Performance of shorted microstrip patch antennas for mobilecommunications handsets at 1800 MHz

We have investigated the application of two different types of novel shorted-patch antennas for mobile communications handsets at 1800 MHz. A single shorted-patch and a stacked shorted-patch antenna offering improved bandwidth are compared with data for a λ/4 monopole. The finite-difference time-domain (FDTD) technique was used to calculate antenna characteristics such as impedance and radiation patterns for two cases: on a handset and on a handset near a (2.5-mm voxel) heterogeneous head model in an actual position of phone use. We also obtained specific absorption rate (SAR) distributions and calculated the spatial peak 1-g SAR values. In addition, the effect on SAR and antenna characteristics of including a block model of the hand was assessed. Similar performance is achieved from the single or stacked shorted-patch antenna with the latter providing greater bandwidth, 8.2% versus 9.4% with the head and hand included. Both antennas reduce the l-g spatial peak SAR value in the head by 70% relative to the monopole. The presence of the hand reduces the efficiency of all three antenna types by approximately 10%     

Design and acceptance test of compact planar monopole antenna for LTE smartphone considering SAR,TRP, and HAC values

Eight different types of compact multiband planar antennas are proposed in this work for covering several long‐term evaluation (LTE) and Wi‐Fi bands in a smartphone antenna design. Gradual inclusion of several sections of a radiator on an inexpensive FR4 substrate is presented for receiving multi‐LTE bands with a handset device. Along with the presently available LTE bands, this antenna design approach also includes upcoming LTE in unlicensed spectrum and LTE licensed‐assisted access. Various techniques such as partial ground, branch line slit, parasitic structure, and meandered lines are used to achieve desired resonant frequencies, bandwidth, matching, and miniaturization. The final type of eight antennas has been implemented in the real‐world mobile phone handset. The interaction between the mobile handset and the human phantom model has been analyzed at few specific frequencies for evaluating specific absorption rate (SAR) and total radiated power (TRP) in a simulated manner. The same type is also studied as a hearing aid compatibility (HAC)–supported wireless device. The simulated results show the SAR and HAC values are at the acceptance level for this proposed design. A prototype model is developed and few parameters are measured for validation.     

On the behaviour of a compact antenna system with non-resonant elements in the presence of the human head

A novel handset antenna technique to solve the increasing demand of mobile bands, the loading effects (mismatching and efficiency losses) and the power absorption introduced by the head is analysed in terms of bandwidth, efficiency and SAR (specific absorption rate). The technique proposed integrates non-resonant elements and its results are compared with those obtained by a planar inverted-F antenna. The main antenna parameters (bandwidth, efficiency in free-space, efficiency regarding the human head presence and SAR) are compared in terms of electromagnetic simulation and measurements. The study concludes that the novel antenna architecture achieves multiband operation from 824–960 MHz and 1710–2170 MHz and become robust to human loading while occupying a reduced volume of just 250 mm³ in a typical handset phone.     

Reducing the influence of feed cables on small antenna measurements

It is shown that in measurements of mobile handset antennas a cap on the coaxial feed cable inserted relatively close to the handset acts practically like an open termination to the induced currents on the surface of the phone chassis. Therefore, the measurement results with the cap are much closer to those of an isolated handset than without any countermeasures or with ferrite chokes     

Resonator-based analysis of the combination of mobile handset antenna and chassis

The performance of the mobile phone handset antenna-chassis combination is analyzed based on an approximate decomposition of the waves on the structure into two resonant wavemodes: the antenna-element wavemode and the chassis wavemode. A double resonator equivalent circuit model is presented and used to estimate the impedance bandwidth and the respective distributions of radiation losses with typical parameter values at 900 and 1800 MHz. It is noticed that at 900 MHz, the radiation losses of the antenna element wavemode represent typically less than 10% of the total power. Thus, the antenna element works mainly as a matching element, which couples to the low-Q resonant wavemode of the chassis. At 1800 MHz, the contribution of the antenna element wavemode is larger. By enhancing the coupling and by tuning the chassis resonance, it is possible to obtain an impedance bandwidth of over 50% (6 dB return loss) at both at 900 and 1800 MHz. The results given by the equivalent circuit study are fully supported by those of three-dimensional phone-model simulations, including calculation of the SAR and efficiency values. In prototyping, the 6 dB bandwidth of 5.5% was obtained at 980 MHz with a nonradiating coupling element with a volume of 1.6 cm/sup 3/ on a 120 mm long chassis.     

