A millimeter-wave (mm-wave) antenna with enhanced gain for new 5G networks is introduced in this work. A rectangular slot antenna operating at the fundamental mode of the desired frequency band is utilized in this study. The antenna gain is improved by employing a Frequency Selective Surface (FSS). The FSS-based reflectors are designed at the same fundamental mode of the antenna and added under the antenna at a specific distance to achieve the required gain enhancement with a suitable dimension of 25 × 25 × 5 mm³. The antenna gain is increased by around 5.3 dBi when the FSS-based reflectors are added under the antenna. The antenna and the FSS are fabricated and tested. The antenna has tested outcomes without FSS with S₁₁ ≤ -10 dB from 26 GHz up to 29.8 GHz and realized gain of around 4.5 dBi within the entire frequency band and radiation efficiency of around 93 %. While the antenna with FSS has achieved bandwidth with S₁₁ ≤ -10 dB from 25.5 GHz up to 30.8 GHz and realized gain around 10.3 dBi at 28 GHz and radiation efficiency around 90 %. The simulated and tested outcomes have the same trend which validates the suggested antenna to be operated in the new 5G applications. All simulation results are completed using the CST Microwave Studio.

This paper proposes the design of a compact sub-6 GHz four-port flexible antenna for utilization in 5G applications. A two-arm monopole with a coplanar waveguide feed line printed on a flexible substrate was proposed to shape the single-element antenna. The single element was designed, fabricated, and measured first; then, four copies of the single element were organized on a single flexible substrate to compose the four-port antenna. The MIMO antenna was simulated, fabricated, and experimentally measured. All the simulations and measurements of the flexible single element and MIMO antennas are presented. The presented MIMO antenna showed good impedance characteristics, with a deep level of −24 dB from 3 to 4.12 GHz. The antenna had omnidirectional and bi-directional patterns in the φ = 0° and φ = 90° planes. As an important parameter evaluation for MIMO, the mutual coupling between the different ports was investigated. The diversity gain (DG), the total active reflection coefficient (TARC), the mean effective gain (MEG), the envelop correlation coefficient (ECC), and the channel capacity loss (CCL) parameters were investigated and showed good performance. All the obtained simulation results were in a high degree of agreement with the measurement results, supporting the usage of the suggested antenna in 5G communications.

The communications in the millimeter wave (mmWave) band, e.g., WiGig (60 GHz), is considered as one of the main components of 5G and beyond 5G (B5G) networks. However, it is characterized by short range transmissions along with high susceptibility to path blockage, e.g., human shadowing. Thus, mmWave multi-hop relaying using device to device (D2D) connections turns to be an efficient solution to extend its communication range and to route around blockages. In this context, relay probing is essential to discover/explore the candidate multi-hop routes from source-to-destination and then select the best route among them. However, a trade-off exists between relay probing and the required overhead coming from mmWave beamforming training. In this paper, taking advantage of the multi-band μW/mmWave relay nodes, an efficient multi-hop relay probing scheme is proposed for mmWave D2D routing. In this scheme, the collected μW received signal strengths (RSSs) among the distributed relay nodes are used to estimate the probability of their mmWave signal-to-noise power ratios (SNRs) while considering line-of-sight (LOS) and non-LOS (NLOS) path availabilities. Then, based on a proposed probabilistic metric, a hierarchical search algorithm is proposed to jointly discover the relay nodes along the candidate multi-hop routes and enumerate the number of routes expected to maximize the spectral efficiency of the whole path from source-todestination. This is done in an offline phase, and only the relay nodes located within the pre-selected multihop routes are requested to do online relay probing. Numerical analysis confirms the superiority of the proposed mmWave multi-hop relay probing scheme over the candidate techniques.

A dual-band high gain monopole antenna interfaced with an artificial magnetic conductor (AMC) reflector is introduced in this paper. The antenna is composed of an open-loop shape radiator fed with a coplanar waveguide (CPW) to achieve the desired frequency bands with a total size of 28 mm × 36 mm × 1.6 mm (0.224λ₀ × 0.288 λ₀ × 0.012 λ₀ at 2.4 GHz). A dual-band AMC array structure is integrated on the back of the antenna to enhance the achieved gain. The total size of the integrated model is 79.9 mm × 79.9 mm × 8 mm (0.63λ₀ × 0.63 λ₀ × 0.064 λ₀ at 2.4 GHz). The suggested models are fabricated and tested in terms of the S₁₁, radiation pattern, and peak gain to validate the simulation results. The tested results of the antenna with the AMC array illustrate that the antenna operates at two bands where S₁₁ ≤ −10 dB from 2.37 GHz to 2.5 GHz and from 4.45 GHz to 4.9 GHz. Furthermore, peak gain values of 5 dBi and 7.5 dBi are achieved at both bands, respectively. The suggested model can be used in sub-6 GHz 5G indoor and outdoor applications.

Recently, unmanned aerial vehicle (UAV)-based communications gained a lot of attention due to their numerous applications, especially in rescue services in post-disaster areas where the terrestrial network is wholly malfunctioned. Multiple access/gateway UAVs are distributed to fully cover the post-disaster area as flying base stations to provide communication coverage, collect valuable information, disseminate essential instructions, etc. The access UAVs after gathering/broadcasting the necessary information should select and fly towards one of the surrounding gateways for relaying their information. In this paper, the gateway UAV selection problem is addressed. The main aim is to maximize the long-term average data rates of the UAVs relays while minimizing the flights’ battery cost, where millimeter wave links, i.e., using 30~300 GHz band, employing antenna beamforming, are used for backhauling. A tool of machine learning (ML) is exploited to address the problem as a budget-constrained multi-player multi-armed bandit (MAB) problem. In this setup, access UAVs act as the players, and the arms are the gateway UAVs, while the rewards are the average data rates of the constructed relays constrained by the battery cost of the access UAV flights. In this decentralized setting, where information is neither prior available nor exchanged among UAVs, a selfish and concurrent multi-player MAB strategy is suggested. Towards this end, three battery-aware MAB (BA-MAB) algorithms, namely upper confidence bound (UCB), Thompson sampling (TS), and the exponential weight algorithm for exploration and exploitation (EXP3), are proposed to realize gateways selection efficiently. The proposed BA-MAB-based gateway UAV selection algorithms show superior performance over approaches based on near and random selections in terms of total system rate and energy efficiency.

A novel dual-wideband textile antenna designed for wearable applications is introduced in this study. Embedding antennas into wearable devices requires a detailed analysis of the specific absorption rate (SAR) to ensure safety. To achieve this, SAR values were meticulously simulated and evaluated within a human voxel model, considering various body regions such as the left/right head and the abdominal region. The proposed antenna is a monopole design utilizing denim textile as the substrate material. The characterization of the denim textile substrate is carried out using two different methods. The first analysis included a DAC (Dielectric Assessment Kit), while a ring resonator technique was employed for the second examination. Operating within the frequency bands of (58.06%) 2.2–4 GHz and (61.43) 5.3–10 GHz, the antenna demonstrated flexibility in its dual-wideband capabilities. Extensive simulations and tests were conducted to assess the performance of the antenna in both flat and bent configurations. The SAR results obtained from these tests indicate that the antenna complies with safety standard limits when integrated with the human voxel model. This validation underscores the potential of the proposed antenna for seamless integration into wearable applications, offering a promising solution for future developments in this domain.