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This work presents a technique to produce radio frequency (RF) and microwave devices with relative permittivity (ε r ) variations in specific locations. It is based on additive manufacturing, using two or more filaments, with different permittivities, which are introduced into the print head and mixed with designed proportions. While other techniques can vary the dielectric permittivity using air cavities along the object, our proposal allows varying permittivity without cavities, which provides devices with more stable properties. As an application of this technique in RF devices, a dielectric planar lens, with varying permittivity, was designed and built to work along with a planar Vivaldi antenna. The antenna plus lens system was experimentally measured, indicating gains of up to 1.98 dBi when compared to the system without the lens. It was also demonstrated that the lens has ultra-wideband properties since it presented an increase in gain when compared to the reference one from 1.5 to 3.0 GHz.

This article addresses the study of the Vivaldi Antipodal Antenna (AVA) seeking to improve the gain, decrease the Side Lobe Level (SLL) and the squint, to make the antenna more directive and obtain a more stable radiation pattern. Its intended application lies in the generation of biological microwave imaging to detect brain tumors. With this objective, the Fractal Slot Edge (FSE) technique was applied with a new fractal developed and based on the Cantor set. The application of this fractal, called Cantor Neogothic Fractal (CNG), formed different-sized cavities resulting, in this work, in three antennas that were analyzed through numerical computational simulation together with AVA. The antennas, called CNG9-FSE-AVA, CNG18-FSE-AVA, and CNG27-FSE-AVA, in which 9, 18, and 27 define the maximum height that the fractal reached in each antenna, have areas equal to 354.66 mm2 , 709.33 mm2 and 1064 mm2 , respectively. All antennas achieved the goal, however, CNG27-FSE-AVA presented the best results at 2 GHz, with a gain of 7.84 dBi, SLL -19.80 dB, and squint of -0.10 degree. Additionally, it was proved that the antenna is suitable to generate a near field microwave imaging of tumors in a brain model.

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