Robert Martens

Inductive and capacitive excitation of the characteristic modes of small terminals

In this paper we present concepts for the selective excitation of orthogonal modes of small terminals by inductive and capacitive coupling elements. The concepts can be used to implement an efficient MIMO (Multiple Input Multiple Output) antenna system based on the TCM (Theory of Characteristic Modes). Both coupling concepts are discussed with respect to their ability to excite specific modes separately. An important result obtained is that inductive couplers offer advantages over capacitive couplers in exciting the desired modes purely even when they are not close to their modal resonance.

Optimal Dual-Antenna Design in a Small Terminal Multiantenna System

This letter introduces a novel 2.6-GHz multiple-input-multiple-output (MIMO) antenna system for mobile terminals. The antenna structures consist of a broadband main antenna covering most of the LTE-A bands and a narrowband second antenna operating at the 2.6-GHz band. The main antenna is a traditional monopole-type capacitive coupling element (CCE) placed on the short edge of the terminal. The second antenna consists of two out-of-phase fed inductive coupling elements (ICEs) placed on the long edges of the chassis. The main purpose of the letter is to demonstrate that this kind of antenna system offers good performance in terms of electromagnetic (EM) isolation and envelope correlation between the antennas. This has been experimentally verified and is originated on the fact that both antennas excite effectively different orthogonal wavemodes, which is studied with the help of the theory of characteristic wavemodes.

A concept for MIMO antennas on small terminals based on characteristic modes

In this paper, we present a concept for a MIMO antenna system on a small terminal platform. The concept is based on the selective excitation of different orthogonal characteristic modes on the chassis of the small terminal. Thereby the chassis of the mobile terminal itself can be effectively used as the MIMO antenna similar to the concept commonly applied to single port (single mode) antennas on mobile terminals. The different modes generate orthogonal radiation patters and are therefore suited to radiate de-correlated signals fed to the different antenna ports. Such modes can be excited selectively by certain sets of couplers distributed around the outer edges of the chassis. First stage numerical investigations show that coupling between the modes is low.

Compact Multimode Multielement Antenna for Indoor UWB Massive MIMO

In this paper, we present a concept for a compact ultra-wideband multielement antenna (MEA) for massive MIMO indoor base stations. The antenna concept is based on the simultaneous excitation of different characteristic modes on each element of the MEA. This enables an effective 484 port antenna using only 121 physical antenna elements. Thereby, a size reduction of 54% compared to a generic MEA based on crossed dipoles is achieved. The antenna operates in the ultra-wide frequency band of 6-8.5 GHz with a reflection coefficient of sii <; -10 dB and the interelement and intraelement mutual coupling of the antenna ports is sji ≤ -20 dB.

Evaluation of Adaptive Impedance Tuning for Reducing the Form Factor of Handset Antennas

In this paper, we evaluate adaptive impedance tuning in combination with intrinsically unmatched antennas in order to reduce the form factor of handset antennas. Thereby, we are able to shrink the size of an antenna element by a factor of four compared to an intrinsically broadband matched antenna while maintaining a similar total efficiency in usage scenarios. The antenna concept is based on an unmatched coupling element in order to obtain a flat impedance behavior, which is relatively insensitive to the user interaction. It enables a broadband adaptive matching by a tunable Π-section network using varactors. The network takes into account the parasitic effects of the impedance detector and the ESD protection circuit.

2-port antenna based on the selective excitation of Characteristic Modes

In this paper we present a two-port MIMO (Multiple Input Multiple Output) - antenna based on the selective excitation of two orthogonal modes on a small terminal. The concept applies the TCM (Theory of Characteristic Modes). The excitation of the chassis modes are realized by two sets of ICEJn (Inductive Coupling Elements) at predefined positions on a commonly used PCB. Feed Networks (FNJn) care for a good impedance match to 50Ω with double-stub tuning and phase shifters realized in stripline technology. Numerical results show a good de-correlation of the antenna ports and a high quality of mode excitation.

On the relation between the element correlation of antennas on small terminals and the characteristic modes of the chassis

In this paper we present some basic investigations to show the relation between the element correlation of antennas on a common small terminal and the characteristic modes on the chassis excited by those antennas. The results show, that the characteristic of an antenna array is heavily affected by the weighted characteristic current modes of the chassis. The actual mode and its weight, however, depend on the dimensions of the chassis and the locations of the antenna elements for a given frequency. In case of a two antenna systems the effect of the common ground plate on the element correlation can be minimized by locating the antennas in such a way that both excite the same mode 180° out of phase.

Comparison of two matching networks for a LTE2600 handset antenna

In this paper two different concepts of matching networks for a LTE2600 handset antenna based on non-resonant coupling elements are investigated. The matching circuits are realized in stripline and lumped element technology. A comparison shows that both concepts offer similar results in terms of the power gain. However the realization using lumped elements offers advantages with respect to the complexity and the small form factor.

Optimization of ultrawideband bow-tie antennas for cable based operation

In this paper we present the design and optimization of an ultrawideband bow-tie antenna for the operations on top of a coaxial cable. The shape of the antenna is derived from canonical analytic equations. In order to reduce parasitic currents on the shielding of the cable caused by the unbalanced transition between the unsymmetric coaxial feed and the symmetric planar radiator the lower plate of the bow-tie is designed to operate as a sleeve in addition. The antenna is shown to be less sensitive to the coaxial cable compared to simple configurations without the sleeve. The study is based on numerical simulations using the FDTD simulator EMPIRETM.