A four-port wideband cavity-backed antenna is presented for indoor base stations applications. The antenna is composed of a square open cavity with an X-shaped isolating block and 4 feeding monopoles symmetrically and orthogonally arranged in the aperture of the cavity. A novel methodology based on Characteristic Modes Analysis (CMA) is used for identifying the modes which are contributing to the coupling. As a result of this analysis, an X-shaped isolating block placed at the center of the cavity is proposed for increasing the isolation between ports. A wide-band four-port antenna with unidirectional radiation patterns is obtained with a measured impedance bandwidth ( S ₁₁ <; -10 dB) ranging from 1.55 to 6 GHz (118%), covering most of the sub-6 GHz 5G bands. The proposed antenna provides four independent radiation patterns, with 16 dB of measured minimum isolation between ports and an efficiency higher than 84%. Multiple-input multiple-output (MIMO) compatibility is confirmed with a 4×4 MIMO simulated system with an envelope correlation coefficient (ECC)<; 0.5 in different propagation conditions. The antenna is easy to fabricate and presents a compact size of 129.5×129.5 ×28.2 mm ³ ( 0.68λ×0.68λ×0.15λ, at a frequency f = f _min = 1.55 GHz). Moreover, the antenna has the advantage of avoiding complex feeding structures with baluns or directional couplers.

In this paper, a path loss characterization at millimeter-wave (mmWave) frequencies is performed in a typical indoor office environment. Path loss results were derived from propagation channel measurements collected in the 25–40 GHz frequency band, in both line-of-sight (LOS) and obstructed-LOS (OLOS) propagation conditions. The channel measurements were performed using a frequency-domain channel sounder, which integrates an amplified radio over fiber (RoF) link to avoid the high losses at mmWave. The path loss was analyzed in the 26 GHz, 28 GHz, 33 GHz and 38 GHz frequency bands through the close-in free space reference distance (CI) and the floating-intercept (FI) models. These models take into account the distance dependence of the path loss for a single frequency. Nevertheless, to jointly study the distance and frequency dependence of the path loss, multi-frequency models were considered. The parameters of the ABG (A-alpha, B-beta and G-gamma) and the close-in free space reference distance with frequency path loss exponent (CIF) models were derived from the channel measurements in the whole 25–40 GHz band under the minimum mean square error (MMSE) approach. The results show that, in general, there is some relationship between the model parameters and the frequency. Path loss exponent (PLE) values smaller than the theoretical free space propagation were obtained, showing that there are a waveguide effect and a constructive interference of multipath components (MPCs). Since the measurements were obtained in the same environment and with the same configuration and measurement setup, it is possible to establish realistic comparisons between the model parameters and the propagation behavior at the different frequencies considered. The results provided here allow us to have a better knowledge of the propagation at mmWave frequencies and may be of interest to other researchers in the simulation and performance evaluation of future wireless communication systems in indoor hotspot environments.

A novel methodology based on the sectorization of multiple-port cavities with azimuthal symmetry into sector unit cells is presented to design 5G multiple-input multiple-output (MIMO) sub-6 GHz antennas. The methodology divides an N-port cavity antenna into N unit cells and predicts the performance of the N-port design with the analysis of two adjacent cells. This approximation reduces the time and complexity of the simulation of cavity antennas with a high number of ports. For the theoretical justification, cavity mode analysis of a closed cavity and characteristic modes analysis of open and sector cavities is addressed. With the use of the proposed methodology, five different cavity designs with circular, square, hexagonal, octagonal, and saw-tooth geometries are presented in this article. In addition, the fabrication of the 4-port circular shape design and its MIMO performance is also studied. Results show an impedance bandwidth of 130% (1.27-6 GHz), and an envelope correlation coefficient (ECC) lower than 0.1.

A low-profile on-ground chip antenna is presented to be installed in size-limited devices for 868 MHz IoT applications. The antenna presents a size of 0.064 $\times 0.045\times 0.007\lambda _{0}^{3}$ , has been fabricated in low-temperature cofired ceramic (LTCC) technology and is meant to be placed on a ground plane without a clearance area required. A study regarding matching and total efficiency is performed by analyzing the antenna in different positions of a variable-size ground plane with the use of characteristic modes analysis (CMA) and the correlation between modal and total radiated fields. The analysis demonstrates through the correlation which are the excited modes of the ground plane and, consequently, which is the best position for the antenna. Results show frequency stability and a total efficiency difference of up to 8.8 dB between different positions.

This paper presents a study on the development of the cross-curricular learning outcome (CCLO) “Ethical, environmental and professional responsibility” for students of different Bachelor’s Degrees taught at Universitat Politècnica de València (Spain). The work involved in the development of this learning outcome entails great complexity, given the double dimension of responsibility that it involves. At the end of their training at the university, students are expected to show ethical, environmental, and professional responsibility towards themselves and others. Interviews have been conducted with lecturers who work and assess this outcome in their subjects, most/all of them related to science and engineering. The objective was to identify the learning approach used in the different subjects to guarantee the acquisition of this CCLO by the students. A focus group has also been carried out with students to determine the importance they give to this learning outcome, and to know their degree of satisfaction with the training received. The methodology used to obtain the data from lecturers and students and to process the information to get a precise diagnosis is fully described in the paper. Results are satisfactory to some extent: most of the lecturers carry out appropriate activities and most students achieve the expected proficiency level. Finally, recommendations are given to improve the development of this cross-curricular learning outcome.