2.6 GHz e GSM-900-1800-1900-2100 MHz). The design adopted only one ultra-wideband microstrip antenna that resonates in the frequencies of these technologies. This kind of antenna is thin, has low cost and good radiation control. Besides, this is the most popular type of antenna in mobile devices; the radiant elements use the manufacturing process of printed circuits. It is built in a plate composed by a conductor (the radiant element of the antenna), a substrate, and by another conductor, which is the ground plate. The principal feature of an ultra-wideband antenna is the usage of 1.5 GHz bandwidth or more. The prototype was manufactured and the simulation results for each type of technology resources are compared.