Thomas Bauernfeind

Influence of the Non-Linear UHF-RFID IC Impedance on the Backscatter Abilities of a T-Match Tag Antenna Design

In ultra-high-frequency radio-frequency-identification (UHF-RFID) the conjugate complex matching of the packaged UHF-RFID transponder IC and the tag antenna structure is important to increase the reading range of the transponder tag. Quite often half-wavelength dipole-like antenna structures are used. Due to the fact that the impedances of the packaged IC and the dipole antenna structure are in different domains, a matching structure is needed to accomplish the conjugate complex matching. A common technique to carry out the matching is the so called T-match. Since the nominal input impedance of the IC depends on the applied antenna voltage (and in a strongly non-linear way), the backscatter abilities of the tag are also functions of the applied voltage. In the present work those dependencies are investigated in terms of full-wave finite element simulations and measurements.

Investigation of UHF Circular Loop Antennas for RFID

In radio frequency identification (RFID), the design and investigation of ultra-high-frequency (UHF) circular loop antennas used as reader antennas as well as tag antennas is of growing importance. Since these antennas are electrically short, a 2-D finite-element method (FEM) analysis using a single-component magnetic vector potential together with perfectly matched layers (PMLs) at the boundary is proposed in this paper in order to perform very fast and accurate axisymmetric simulations compared to very time-consuming 3-D calculations. In addition, the capacitances of the tag loops have been calculated using a 3-D quasi-static electric approach taking the gap of the loops into account.

Finite Element Simulation of Impedance Measurement Effects of NFC Antennas

In this paper, the problem of connecting the unbalanced measurement setup on the balanced antenna of the near-field communication (NFC) system is addressed. The parameters of the antennas equivalent circuit were determined using quasi-static and full-wave vector field finite element simulations. Measurements and simulations are carried out on three different prototypes of 13.56 MHz NFC rectangular four turns antenna printed on FR4 substrate material. The obtained results concerning the RLC equivalent circuit parameters show that a direct connection of the unbalanced measurement devices to the balanced antenna structure impairs the accuracy of the obtained measurement data because of the mode mismatch at the antenna terminals.

Limitations of the pattern multiplication technique for uniformly spaced linear antenna arrays

Linear antenna arrays find wide applications in wireless communication systems. Typically, arrangements with uniform spacing between the array elements are applied to gain highly directive radiation patterns. Although the numerical capabilities of modern computing infrastructures allow the numerical analysis of complex modern antenna array configurations the so called pattern multiplication technique is still applied, especially within the numerical optimization of antenna array arrangements. In the present paper the limitations of this technique are investigated in terms of numerical analyses of typical array configurations.

Interactive Toolbox for the Visualization of Typical Antenna Attributes

To understand wave propagation phenomena, complex mathematical and physical theory is needed. Therefore, many undergraduate students find it very difficult to deal with this area of research. In this paper, an interactive toolbox is proposed which can help students to gain profounder knowledge and understanding of wave propagation effects. Great importance was attached to the design of a very simple user interface to help the students focus on the essential. The data interface was created to be very general and simple for an easy extension.

Interactive toolbox for the visualization of typical antenna attributes

To understand wave propagation phenomena, complex mathematical and physical theory is needed. Therefore, many undergraduate students find it very difficult to deal with this area of research. In this paper, an interactive toolbox is proposed which can help students to gain profounder knowledge and understanding of wave propagation effects. Great importance was attached to the design of a very simple user interface to help the students focus on the essential. The data interface was created to be very general and simple for an easy extension.

UHF RFID antenna impedance characterization: Numerical simulation of interconnection effects on the antenna impedance

A major design criterion of wireless communication devices is the matching between the impedance of the analog frontend and the input impedance of the antenna structure. Especially for passive communication systems, the matching is essential to ensure good performance. Numerical design tools are typically utilized in the antenna design process to determine the antenna impedance. Additionally, measurements on prototype designs are carried out to verify the simulation results. Frequently, vector network or impedance analyzers are used to measure the impedance of the antenna design. Regardless of the measurement device in use, a connection between it and the device under test has to be established. In this paper, the interaction between the interconnection structure and the antenna under test is investigated. Special attention is paid to the influence of the interconnection structure on the antenna impedance obtained. The investigations are carried out on a typical test problem by numerical field simulations by means of the finite-element method.

Investigations on ground compensation coils and their influence on the field distribution of electrically short loop antennas

Electrically small loop antennas are balanced devices by nature. Quite often such antennas are directly connected to a coaxial feed line e.g. the ISO/IEC 10373 test PCD antenna. The direct connection of such an antenna to the coaxial feed line leads to a mode conversion at the antenna terminals. In the present paper the influence of this mode conversion on the field distribution of an electrically short loop antenna is investigated in terms of finite element simulations applying an in-house software package. A method is introduced which allows the unbalanced mode excitation in the full wave simulation by prescribing appropriate boundary conditions.

An Iterative Domain Decomposition Method for Solving Wave Propagation Problems

Abstract Solving electromagnetic wave propagation problems with the finite-element method results in a large number of unknowns due to the necessity of modeling an extensive portion of the surroundings of the conducting structures. These equation systems are often ill-conditioned because of the great material differences as well as changes in size between neighboring elements. In addition, the resulting matrices are indefinite. Common iterative methods exhibit poor convergence due to these conditions. Direct solution techniques result in high memory requirements. The aim of this article is to present an approach with smaller memory demand than the direct methods and better convergence properties than common iterative techniques. An iterative method based on domain decomposition is presented and compared to various conventional iterative and direct solution techniques.