Estimation of Peak Power Density in the Vicinity of Cellular Base Stations, FM, UHF and WiMAX Antennas

Transcription

1 International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 0 58 Estimation of in the Vicinity of Cellular Base Stations, FM, UHF and WiMAX Antennas Bexhet Kamo 1, Rozeta Miho 1, Vladi Kolici 1, Sanie Cela 1, Algenti Lala 1 1 Faculty of Information Technology, Polytechnic University of Tirana ALBANIA {bkamo, rmiho, vkolici, scela, alala}@fti.edu.al Abstract Estimation of peak power density, in the vicinity of cellular base stations, FM, UHF and WiMAX antennas, and comparison of theoretical values with exposure limits for public and occupational, offers the possibility of knowing the safety distance from those antennas. Results of estimations, for the peak power density radiated from antennas, are given by eliminating or not considering reflected waves from different surfaces. By simplifying the method of theoretical calculation, we can have values which, for relatively small distances from the antennas, are almost real. The safety distances, from those antennas, are estimated for real frequencies and applications in order to have a clear idea for the safety distances. Index Term Antennas, base station, non ionizing radiation, safety distance. I. INTRODUCTION The value of peak power density radiated from cellular base stations, FM, UHF and WiMAX antennas and its effect on the human body, is a problem that has been concerning the society, specialist and research institutes for many years. International organizations like ICNIRP and WHO have published limits for public and occupational exposure and many countries use these references to decide if the radiation level is acceptable or not, in a given distance from antennas. There are some ways to estimate the peak power density, but all of them can be grouped in two categories: analytic and statistical methods. In this paper we use an analytic method for estimation of peak power density, radiated from a cellular base station, FM, UHF or WiMAX antenna. What we intend to estimate, is the peak power density that comes from a source, that is not a single point but a field radiated from a group of elements, connected to each other in a predefined way, in order to increase the power level radiated in a given direction. Antennas used in cellular base stations, FM, UHF or WiMAX are in general dipole antennas or better saying an array of dipole antennas, known as collinear antennas. For these antennas, we used the theoretical way to estimate the radiation level versus distance. The estimated values are compared to ICNIRP limits for public and occupational and compliance distances are calculated based on this theoretical method. The paper initially presents the theoretical method used for calculating the power density. The method presented is derived from current method of calculation by the simplified it further, to calculate, in a simple manner, the maximum possible value of power density of radiation from the BTS antennas or from FM, UHF and WiMAX antennas. Theoretical calculated values, are used to construct the graph that represents the dependence of the peak of power density versus distance. Graph is built only for the power density values that are lower than the ICNIRP limits for public and occupational. Calculations and assessments, aim to provide the distance range of security which must be respected by the public and experts of relevant fields, who work with antennas or in their vicinity. II. ESTIMATION OF PEAK POWER DENSITY, THEORETICAL METHOD Estimation of power density radiated from a collinear antenna (far field) is given by formula (1): PT G S (1) 4R where: - S ( w/m ) is the power density in the distance R - P T (w) is the power radiated by the antenna - G is the Gain of the antenna - R (m) is the distance from the antenna Formula (1), is valid for the density in the far field where the E-M field has spherical character and the distance R from antenna is much higher than the distance ρ 0 (ρ 0 is the distance

2 International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 0 59 where the cylindrical character converts to spherical character of the E-M field). For a certain antenna, the peak power density in a given direction as in Fig. 1 can be estimated using formula (). Antenna R The distance from the antenna where the power density is equal to the limit (limit is defined by ICNIRP), is calculated using formula (4) [1], [], [3], [4], [5]. Peak Peak) q R R( S 0 (4) 4 1 (4q) where q is calculated by formula (5) [1], [], [3], [4], [5]: L O φ Fig. 1. Collinear antenna and the horizontal plan (XOR) where we estimate peak power density Maximum values of the radiated power from antenna will be in the XOR plan (O is the center of the antenna and XOR plan is perpendicular with the antenna considering the down tilt, so if the down tilt is zero the XOR plan is horizontal and if the down tilt is the XOR plan has an angle with the horizontal plan. So, the OX line is always the axis of the main lobe) and the maximum values in this plan are in OX direction (considering that antenna radiates in this direction). The peak power density in a distance R (that has an azimuth angle φ with OX direction), is estimated using formula () [1], [], [3], [4], [5]. S Peak ( R, ) W 3dB rad RL ( R 1 ( ) where φ 3dB is the beam-width at 3 db (the angular width of the E plane main lobe at the half power or 3dB down compared to the peak) and W rad = η P in; where η is the efficiency of the antenna and P in is the input power in the connector of the antenna. ρ 0 is calculated using formula (3) [1], [], [3], [4], [5]. 3dB 0 D A L (3) 6 where D A is directivity of the antenna. 3dB X () Nr. Application Frequency ICNIRP limit value for public ) 0 Table I Values of R Peak (S Peak ) for different applications q ( ) 3W Rad 3dB Peak (5) 3dBL DAS Considering the azimuth angle φ = 0, we can estimate the peak power density in the OX direction. This value at φ = 0, is the maximum value of S Peak (R, φ). For all estimations we did, for GSM 900, 1800, 100MHz (3G), FM, UHF and WiMAX, the azimuth angle is taken as φ = 0. All the above considerations and formulas are for directional antennas, so if we have to calculate the power density for Omni-directional antennas ρ 0 and q are respectively given by formulas (6) and (7) [1], [ ], [3], [4], [5]: (6) 0 W D A L Rad q Peak L DAS (7) To calculate the R Peak and S Peak, we may use the flowchart as in Fig.. III. RESULTS AND DISCUSSIONS Using the above mentioned theoretical method, we have estimated the peak power density over the distance and the distance where Power Density is equal to the limit for FM, UHF, GSM900, GSM1800, 3G (100MHz) and WiMAX applications. In table I, you will find the results from estimations for each application. The values of R Peak (S Peak ) are selected as random from values of the total sites where the estimations are done. ICNIRT limit value for occupational 1 FM 96 MHz watt/m 10 watt/m 1m/7m UHF 690 MHz 3.45 watt/m 17.5 watt/m 18m/4m 3 GSM MHz 4.5 watt/m.5 watt/m 0.4m/m 4 GSM MHz 9 watt/m 45 watt/m 0.3m/1m 5 3G 100 MHz 10 watt/m 50 watt/m 0.44m/.19m 6 WiMAX 3.5 GHz 10 watt/m 50 watt/m 3m/0.015m R Peak (S Peak ) for occupational /public

