Juha Villanen

Coupling element based mobile terminal antenna structures

In this paper, internal low-volume antenna structures for mobile terminals are studied. The work concentrates on the possibilities to reduce the volume of mobile terminal antenna elements by efficiently utilizing the radiation of the currents on the mobile terminal chassis. Essentially nonresonant coupling elements are used to optimally couple to the dominating char- acteristic wavemodes of the chassis. The antenna structures are tuned to resonance with matching circuits. During the last few years, the approach has achieved growing interest—also among industrial manufacturers of mobile terminals. There exist, how- ever, no systematical feasibility and performance studies of the idea. During the work, two antenna models with very low-volume coupling elements are designed and in total four prototypes are constructed. The simulation and measurement results show that the studied antenna concept is a very promising alternative for traditional antenna technologies. The presented analysis provides useful and novel information for the designs of the future low-pro- file and low-volume mobile terminal antennas.

Antenna for Handheld DVB Terminal

For the reception of terrestrial television, traditionally Yagi or whip antennas are used. Due to their large size they cannot be used in the reception of digital television on handheld devices (DVB-H), which operate at the frequency band 470 – 702 MHz. The DVB-H system is under development and small internal antenna solutions for handheld devices are not yet available. Due to the long wavelengths, any antenna placed inside a portable terminal will be electrically small. The antenna volume is the fundamental factor determining its performance. With traditional microstrip antennas such as PIFAs the required bandwidth could not be obtained inside a pocket-size terminal. Therefore, a broadband planar antenna structure for a DVB-H receiver is presented in this paper. The antenna structure is based on the compact coupling element antenna structure [1] that was earlier applied for GSM systems [2].

Compact antenna structures for mobile handsets

In this paper, novel compact antenna structures for mobile handsets are studied. The antennas are based on non-resonant coupling elements, which are used to optimally couple to the characteristic wavemodes of the chassis. The resonances for the antenna structures are created with matching circuits. Two different antenna models are designed based on the novel antenna structure. From each model, single-band prototypes for the E-GSM900 and GSM1800 systems are constructed. The volume of the smaller antenna model is only 1.3 cm/sup 3/. Both models meet the bandwidth and SAR requirements of the E-GSM900 and GSM1800 systems. Efficiencies are high and the radiation patterns are suitable for use in mobile handsets. The measurement results of the constructed prototypes suggest that the compact antenna structure studied in this paper has great potential for use in mobile handsets.

Evaluation of the Performance of Multiantenna Terminals Using a New Approach

In this paper, an advanced experimental plane-wave-based method (EPWBM) for evaluation of the performance of multiantenna systems is considered. The method enables a statistical antenna evaluation without performing long routes of radio-channel sounder measurements to be carried out separately for each antenna under test. The EPWBM utilizes the joint contribution of the estimated signal spectrum and the simulated or measured complex three-dimensional (3-D ) radiation patterns of antennas under test. The proposed method enables more comprehensive antenna evaluation in a shorter time period compared to direct measurements. For validation purposes, the results obtained with the EPWBM are compared with the results of direct radio-channel measurements. The method is shown to be sufficiently accurate for comparing the performance of different antenna configurations. The average difference between the two methods is below 1 dB when estimating the diversity gain of two-element antennas. Further, the maximum difference between the methods in multiple-input multiple-output analysis is below 1 b/s/Hz in estimating mean capacity

Mobile terminal antennnas implemented by using direct coupling

The current trend in mobile terminals is an increasing number of systems. The volume occupied by the antennas of the radio systems is becoming more and more problematic and new low-volume antenna solutions are needed. Since the EMC shielding and the ground plane operate as the main radiating structure especially below 1 GHz, a very small antenna structure can be achieved by using a direct feed, i.e. galvanically inducing currents on the surface of the chassis. The feed can be placed over an impedance discontinuity, e.g. formed by a slot. Using this approach, an antenna structure for a small handheld digital television (DVB-H) receiver is presented. The antenna gain exceeds the specification by a 4-dB margin. The introduced antenna structure can also be used for multi-system terminals.

Evaluation of performance of multi-antenna terminals using two approaches

In this work, a novel and fast plane-wave based method for evaluation of multi-antenna terminals is presented. This method is shown to be accurate enough for comparing the performance of antenna configurations. The method enables a statistical antenna evaluation without requirements to perform long routes of radio channel sounder measurements with several antenna configurations in several environments. The results of the plane-wave based method utilizing the joint contribution of environmental data and the radiation pattern of an antenna are compared with the results of direct radio channel measurements. The average difference between the methods is below 1 dB in estimating diversity gain of two-element antennas. Further, the maximum difference between the methods in multiple-input multiple-output (MIMO) analysis is below 1 bit/s/Hz in estimating ergodic capacity.

Behavior of Mobile Terminal Antennas near Human Tissue at a Wide Frequency Range

In this paper, the behavior of the impedance bandwidth, SAR and radiation efficiency of mobile terminal antennas are studied by FDTD-based simulations at a wide frequency range, from 0.6 GHz to 6 GHz. The used models comprise a basic coupling element based antenna structure placed beside a simple dielectric block modeling the user. The results of this paper give novel information about the behavior of the bandwidth, SAR and radiation efficiency of mobile terminal antennas near the user. It is shown that even if the resonance frequency changes when dielectric material is brought close to the antenna, the frequency responses of the bandwidth or SAR do not necessarily change accordingly. It is shown also that the locations of the SAR maxima strongly depend on the permittivity of the nearby material. Close relations between the current distribution of the chassis of the antenna and the peak SAR locations are found. The results of this paper give novel information which can be utilized when designing antennas with as low interaction with the user as possible.

A Wideband Study of the Bandwidth, SAR and Radiation Efficiency of Mobile Terminal Antenna Structures

In this paper, the frequency dependence of bandwidth, SAR and radiation efficiency of mobile terminal antennas are studied at wide frequency range, from 0.6 GHz to 6 GHz. Two antenna models are studied with simulations in free space and in talk-position beside a head model and two hand models. The results show a connection between chassis resonant frequencies, impedance bandwidth, SAR, and radiation efficiency, increase in SAR and decrease in radiation efficiency occur when bandwidth reaches its maximum due to a chassis resonance. Above 3 GHz this trend is shown to be not valid any more, as radiation of the antenna/coupling element become dominant. The results of the paper provide novel and useful information for the antenna designers of future mobile terminals

Radiation Characteristics of Antenna Structures in Clamshell-Type Phones in Wide Frequency Range

In this paper, the radiation and resonance characteristics of open and closed position clamshell-type phone structures are studied at wide frequency range (from 0.6 GHz to 3 GHz) with help of coupling elements. In the closed position of the phone, the lambda/2 resonance of the chassis located close to the operating band of E-GSM900 system shows to be problematic due to low bandwidth potential and a radiation efficiency minimum. To improve the closed position performance of the antenna structure, a novel frequency tunable matching circuitry is proposed and studied with simulations. The results of this paper provide useful and novel information for the designers of antennas for clamshell-type phones. The findings of this paper can be also applied with traditional self-resonant antennas.

The design of optinum impedance matching networks for coupling element based antenna structures

In this paper, first explicit equations are derived for a matching network providing an optimum dual-resonant impedance matching for a connected series-RLC resonant circuit. This is followed by presentation of a practical discrete-component realization of the matching network. Emphasis has been put on minimizing the complexity of the matching network when used with non-resonant coupling elements. Finally, the presented theory and methodology is applied in the designing of an optimized matching network for a coupling element based mobile terminal antenna structure.