High-Quality Nickel Ferrite Synthesized by a Modified Sol–Gel Technique Applied as Microstrip Patch Antenna Substrate

Abstract

This paper presents the production of nickel ferrite powder synthesized by a sol–gel technique modified by ionic coordination reaction. Morphological powder characterization is presented via X-ray diffraction, scanning electron microscopy and energy-dispersive spectrometry. Bulk manufacturing by uniaxial press is developed, and its electrical characterization is shown. Three ferrite bulks were manufactured and characterized to evaluate the quality of the compression procedure. Permittivity and conductivity parameters were obtained and discussed according to reference papers. Characterized bulks were applied as a microstrip patch antenna with rectangular and circular geometries, designed by transmission line and cavity methods, respectively, to evaluate bulk features as substrate. Reflection coefficient and radiation patterns were simulated by a high-frequency structure simulator, and measurements of reflection coefficient were performed. The obtained radiation patterns presented good agreement between them and were consistent with the performed design. A maximum gain of 1.55 dB in the E plane could also be achieved despite the relatively high $$ tg\left( \delta \right) $$ for radiating devices. Simulated cross-polarization results are also displayed, where the maximum value obtained was −29.35 dB, highlighting the device's directivity. Good agreement between simulated and measured reflection coefficient was achieved in both geometries, reinforcing the high-quality ferrite powder production process. It was possible to reach 0.00% relative error between simulated and measured resonance frequency in one of the three circular patch devices, at 6.05 GHz. Maximum resonance frequency error presented in all performed measurements is 6.51%, associated with manufacturing and measurement issues. Despite that, the quality of the synthesized material could be observed in each discussed result.