Performance analysis of E-shaped dual band antenna for wireless hand-held devices
© Rajagopal and Rajasekaran; licensee Springer. 2015
Received: 25 May 2014
Accepted: 26 January 2015
Published: 6 March 2015
Due to evolution in wireless applications, the high performance dual band handsets were blooming in the market. In this paper, a compact dual band E shaped planar inverted F antenna is presented, which is suitable for GSM application in handheld devices. Here, antenna is described for GSM (900 MHz and 1800 MHz), which covers (831 MHz – 973 MHz and 1700 MHz – 1918 MHz) 10 dB bandwidth. The designs and simulations are performed using Finite Difference Time Domain (FDTD) technique based General Electro Magnetic Simulator – Version 7.9 (GEMS-7.9). The performance analysis of E-shaped antenna also includes real world interaction between antenna element and Spherical human head model composed of three layers, skin, skull and brain. The simulated results including, S-Parameter, radiation pattern, current distributions and Specific absorption rate, thermal distributions have validated the proposed E shaped antenna design as useful for compact mobile phone devices with comparatively low average Specific Absorption Rate in market.
KeywordsDual band antenna GSM (Global System for Mobile communication) PIFA (Planar Inverted F-antenna) S - Parameter Specific Absorption Rate (SAR) Finite Difference Time Domain (FDTD) General Electro Magnetic Simulator (GEMS)
Over last decade, the evolution of wireless communication devices has increased rapidly to fulfill the requirement of high performance mobile portable devices which includes smart phones, Tablets, Notebooks etc. The handset antenna which, plays a transceiver role in mobile phone handset, should be optimized for better performance. In addition to the electrical requirements, the design of a handset antenna has to take into account the resulting exposure of the user. However, there has also been increase in concern regarding ill effects of Radio Frequency (RF) emitted by mobile phone antennas. These adverse health effects can be assessed by measuring power coupled to human tissue and thermal change, by using dosimetry called Specific Absorption Rate. The international commission on non-ionizing radiation protection and IEEE provides radiation level limit for the consumer products in free space.
Now a days variety of multiband internal antennas are reported, which are highly preferred for slim mobile phone due to their compactness [2,7]. The following literature survey shows the implication of dual band antenna in mobile phone communications. Dual band antenna (MIMO) can be used for LTE band (0.746 – 0.787 GHz) and the M-WiMAX (2.5 – 2.69 GHz). It consists of two identical elements, each of which is 15 × 13.25 mm2. The minimum separation between two elements is 0.5 mm . Novel coplanar waveguide fed planar monopole antenna with dual-band operation for Wi-Fi and 4G LTE. It’s operating bands consists of 2.3 – 3.0 GHZ, 4.7 to 5.9 GHz are achieved by carefully optimizing the position and size of a smiling slot. Antenna is characterized in terms of return loss, radiation pattern, and measurement in anaerobic champers .
A connected E-shaped and U-shaped dual band patch antenna for operating frequencies 2.46 GHz and 4.9 GHz is designed and the bandwidth variation is analyzed by changing the height of substrate, bridge width etc. for different wireless LAN applications. The simulation studies are performed using GEMS simulation software . A compact planar inverted E-shaped dual band antenna is designed over PCB board of 10 × 5 × 4 mm3 and good performance characteristics observed at 2.4 GHz and 5.5 GHz makes this antenna suitable for mobile device applications .
In many commercial wireless applications, PIFA and PMA are extensively used because it is simple, compact with good radiation pattern with sufficient Bandwidth. Normally, the electrical characteristics of handset antenna mainly depend on the ground plane on which the antenna is fabricated and also on the phone casing. The bandwidth of the antenna element increases, if the casing also resonates at operating frequency. Bandwidth and radiation characteristics make the 2G dual band antenna suitable to be used for Wi-Fi and 4G LTE applications in the 2.4 GHz to 2.7 GHz band and also 5.1 GHz to 5.875 GHz band . Currently, GSM (Global System for Mobile Communication) is a standard protocol for digital mobile communication used for phone calls and transmission of text messages, which is addressed in this paper .
In this paper, E shaped PIFA with dual band 900/1800 MHz has been introduced . The design considerations and simulated results for the Proposed E shaped antenna such as, return loss, radiation pattern and current distributions were also analyzed. Further, the performance analysis of E shaped antenna is described by considering the real world environment in which, mobile phone is expected to operate. The near field environment are created with mobile phone model which includes antenna element, battery, exterior plastic shell and three layered human head model. Simulation and performance analysis of proposed E shaped antenna are performed using FDTD based GEMS simulator .
Section Numerical modelling includes the modeling technique and the modeling of antenna and near field interactive devices. Section Performance analysis of antenna in free space involves parametric analysis of E shaped antenna and current distributions in free space. Section Influence of near field on antenna performance discusses the influence of near field environment when antenna is in close proximity to a human head model. Finally, section Conclusion provides conclusion.
Maxwell’s equations can be solved in the time whereas for frequency domain many EM simulation techniques available using FDTD [17,18]. If the problem size grows, FDTD approach provides excellent scaling and the Broadband output can be obtaining using time domain approach. FDTD leads other computational methods say Finite Element method, Method of Moments etc. when the number of size of computational space increases. For studying, biological effects of Electromagnetic radiation from Wireless devices FDTD is better, which is the technique employed in our work. Further, FDTD also provides accurate results of the filed penetration into biological tissues.
