Evaluation of performance of mobile terminal antennas

Fast development of new mobile communications equipment results in demand for fast and reliable evaluation methods to estimate the performance of mobile terminals because the performance of antennas located on the terminals varies in different multipath propagation environments. Two methods presented in this thesis provide new possibilities in antenna design because, from now on, the performance of new antennas can be tested already before a prototype antenna is constructed by using existing radio channel libraries and simulated radiation patterns of the antennas. The performance can be estimated by calculating the mean effective gain (MEG) of the antenna using the elevation power distribution or by a plane wave -based method using sets of incident plane waves and the radiation pattern of an antenna. In addition to different propagation environments, the effects of the user on performance can be included in the evaluation. In this thesis, estimating the MEG of different antennas using the elevation power distribution and the power patterns of the antennas is shown to be an accurate and fast method by comparing the results with direct radio channel measurements. The mean difference between the methods is −0.18 dB with standard deviation of 0.19 dB. The usefulness of the evaluation method is demonstrated by evaluating the performance of several antennas located on mobile terminals. The antenna evaluation provided important and unique knowledge of the effect of both the environment and the user on performance. Because in calculating the radiation efficiency of the antenna we assume uniform incident field, the efficiency can result in a performance estimation that does not correspond to real usage situations. Therefore, including the environmental effects in the evaluation procedure is important, although the effect of the antenna is more important than the effect of the environment on MEG. It was noticed with calculated Gaussian-shaped beams that tilting or changing the beamwidth of a mobile terminal antenna has an effect of about 2 dB on MEG in multipath environments. Matching the polarization of the antenna to that of the environment can improve the performance more. A novel incident plane wave -based tool has been developed for evaluating the performance of antenna configurations designed for diversity and Multiple-Input Multiple-Output (MIMO) systems. In this thesis, the instantaneous joint contribution of incident field consisting of a number of extracted plane waves and the complex three-dimensional radiation pattern of the antenna is shown to be accurate and extremely fast way to estimate the diversity advantages of different antenna configurations in time-variable radio channels. The difference between the diversity gains achieved by the plane wave -based method and by the direct radio channel measurements is on average less than 0.9 dB. Moreover, the radio channel can be exactly the same for all antenna configurations under test. Furthermore, this thesis includes evaluation of the performance of different MIMO antenna configurations. The studied antenna configurations have been selected from the 16×64 MIMO channel measurement data. A novel way of using one omnidirectional reference antenna in a normalization procedure is shown to be reasonable especially in cases of antenna arrays consisting of directive elements. Three different propagation environments are used as evaluation platforms. The azimuth orientation of mobile terminal antennas may influence the performance of a MIMO antenna configuration significantly. In MIMO configurations compact dual-polarized receiving antennas provide capacity performance almost equal to the arrays employing single polarization.reviewe

Design considerations of MIMO antennas for mobile phones

YesThe paper presents a new modeling and design concept of antennas using polar- ization diversity of 2 £ 2 and 3 £ 3 Multiple Input Multiple Outputs (MIMO) system that is proposed for future mobile handsets. The channel capacity is investigated and discussed over Raleigh fading channel and compared to a linear/planner antenna array MIMO channel. The capacity is also discussed over three types of power azimuth spectrums. The results are compared to the constraints capacity limits in which the maximum capacity observed

