Multiple Antenna Environment Research Articles

Design of Coating Materials for Cloaking and Directivity Enhancement of Cylindrical Antennas Using Transformation Optics

In this letter, a novel bifunctional coating layer is proposed for a cylindrical antenna using transformation optics. This layer not only cloaks the omnidirectional antenna from an external source, but also enhances its directivity at the same time. To achieve this, an appropriate coordinate transformation is established so that the cylindrical wavefronts originating from the antenna would be transformed into plane waves. The material properties of the proposed cover are numerically derived by solving the Laplace's equation. Full-wave simulations are performed to verify both the directivity enhancement and cloaking functions of the designed coating layer. Thus, it can be effectively utilized in highly scattering multiple-antenna environments as a shielding mechanism.

Separation of Doppler radar-based respiratory signatures.

Respiration detection using microwave Doppler radar has attracted significant interest primarily due to its unobtrusive form of measurement. With less preparation in comparison with attaching physical sensors on the body or wearing special clothing, Doppler radar for respiration detection and monitoring is particularly useful for long-term monitoring applications such as sleep studies (i.e. sleep apnoea, SIDS). However, motion artefacts and interference from multiple sources limit the widespread use and the scope of potential applications of this technique. Utilising the recent advances in independent component analysis (ICA) and multiple antenna configuration schemes, this work investigates the feasibility of decomposing respiratory signatures into each subject from the Doppler-based measurements. Experimental results demonstrated that FastICA is capable of separating two distinct respiratory signatures from two subjects adjacent to each other even in the presence of apnoea. In each test scenario, the separated respiratory patterns correlate closely to the reference respiration strap readings. The effectiveness of FastICA in dealing with the mixed Doppler radar respiration signals confirms its applicability in healthcare applications, especially in long-term home-based monitoring as it usually involves at least two people in the same environment (i.e. two people sleeping next to each other). Further, the use of FastICA to separate involuntary movements such as the arm swing from the respiratory signatures of a single subject was explored in a multiple antenna environment. The separated respiratory signal indeed demonstrated a high correlation with the measurements made by a respiratory strap used currently in clinical settings.

Restoration of antenna parameters in scattering environments using electromagnetic cloaking

It is proposed that electromagnetic cloaks be used as effective shielding devices which enable improved antenna performance in highly scattering, multiple-antenna environments. In multiple frequency, multiple-antenna environments, each antenna is enclosed in a dispersive cloak that is designed to operate at the transmitting frequencies of the neighboring antennas. The loading effect of large objects in close proximity to a radiating antenna can be removed by enclosing the scatterer with a cloak. Application of cloaks to microwave antenna shielding only requires narrow band performance, which can be realized using currently available metamaterials technology.

Applications of representation theory to wireless communications

In this paper, we demonstrate a new and original way to apply the representation theory of finite groups to the development of space---time codes for use in multiple antenna wireless communications. We include a summary of the relevant mathematical model for wireless communications on a multiple-antenna environment. We apply our construction in two examples and demonstrate that they outperform other designs in the literature.