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This article introduces an innovative approach to significantly broaden the bandwidth of Cylindrical Dielectric Resonators. A four-element Camembert-Shaped Cylindrical Dielectric Resonator Antenna (CDRA) is presented, using an air gap separating the resonators to enhance the antenna bandwidth. The radiators, i.e., the DRA blocks, are made of high relative-permittivity ceramic material (εr = 25 & 30) and are excited by microstrip-line feed. The proposed methodology involves the strategic design of these resonators, incorporating dielectric materials to finely optimize the frequency response. Experimental validation demonstrates a remarkable improvement in bandwidth when compared to conventional methodologies. This novel technique holds immense promise for applications requiring wideband antennas. The demonstrated effectiveness of this approach not only addresses contemporary challenges but also opens up new avenues in antenna design, catering to the escalating demands of modern communication systems. In addition to the compact dimensions of the elementary radiating element, the separation distance between them, set at λ/4, enhances the array antenna overall size, and its gain is nearly 10 dBi. The proposed antenna covers cellular network applications such as UMTS mobile phone band around 2.1 GHz, as well as wireless DECT phone bands around 1.9 GHz, facilitating data transmission over short distances and beyond, with an impedance bandwidth of 20%.

This work introduces a novel approach to improve the precision of distance estimation in localization systems by using existing LoRaWAN and RSSI-based techniques. Despite the benefits of range and power efficiency, these systems exhibit limited accuracy in practical situations. To address the limitation, this study provides an innovative technique that greatly improves the precision of distance estimations, particularly in urban environments. The fundamental basis of this approach lies in the use of a dynamic path loss model. An additional element is to accommodate the varied and dynamic conditions of signal transmission in metropolitan areas. A better Kalman filter is also used in the study. This is important because it reduces the effects of multipath fading and environmental noise that often make RSSI-based localization in LoRaWAN networks less accurate. The study further examines the influence of the environmental exponent, also known as the path loss exponent, on the RSSI results and the precision of the distance measurements. This methodology achieves the average error under 1 meters for indoor environments and under 7 meters for outdoor environments. Finally, the Cumulative Density Function (CDF) shows 90 % of the distance estimation algorithm error for indoor environment is lower than 1.08 meters while for outdoor environment is lower than 7.55 meters. Based on these improvements, the introduced methodology not only enhances and improves existing approaches but also optimizes the precision and dependability of urban localization technologies, with substantial implications for a variety of practical applications.

Wearable waveguide surfaces can be integrated into textiles to improve Wireless Body Area Networks (WBANs). In this work, a compact 30 mm x 30 mm dual-branch resonator end-launcher to enable communication through a waveguide surface manufactured with textile-compatible material at 2.4GHz is proposed. A 25 mm x 25 mm clearance zone area is respected for electronic component integration. The end-launcher topology uses a balanced dual-branch configuration to maximize electromagnetic coupling with the flexible waveguide surface. A design methodology is proposed to co-design the end-launcher and the waveguide surface. Experimental measurements on the human body torso are presented with 0.3 dB/cm insertion loss between 2.4 and 2.48 GHz. The final result is an autonomous, compact, wireless-contact, and battery-powered end-launcher for innovative clothing applications.

This paper presents a 3D-printed fully dielectric bi-material reflectarray with bandgap characteristics for multi-band applications. To achieve bandgap characteristics, a “1D Bragg reflector” unit cell is used. The latter is a layered structure characterized by a spatial distribution of refractive index that varies periodically along one dimension. By appropriately selecting the dimensions, the bandgap can be shifted to cover the desired frequency bands. To validate this bandgap characteristic, a (121.5 mm × 121.5 mm) with an f/D ratio of 0.5 reflectarray was fabricated. The measured gain at 27 GHz is 27.22 dBi, equivalent to an aperture efficiency of 35.05%, demonstrating good agreement between simulated and measured performances within the frequency range of 26–30 GHz. Additionally, the transparency of the reflectarray was verified by measuring the transmission coefficient, which exhibited a high level of transparency of 0.32 dB at 39 GHz. These features make the proposed reflectarray a good candidate for multi-band frequency applications.

Near-infrared (NIR) spectroscopy has become a popular technique for assessing food quality due to its advantages over complex chemical analysis methods. However, the application of NIR spectroscopy for evaluating fish quality based on urea content has not been extensively explored. This study investigates the use of NIR spectroscopy in combination with machine learning (ML) techniques to classify fish samples into two safety classes—Safe and Unsafe—based on their urea content. A comprehensive NIR dataset comprising 11,960 spectra collected from eight distinct positions within the fish body was obtained from 299 fish samples of mackerel, tuna, and pompano species. ML experiments were conducted to classify fish samples based on whether their urea content exceeded the permissible limit of 1000 ppm. To address class imbalance and optimize ML models, various data pre-processing and feature extraction techniques, as well as ML algorithms, were explored. The results demonstrated that utilizing NIR data specifically obtained from the outer skin of the stomach yielded superior models for fish safety classification. A feature extraction method employing pre-processed NIR spectra and their first derivatives, combined with an optimized convolutional neural network architecture, outperformed traditional ML classifiers, achieving an accuracy of up to 83.9%.

