Study on the Evaluate Methods of Head and Hand Influence on Mobile Antenna Radiation Performance

Transcription

1 212 7th International ICST Conference on Communications and Networking in China (CHINACOM) Study on the Evaluate Methods of Head and Hand Influence on Mobile Antenna Radiation Performance Xinzhong Li, Jun Yang, Bin Fan, Jianquan Wang Department of wireless research China Unicom Research Institute Beijing, China Abstract The radiation performance of the terminal antennas is influenced by the head and hand of the person who is holding the device. At the antenna design phase, the performance reduction should be considered sufficiently in order to make sure the Total Radiated Power (TRP) and Total Radiated Sensitivity (TRS) of the terminal satisfy the requirement of the system. In this paper, an evaluate method of head and hand influence to the radiation performance of is illustrated, through which tolerance of the terminal antenna TRP/TRS decrease could be evaluated conveniently and efficiently. Keywords-Antenna radiation; TRP/TRS; SAR; Head and hand; CST I. INTRODUCTION Terminal design has changed significantly over the past few years, which results in increasingly elegant and user friendly devices. However, antennas, which were external in many cases, have now been moved inside the terminal body and have evolved to be light-weight and low-volume, making use of the device enclosure where possible. As a consequence, the radio performance of the antenna systems suffers and makes devices more sensitive to the position of user hand holding the terminal. Currently, the design of the new terminal devices is mainly focus on the external appearance, which may induce high effect on the performance of the radio technologies. Figure 1. 3G cells shrinking due to terminal performance According to evaluation results of the 3G networks, the impact of one low performance terminal is equivalent to shrinking the 3G cell cover by up to 2%, as shown in Figure 1. The consequential impacts of this includes inconvenience to customers.3g devices fall back to 2G, resulting in additional 2G traffic and degradation of customer experience. Additionally, the 3G to 2G handover may cause call dropping. It costs high levels of network OPEX/CAPEX. II. TRP/TRS REQUIREMENTS FOR TERMINAL ANTENNAS Total Radiated Power (TRP) is one of the measurements of how much power the device actually radiates. TRP is defined as the integral of the power transmitted at different directions over the entire radiation sphere. 1 TRP = ( EIRPq(; W f ) + EIRPf (; Wf ) 4 ) dw pò where W is the solid angle describing the direction; f is frequency; q and f denotes the two orthogonal polarizations; EIRP q and EIRP f are the actually transmitted power on the corresponding polarizations. Total Radiated Sensitivity (TRS) is one of the measurements of the receiver performance of the devices. This measurement records reduction of the base station transmitted signal at the point that BER equals to 2.44%. It can be formulated as: 4p TRS = é 1 1 ù ò + dw êeisq(; Wf ) EISf (; Wf ) ú ë û where effective isotropic sensitivity (EIS) is defined as the power available at the antenna output such as the sensitivity threshold is achieved for each polarization;wis the solid angle describing the direction; f is frequency;q and f are the two orthogonal polarizations. Requirements are defined for roaming bands for both speech position (beside the head) and data transfer position (free space). Requirements for free space are applicable to devices used in the data transfer position, including laptop mounted equipment (LME) plug-in UEs and laptop embedded equipment (LEE) UEs. All bands are potential roaming bands, and the requirements for roaming bands shall therefore be fulfilled for all bands supported by a UE/MS. Requirements for operating bands depend on the deployment and configuration of the network. Recommended performance values for operating bands are included in this (1) (2) /12/$ IEEE

