Pertti Vainikainen

Resonator-based analysis of the combination of mobile handset antenna and chassis

The performance of the mobile phone handset antenna-chassis combination is analyzed based on an approximate decomposition of the waves on the structure into two resonant wavemodes: the antenna-element wavemode and the chassis wavemode. A double resonator equivalent circuit model is presented and used to estimate the impedance bandwidth and the respective distributions of radiation losses with typical parameter values at 900 and 1800 MHz. It is noticed that at 900 MHz, the radiation losses of the antenna element wavemode represent typically less than 10% of the total power. Thus, the antenna element works mainly as a matching element, which couples to the low-Q resonant wavemode of the chassis. At 1800 MHz, the contribution of the antenna element wavemode is larger. By enhancing the coupling and by tuning the chassis resonance, it is possible to obtain an impedance bandwidth of over 50% (6 dB return loss) at both at 900 and 1800 MHz. The results given by the equivalent circuit study are fully supported by those of three-dimensional phone-model simulations, including calculation of the SAR and efficiency values. In prototyping, the 6 dB bandwidth of 5.5% was obtained at 980 MHz with a nonradiating coupling element with a volume of 1.6 cm/sup 3/ on a 120 mm long chassis.

Angular power distribution and mean effective gain of mobile antenna in different propagation environments

We measured the elevation angle distribution and cross-polarization power ratio of the incident power at a mobile station in different radio propagation environments at 2.15 GHz frequency. A novel measurement technique was utilized, based on a wideband channel sounder and a spherical dual-polarized antenna array at the receiver. Data were collected over 9 km of continuous measurement routes, both indoor and outdoor. Our results show that in non-line-of-sight situations, the power distribution in elevation has a shape of a double-sided exponential function, with different slopes on the negative and positive sides of the peak. The slopes and the peak elevation angle depend on the environment and base-station antenna height. The cross-polarization power ratio varied within 6.6 and 11.4 dB, being lowest for indoor and highest for urban microcell environments. We applied the experimental data for analysis of the mean effective gain (MEG) of several mobile handset antenna configurations, with and without the users head. The obtained MEG values varied from approximately -5 dBi in free space to less than -11 dBi beside the head model. These values are considerably lower than what is typically used in system specifications. The result shows that considering only the maximum gain or total efficiency of the antenna is not enough to describe its performance in practical operating conditions. For most antennas, the environment type has little effect on the MEG, but clear differences exist between antennas. The effect of the users head on the MEG depends on the antenna type and on which side of the head the user holds the handset.

Millimeter-Wave Propagation Channel Characterization for Short-Range Wireless Communications

This paper presents and analyzes the results of millimeter-wave 60-GHz frequency range propagation channel measurements that are performed in various indoor environments for continuous-route and direction-of-arrival (DOA) measurement campaigns. The statistical parameters of the propagation channel, such as the number of paths, the RMS delay spread, the path loss, and the shadowing, are inspected. Moreover, the interdependencies of different characteristics of the multipath channel are also investigated. A linear relationship between the number of paths and the delay spread is found, negative cross correlation between the shadow fading and the delay spread can be established, and an upper bound exponential model of the delay spread and the path loss is developed to estimate the worst case of the RMS delay spread at given path loss. Based on the DOA measurements that are carried out in a room [line of sight (LOS)] and in a corridor with both LOS and nonline-of-sight (NLOS) scenarios, radio-wave propagation mechanisms are studied. It is found that considering the direct wave and the first-order reflected waves from smooth surfaces is sufficient in the LOS cases. Transmission loss is very high; however, diffraction is found to be a significant propagation mechanism in NLOS propagation environments. The results can be used for the design of 60-GHz radio systems in short-range wireless applications.

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.

Bandwidth, SAR, and efficiency of internal mobile phone antennas

This paper presents a thorough investigation into the effects of several phone chassis-related parameters-length, width, thickness, and distance between the head and phone-on the bandwidth, efficiency, and specific absorption rate (SAR) characteristics of internal mobile phone antennas. The studied antenna-chassis combinations are located beside an anatomical head model in a position of actual handset use. The effect of the users hand is also studied with two different hand models. The main part of the study is based on FDTD simulations, but also experimental results, which support the computationally obtained conclusions, are given. The presented analysis provides novel and useful information for future design of mobile handset antennas. The results show the general trends of bandwidth, SAR, and efficiency with different chassis parameters. The results also reveal a connection between these three performance parameters: an increase in SARs and a decrease in radiation efficiency occur compared to the general trend when the bandwidth reaches its maximum. This happens when the resonant frequency of the chassis equals that of the antenna.