This work presents the design of a compact dual-port circularly polarized antenna based on the new coupler topology. The antenna can radiate a right-hand circular polarization (RHCP) in two opposite directions depending on the input port. In the proposed structure, the radiating system has three inverted F antennas connected to a 120° hybrid coupler. The modeling and design of the 5-ports hybrid coupler are described and experimentally validated. The antenna prototype is fabricated using two 1.6mm-thick low-cost FR4 Epoxy substrates assembled with metal wires, with a dimension of 80mm $\times80$ mm $\times12$ mm (ka $ < 0.74$ ). The proposed antenna provides the realized RHCP gain of 2.4 dBic and 1.8dBic at 868 MHz for Port 1 and Port 2, respectively.

Indoor object localization and positioning is part of the space-awareness concept which has seen a rising popularity in recent Internet of Things (IoT) research and applications. This article presents a novel method to improve the localization performance of ultra-wide band (UWB) real-time locating systems (RTLS) by improving the transmitting and receiving reader and tag antennas. Patch directional UWB antennas with relatively higher gain compared to the generally used standard omnidirectional monopole UWB antennas have been exploited to achieve a larger localization range. Furthermore, the patch antennas were designed to have wideband circular polarization to achieve two objectives: a received power independent of the orientation of the tagged objects that need to be detected, and the filtering of unwanted multipath signals. A measurement campaign was conducted using a commercially available RTLS with conventional antennas and then with the newly designed antennas. A comparison between the localization results of the two antenna types demonstrates an improved range with almost 100 m difference, received power independent of tag orientation, and increased multipath mitigation with the directional circularly polarized antennas.

A new compact multifunctional pattern reconfigurable $2\times 2$ antenna array at 3.65 GHz with high gain and 16 (Multiple Input Multiple Output) MIMO modes is proposed. The single-element antenna includes 4 U-slots etched on the ground plane, with orthogonal slot orientations for polarization un-correlation, and fed using a reconfigurable feeding network with 4 PIN diodes. Hence, the single-element antenna is a pattern reconfigurable U-slot antenna with four pattern configurations. The average efficiency of 80%, the peak gain of 9.4 dB, and an overlapped −10 dB impedance-bandwidth of 200 MHz at a resonant frequency of 3.65 GHz in the n78 5G band are achieved. The single-element size is $55.5\times 54$ mm2, $0.66 \lambda _{0} \times 0.65 \lambda _{0}$ . The horizontal and vertical distances between the U-slots in a single-element are 30 mm $(0.36\lambda _{0})$ , and 27 mm $(0.32\lambda _{0})$ , respectively. The $2\times 2$ antenna array of such an element with a 58.5 mm $(0.7\lambda _{0})$ between the elements occupies a volume of $140\times 140\times 21$ mm3. The $2\times 2$ elements provide 16 reconfigurable U-slots with two modes of operation, Array Mode and Multiple-Input-Multiple-Output (MIMO) Mode. For the MIMO Mode, the antenna has a maximum Envelope Correlation Coefficient (ECC) of 0.1194 between the radiation patterns and a minimum isolation of 20 dB between the four ports. For the array Mode, a $4\times 4$ antenna array has a peak gain of 17 dBi, and a beam-steering range of $-50^{\circ} \leq \theta \leq 50^{\circ} $ in the two principle planes. The antenna is suitable for small cell base-station applications.

This article presents a multi-band right-hand circularly polarized antenna designed for the Cube Satellite (CubeSat). Based on a quadrifilar structure, the antenna provides circular polarization radiation suitable for satellite communication. Moreover, the antenna is designed and fabricated using two 1.6 mm thickness FR4-Epoxy boards connected by metal pins. In order to improve the robustness, a ceramic spacer is placed in the centerboard, and four screws are added at the corners to fix the antenna to the CubeSat structure. These additional parts reduce antenna damage caused by vibrations in the launch vehicle lift-off stage. The proposal has a dimension of 77 × 77 × 10 mm3 and covers the LoRa frequency bands at 868 MHz, 915 MHz, and 923 MHz. According to the measurements in the anechoic chamber, antenna gains with the values of 2.3 dBic and 1.1 dBic are obtained for the 870 MHz and 920 MHz, respectively. Finally, the antenna is integrated into a 3U CubeSat that was launched by a Soyuz launch vehicle in September 2020. The terrestrial-to-space communication link was measured, and the antenna performance was confirmed in a real-life scenario.

