The rapid progress in additive manufacturing (AM) has unlocked significant possibilities for producing 316/316L stainless steel components, particularly in industries requiring high precision, enhanced mechanical properties, and intricate geometries. However, the widespread adoption of AM—specifically Directed energy deposition (DED), selective laser melting (SLM), and electron beam melting (EBM) remains challenged by inherent process-related defects such as residual stresses, porosity, anisotropy, and surface roughness. This review critically examines these AM techniques, focusing on optimizing key manufacturing parameters, mitigating defects, and implementing effective post-processing treatments. This review highlights how process parameters including laser power, energy density, scanning strategy, layer thickness, build orientation, and preheating conditions directly affect microstructural evolution, mechanical properties, and defect formation in AM-fabricated 316/316L stainless steel. Comparative analysis reveals that SLM excels in achieving refined microstructures and high precision, although it is prone to residual stress accumulation and porosity. DED, on the other hand, offers flexibility for large-scale manufacturing but struggles with surface finish and mechanical property consistency. EBM effectively reduces thermal-induced residual stresses due to its sustained high preheating temperatures (typically maintained between 700 °C and 850 °C throughout the build process) and vacuum environment, but it faces limitations related to resolution, cost-effectiveness, and material applicability. Additionally, this review aligns AM techniques with specific defect reduction strategies, emphasizing the importance of post-processing methods such as heat treatment and hot isostatic pressing (HIP). These approaches enhance structural integrity by refining microstructure, reducing residual stresses, and minimizing porosity. By providing a comprehensive framework that connects AM techniques optimization strategies, this review serves as a valuable resource for academic and industry professionals. It underscores the necessity of process standardization and real-time monitoring to improve the reliability and consistency of AM-produced 316/316L stainless steel components. A targeted approach to these challenges will be crucial in advancing AM technologies to meet the stringent performance requirements of various high-value industrial applications.

Unmanned aerial vehicles (UAVs) need high data rate connectivity, which is achievable through mm-waves and sub-THz bands. The proposed two-port leaky wave MIMO antenna, employing a coplanar proximity technique that combines capacitive and inductive loading, addresses this need. Featuring mesh-like slots and a vertical slot to mitigate open-stopband (OSB) issues, the antenna radiates broadside and bidirectionally. H-shaped slots on a strip enhance port isolation, and a coffee bean metasurface (MTS) boosts radiation efficiency and gain. Simulations and experiments considering various realistic scenarios, each at varying vertical and horizontal distances, show steered beam patterns, circular polarization (CP), and high-gain properties, with a maximum gain of 13.8 dBi, an axial ratio (AR) 9.98 dB, and an envelope correlation coefficient (ECC) <0.003. This design supports drones-to-ground (D2G), drone-to-drone (D2D), and drone-to-satellite (D2S) communications.

In this study, at ultra-wideband (UWB) frequency band (3.1–10.6 GHz), we propose the use of compact 2:1 and 3:1 nonuniform transmission line Wilkinson power dividers (NTL WPDs) as feeding networks for simple 2 × 1 linear UWB Vivaldi tapered and nonuniform slot antenna (VTSA and VNSA) arrays. The 2:1 and 3:1 tapered transmission line (TTL) WPDs are designed and tested in this work as benchmarks for NTL WPDs. The VTSA array provides measured S₁₁ < −10.28 dB at 2.42–11.52 GHz, with a maximum gain of 8.61 dBi, which is 24.39% higher than the single element. Using the VNSA array, we achieve 52% compactness and 6.76% bandwidth enhancement, with good measured results of S₁₁ < −10.2 dB at 3.24–13 GHz and 15.11% improved gain (8.14 dBi) compared to the VNSA single element. The findings show that the NTL and Vivaldi nonuniform slot profile antenna (VNSPA) theories are successful at reducing the size of the UWB WPD and VTSA without sacrificing performance. They also emphasize the Vivaldi antenna’s compatibility with other circuits. These compact arrays are ideal for high-resolution medical applications like breast cancer detection (BCD) because of their high gain, wide bandwidth, directive stable radiation patterns, and low specific absorption rate (SAR). A simple BCD simulation scenario is addressed in this work. Detailed parametric studies are performed on the two arrays for impedance-matching enhancement. The computer simulation technology (CST) software is used for the simulation. Hardware measurement results prove the validity of the proposed arrays.