Propagation characteristics for wideband outdoor mobile communications at 5.3 GHz

In this paper, empirical channel models and parameters are derived from the wideband measured data at 5.3 GHz in outdoor mobile communications. The path loss exponents and intercepts are obtained by using the least square method. The mean excess delay and mean root-mean-square (rms) delay spread are within 29-102 ns and 22-88 ns, respectively. The correlation distances and bandwidths are within 1-11 /spl lambda/ and 1.2-11.5 MHz, respectively, when the envelope correlation coefficients equal 0.7 in line-of-sight cases. These correlation values depend strongly on the base station antenna heights. The window length for averaging out the fast fading components is about 1-2 m for microcells and picocells. The multipath number distributions follow both Poissons and Gaos distributions, but Gaos distribution is better in the high probability region. Large excess delays up to 1.2 /spl mu/s and rms delay spread about 0.42 /spl mu/s are found in the urban rotation measurements, where the receiver is close to a large open square.

The distribution of the product of independent Rayleigh random variables

We derive the exact probability density functions (pdf) and distribution functions (cdf) of a product of n independent Rayleigh distributed random variables. The case n=1 is the classical Rayleigh distribution, while n/spl ges/2 is the n-Rayleigh distribution that has recently attracted interest in wireless propagation research. The distribution functions are derived by using an inverse Mellin transform technique from statistics, and are given in terms of a special function of mathematical physics, the Meijer G-function. Series forms of the distribution function are also provided for n=3, 4, 5. We also derive a computationally simple moment-based estimator for the parameter occurring in the distribution, and evaluate its variance.

Empirical characterization of wideband indoor radio channel at 5.3 GHz

Characteristics of wideband indoor radio channel at 5.3 GHz were defined based on an extensive measurement campaign using a wideband channel sounder with 19 ns delay resolution. Pathloss exponents were 1.3-1.5 in LOS and 2.9-4.8 in non-line of sight (NLOS). Large difference in NLOS exponents was due to different dominating propagation mechanisms in different types of building structures. The delay dispersion was characterized by cumulative distribution functions (CDF) of the RMS delay spreads, the values for CDF=0.9 varied from 20 to 180 ns in different setups in an office building and large hall environments. The correlation functions of the radio channel in spatial and frequency domains were extracted. Small scale models for five typical indoor scenarios were developed using tapped delay lines.

Statistical characterization of urban spatial radio channels

We present a statistical analysis of wideband three-dimensional channel measurements at base station locations in an urban environment. Plots of the received energy over azimuth, elevation, and delay planes suggest that the incident waves group to clusters in most measured transmitter positions. A super-resolution algorithm (Unitary ESPRIT) allows one to resolve individual multipath components in such clusters and hence enables a detailed statistical analysis of the propagation properties. The origins of clusters-sometimes even individual multipath components-such as street apertures, large buildings, roof edges, or building corners can be localized on the city map. Street guided propagation dominates most of the scenarios (78%-97% of the total received power), while quasi-line-of-sight over-the-rooftop components are weak(3%-13% of the total received power). For this measurement campaign, in 90% of the cases, 75% of the total received power is concentrated in the two strongest clusters, but only 55% in the strongest one. Our analysis yields an exponential decay of power with 8.9 dB//spl mu/s, and a standard deviation of the log-normally distributed deviations from the exponential of 9.0 dB. The power of cross-polarized components is 8 dB below copolarized ones on average (vertical transmission).

Comparison of MIMO antenna configurations in picocell and microcell environments

This paper presents the results achieved with a dual-polarized multiple-input multiple-output (MIMO) measurement system in the 2 GHz range. Results from continuous measurement routes were used in evaluating and comparing different MIMO antenna configurations. Different pattern and polarization diversity possibilities were studied using two methods: elements were selected from the antenna arrays used in measurements, and as another option, in the mobile station the incident waves were estimated and used in different dipole antenna arrays. The capacity limit seems to be higher in an indoor picocell than in an outdoor microcell environment. At the mobile station, directive elements result in 35% higher average capacities than those of the omnidirectional elements; however, the capacity of the directive elements also depends on the azimuth direction of arrival of the incident field. Dual-polarized antenna configurations have approximately 14% higher capacities than copolarized configurations. Increasing the number of mobile antenna elements increases the capacity in those environments where the angular spread of the incident field is large. Increasing the distance between elements at the fixed station increases the capacity - especially in microcells where signals arrive from specific directions.