Joonas Krogerus

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.

Use of balun chokes in small-antenna radiation measurements

Measurements of the free-space radiation characteristics of small antennas, such as in mobile communications handsets, typically suffer from the influence of the attached radio frequency (RF) feed. A sleeve-like balun choke placed on the feed cable close to the antenna under test (AUT) prevents surface currents of the AUT from propagating onto the outer shield of the RF feed cable. Therefore, measurement results with the balun correspond well to those of an isolated AUT, much better than without any measures against cable effects. The balun can typically be used at a 10% relative bandwidth. A dual-frequency balun minimizes the cable-related effects at two separate frequency bands. This is useful in the measurements of dual-frequency antennas. The results of both simulations and measurements for a dual-band balun are presented in this paper, proving the usefulness of the proposed balun and its advantages over alternative means to decrease the cable-related effects.

Effect of the Human Body on Total Radiated Power and the 3-D Radiation Pattern of Mobile Handsets

We investigate how the users body affects the radiation characteristics, e.g., radiation pattern and total radiated power (TRP), of mobile phones. We carried out measurements for two Global System for Mobile Communications (GSM) 900/1800 phones with two measurement systems: a 3-D far-field pattern measurement system and the Rapid Antenna Measurement System (RAMS). Up to 13 mobile phone users participated in the measurements. The main objectives are to study how much the TRP varies between the users and how large an influence the users hand, particularly its position on the mobile phone, has on the TRP. The contributions of the head and the hand to the total loss are separately studied as well. The standard deviation of the TRP results between the 13 users in the RAMS measurements was relatively low, i.e., less than 1 dB, when the users held the mobile phone in a predefined talk position on the left side of their heads. The standard deviation of the corresponding result was up to 3 dB when the users were allowed to freely select the way to hold the phone. The TRP results for two phantoms agreed well with the average TRP results for the test persons when only the loss contribution of the head was included. Hence, we conclude that the variable hand position and grip on the mobile phone are the main reasons for the large differences in the TRP between the users.

Evaluation of three methods for measuring total radiated power of handset antennas

Three methods for measuring total radiated power of GSM handsets have been evaluated by an experimental comparison. Evaluated methods were scattered field measurement method, stirred-mode chamber method and three-dimensional pattern integration method (3-D PIM). The parameter investigated was total radiated power in talk position beside a torso phantom and in free space. The handset antenna performance testing including a human body phantom is a novel application for stirred-mode chambers and is presented. Based on the evaluation of the three methods, the 3-D PIM seems to be the most suitable method for antenna performance measurements of mobile terminals.

User effect on total radiated power and 3-D radiation pattern of mobile handsets

We investigate how the user¿s body affects the radiation characteristics, i.e., 3-D radiation pattern and total radiated power (TRP) of mobile handsets. In previous studies up to 10 dB difference was found in TRP of a mobile handset between individual users. Our objective is to investigate the reasons for the large differences. Thirteen test persons were measured with an active GSM 900/1800 mobile phone. The standard deviation of the TRP results between the test persons was relatively low when the test persons held the phone in a predefined talk position. The variation in the corresponding results was much larger when the users could freely select the talk position. The variable hand position and the grip on the handset seems to be the major reason for the large differences whereas the anatomical differences between the users play only a smaller role.

Evaluation of diversity and MIMO performance of antennas from phaseless radiation patterns

We investigate the significance of phase information of radiation patterns for the performance estimates of diversity and multiple-input-multiple-output (MIMO) antenna configurations at 2 GHz band. We also propose a random-phasing technique for performance analysis when the phase information is not available. In the performance analysis we use the Experimental Plane-Wave Based Method (EPWBM) where 3-D radiation patterns of the antennas and measured 3-D signal distribution of the propagation environment are combined. The results show that use of phaseless radiation patterns leads to unacceptable underestimation of performance of multielement antenna systems. However, the use of a random phasing technique with phaseless radiation patterns is shown to be an attractive method for simplifying the antenna evaluation process.

Extension to Characterization Model for GPS Antenna Performance in Mobile Terminals

A new, extended model to evaluate the performance of Global Positioning System (GPS) antennas in mobile terminals is introduced. The new model is demonstrated using three different antennas with two orientations, and it is shown to give a more reliable prediction of the GPS antenna performance compared to the earlier model. Also, a new parameter for characterizing the ability of the GPS antenna to reject the reflected waves from the ground is introduced.