Numerical formulation using FD-TD technique
Where, the equation involves electric field strength (E) and electric flux density (D), magnetic field strength (H) and magnetic flux density (B), electric current density (J) and electric charge density (ρe). Current density produces magnetic field around it. From the curl equation, we observed that the time derivative of the E-field depends on the change of the H-field across space. Hence, the value of the E-field can be computed if we know its previous value and the space-derivative of the H-field, which in turn is time-stepped and if initial field value, initial conditions and boundary conditions are known . The FDTD technique divides the computational space into a Cartesian coordinate’s grid of voxels and then allocates the components of the electric and magnetic fields as every E field is surrounded by H field and vice versa. This scheme is known as Yee lattice. If, the current changes over time, alternating magnetic field causes alternating electric field, which in turn causes another magnetic field, results in the creation of propagating electromagnetic wave of higher frequency.
There are certain commercially available EM simulators (say SEMCADx, GEMS etc.) which employ FDTD technique for computation. The computational performance of SEMCADx is as follows (Min grid size (mm) is 300, Computational domain is 14.2 M cells; Simulation time is <15 min, Simulation Speed is 300 M cells/s [19,20].
A FDTD based electromagnetic simulator (GEMS version −7.9) is used throughout the work. The FDTD modeling including head and hand model consists of 739675 cells. The convergence of the simulated solutions has been checked for every 100 time steps and the solutions are set to be converged for S- parameter calculations.
E - shaped antenna design
The substrate material used is of thickness t = 2 mm. The dimension of the shorting plate (S4) is 10 mm × 1.8 mm. The distance between the feeding and the shorting plate is 27 mm . The radiating E element is modeled as perfect electric conductor. The excitation port is modeled as lumped port with internal resistance being 50 Ω. Maximum working frequency of 3 GHz is allowed for performance analysis of radiating antenna.
Handheld device model and user head model
Properties of human tissues
Brain diameter (mm)
Skull thickness (mm)
Skin thickness (mm)
Tissue density (Kg/m3)
Performance analysis of antenna in free space
The design objective is a dual band portable handheld device antenna suitable for 900/1800 MHz GSM application. We optimize the design through simulation using General Electro – Magnetic Simulator (GEMS), a commercial software package based on Finite Difference Time Domain(FDTD) technique .
While using the handset, the pulsed current flows from the battery to radiating element. This excitation gives rise to magnetic field around the handset.
Bandwidth is one of the very important characteristics which make the 2G dual band antenna suitable to be used for 4G LTE applications. For example, the 10 dB bandwidth of proposed antenna covers LTE band-19 of NTT Docomo (Japan) which has uplink of (830–845) MHz and downlink of (875–890) MHz and LTE band-3 of NTT Docomo (Japan) has uplink of (1764–1784) MHz and downlink of (1859–1879) MHz. Similarly, FAReastone (Taiwan) covers LTE band-3 with uplink (1735–1755) MHz and downlink of (1830–1850) MHz. Hence, the proposed antenna can also be employed for 4G LTE applications .
3D- radiation pattern
The antenna radiates possibly in all direction to cover the range. However, it radiates more in positive Z - direction, since reflected by the ground plane. The user head in Z direction acts as obstacle and absorbs certain amount of radiated power in Z direction thereby decreasing the efficient performance of E- antenna. Figures 6(b) and 7(b) show the altered radiation pattern due to human head interaction which absorbs certain amount of power radiated by phone, there by impacting mobile phone E-antenna performance .
Influence of near field on antenna performance
Specific Absorption Rate is the subject of strict regulation for health protection. This section focuses to describe the impact of human head model interaction with mobile phone handset .
Specific absorption rate
SAR is averaged over tissue masses of 1 or 10 g tissue . The human body which is a good conductor acts like a receiving antenna, absorbs the EM energy from the space. The tissues which are composed of different salts and organic compounds owns its permittivity and conductivity which are also function of frequency, impacts the power coupled to tissues. The internal coupled fields can be calculated using numerical method based computational technique (FDTD), which gives information regarding realistic RF exposure.
SAR analysis and discussions
SAR averaged over 1 g and 10 g tissue when exposed to handheld device
Placement of mobile handset device with respect to head model
Placed near (d = 0 mm)
d = 5 mm
d = 10 mm
1-g SAR (W/Kg)
10-g SAR (W/Kg)
Max SAR (W/Kg)
Average SAR (W/Kg)
The results indicate that, power coupled to the human tissue gets decayed with increase in distance from handset. SAR values are well below the SAR limit which substantiates the suitability of antenna design for wireless handheld device application, when handset is placed at 10 mm from the head, which is a normal placing position of phone during operation.
From Figure 12b, it is observed that, for 1800 MHz frequency, the 1 g SAR and 10d SAR are more than three times higher than SAR values observed at 900 MHz operating frequency. The values used for comparison and analysis may be little bit inaccurate due to modeling of human head as layered spherical model which is far different from real time EM exposure to real human. However in this study, for both 0.9 GHz and 1.8 GHz frequencies, 1 g and 10 g SAR values get decreased with increased separation between mobile and head model.
In this paper, a compact dual band E shaped antenna with comparatively low average SAR and better Bandwidth is introduced for GSM application in handheld devices. Simulations were performed for different scenarios. The antenna in free space and the handset device placed close to a user head model. The return loss was better than 25 dB at 900 MHz and 1800 MHz with bandwidth of 142 MHz and 218 MHz in the lower band and in the upper band respectively as compared to existing antennas. The 10 dB bandwidth of proposed E shaped antenna covers GSM 850/ GSM 900/ GSM 1800 bands. Further, the average specific absorption rate, due to human interaction with handset is well below the specified limit. The obtained results, including surface current distributions, S-parameters, radiation patterns, SAR values, have demonstrated that the proposed antenna design is suitable for GSM and 4G network and is able to achieve good performance for real world scenario.
Authors would like to thank Doctors of various hospitals for their valuable explanations concerning human tissue property.
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