Abstract In this article, the authors propose changes to a microwave system for measuring the relative humidity of hollow concrete blocks presented in the literature, aiming to improve the system’s sensitivity. The operating frequency range was changed from 2.5 GHz to 5.8 GHz. This reduced the dimensions of the antenna arrays used in the system. Five block samples were used in this work. The frequency selective surface (FSS) used as a sensor has been modified, from a double circular ring to a square loop, which presents a single-band frequency response. The results obtained in this work showed a high correlation between the frequency variation and the relative humidity level. First, second, and third-order functions were compared to see which would better relate resonance frequency to relative humidity. The second-order function presented the best results, considering the Mean Absolute Percentage Error (MAPE), the Mean Square Error (RMS), and the coefficient of determination. We performed a sensor sensitivity analysis showing that the new proposed system is more sensitive than others presented in the literature. article literature systems s 25 2 5 2. 58 8 5. FSS (FSS modified loop singleband single band response level First second thirdorder third order secondorder MAPE, MAPE , (MAPE) RMS, RMS (RMS) determination (MAPE (RMS

Abstract This work proposes the integration of a monopole antenna with a frequency selective surface (FSS) with double square loop geometry, which operates in the ISM (2.4 - 2.4835 GHz) and IEEE 802.11 WLAN (5.15-5.725 GHz) bands. The FSS was developed to be integrated into a microstrip monopole antenna, aiming to improve some of its radiative features, such as gain, directivity, and front-to-back ratio (FBR). We show that the double square loop FSS operates in bands from 1.91 to 3 GHz and from 4.64 to 6.56 GHz, fully covering the bands of interest. A prototype of the proposed structure was assembled and both the numerical simulation and the experimental results show that the antenna integrated with FSS presents significant improvements in all parameters, compared to the antenna without FSS. Because of the interest frequency ranges the proposed structure can be applied in non-invasive biomedical applications. (FSS geometry 2.4 24 2 4 (2. 24835 4835 2.483 80211 802 11 802.1 5.155.725 5155725 5.15 5.725 5 15 725 (5.15-5.72 features gain directivity fronttoback front back FBR. FBR . (FBR) 191 1 91 1.9 464 64 4.6 656 6 56 6.5 parameters noninvasive non invasive applications 2. (2 2483 483 2.48 8021 80 802. 155 5.155.72 515572 515 5.1 5725 5.72 72 (5.15-5.7 (FBR 19 9 1. 46 4. 65 6. ( 248 48 8 5.155.7 51557 51 5. 572 5.7 7 (5.15-5. 5.155. 5155 57 (5.15-5 5.155 (5.15- (5.15 (5.1 (5. (5

Abstract In this article, bandwidth enhancement of a microstrip patch antenna using a new kind of metasurface is discussed. This new geometry is used to generate new resonances in antenna and with an optimal position of the metasurface in relation to antenna we can overlap the resonances and obtain a large bandwidth. The proposed antenna showed a bandwidth from 5.1 GHz to 8.0 GHz what can it able to be applied in WiFi 5 and 6. Numerical results were obtained with Ansys HFSS software. A prototype was built and measurements for S11, Smith chart and gain were performed. Numerical and experimental results are in good agreement.

Abstract In this paper, the authors present a proposal for an application of electromagnetic bandgap (EBG), for suppression of grating lobes, in frequency selective surfaces (FSS), not yet studied in the literature. An alternative type of EBG with square holes was proposed to reduce the computational effort in simulations. The study consists of an application of a rectangular periodic array of cylindrical and square holes in FSS dielectric substrate to create rejection bands and suppress specific resonant frequency modes. We built four prototypes and compared measured results with simulated results obtained with ANSYS HFSS. Simulations and measurements show suppression levels up to 6 dB. A good agreement between the results is observed. The FSS with EBG with square holes allows a simulation time 70 % lower than FSS with EBG with cylindrical holes.

Abstract This work proposes the application of a slot in the ground plane, Defected Ground Structure (DGS), of a microstrip patch antenna. The application of this technique aims to attenuate higher-order excited modes without deteriorating the antenna parameters in the fundamental mode. The methodology for the design of the slot in H-format is presented, based on the physical dimensions of the microstrip patch antenna. The positioning of the DGS concerning the feed line was determined from a detailed parametric analysis. The antenna was designed for the fundamental mode at 2.45 GHz frequency. Two antenna prototypes were built, with and without DGS, and measurements of reflection coefficient, gain, and radiation pattern were performed. The measured results show that the application of DGS considerably attenuated higher-order excited modes. A good agreement between simulated and measured results is achieved.

Self-affine property of a modified multifractal Cantor geometry is exploited to design frequency selective surfaces (FSS) with multiband response. The main advantage of the proposed structure is to design multiband FSS with multiple frequency ratios between the adjacent bands and easily-built structures. In addition, the proposed structure increases the degree of freedom in design of multiband FSS response according to the number of fractal iterations. The validation of the proposed structure was initially verified through simulations in Ansoft Designer 3.5 and then a prototype was built with a validation purpose.

In this paper a three layer FSS is described which provides a ultrawide band (UWB) response. The layers use plain rectangular patches, and rectangular patches with one or two notches which provide multi-band responses; by cascading them an UWB response is obtained covering the band 4.05 - 14.12 GHz, for vertical polarization and the band 5.05 - 15.00 GHz, for horizontal polarization. Transmission properties of the proposed structure were simulated and measured.

This paper presents a numerical investigation for a double screen frequency selective surface (FSS) with perfectly conducting rectangular patch elements. The analysis uses a full wave technique to obtain the scattering characteristics. The analysis combines the immitance approach and the method of moments to obtain the scattered fields and, consequently, the scattering characteristics of the structure. For validation of the analysis, numerical results are compared with measured and numerical results presented by another authors. A good agreement was obtained with experimental results.