On the Relation of Characteristic Modes of Different Conducting Structures

A formalism is derived to analyze the scattering of a conducting structure based on the characteristic modes of another structure whose surface is a superset of the first structure. This enables the analysis and comparison of different structures using a common basis of characteristic modes. Additionally, it is shown that the scattering matrices and perturbation matrices are no longer diagonal in these cases. Based on this, a modal transformation matrix is defined to describe the mapping between the characteristic fields and the weighting coefficients of the two structures. This matrix enables the conversion of the perturbation matrices in different bases. Finally, two examples are provided along with a discussion of some aspects of the theory. The first example aims to validate and illustrate the formalism. The second example shows how the formalism can be applied in the design process of an antenna element that is gradually modified, starting from a base structure.

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.

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.