Mikael Bergholz Knudsen

Spherical outdoor to indoor power spectrum model at the mobile terminal

Mobile terminals are often used indoor with the base station outdoors. At the mobile terminal the major part of the signal energy comes through openings in the building such as windows. Typically, only one of the sides in a room has windows, and seldom does a room have windows on all sides. Hence, the dominating signal can be expected to arrive at the mobile terminal from a narrow range of angles. Mobile terminal antennas used next to the head in the speaking position will be directional due to the fact that part of the radiation pattern facing the head will be attenuated and reflected. Having a directive antenna in a directive environment, the performance will depend on the orientation of the antenna in the radio environment. A new statistical spherical outdoor to indoor power spectrum model has been proposed to be able to calculate the directional performance of mobile terminals with a single or multiple antennas. The model consists of a major scattering area in one direction and more uniformly distributed minor scatterers in the other directions. A verification of the proposed model was performed and 60 data sets of spherical power spectrum measurements were collected in a typical urban environment. Using the new model, the directional performance of mobile terminal antennas including a human operator has been investigated through directional mean effective gain, branch power ratio, and correlation calculations using spherical radiation pattern measurements of a mobile terminal including the effect of 42 different persons. The accuracy of the calculated values was verified by directly measured values using 200 persons walking with the mobile terminal in the same office-like environments as where the spherical power spectrum measurements were performed.

Multiple Antenna Systems With Inherently Decoupled Radiators

In multiple antenna systems mutual coupling needs to be minimized. We propose an alternative novel decoupling technique, investigating several multiple antenna configurations for small handsets through measurements and numerical simulations. The influence of different novel designs on performance metrics such as total loss, antenna isolation and envelope correlation coefficient are investigated. By varying antenna impedance bandwidth and antenna location with respect to the handset, both planar inverted F antenna (PIFA) and inverted F antennas (IFA) were investigated in different UMTS frequency bands in proximity with the users body. Results show that antennas may experience very different losses and envelope correlation coefficients depending on their relative position with respect to the handset, as the influence of the users hand is not symmetrical in most cases. Narrow-band antennas are inherently decoupled when integrated on the same handset, while also other parameters such as frequency duplex distance and interaction with the users body influence the mutual coupling.

Emulating Spatial Characteristics of MIMO Channels for OTA Testing

This paper discusses over-the-air (OTA) testing for multiple-input multiple-output (MIMO) capable terminals with emphasis on channel spatial characteristics emulation. A novel technique to obtain optimum power weights for the OTA probes based on convex optimization is proposed. The proposed technique emulates spatial correlation as well as introduces constraints on the maximum deviation between the target power azimuth spectrum (PAS) and the emulated PAS in terms of mean angle of arrival (AoA) and azimuth spread (AS). Simulation results show that the proposed emulation technique presents better performance compared with existing techniques in the literature. This improvement is further demonstrated by measurement results in a practical MIMO OTA setup.

Radiation efficiency of handheld phones

Measurements of radiation efficiency for a handheld phone equipped with a patch and a helical antenna operated near the human user have been performed. Both measurements include a simple head plus hand phantom and live persons are considered. The position of the hand on the phone is found to be the main reason for the large variation in radiation efficiency among persons. The tilt angle of the phone and the distance between the head and phone only play a minor role.

Breaking the Transmitter–Receiver Isolation Barrier in Mobile Handsets With Spatial Duplexing

In full-duplex radio communication systems like e-UTRAN, CDMA-2000, the radio transmitter (Tx) is active at the same time as the radio receiver (Rx). The Tx and the Rx will be using separate dedicated frequency bands and the Tx-Rx isolation is ensured by duplex filters. However, agile duplexers required for multiband operation are almost nonexistent while dedicating a bank of narrowband filters is bulky and incurs considerable switching losses. In this paper, we propose an approach that dramatically reduces the complexity of the RF frontend, first by replacing the duplex filter with a spatial filter and second, by codesigning the filtering antennas and the RF frontend. The spatial filter is synthesized by equipping the Tx with redundant antennas. By properly weighting the Tx antennas, the Tx signal is selectively attenuated in the Rx direction. The spatial filter can be tuned to different frequency bands as long as the antennas are made tunable. Moreover, the spatial filter may directly benefit from the balanced architecture of the power amplifiers (PAs) thus reducing the total system complexity and insertion loss. Finally, simulation and initial measurement results are provided in a challenging low-frequency band, serving as a proof-of-concept.