EM interaction of handset antennas and a human in personalcommunications

In personal communications, the electromagnetic interaction between handset-mounted antennas and the nearby biological tissue is a key consideration. This paper presents a thorough investigation of this antenna-tissue interaction using the finite-difference time-domain (FDTD) electromagnetic simulation approach with detailed models of real-life antennas on a transceiver handset. The monopole, side-mounted planar inverted F, top-mounted bent inverted F, and back-mounted planar inverted F antennas are selected as representative examples of external and internal configurations. Detailed models of the human head and hand are implemented to investigate the effects of the tissue location and physical model on the antenna performance. Experimental results are provided which support the computationally obtained conclusions. The specific absorption rate (SAR) in the tissue is examined for several different antenna/handset configurations. It is found that for a head-handset separation of 2 cm, the SAR in the head has a peak value between 0.9 and 3.8 mW/g and an average value between 0.06 and 0.10 mW/g for 1 W of power delivered to the antenna. Additionally, the head and hand absorb between 48 and 68% of the power delivered to the antenna     

Is the SAM phantom conservative for SAR evaluation of all phone designs?

The specific anthropomorphic mannequin (SAM) phantom was designed to provide a conservative estimation of the actual peak spatial specific absorption rate (SAR) of the electromagnetic field radiated from mobile phones. However, most researches on the SAM phantom have been based on early phone models. Therefore, we numerically analyze the SAM phantom to determine whether it is sufficiently conservative for various types of mobile phone models. The peak spatial 1‐ and 10‐g averaged SAR values of the SAM phantom are numerically compared with those of four anatomical head models at different ages for 12 different mobile phone models (a total of 240 different configurations of mobile phones, head models, frequencies, positions, and sides of the head). The results demonstrate that the SAM phantom provides a conservative estimation of the SAR for only mobile phones with an antenna on top of the phone body and does not ensure such estimation for other types of phones, including those equipped with integrated antennas in the microphone position, which currently occupy the largest market share.     

Low SAR Ferrite Handset Antenna Design

The benefits resulting from the inclusion of ferrite in material loaded antennas are investigated, initially through the use of a spherical analytic model and then through a transmission line matrix simulation tool applied to a rectangular slab geometry. It is observed that a material with equality of relative permittivity and permeability in combination with specific positioning of the antenna in relation to the head, can result in the definitive small-size, high efficiency and bandwidth, low specific absorption rate (SAR) antenna. The accuracy of the simulations is validated both through efficiency and SAR measurements of three material coated monopole samples. Further research into optimizing the above attributes and translating them into a handset antenna leads to a multiband antenna design covering the GSM 1800, 1900, UMTS and Bluetooth bands, with a SAR value reduced by 88% compared to conventional phones and an efficiency of 38% at 1.8 GHz. A tri-band antenna design is also presented, utilizing currently available lossy ferrite material and it is considered as the first step towards the feasibility of the ultimate low SAR multiband ferrite handset antenna, until further material development specifically for antenna applications takes place     

利用FDTD方法比较手提电话天线的方向图,输入阻抗及人头部的比吸收率(SAR)(英文)

本文给出了利用FDTD电磁模拟方法对常用的五种个人通信手提电话的天线和人头部组织相互作用的比较研究。在研究中考虑的蜂窝通信手提电话常用的天线种类为单极子、偶极子和倒F型（IFA）天线。不均匀的实际人头模型被用于预测天线特性（包括输入阻抗，方向图和辐射效率等）和对操作作者耦合的电磁效应。天线在人头部的潜在危险影响是用1W辐射功率在人组织产生的比吸收率（SAR）来评估。     

Comparisons of computed mobile phone induced SAR in the SAM phantom to that in anatomically correct models of the human head

