Array Coupling in Terms of Characteristic Modes and Generalized Scattering Matrices

Modeling of mutual coupling in antenna arrays using generalized scattering matrices in terms of characteristic modes is proposed. Potential applications of this model are diverse. On the one hand, the proposed model can be used as a basis for mutual coupling calculation methods. On the other hand, the parameters introduced by the model provide a new intermediate level to understand coupling phenomena at a higher and more abstract level. After introducing the model, the question of how to describe the degrees of freedom of an antenna in this model is addressed. For this purpose, a formalism to synthesize antennas from a predefined geometry with still undefined ports is mathematically formulated. Furthermore, three exemplary applications of the model are given. A first example illustrates the accuracy of the model and the validity of the implementation. A second example illustrates the intuitiveness of the model based on a simple application, and a third example shows the application to a complex real-world design problem of a circularly polarized patch antenna array.

Deriving Characteristic Mode Eigenvalue Behavior Using Subduction of Group Representations

A method to derive features of modal eigenvalue traces from known and understood solutions is proposed. It utilizes the concept of subduction from point group theory to obtain the symmetry properties of a target structure from those of a structure with a higher order of symmetry. This is applied exemplary to the analytically known characteristic modes (CMs) of the spherical shell. The eigenvalue behavior of a cube in free space and a cuboid on a perfectly electrically conducting plane are continuously derived from this. In this process, formerly crossing eigenvalue traces are found to split up, forming a split trace crossing avoidance (STCA). This finding is used to explain indentations in eigenvalue traces observed for three-dimensional structures, that are of increasing interest in recent literature. The utility of this knowledge is exemplified through a demonstrator antenna design. The dimensions of the antenna structure are chosen so the STCA is outside the target frequency range, avoiding negative impacts on input matching and the frequency stability of the far field patterns.

Evaluation Method and Design Guidance for Direction Finding Antenna Systems

A deterministic evaluation procedure for multi-port direction finding antennas is proposed. It is based on a direction finding uncertainty parameter, which describes how well different directions of arrival and polarizations are distinguishable. By investigating a simple antenna array, it is shown that the proposed parameter provides additional insight into the behavior of an antenna system, when compared to established methods. Moreover, since the uncertainty parameter is calculated from a set of far fields, it is applicable to port far fields as well as Characteristic Modes. This finding is utilized to derive a design guidance: Starting with a set of Characteristic Mode far fields, the angular distribution of the uncertainty is investigated to verify that no ambiguities are present. Different sets of far fields are compared and the differences regarding their direction finding behavior are visualized and explained using the uncertainty in conjunction with an estimate of the incident field. To quantify these differences, a key performance indicator is introduced that summarizes the direction finding capabilities over a selected angular region. To demonstrate the design process, a Multi-Mode Multi-Port Antenna with three uncorrelated ports is developed, manufactured and measured.

Joint Communication, Sensing and Localization for Airborne Applications

With the upcoming trends in autonomous driving and urban air mobility, the number of self-navigating vehicles will increase, since they are foreseen for deliveries as well as autonomous taxis among other applications. To this end, a multitude of on-board systems for wireless communication, environment sensing, and localization will become mandatory. This is particularly true for unmanned aerial vehicles (UAVs), since participation in the airspace requires compatibility to and safe interaction with established users. A certain number of systems are already in-use and occupy defined spectra as well as installation space, which limits the freedom in the design of new systems. The miniaturization of aerial vehicles like drones for delivery services further reduces the degrees of freedom, especially in terms of size and weight of any additional equipment. Hence, in this paper a joint approach of the design of joint communication, sensing and localization for UAVs is discussed. Towards this goal, multi-mode multi-port antennas and joint waveform design are proposed as a part of the solution, when elevating autonomous driving to the third dimension.

Antenna De-Embedding in FDTD Using Spherical Wave Functions by Exploiting Orthogonality

De-embedding antennas from the channel using Spherical Wave Functions (SWF) is a useful method to reduce the numerical effort in the simulation of wearable antennas. In this paper an analytical solution to the De-embedding problem is presented in form of surface integrals. This new integral solution is helpful on a theoretical level to derive insights and is also well suited for implementation in Finite Difference Time Domain (FDTD) numerical software. The spherical wave function coefficients are calculated directly from near-field values. Furthermore, the presence of a near-field scatterer in the de-embedding problem is discussed on a theoretical level based on the Huygens Equivalence Theorem. This makes it possible to exploit the degrees of freedom in such a way that it is sufficient to only use out-going spherical wave functions and still obtain correct results.

Antenna Optimization for WBAN Based on Spherical Wave Functions De-Embedding

Antennas for wireless body area networks (WBAN) need to be modeled with adapted methods because the coupling with the body tissue does not allow for a clear separation between antenna and channel. Especially for dynamically varying on-body channels due to changing body poses, e.g. with head-worn antennas, modeling is challenging and design goals for optimal antennas are difficult to determine. Therefore, in this paper, the modeling of WBAN channels using spherical wave functions (SWF) is utilized for antenna de-embedding and for deriving optimal antenna characteristics that maximize the transmission coefficient for the respective channel. It is evaluated how typical factors influencing WBAN channels (different body anatomies, body postures, and varying positions of the communication nodes), can be modeled statistically with SWF. An optimized antenna design is developed based on the derived optimization method, specifically adapted to the channel of on-body links with eye-wear applications. The results with the optimized antenna are compared to other standard antenna designs and validated against measurements.