In this paper, an electronically pattern reconfigurable antenna for Internet of Things (IoT) applications is presented. The antenna consists of 4 wire-patches sharing the same ground plane. This radiating element can switch between four end-fire radiation states in less than 5 us and achieves a 290 MHz frequency bandwidth from 2.25 to 2.54 GHz. The results show that this antenna can realize a peak gain of 3.9 dBi at 2.44 GHz and a front-to-back ratio greater than 6.5 dB. A single low-power, low-insertion loss SP4T switch enables the radiation pattern steering. This approach avoids the use of multiple electronic components in the reconfiguration mechanism, thus accommodating the IoT microcontroller’s limited resource constraints. The antenna structure is compact and printed on two cost-effective FR-4 printed circuit boards (PCBs). Thanks to its high performance, small size, low cost, and low-power characteristics, the proposed structure is suitable for IoT applications.

A compact pattern reconfigurable antenna with four radiation patterns is proposed for sub-GHz IoT applications. The antenna has two functional modes; Mode I has three uncorrelated patterns, while Mode II has electric and magnetic omnidirectional patterns. The resonant frequency of the antenna is 868 MHz with measured overlapped −6 dB impedance-bandwidths of 22 MHz and 20 MHz for Mode I and Mode II, respectively. The antenna is integrated in an $80\times 55$ mm2 terminal. The radiating elements consist of two meandered slots and one meandered monopole. Four pattern configurations are obtained with an average peak gain of 0 dBi, and an average radiation efficiency of 43.3%. Two of the patterns are with 5 dB directivity, and the other two are omnidirectional patterns. Pattern reconfigurability is achieved using four PIN diodes. The antenna is fabricated on a low-cost FR-4 substrate. By removing FR-4 material inside the slots, slots’ radiation efficiencies were improved by 2.25 dB.

Fruit classification is required in many smart-farming and industrial applications. In the supermarket, a fruit classification system may be used to help cashiers and customer to identify the fruit species, origin, ripeness, and prices. Some methods, such as image processing and NIRS (near-infrared spectroscopy) are already used to classify fruit. In this paper, we propose a fast and cost-effective method based on a low-cost Vector Network Analyzer (VNA) device augmented by K-nearest neighbor (KNN) and Neural Network model. S-parameters features are selected, which take into account the information on signal amplitude or phase in the frequency domain, including reflection coefficient S11 and transmission coefficient S21. This approach was experimentally tested for two separate datasets of five types of fruits, including Apple, Avocado, Dragon Fruit, Guava, and Mango, for fruit recognition as well as their level of ripeness. The classification accuracy of the Neural Network model was higher than KNN with 98.75% and 99.75% on the first dataset, whereas the KNN was seen to be more effective in classifying ripeness with 98.4% as compared to 96.6% for neural network.

This article presents a reconfigurable antenna using digitally tuneable capacitors (DTCs). Mounted on a 120 × 200 mm2 ground plane, the radiating element has very compact dimensions of 0.06λg × 0.016λg × 0.0016λg (with λg being the wavelength at 585 MHz). The proposed structure could be operated in the white-space frequency band from 470 to 700 MHz. The antenna system is composed of two radiated elements that are placed at the corner of the board. The active components were soldered onto the antennas and controlled by an embedded microcontroller via the I2C interface. Antenna impedances were simulated and evaluated by measurement with an impedance-matching bandwidth of 39.32% (470–700 MHz) for an S11 less than −6 dB. Furthermore, the numerical results show a realized maximal gain ranging from −2.2 dBi at 470 MHz to 1.87 dBi at 700 MHz. Lastly, the diversity gains based on the radiation pattern of two resonators were calculated. The results show envelope correlation coefficient (ECC) values lower than 0.5 for the different configurations.

This manuscript reports the first leaky-wave antenna (LWA) array excited by a photomixer as well as its potential application for alignment in wireless links. The designed array is manufactured in printed circuit board (PCB) technology, works at the E-band (from 75 to 85 GHz), and provides a directive beam of about 18 dBi with a frequency scanning span of 22°. The antenna element consists of a microstrip line periodically loaded with stubs, and it has been designed employing a hybrid approach combining full-wave simulations and transmission line theory. This approach enables the optimization of the periods when the open-stopband of the LWA is mitigated or removed at the frequency of broadside emission. The proposed antenna was first tested using a ground signal ground (GSG) probe; the measured return loss and radiation patterns of the fabricated prototype were in good agreement with full-wave simulations. Then, the LWA array was integrated with the photomixer chip using conductive epoxy threads. Measurements of the radiated power yielded a maximum of 120 µW at 80.5 GHz for a 9.8 mA photocurrent. Finally, the antenna was used in a 25 cm wireless link, obtaining a 2.15 Gbps error-free data rate.

A 4 × 4 MIMO multiband antenna system for mobile handsets is proposed in this paper. The placement of the elements on the terminal chassis as well as the single structure has been optimized in order to reduce the Envelope Correlation Coefficient (ECC). Simulated and measured results, including also the integration with a a real 7-inch commercial tablet, aimed at validating the proposed solution are presented.