2 specification for information. It should be noted that the ability to meet the recommended performance values depends on the number of frequency bands supported by the UE/MS. The minimum TRP performance requirements for FDD roaming bands are shown in Table I. TABLE I. TRP MINIMUM PERFORMANCE REQUIREMENT FOR FDD ROAMING BANDS IN THE SPEECH POSITION AND THE PRIMARY MECHANICAL MODE Operati Power Class Power Class Power Class 4 ng band 3 Power (dbm) 3bis Power (dbm) Power (dbm) Aver Min Aver Min Aver Min I II III IV V VI VII VIII IX NOTE: applicable for dual-mode GSM/UMTS. For terminal with GSMK modulation in the speech position and the primary mechanical mode, the minimum TRP performance requirements are shown in Table II. TABLE II. TRP MINIMUM PERFORMANCE REQUIREMENT FOR GSM ROAMING BANDS IN THE SPEECH POSITION AND THE PRIMARY MECHANICAL MODE Operating Power Class 1 Power Class 4 band Power (dbm) Power (dbm) Aver Min Aver Min GSM GSM DCS PCS NOTE: applicable for dual-mode GSM/UMTS. The minimum TRS performance requirements for FDD roaming bands are shown in Table III. [The values in the tables are Î or with no interference.] TABLE III. TRS MINIMUM REQUIREMENTS FOR FDD ROAMING BANDS IN THE SPEECH POSITION FOR THE PRIMARY MECHANICAL MODE Operating Band Unit <REFÎ or> Aver Max I dbm/3.84 MHz II dbm/3.84 MHz III dbm/3.84 MHz IV dbm/3.84 MHz V dbm/3.84 MHz VI dbm/3.84 MHz VII dbm/3.84 MHz VIII dbm/3.84 MHz IX dbm/3.84 MHz NOTE 1 For Power Class 3, 3bis and 4 this shall be achieved at the maximum output power. NOTE 2 For the UE which supports both Band III and Band IX operating frequencies, the reference level of TDB dbm TRS <REFÎor> [aver and min] shall apply for Band IX. NOTE3 Applicable for dual-mode GSM/UMTS. NOTE 4 For the UE which supports DB-DC-HSDPA configuration 2, aver <REFÎor> level of -98 dbm/3.84 MHz and max <REFÎor> level of -95 dbm/3.84 MHz shall apply for Band II. NOTE 5 For the UE which supports DB-DC-HSDPA configuration 2, aver <REFÎor> level of -1 dbm/3.84 MHz and max <REFÎor> level of -97 dbm/3.84 MHz shall apply for Band IV. The sensitivity oftransmission radiationin the primary mechanical mode for TCH/FS at 2% class II (RBER). TABLE IV. TRS MINIMUM REQUIREMENTS FOR FDD ROAMING BANDS IN THE SPEECH POSITION FOR THE PRIMARY MECHANICAL MODE Operating Band Unit <REFÎ or> Aver Max GSM 85 dbm GSM 9 dbm DCS 18 dbm PCS 19 dbm NOTE 1:For Power Class 1 and 4 this shall beachieved at the maximum output power. NOTE2:Applicable for dual-mode GSM/UMTS. III. ANALYSIS OF HEAD AND HAND INFLUENCE ON ANTENNA RADIATION PERFORMANCE The antenna radiation has two fields, i.e. near-field and farfield. Near-field is more sensitive than far-field. When terminal is working, head and hand which is close to antenna near-field have influence on the antenna performance. Research results of the influence could be used to guide the optimization of the terminal performance and antenna design to reduce the sensitivity to work conditions and the radiation which may do harm to humans. 685

3 mm 2mm mm 2mm (a) f plane, q = 9 o mm 2mm (c) q plane, f = o ( point to head) Figure 2. The relationship between unipole antenna pattern and the antenna distance to head model (without hand, antenna is set in the surface of a metal box with insulated cover) at 915MHz without hand with hand with hand and choke (b) q plane, f = 18 o (not point to head) Figure 3. The unipole antenna patterns for the case that antenna 2cm away from head model ( without hand,with hand and with hand & choke, antenna is set in the surface of a metal box with insulated cover) at 915MHz According to the research results, the antenna radiation performance is related to the antenna distance to head and hand. Figure 2 gives the antenna working condition and the related simulation results. From q plane, it can be observed that when antenna is close to head, gain decreases and sidelobe increases. Additionally, evaluation results of the influence of hand are given in Figure 3. Hand holding the mobile phone shell has huge influence on transmission impedance performance. Figure 4 gives S 11 with/without hand and the relationship between S 11 and the distance of PIFA antenna to hand (d). These results show that hand has influence on S 11, the distance between PIFA antenna and the reflection coefficient. Specifically, it could cause resonant frequency 686