User's Impact on PIFA Antennas in Mobile Phones

Thanks to a recent grip study, CAD models of the human hand have been generated, investigating users impact on PIFA antennas in mobile phones. The simulation results show that the hand and especially the index finger exhibit a major contribution in determining the total loss when compared to the upper torso alone, while the influence of the position of the fingers on the handset is found to be more important when close to the antenna. The palm-handset gap and the index finger location are the main responsible for both absorption and mismatch loss.

Validation of handset antenna test methods

In this work an investigation of a test method for validating the transmitted power by a mobile handset proposed by Olsson and Larsson (see COST 259 WG2.2, 1998) and by Olsson (see COST 259 WG2.2, Leidschendam, Netherlands, 1999) has been made for 1800 MHz GSM handsets. Test results of 8 commercially available GSM1800 handsets measured in the setup has been compared with measurements of the EIRP (equivalent isotropic radiated power), based on 3D radiation pattern measurements performed in an anechoic room. Comparing the EIRP of the phones with the results obtained in the setup a rather large deviation was observed. The principal difference between the measurement methods is the radio environment. This difference has been investigated in this paper by performing 3D radio environment measurements. The radio environment measurements has been performed at both 900 MHz and 2000 MHz.

Measurement Verification of Plane Wave Synthesis Technique Based on Multi-Probe MIMO-OTA Setup

Standardization work for MIMO OTA testing methods is currently ongoing, where a multi-probe anechoic chamber based solution is an important candidate. In this paper, the probes located on an OTA ring are used to synthesize a plane wave field in the center of the OTA ring. This paper investigates the extent to which we can approach the synthesized plane wave in practical measurement systems. Both single plane wave with certain AoA and multiple plane waves with different AoAs and power weightings are synthesized and measured. Deviations of the measured plane wave and the simulated plane wave field are presented in terms of phase and power. Possible reasons for the deviations are also investigated.

Antenna Pattern Impact on MIMO OTA Testing

This paper investigates the impact of the DUT antenna pattern on the test area performance for multi-probe based MIMO OTA setup in terms of received voltage and spatial correlation. The plane wave synthesis (PWS) technique has been proposed for vertical polarization in the literature, where the goal is to approximate plane waves with arbitrary directions. The received voltage at the antenna terminal depends on the antenna radiation pattern and the impinging plane waves. A novel closed form technique to reproduce the received voltage with arbitrary incoming plane waves based on trigonometric interpolation is presented. The proposed technique provides a closed form solution for the PWS when the probe ring radius is infinite. The proposed technique shows that the impact of the antenna pattern on the induced received voltage accuracy is ruled by Nyquist sampling theory. Furthermore, the impact of the antenna pattern on spatial correlation accuracy for prefaded signal synthesis (PFS) technique is investigated as well. Simulation and measurement results show that the number of required probes depend directly on the DUT antenna pattern. To test realistic DUTs with higher variations in directivity, we need more probes to maintain the same received voltage and spatial correlation accuracy level.

Probe Selection in Multiprobe OTA Setups

Standardization work for over-the-air (OTA) testing of multiple-input-multiple-output (MIMO) capable terminals is currently ongoing in COST IC1004, 3GPP, and CTIA, where a multiprobe anechoic chamber based method is a promising candidate. Setting up a multiprobe configuration with channel emulators is costly, so finding ways to limit the number of probes while still reproducing the target channels accurately could make the test system both cheaper and simpler to implement. Several probe selection algorithms are presented in this paper to address this issue. The proposed techniques provide a probe selection framework for the channel emulation techniques published in the literature. Simulation results show that good channel emulation accuracy can be achieved with the selected subset of probes for the considered target channel models. The probe selection algorithm is further supported by measurement results in a practical multiprobe setup.