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Anechoic chambers are widely used to measure antenna parameters because of the free reflection conditions inside them. Recently, there has been increasing research into antennas working at frequencies from 20 to 70 GHz. General-purpose anechoic chambers are usually between 5 and 10 m in size, which leads to free-space distances longer than required at millimeter-wave frequencies and corresponding larger cables losses. Designing anechoic chambers tailored to such a frequency range would lead to minimum losses and improve measurement performance. If uncertainty is considered all the way from the design stage to operation, it will be easier to obtain highly accurate measurement outcomes. This article focuses on the issues related to uncertainty in a tailor-made millimeter-wave anechoic chamber at every step before achieving a fully functional measurement system. This includes setting the requirements for the chamber, calculating its dimensions, designing the structure, and selecting the building materials, in order finally to characterize its performance by measuring the insulation from external signals and the ripple in the quiet zone. This process has resulted in a full description of design, construction, and operation stages of an anechoic chamber from the point of view of the control on the measurement uncertainty. [ABSTRACT FROM AUTHOR]

The concept of controlling the radiofrequency (RF) transparency of building wall structures is analyzed in this article with a focus on southern European architecture, where it is demonstrated that some materials have a significant impact on wireless propagation. As such, the integration of frequencyselective surfaces (FSSs) in some building structure arrangements might have few overall benefits. This work provides an analysis of the different elements required to modify the electromagnetic (EM) transparency of building wall layers: 1) different methods to control the frequency selectivity are identified with a special focus given to FSS, 2) some proposals on the integration of the FSS on current and new building structures are provided, 3) measurement results are presented regarding the penetration losses of multilayered wall samples, with and without the presence of FSS layers, and 4) a multilayer EM simulation tool developed in MATLAB is introduced and validated against measurement results, allowing the simulation and analysis of additional scenarios. Results are provided for a frequency range of 800 MHz up to 10 GHz. [ABSTRACT FROM AUTHOR]

The radiowave propagation through hollow clay brick walls, which are common in southern European construction, is analyzed. The brick walls have thicknesses of 11, 15, and 20 cm, common in both interior and exterior walls, and are bound with a portland cement, water, and sand mixture. For each brick dimension, three prototypes were assembled, varying in the type of wall finish, i.e., exposed brick, smooth painted plaster, and rough painted plaster. A 10 cm concrete wall was also included for comparison purposes. Penetration loss metrics were evaluated in an anechoic chamber at frequencies ranging from 680 MHz to 10 GHz. Results demonstrate that the brick wall internal heterogeneity, as well as the type of finish, significantly influences the propagation phenomena and thus the frequency response of the walls, with relatively high penetration losses observed at some relevant commercial frequency bands. Finally, an alternative brick design, with reduced penetration losses, is also proposed and evaluated under simulation environment only. [ABSTRACT FROM AUTHOR]

This communication presents a hybrid frequency selective surface (FSS) and rectenna design for wireless power harvesting. To this extent, the center of the original FSS structure acts as a probe-fed patch antenna and an additional layer was added to the rear of FSS structure to mimic the required antenna ground plane, while minimizing its impact on FSS performance. The proposed hybrid solution yields a bandpass frequency response at GSM 900-MHz frequency band, with band reject behavior at 2.4 GHz and, on the other hand, act as a energy harvesting system through the antenna element at the 2.4-GHz ISM band, e.g., for recycling ambient Wi-Fi energy. The developed prototype, consisting of an array of 12 unit cells, was able to power a 56-mW LED at a 2-Hz rate from an incident power level of -10\;\textdBm, resulting in an average output power of 300\;\upmu\textW and an unit cell RF–DC conversion efficiency of 50%. [ABSTRACT FROM PUBLISHER]

Modeling vegetation usually implies obtaining experimental data by means of measurement campaigns. In general, the most accurate models need the reradiation pattern of the vegetation volume under study, or some of its related parameters. Obtaining this function might not be easy, and the measurement procedure may introduce errors depending on the location of the vegetation mass. An accurate tool to simplify this process is presented, based on the ability of artificial neural networks to infer behavioral patterns. This proposal reduces the acquisition of the experimental data to a scarce set of angles around the tree or bush, which will then be used to train a neural network capable of retrieving the desired reradiation function desired. [ABSTRACT FROM PUBLISHER]

This paper presents a short-term analysis of the radio propagation channels within vegetation media at the most commonly used wireless network frequency bands: 2.4, 3.5, and 5.8 GHz. Fading effects underlying this short-term analysis would determine whether the radio channel could support a stable link or not. The configuration used in this study is a peer-to-peer system, where the transmitter and the receiver are located at low heights inside several vegetation media, including forests and meadows. The distribution function that best fits the received power was determined to be Weibull, and the evolution of its parameters was studied as the distance between transmitter and receiver increases. [ABSTRACT FROM PUBLISHER]