4 migration and antenna detuning. From Figure 5, it can be seen that hand has different influence on side-set PIFA antenna and top-set PIFA antenna. Actually, for side-set PIFA antenna, 2.62 cm distance to hand could cause detuning. For top-set PIFA antenna,.66 cm distance to head could cause detuning. In [4] and [5], it gives the other results about head and hand influence on antenna radiation performance. IS11I/dB -1-2 FDTD-without hand FDTD-d=7.21cm FDTD-d=6.56cm FDTD-d=2.62cm Test Results-without hand Test Results-d=6.56cm Frequency / GHz S Figure 4. The 11 calculation results of side-set PIFA antenna in mobile phone at 3 different distance to hand and without hand IS11I/dB S Frequency / GHz without cover & without hand with cover & without hand with hand d=7.21cm with hand d=3.93cm with hand d=2.62cm with hand d=.66cm Figure 5. The 11 calculation results of top-set PIFA antenna in mobile phone at 4 different distance to hand, without insulated cover, with insulated cover and with hand & insulated cover As illustrated above, head and hand closed to terminal have influence on antenna radiation performance. At the beginning of antenna design, working environments, frequency and distance to head and hand should be considered, and the performance allowance should be reversed to make sure terminal antenna TRP/TRS meet system requirements. Therefore, it is crucial to evaluate the tolerance of the antenna TRP/TRS decline in speech position with head and hand in a convenient and efficient way. IV. EVALUATION ON TRP/TRS DECLINE TOLERANCE BY SIMULATING SAR IN CST MWS A. SAR definition Specific Absorption Rate (SAR) is one measurement of the electromagnetic energy absorbed by biological tissue mass when exposed to radiating device (e.g. mobile phone). 2 2 P s E J SAR = = = r 2r 2rs where P is power loss density, E is electric field strength, J is current density, s is conductivity and r is density. Obviously, SAR is determined by power loss density. Power loss means antenna transmission power and receiving sensitivity decline. Then, we can evaluate the tolerant of the antenna TRP/TRS decrease in speak position by getting power loss caused by head and hand. B. Power loss simulation results Several guidelines and standards specify the limitation on SAR safety (i.e. ICNIRP, IEEE, Cenelec). Standards as IEEE 1528have defined the measurement methods for practical assessment of compliance. The SAR averaging scheme for simulation is specified in IEEE C95.3 Annex E. CST MICROWAVE STUDIO has already been approved by the FCC (USA) to comply with standard drafts. CST MWS has several advants for SAR simulation: a) Direct CAD import from various formats, intuitiveparameterization of imported data, automatichealing if required. b) Excellent geometry approximation due to PBA and TST and NO staircase representation used. c) Sub-gridding available for high detail level. d) Broadband material definition: Multiple frequencies can beevaluated in one simulation run. e) Full control of the reference power (input or accepted power). By CST MWS, the parameters, such as return loss, near fields, far-fields, power loss and SAR distribution of the antenna, can be easily obtained for all required frequencies in one simulation run. According to the hand and head Phantom specified in IEEE 1528 and IEE C95.3,we could simulate the power loss of terminal antenna in all required frequencies. Direct step CAD import of a mobile phone and set SAM and hand model. A power-loss monitor needs to be defined at the frequencies of interest. Simulation with head and Hand model can be completed in 2 hours on 2 GHz processor. All required frequencies, antenna far-fields and power loss can be obtained in one simulation run. The simulation model and results are shown in Fig.6-Fig.8. (3) 687

5 Figure 6. Simulation model-cad import of a mobile phone Figure 7. Simulation results-antenna E field and far-field at 18MHz Power Loss 5 4 According to the simulation results, it is obvious that the antenna power loss values are different on different frequency. For 9MHz case, the antenna power loss is about 2.8dB. For 18MHz case, the loss value is about 3.7dB. For 21MHz case, it is about 2.7dB. In sum, we can obtain the suggested values of TRS & TRP based on 3GPP TS , which gives the TRP&TRS recommended performance for GSM and WCDMA in free space. C. TRP/TRS test results of Smartphone devices In order to inspect whether TRP/TRS of the smart phone antennas meet the minimum requirements in speak position with head and hand, GSMA TSG work group have tested a number of handsets to evaluate the antenna performance. As shown by these results, handsets could meet TRP/TRS requirements (red lines mark) in free space, but TRP/TRS declines greatly due to the influence of head and hand. It is proved that head and hand closed to terminal depresses the antenna radiation performance. Only few of handsets TRP/TRS meet the minimum requirements, and TRP/TRS decline is over tolerance (black lines mark). It shows that the influence of head and hand on antenna radiation performance had not been considered sufficiently at the beginning of most handset antenna design. V. CONCLUSION Terminal antenna radiation performance is influenced by head and hand in speak position. At the beginning of antenna design, the performance decline should be considered sufficiently in order to make sure terminal antenna TRP/TRS meet the system requirements. An evaluate method of head and hand influence on antenna radiation performance is given in this paper, through which terminal antenna TRP/TRS decline tolerance could be evaluated conveniently and efficiently. Power Loss (db) Frequency (MHz) Figure 8. Simulation results-antenna power loss REFERENCES [1] 3GPP TS V11..:, User Equipment (UE) and Mobile Station (MS) over the air performance requirements(release 11), (211-12). [2] 3GPP TS , V1.1.1: User Equipment (UE) / Mobile Station (MS) Over The Air (OTA) antenna performance;conformance testing(release 1), (211-12). [3] 3GPP TS 36.11, V1.3.: Evolved Universal Terrestrial Radio Access (E-UTRA);User Equipment (UE) radio transmission and reception (Release 1),(211-6). [4] K.W.Kim and Y.Rahmat-Samii, Hantset antennas and humans at Kaband: the importance of directional antennas, IEEE Transactions on Antennas and Propagation, vol.46, no.6, pp , Jun [5] H.Arai, N.Igi, and H.Hanaoka, Antenna-gain measurement og handheld terminals at 9MHz, IEEE Transactions on Vehicular Technology, vol. 46, no.3, pp , Aug