This paper introduces a novel miniaturized, four-mode, semi-flexible leaky wave Multiple-Input Multiple-Output (MIMO) antenna specifically designed to advance vehicular communication systems. The proposed antenna addresses key challenges in 5G low- and high-frequency bands, including millimeter-wave communication, by integrating innovative features such as a periodic Spoof Surface Plasmon Polariton Transmission Line (SSPP-TL) and logarithmic-spiral-like semi-circular strip patches parasitically fed via orthogonal ports. These design elements facilitate stable impedance matching and wide impedance bandwidths across operating bands, which is essential for vehicular networks. The hybrid combination of leaky wave and SSPP structures, along with a defected wide-slot ground structure and backside meander lines, enhances radiation characteristics by reducing back and bidirectional radiation. Additionally, a naturalization network incorporating chamfered-edge meander lines minimizes mutual coupling and introduces a fourth radiation mode at 80 GHz. Compact in size (14 × 12 × 0.25 mm³), the antenna achieves high-performance metrics, including S11 < −18.34 dB, dual-polarization, peak directive gains of 11.6 dBi (free space) and 14.6 dBi (on vehicles), isolation > 27 dB, Channel Capacity Loss (CCL) < 3, Envelope Correlation Coefficient (ECC) < 0.001, axial ratio < 2.25, and diversity gain (DG) > 9.85 dB. Extensive testing across various vehicular scenarios confirms the antenna’s robustness for Vehicle-to-Vehicle (V2V), Vehicle-to-Pedestrian (V2P), and Vehicle-to-Infrastructure (V2I) communication. Its exceptional performance ensures seamless connectivity with mobile networks and enhances safety through Specific Absorption Rate (SAR) compliance. This compact, high-performance antenna is a transformative solution for connected and autonomous vehicles, addressing critical challenges in modern automotive communication networks and paving the way for reliable and efficient vehicular communication systems.

This work presents a compact ultra-wideband (UWB) Vivaldi tapered slot antenna for short-range vehicular communication and broadband UWB applications. The proposed design is developed using two simple performance-enhancement and size-reduction techniques: a radial-to-radial microstrip-to-slot transition and an impedance-matching transformer. The antenna employing only the radial-to-radial transition is referred to as VTSAR, while the final design incorporating both the radial-to-radial transition and the matching transformer is referred to as VTSARMT. Unlike many compact UWB antenna designs that rely on complex structural loading, parasitic elements, or additional decoupling components, the proposed approach improves compactness, impedance bandwidth, and gain through a simple feeding-transition modification supported by systematic parametric analysis. The intermediate VTSAR provides a 9.84% footprint-area reduction relative to the reference VTSA, while the final VTSARMT further increases the footprint-area reduction to 16.67%. The fabricated VTSARMT exhibits measured impedance matching below −10.61 dB from 2.58 to 22.34 GHz, corresponding to a 47.67% measured bandwidth improvement relative to the reference VTSA. The maximum measured realized gain increases from 6.51 dBi for the reference VTSA to 7.45 dBi for the VTSARMT, while the measured total radiation efficiency ranges from 47.7% to 94.08%. An approximately stable measured group delay of 1 ns is obtained across most of the operating band. To assess the effects of vehicle integration, the proposed antenna is further evaluated through CST-based stationary rooftop-mounted two-vehicle and three-vehicle configurations. The analysis includes radiation-pattern assessment, transmission coefficients, and CST-based received-power evaluation. These simulations provide a comparative assessment of stationary directional links rather than experimental validation of a dynamic V2V channel. The CST-based vehicle analysis provides a preliminary assessment of rooftop integration and stationary directional V2V links under controlled simulation conditions.

This paper proposes a compact four-port Hilbert-slot MIMO antenna (HSMA)for 5G FR2 mmWave wearable medical telemetry and body-centric communication. The antenna is realized on a semi-flexible Rogers RT/Duroid 5880 substrate with an overall footprint of 12.32 × 12.32 × 0.508 mm³. The proposed work develops a compact Hilbert-slot radiator into a four-port 2 × 2 MIMO configuration to enhance port diversity, inter-port isolation, and body-centric link robustness. The simulated four-port HSMA provides super-wideband impedance matching from 24.05 to 62.64 GHz, while the fabricated prototype achieves measured matching from 24.71 to 63.81 GHz, corresponding to a 39.1 GHz measured bandwidth. The measured inter-port transmission coefficients remain mostly below −20 dB across the main operating band, confirming suitable MIMO isolation within the compact layout. The proposed HSMA also demonstrates practical radiation and diversity performance over the highlighted 24–64 GHz band. The measured realized gain reaches 7.52 dBi, and the measured radiation efficiency remains between 51.43% and 76.23%. The calculated measured MIMO diversity parameters show ECC values below 0.0175 and DG values above 9.998 dB, confirming weak correlation between ports and near-ideal diversity behavior. To assess wearable suitability, the antenna is further investigated under bending and realistic body-loading conditions using the CST Gustav voxel human model. In addition, orientation-based body placements are considered to evaluate telemetry paths between distributed body-worn nodes. CST-simulated S₂₁ parameters are then used to calculate received power and link margin, providing a link-level assessment of the proposed wearable telemetry system. The results show that the proposed compact four-port HSMA combines continuous super-wideband operation, good MIMO isolation, low ECC, high DG, SAR compliance, bending robustness, and body-centric link feasibility, making it a promising candidate for 5G FR2 wearable biomedical telemetry, WBAN, and future mmWave body-centric communication systems.