Radio Base Station Antennas Research Articles

On Actual Maximum Exposure From 5G Multicolumn Radio Base Station Antennas for Electromagnetic Field Compliance Assessment

The traditional approach of radio frequency electromagnetic field exposure compliance assessment is highly conservative when applied to radio base station antennas implementing dynamic beamforming. In this article, an analytical model based on the queuing theory with a hyperexponential service distribution time is developed to assess the time-averaged actual maximum downlink exposure of 5G multicolumn radio base station antennas by taking into account the effects of beam scanning over time in free space. Using the measured antenna radiation patterns, the 5G downlink antenna precoding codebook, and assuming a conservative user equipment distribution, the ratio of the actual maximum exposure to the theoretical maximum exposure with 100% traffic load and 75% time-division duplex downlink duty cycle is found to be less than 0.5 and 0.3 for four-transmitter and eight-transmitter radio base station antennas, respectively. These results show that assuming constant peak power transmission in a fixed direction leads to an overestimate of downlink exposure also from conventional antennas characterized by only a few transmitters in addition to massive multi-input multi-output products.

Whole-body average SAR measurement using flat phantoms for radio base station antennas and its applicability to adult and child human models

The specific absorption rate (SAR) measurement procedure for radio base station antennas using flat phantoms has been investigated and standardized by the International Electrotechnical Commission (IEC). This paper discusses the effectiveness of this procedure for considering Japanese human models based on numerical simulations with validation of whole-body average SAR (WBSAR) measurement. The WBSAR in two Japanese anatomical human models (adult male and 3-year-old child) and two box-shaped phantoms (large and small) using a standardized SAR measurement procedure are compared at 788 MHz and 3.5 GHz. Computational results show that the SAR measurement procedure in the IEC leads to overestimated WBSAR compared to those in Japanese anatomical human models. These results imply that the SAR measurement procedure above is applicable to not only some commonly used but Japanese human models. The WBSAR obtained using SAR estimation formulae in the IEC is also overestimated compared to those in Japanese anatomical human models. In addition, to reduce the measurement time and simplify the post-processing, this paper introduces a SAR measurement procedure based on the two-dimensional SAR distribution around the surface of the bottom of the phantom and the one-dimensional exponential decay of the SAR distribution in the direction of the phantom depth. SAR measurement examples of antennas for small radio base stations are also presented.

Measurements of the Outdoor-To-Indoor Attenuation of Mobile Phone Signal

This work reports a series of measurements of the attenuation of UMTS and GSM mobile phone signal by buildings structures in the city of Rome. The context of the research is the concern about the exposure of the population resident in the buildings to electromagnetic fields emitted by the radio base stations of the mobile phone radio access network. The aim of the research is to analyze a conservative method of measurement for the outdoor-to-indoor attenuation. The measurement method takes intrinsically into account the presence of apertures like doors and windows on the wall of the buildings, the materials around the apertures and within the buildings. The measurements of attenuation are carried out by instrumentations able to demodulate the radio base station antennas RF carriers. Four different topologies of urban buildings are considered: reinforced concrete buildings, buildings between late 1800 and early 1900th century, historical buildings in the inner Rome and steel and glass buildings structures. Measurements of electromagnetic attenuation are in the range 6 - 27 dB. A numerical analysis of the attenuation of apertures like door/windows has been computed and the results discussed. The results show that the attenuation depends on the material of the walls and by the objects indoor located.

Efficient Whole-Body SAR Assessments by Means of Surface Scan Measurements

In this study, an experimental method has been investigated for efficient assessments of whole-body specific absorption rates (SAR) from radio base station antennas. Using surface amplitude measurements of the electric field components together with an integral equation technique, a method is obtained which is not biased to specific antenna designs or phantom shapes. For realistic material parameters, it has been found that only the amplitude of the tangential field components over the phantom boundary is needed to accurately assess whole-body SAR, which makes the proposed method well suited for integration with commercially available SAR measurement systems. The method has been validated with simulations and measurements. Compared with a volumetric scan, and for the cases investigated, the measurement time was reduced with a factor larger than 3 while keeping the relative error smaller than 8%.

Automated optimization of service coverage and base station antenna configuration in UMTS networks

Deployment and maintenance of UMTS networks involve optimizing a number of network configuration parameters in order to meet various service and performance requirements. In this article we address automated optimization of service coverage and radio base station antenna configuration. We consider three key configuration parameters: transmit power of the common pilot channel (CPICH), antenna tilt, and antenna azimuth. CPICH power greatly influences coverage. From a resource management point of view, satisfying the coverage requirement using minimum CPICH power offers several performance advantages. In particular, less CPICH power leads to less interference and higher system capacity. Optimal CPICH power, in its turn, is highly dependent on how the other two parameters, tilt and azimuth, are configured at radio base station antennas. Optimizing antenna tilt and azimuth network-wise, with the objective of minimizing the CPICH power consumption, is a challenging task. The solution approach in this article adopts automated optimization. Our optimization engine is a simulated annealing algorithm. Staring from an initial configuration, the algorithm searches effectively in the solution space of possible configurations in order to find improvements. The algorithm is computationally efficient; thus, we can optimize large networks without using excessive computing resources. We present a case study for a UMTS planning scenario in Lisbon. For this network, automated optimization saves up to 70 percent of the CPICH power used in the reference network configuration. In addition, the optimized network configuration offers significant performance improvement in terms of fewer overloaded cells and lower downlink load factor