The specific absorption rates (SAR) determined computationally in the specific anthropomorphic mannequin (SAM) and anatomically correct models of the human head when exposed to a mobile phone model are compared as part of a study organized by IEEE Standards Coordinating Committee 34, Sub-Committee 2, and Working Group 2, and carried out by an international task force comprising 14 government, academic, and industrial research institutions. The detailed study protocol defined the computational head and mobile phone models. The participants used different finite-difference time-domain software and independently positioned the mobile phone and head models in accordance with the protocol. The results show that when the pinna SAR is calculated separately from the head SAR, SAM produced a higher SAR in the head than the anatomically correct head models. Also the larger (adult) head produced a statistically significant higher peak SAR for both the 1- and 10-g averages than did the smaller (child) head for all conditions of frequency and position.     

Enhancing robustness of handset antennas to finger loading effects

A novel handset antenna consisting of two small antennas is proposed to mitigate finger loading effects. Both antennas are excited with a different phase in order to maximise the bandwidth. A phantom hand has been used to perform the experiments. It demonstrates how the finger affects the radiation behaviour for three particular positions of the finger over the antenna area. Experimental results feature a wider input impedance bandwidth and a higher degree of immunity to finger loading effects when compared with a single-element approach.     

A planar diversity antenna for handheld PCS devices

A polarization diversity antenna (PDA) is described, and its performance is compared to that of a monopole antenna at frequencies near 900 MHz. Numerical modeling of each antenna, using the finite-difference time-domain (FDTD) technique, incorporates a cellular telephone handset in the vertical orientation, the user's head and hand, and the mobile communications environment. Results indicate that the two modes of the PDA are sufficiently uncorrelated for diversity operation and that, overall, the values of the mean effective gain (MEG), efficiency, and averaged specific absorption rate (SAR) in the head are better for the PDA than for the monopole antenna. However, in terms of the MEG, the PDA is more sensitive than the monopole antenna to the presence of the user's body. For the PDA, most of the power absorbed in the user's body is deposited in the hand, whereas for the monopole antenna, most of the absorbed power is deposited in the head. For both antennas, the MEG depends on the environment (urban or suburban)     

Evaluation of the SAR induced in a multilayer biological structure and comparison with SAR in homogeneous tissues

Wireless systems usage has evolved, for instance, with the recent increase in the use of a hands-free kit, the mobile phone is used more and more in a body-worn position. Therefore, to check the compliance to the international limits, new methods have to be developed. In this study, we analyze the relevance of using the equivalent head liquid for the biological structure of organs that are different from that of the head. This paper compares the Specific Absorption Rate (SAR) values assessed using simulations in a flat phantom filled with the liquid used to test the compliance of mobile phone close to the head to those values obtained using a multilayer model representing the tissues of the trunk. The multilayer structures are derived from the anatomical analysis of the visible human model and corresponding to reasonable positions of a handset in a body-worn configuration. The employed sources are half-wavelength dipoles placed at different distances from those structures and operating at frequencies between 300 MHz and 6 GHz.     

Human proximity effects on circular polarized handset antennas inpersonal satellite communications

Satellite-based systems are the next step in mobile communications. Several low and medium Earth orbit mobile communication satellite systems have been proposed and are currently being deployed. For all these systems, high-performance circularly polarized antennas for the mobile terminals are of importance. Although considerable material is available on circularly polarized antennas, there is an absence of information on how the human's close proximity to the antenna affects the circular polarization purity of the radiated field. This paper presents an analysis of representative circularly polarized helical handset antennas. The helix is used because of its wide bandwidth properties and capability to provide both circular and linear polarization. Thus, this element could be used for handsets that are planned to work with both the terrestrial-based communications systems of today and the satellite-based communication systems of tomorrow. The intent is to characterize the effects the close proximity of a human head model has on the computed performance of the circular polarized antenna. The method of moments (MoM) and finite-difference time-domain (FDTD) numerical techniques are used to study various helix structures on top of a small box representing a handset. In order to be able to effectively apply the FDTD, a novel square helix structure is introduced. Results computed with these two techniques are compared to illustrate the accuracy of each implementation. The results indicate significant polarization purity degradation caused by the presence of a human head. For the particular geometry simulated, the presence of a head model degraded the average axial ratio within a 50° vertical cone from 2.9 to 9.1 dB. This significant increase in axial ratio can have profound effects on link budgets     

