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A planar sensor designed using the fourth Hilbert fractal curve iteration for solid material characterization at multiple frequencies is reported in this paper. The fractal curve is self-similar with space filling properties. The Hilbert fractal geometry is used to form a compact resonator, with a multiband frequency response where miniaturization is achieved, since a large transmission line length is effectively confined in a limited area. The sensor provides five resonances in the frequency range from 0 to 5 GHz. The resonant frequencies are 0.56, 1.68, 2.72, 3.69 and 4.72 GHz, all used to measure the real permittivity of known samples with a sensitivity of 7, 20, 27, 43 and 50 MHz/permittivity, respectively. The sensor is used to measure dielectric samples with 20 x 20 mm2 areas with several thicknesses. Simulations and measurements demonstrate that the Hilbert fractal geometry can be used to design a multiband planar sensor for solid dielectric material characterization.

This paper presents a compact and planar reconfigurable filtenna for application in Wireless systems. The filtenna is composed of a UWB circular antenna and a filter with two trapezoidal resonators. The filter is integrated on the antenna feed line and has a band-pass frequency response. The filtenna frequency response reconfiguration is achieved by changing the capacitance of a varactor diode, placed between filter resonators; the capacitance varies continuously from 1.32 pF to 4.09 pF according to an applied bias voltage. The varactor capacitance analog variation defines the filtenna frequency of operation, which can be varied from 2.2 GHz to 3.4 GHz with an average bandwidth of 200 MHz, while maintaining the radiation characteristics of the UWB antenna. Simulated and measured filtenna results are shown according to varactor diode bias, demonstrating multiband operation using a compact planar design. © 2021 SBMO/SBMag.

In this paper, a new frequency selective surface (FSS) for antenna gain enhancement is proposed. The antenna and FSS have an isosceles trapezium geometry. Three different versions of an antenna are created. For each version, the S-parameters S11 and S21 were simulated with the software CST Microwave Studio®. Then, one of the three trapezoid antennas is simulated with an FSS. These two devices, antenna and FSS, were manufactured and had the S11 and S21 parameters measured at the laboratory. The resonance frequency obtained for the trapezium FSS was equal to 2.27 GHz for $\alpha$ equal to 0 °, 2.70 GHz for $\alpha$ equal to 15 ° and 3.12 GHz for $\alpha$ equal to 30 °. The simulated antenna gain increased when the FSS is used as superstrate. Without the presence of the FSS, a maximum gain of approximately 1.50 db occurs at 2.20 GHz, when using the FSS as superstrate, the gain increases to approximately 5.25 db. The measured results agree with the simulated results.