3 International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 0 60 Start Get values of L, G, h, P in, 3dB Directional or Omnidirectional Omnidirectional Calculate 0, q, R peak for omnidirectional antennas Directional Calculate 0, q, R peak for directional antennas Calculate values of S peak for some values of R>R Peak End Plot S Peak over the distance and compare it to the limit value Fig.. Flowchart for estimating the peak power density over the distance The peak power density changes over distance and in the graphics below are shown examples for each application. Fig. 3, shows S Peak over distance for a FM application, compared to the limits, for occupational and public exposures. It seems that the range of the distance, where S Peak is equal to the limit for occupational, is around 1m and for public exposures, is around 7m [9]. Fig. 4, shows S Peak over distance for a UHF application, compared to the limits, for occupational and public exposures. It seems that the range of distance, where S Peak is equal to the limit for occupational exposures, is around 18m and for public exposures, is around 4m [7], [8]. Fig. 5, shows S Peak over distance for a GSM 900MHz application, compared to the limits, for occupational and public exposures. It seems that the range of the distance, where S Peak is equal to the limit for occupational exposures is around 0.4m and for public exposures is around m [6]. Fig. 6, shows S Peak over distance for a GSM 1800MHz application, compared to the limits for occupational and public exposures. It seems that the range of distance, where S Peak is equal to the limit for occupational exposures is around 0.3m and for public exposures, is around 1m [6]. Fig. 7, shows S Peak over distance for 3G (100MHz) application, compared to the limits for occupational and public exposures. It seems that the range of distance where S Peak is equal to the limit, for occupational exposures, is around 0.44m and for public exposures, is around.19m [11]. Fig. 8, shows S Peak over distance for a WiMAX application, compared to the limits for occupational and public exposures. It seems that the range of distance, where S Peak is equal to the limit, for occupational exposures, is around 3m and for public exposures, is around 0.015m [10]. All estimations are done for real antennas and applications, so the results are only for these applications with specific data of antennas and their parameters. The results do not give the range of R Peak for a certain application but they just create an idea for this range. For a certain application R Peak should be calculated using specific data like frequency, input power of the antenna, height of the antenna, efficiency etc. It is important to mention that the results take place for ideal conditions of the propagation wave, so we do not consider the reflected waves and other effects that accompany the process of propagation wave in reality. Looking at the results it seems that in higher frequency applications, the ICNIRP limits are higher and they are increasing from FM to UHF, GSM900, GSM1800, 3G and WiMAX (for 3G and WiMAX the limits are the same) antennas for both public and occupational limits. From the results, the R Peak parameter is decreasing from UHF to GSM900, GSM1800 and WiMAX application.

4 International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: Distance in m from FM antenna Standart for public Fig. 3. S Peak over distance for FM application compared to the limit for public and occupational exposures Distance in m from UHF antenna Fig. 4. S Peak over distance for UHF application compared to the limit for occupational and public exposures.

5 International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: Distance in m from GSM 900 antenna Fig. 5. S Peak over distance for GSM 900MHz application compared to the limit for occupational and public exposures Distance in m from GSM 1800MHz antenna Fig. 6. S Peak over distance for GSM 1800MHz application compared to the limit for occupational and public exposures.

6 International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: Peak power density Distance in m from 3G antenna Fig. 7. S Peak over distance for 3G 100MHz application compared to the limit for occupational and public exposures Distance in m from WiMax antenna Fig. 8. S Peak over distance for WiMAX 3.5GHz application compared to the limit for occupational and public exposures.