Study of specific absorption rate (SAR) induced in two child head models and in adult heads using mobile phones

This paper gives a first comparison of specific absorption rate (SAR) induced in a child-sized (CS) head and an adult head using a dual-band mobile phone. In the second study, the visible human head is considered and comparison of SAR induced in a CS or child-like (CL) head and an adult head using a dual-band mobile phone is given. All the peaks of average SAR over a mass of 10 and 1 g in the head and the power budget are determined in the two comparisons using the finite-difference time-domain method. The differences between the results for adult and CS or CL heads are given at 900 and 1800 MHz. No important differences are noted for the peak SAR averaged over 10 g (SAR10 g), between the two adult head models, as well as between the two child head models. The peak SAR10 g in the brain of the CS or CL head is slightly more significant than that for the adult one.     

Optimization of PIFA-IFA combination in handset antenna designs

As commercial needs have expanded the functions of the wireless cellular handsets, multiantenna development in one handset has become more and more common. This paper addresses a multiantenna solution for the wireless handset application. A planar inverted "F" antenna (PIFA) was designed as the main antenna of the handset to cover the 800 MHz band (824 MHz-894 MHz) and the 1900 MHz band (1850 MHz-1990 MHz). A side-mounted inverted "F" antenna (IFA) was designed as the 1575.42 MHz global positioning system (GPS) antenna. The location of the feed/ground pins of both antennas affected not only the total antenna efficiency, but also the polarization of the GPS IFA. The length of the GPS IFA affected the isolation between the two antennas and the specific absorption rate (SAR) of the PIFA at the 1900 MHz band. A three-dimensional efficiency measurement of the prototypes in both free space and against-head position will be presented. Measurement of SAR and its distribution will also be presented to demonstrate the impact of the IFA on the near field of the PIFA.     

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 user's 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 user's head on the MEG depends on the antenna type and on which side of the head the user holds the handset.     

Reliable prediction of mobile phone performance for realistic in-use conditions using the FDTD method

The objective of this study was to analyze whether advanced simulation platforms provide the effectiveness, accuracy, reliability, and efficiency to predict impairment of mobile-phone RF performance under various usage patterns. The investigation was based on the mechanical CAD data of a commercial phone with two alternative antennas. Three significant hand positions were modeled and evaluated with the device against the SAM head. The results demonstrated high reliability and suitability for providing decision rationale for the design of complex high-end multi-band mobile phones.     

On the use of wide-band, high-gain, microstrip antennas for mobiletelephones

The increasing use of cellular telephones has spawned considerable research effort on the design of compact, high-efficiency antennas for mobile telephones, exhibiting low EM coupling to the human head. Microstrip antennas seem now to render possible the achievement of all these characteristics. We present some results on a stacked microstrip antenna designed at the University of Utah, comparing its performance with that of a typical handset equipped with the conventional monopole antenna. The main thrust is to highlight the problems associated with typical mobile-telephone antennas, and to show how microstrip-antenna technology could solve most of these problems     

Specific absorption rates (SARs) induced in head tissues by microwave radiation from cell phones

The cellular/mobile phone industry has been reluctant to disclose SAR values to the public in the past. The decision by the Cellular Telecommunication Industry Association (CTIA) to require manufacturers to disclose SARs emerged after it became clear that SAR information was going to appear on the FCC Web site in a user-friendly form. It was also prompted by a British government panel's call, on May 11, 2000, for the SAR of each mobile phone to be printed on the box in which the phone is sold. The wireless telephone industry is concerned about how the public may use the SARs, because, according to one industry source, "SARs by themselves may be misleading and variations in SARs do not represent a variation in safety." Indeed, SAR values can vary as a function of the carrier frequency-for example, 850 or 1900 MHz, used to transmit the telephone message-or how the handset is held. The article presents some insights into SAR, what it is, how is it determined, and what it means.