Systematic design method of a mobile multiple antenna system using the theory of characteristic modes

Abstract

In this study, the authors present a systematic design method of a three‐port multiple‐input–multiple‐output antenna system for small terminals, such as smart phones based on the selective excitation of orthogonal chassis modes. The underlying idea is based on the theory of characteristic modes (TCM). Selective excitation of these modes is realised by sets of non‐resonant inductive coupling elements integrated at predefined positions into the printed circuit board (PCB) layout. Stripline feed networks also integrated within the multi‐layer PCB layout care for a good impedance match to 50 Ω. The design method of this antenna system is a straight forward application of the TCM and is therefore of general interest for the design of small terminal antennas. Furthermore, owing to the electrically small couplers that require only limited area at the outer edge of the PCB the method represents an interesting solution with the clear potential to be extended to more ports. The realised prototype resembles the predicted performance very well and therefore proves the applicability of the proposed method.

A massive MIMO terminal concept based on small‐size multi‐mode antennas

“…The theory of characteristic modes concept has recently been applied to realize a three‐port MIMO antenna prototype using three sets of miniature distributed inductive couplers, which are driven by three different strip line feed networks. Measurement results show excellent performance in terms of sufficiently decoupled antenna ports .…”

“…Similar to the surface current J , in the far field, the electrical field E can be written as a linear superposition of so‐called eigenfields E m (also called characteristic fields): Because of the fact that the characteristic modes are ortho‐ gonal, the modal far fields represent orthogonal patterns that can be either used in combination (if excited simultaneously ) or as individual antenna patterns (when excited selectively by the different ports of a multi‐antenna system ). Figure illustrates the surface current J and the electrical field E .…”

“…Because of the fact that the characteristic modes are orthogonal, the modal far fields represent orthogonal patterns that can be either used in combination (if excited simultaneously [14]) or as individual antenna patterns (when excited selectively by the different ports of a multi-antenna system [13,15]). Figure 1 illustrates the surface current J and the electrical field E .…”

Theory of characteristic modes for lossy structures: Formulation and interpretation of eigenvalues

“…Recently, the electric field integral operator (EFIO) based TCM approach for perfect electric conductors (PEC) has become very popular in antenna design . This methods provides excitation independent eigensolutions, eigencurrents and eigenvalues, known as characteristic modes (CMs), which can be used to analyze fundamental electromagnetic properties of a given structure without need to rely on specific excitation configuration…”

“…Recently, the electric field integral operator (EFIO) based TCM approach for perfect electric conductors (PEC) 4 has become very popular in antenna design. 6 This methods provides excitation independent eigensolutions, eigencurrents and eigenvalues, known as characteristic modes (CMs), which can be used to analyze fundamental electromagnetic properties of a given structure without need to rely on specific excitation configuration [6][7][8][9] The theoretical background of TCM is well-established for (lossless) PEC structures. 4 The eigensolutions obtained with the EFIO-based formulation form a weighted orthogonal set of eigencurrents on the surface of a conducting object with orthogonal far-field patterns and real eigenvalues giving the ratio of reactive and radiated power of a mode.…”