User Effect Mitigation in MIMO Terminal Antennas

The rapid growth of cellular technology over the past decade transformed our lives, enabling billions of people to enjoy interactive multimedia content and ubiquitous connectivity through a device that can fit into the palm of a hand. In part the explosive growth of the smartphone market is enabled by innovative antenna system technologies, such as multiple-input multiple-output (MIMO) systems, facilitating high data rates and reliable connections. Even though future deployment of Long Term Evolution Advanced (LTE-A) is expected to provide seamless internet connectivity at even higher speeds over a wide range of devices with different form factors, fundamental terminal antenna limitations can severely impact the actual performance of the terminal. One of the key challenges in terminal antenna design are user-induced losses. It has been shown that electromagnetic absorption in body tissues as well as antenna impedance mismatch due to user proximity significantly degrade terminal antenna performance. Moreover, user interactions are non-static, which further complicates terminal design by leading to the requirement of evaluating a wide range of hand grips and usage scenarios. This doctoral thesis explores these challenges and offers useful insight on effective user interaction mitigation. In particular, state-of-the-art multiple antenna designs have been investigated in an attempt to formulate guidelines on efficient terminal antenna design in the presence of a user (Paper I). Moreover, the major part of the thesis considers the method of adaptive impedance matching (AIM) for performance enhancements of MIMO terminals. Both ideal and very practical and realistic AIM systems have been studied in order to extend the knowledge in the area by determining achievable performance gains and providing insights on AIM gain mechanisms for different terminal antenna designs, propagation environments and user scenarios. In Paper I, five different MIMO terminal antenna designs were evaluated in 11 representative user scenarios. Two of the prototypes were optimized with the Theory of Characteristic Modes (TCM), whereas the remaining three were based on more conventional antenna types. Multiplexing efficiency (ME) was used as the MIMO system performance metric, assuming an ideal uniform 3D propagation environment. The paper focuses on performance at frequency bands below 1 GHz due to the more stringent size limitations. Paper II presents a simulation model of the complete physical channel link based on ideal lossless AIM and evaluates the potential of AIM to mitigate user effects for three terminal antennas in four user scenarios. The prototypes studied have different performances in terms of bandwidth and isolation. MIMO capacity was used as the main performance metric. In order to gain insight on the impact of terminal bandwidth, as well as system bandwidth on AIM performance, capacity calculations were performed both for the center frequency and over the full LTE Band 13. In Paper III, a practical AIM system was set up and measured in both indoor and outdoor propagation scenarios for a one-hand and a two-hand grip, including a torso phantom. The AIM system consisted of two Maury mechanical tuners controlled with LabView. MIMO capacity was used to determine performance in the different user and channel cases. The impact of different propagation environments and user cases was discussed in detail. Moreover, tuner loss estimation was done to enable the calculation of AIM net gains. In Paper IV, the simulation model from Paper II was extended to include real antenna parameters as well as simulated environments with non-uniform angular power spectra. Two fundamentally different antenna designs were measured in three user scenarios involving phantom hands, whereas non-uniform environments of different angular spreads were simulated in post-processing. The study presents results and analysis on the impact of user scenarios and environment on the AIM gains for the terminals with different antenna designs. Finally, Paper V describes a realistic AIM system with custom-designed CMOS-SOI impedance tuners on a MIMO terminal antenna. Measurement setup control, as well as MIMO system evaluation, was achieved through a custom-developed LabView software. Detailed propagation measurements in three different environments with both phantom users and real test subjects were performed. The analysis and discussions provided insights on the practical implementation of AIM as well as on its performance in realistic conditions

Experimental investigation of adaptive impedance matching for a MIMO terminal with CMOS SOI tuners

It is well known that user proximity introduces absorption and impedance mismatch losses that severely degrade multiple-input multiple-output (MIMO) performance of handset antennas. In this work, we experimentally verified the potential of adaptive impedance matching (AIM) to mitigate user interaction effects and identified the main AIM gain mechanism in realistic systems. A practical setup including custom-designed CMOS silicon-on-insulator (SOI) impedance tuners implemented on a MIMO handset was measured in three propagation environments and 10 real user scenarios. The results indicate that AIM can improve MIMO capacity by up to 42% equivalent to 3.5 dB of multiplexing efficiency (ME) gain. Taking into account the measured losses of 1 dB in the integrated tuners, the maximum net ME gain is 2.5 dB suggesting applicability in practical systems. Variations in ME gains of up to 1.5 dB for different hand-grip styles were mainly due to differences in impedance mismatch and tuner loss distribution. The study also confirmed earlier results on the significant differences in mismatch and absorption between phantoms and real users, in which the phantoms underestimated user effects and therefore AIM gains. Finally, propagation environments of different angular spreads were found to give only minor ME gain variations