This paper presents a multiple input multiple output (MIMO) system for sub-6 GHz using a two-port cylindrical dielectric resonator (CDR). This band is ideal for 5G applications, providing a balanced combination of coverage and capacity, as well as offering high data rates and low latency. The proposed MIMO is excited by an aperture-coupled feed structure composed of driven elements consisting of an elliptical-shaped step impedance transform line to enhance CDR coupling. Aperture coupling is used to excite the HEM11δ mode without the involvement of any hybrid mode. The purpose of the aperture coupling in the CDR antenna is to launch the HEM11δ mode, which is a magnetic dipole that provides a stable radiation pattern in the 3.2–3.7 GHz band, allowing for efficient transmission and reception of the data. Symmetrically oriented CDR and the presence of orthogonal fields provide good isolation, which can be further improved by the insertion of an asymmetric cross slot. The designed CDR-based MIMO antenna achieves excellent isolation of over 20 dB and demonstrates improved envelope correlation coefficient (ECC) values, resulting from low field correlation, across the entire frequency band of operation. Almost all the major diversity analysis was carried out for the desired sub-6 GHz band while maintaining a relatively compact size. Based on the measured results, it is confirmed that the proposed CDR-based MIMO antenna is appropriate for sub-6 GHz applications.

Hydrogen is a leading candidate for zero-emission propulsion in aviation, particularly when stored and utilised in its liquid form. However, key components such as composite cryogenic pressure vessels remain at low Technology Readiness Levels (TRL), requiring further investigation into their structural performance under realistic operational conditions. The present work aims to provide a validated numerical methodology for simulating the thermomechanical behaviour and the progressive damage evolution of composite cryogenic hydrogen tanks. The finite element framework incorporates ply-level failure criteria and stiffness degradation laws to capture intra-laminar damage mechanisms under combined pressure and temperature loads. The modelling approach is validated against experimental data from coupon-level open-hole tension tests and subcomponent-scale composite pipes burst tests, demonstrating strong correlation in terms of failure onset and progression.

The validated methodology is subsequently applied to a demonstrator, comprising a composite liquid hydrogen tank, subjected to three representative loading scenarios: internal pressure, cryogenic temperature and combined cryogenic-mechanical loading. Results reveal that matrix-dominated damage initiates near the cylinder – dome interfaces of the tank and propagates across the laminate, while fibre failure is not observed in the investigated load cases. This suggests that potential hydrogen leakage is the initial critical failure condition that occurs before any other important structural damage of the tank, highlighting the need for appropriate tank design. The performed study contributes to the understanding of structural integrity of composite cryogenic tanks and offers a computational basis for future design and certification efforts in hydrogen aviation systems.

The design of a hexagonal six-ridged waveguide (H6RWG) phased array antenna (PAA) element featuring a wide scan angle matched slotted horn aperture is presented for Ka-band satellite downlink in low Earth orbit non-terrestrial network applications. The proposed PAA element is evaluated against an open-ended waveguide (OEWG) PAA element and achieves a very low active reflection coefficient (ARC) of less than -18 dB and a total antenna efficiency greater than 84% over a wide bandwidth from 17.3 to 20.2 GHz with a $\pm$ 50$^\circ$ scan range. Specifically, the aperture of the H6RWG was designed to limit the variations in ARC during scanning, thereby minimizing load pulling of integrated active devices, as demonstrated with a power amplifier (PA) in a co-simulation. As a result, the power-added efficiency, output power, and linearity of the PA remained stable over the bandwidth and scan range. Compared to the OEWG PAA, the co-polarized system efficiency and equivalent isotropic radiated power are improved for most scan angles within the bandwidth, especially at high scan angles.