7 International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 0 64 From the results, for FM application the R Peak parameter is lower than the same parameter in UHF due to the big difference in the input power of the antennas. For that FM application, the input power is twice lower than in the UHF application. This big difference in power causes the difference in the R Peak parameter. The diffence in power (the input power in the connector of the antenna) couses the difference in the R Peak parameter for 3G application (100MHz) compared to GSM900MHz and GSM1800MHz. IV. CONCLUSIONS, for over distance, for cellular base stations, FM, UHF and WiMAX antennas can be taken using a simplified theoretical way considering ideal conditions for wave propagation. From the theoretical results, we see that the peak power density is equal to the limits, for public and occupational exposures, for different distances from antennas, based on the parameters like: height of the antenna, input power, efficiency, directivity etc. Comparing the estimated values with ICNIRP values, we create an idea for the compliance distance where the radiation level is lower than the limits for public and occupational exposures. For applications like FM, UHF, GSM900, GSM1800, 3G and WiMAX the ICNIRP limit values take place in different distances from antennas but based on the results the distances are decreasing starting from UHF to WiMAX frequencies, since the limit values are increasing from UHF to WiMAX frequencies. The same thing can be said also for FM(3G) application compared to UHF(GSM900 and GSM1800MHZ) application even if in the case studied the distance is higher in UHF(3G) frequencies due to the difference in power in the two applications. Regarding GSM900, 1800 and 3G(100MHz), it is important to mention that practically, results are valid for cases where the antennas are mounted on roofs of buildings and XOR plan captures the upper floors of neighboring buildings (since calculations are made to plan XOR). For that reason, it is important to define safety distances and power density of radiation from the BTS antennas. This is important also for the fact that people living in these areas are under the effect of continuous radiation, which, in terms of XOR, reaches its maximum possible values. The results presented do not take into account the effect of other mobile operators. So, practically it is expected to have a higher level of power density as a result of the impact of other BTS antennas. For this reason the accurate determination of the safety distance, or the value of power density in the vicinity of BTS antennas can be determined through the measurements in the field or through calculations that take into account all possible sources, in that frequency range. Another important element that should be taken into consideration is the level of radiation, when a phone call is generated in the vicinity of BTS antennas. What is expected is to have a increased level of radiation caused by mobile device itself. Determination of change in the level of radiation in this case is difficult to do theoretically, therefore, practical measurements can provide the possibility of determining the radiation in such cases. Taking into consideration the above issues, future work will consist on real measurements in the vicinity of antennas. Measurements should also be made in high-density areas and should measure the impact of different frequencies or special contribution of GSM operators, FM, UHF and WiMAX. It is important to be judged on the average power density radiated from the antenna but also for determining the contributors, with greater weight. [1]. REFERENCES [1] S. Miclaus, P. Bechet, Estimated and measured values of the radiofrequency radiation power density around cellular base station, 7 th International Balkan Workshop on Applied Physics, 5-7 July 006, Romania [] ICNIRP Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields (up to 300 GHz), Health Physics 74 (4), pp , 1998 [3] A. Faraone, R. Yew-Siow Tay, K. H. Joyner, Q. Balzano, Estimation of the Average Power Density in the Vicinity of Cellular Base-Station Collinear Array Antennas, IEEE Trans. On Vehicular Technology, vol 49, no. 3, pp , May 000 [4] R. Cicchetti, A. Faraone, Estimation of the Peak Power Density in the Vicinity of Cellular and Radio Base Station Antennas, IEEE Trans. on Electromagnetic Compatibility, vol. 46, no., pp , May 004 [5] R. Cicchetti, A. Faraone, Q. Balzano, A Uniform Asymptotic Evaluation of the Field Radiated from Collinear Array Antennas, IEEE Trans. on Antennas and Propagation, vol. 51, no. 1, pp , Jan. 003 [6] R. Miho, B. Kamo, Estimation and theoretical evaluation of the E - M radiation field in the vicinity of GSM900 and GSM1800 antennas. VNM report for GSM900 and GSM1800, DET, FTI, Tirana 008 [7] R. Miho, B. Kamo, Estimation and theoretical evaluation of the E - M radiation field in the vicinity of UHF 594MHz antennas. VNM report for UHF 594MHz, DET, FTI, Tirana 009 [8] R. Miho, B. Kamo, Estimation and theoretical evaluation of the E - M radiation field in the vicinity of UHF 690MHz antennas. VNM report for UHF 690MHz, DET, FTI, Tirana 009 [9] R. Miho, B. Kamo, Estimation and theoretical evaluation of the E - M radiation field in the vicinity of FM 96MHz antennas. VNM report for FM 96 MHz, DET, FTI, Tirana 009 [10] R. Miho, B. Kamo, Estimation and theoretical evaluation of the E - M radiation field in the vicinity of WiMAX 3.5GHz antennas. VNM report for WiMAX 3.5GHz, DET, FTI, Tirana 009 [11] R. Miho, B. Kamo, Estimation and theoretical evaluation of the E - M radiation field in the vicinity of 3G (100MHz) antennas. VNM report for WiMAX 3.5GHz, DET, FTI, Tirana 010 [1] O. Shurdi, B.Kamo, A.Lala, EMF measurements in the vicinity of BTS cellular stations of Vodafone Albania. Balwois 010 Int. Conference.