Boundary element modeling of radio base station antennas

The paper presents an accurate and efficient boundary element procedure for the analysis of radiation from base station antennas. The base station antenna system is represented by the vertical antenna array in front of perfectly conducting (PEC) ground plane reflector. The formulation of the problem is based on a set of coupled Pocklington integro-differential equations for vertical antenna array. This set of coupled equations has been numerically treated by the indirect Galerkin–Bubnov boundary element method (GB-IBEM). The numerical results for the currents induced along the wires obtained via GB-IBEM are compared to the results computed via numerical electromagnetic code (NEC). Knowing the current distribution along the antenna array the corresponding radiated field is calculated. Some illustrative numerical results are presented in the paper.

Estimation of the Peak Power Density in the Vicinity of Cellular and Radio Base Station Antennas

Prediction formulae for estimating the peak equivalent power density in the near-field of cellular base-station array antennas are demonstrated. Theoretical justification stemming from a uniform asymptotic expansion of the field radiated by collinear arrays is described, and verification is carried out by means of an extensive computational analysis of different classes of base station antennas. The formulae, which depend on a few, readily available parameters, can be conveniently employed for the estimation of compliance distances with respect to RF safety guidelines issued by the International Committee on Non-Ionizing Radiation Protection (ICNIRP), which have been adopted in many countries throughout the world, without requiring necessarily extensive and expensive nearfield measurements campaigns.

Optimal modeling of real radio base station antennas for human exposure assessment using spherical-mode decomposition

This article presents an innovative way to derive a radio station antenna model that can match very closely real antennas described by their measurements. The derived model can then be used for the assessment of human exposure to the electromagnetic field in the vicinity of the antennas, including the near field and the interactions with the environment. The technique is based on the principle of decomposing a whole antenna into subantennas enhanced by spherical-harmonic fields decomposition. A singular values decomposition (SVD) is used to find the model parameters. The proposed technique is applied on a real antenna used in mobile networks.

Human exposure to radio base-station antennas in urban environment

In this paper, the human exposure to the electromagnetic field radiated by a radio base-station antenna operating around 900 MHz in an urban environment has been analyzed. A hybrid ray-tracing/finite-difference time-domain (FDTD) method has been used to evaluate the incident field and the power absorbed in an exposed subject in the presence of reflecting walls. The base-station antenna has been characterized by means of its radiation pattern, evaluated with an FDTD analysis of a typical panel antenna. Three particular situations for a rooftop mounted antenna have been considered. In all the examined cases, the obtained results, in terms of incident field and absorbed power, are below the most recognized safety standard levels. The importance of an accurate modeling of the environment in which the exposure takes place has been evidenced.

Effects on Correlation Between Two Mobile Radio Base-Station Antennas

The correlation between signals received by two mobile radio base-station antennas is investigated to determine spacing requirements for space diversity. Measurements of the fading of UHF signals received by two base-station horn antennas oriented at different angles with respect to the incoming mobile radio signal were made for different antenna spacings. The experimental results are compared with an analytical expression derived in this paper; they agree fairly well. A further experiment was made after removing the possible local scatterers surrounding the base station. Comparing these two experimental results, we find that the following are true. 1) Propagation in the direction of a line connecting the two base-station antennas is the critical case and requires a large separation of 70 wavelengths. As soon as the incoming wave is 10° away from the inline axis, the spacing requirement drops to 30 wavelengths. 2) Local scatterers at the base station tend to decrease the correlation between signals received at the two antennas. We conclude that an upper limit to the spacing of antennas used for diversity can be obtained and that it is within the achievable range.

Effects on correlation between two mobile radio base-station antennas

The correlation between signals received by two mobile radio base-station antennas is investigated to determine spacing requirements for space diversity. Measurements of the fading of UHF signals received by two base-station horn antennas oriented at different angles with respect to the incoming mobile radio signal were made for different antenna spacings. The experimental results are compared with an analytical expression derived in this paper; they agree fairly well. A further experiment was made after removing the possible local scatterers surrounding the base station. Comparing these two experimental results, we find that the following are true. 1) Propagation in the direction of a line connecting the two base-station antennas is the critical case and requires a large separation of 70 wavelengths. As soon as the incoming wave is 10° away from the in-line axis, the spacing requirement drops to 30 wavelengths. 2) Local scatterers at the base station tend to decrease the correlation between signals received at the two antennas. We conclude that an upper limit to the spacing of antennas used for diversity can be obtained and that it is within the achievable range.