Abdel-Fattah Sheta

A New Low SAR Antenna Structure for Wireless Handset Applications

This paper proposes a new mobile handset antenna structure to reduce the value of the speciflc absorption rate (SAR). The antenna is based on the PIFA structure and operates at dual-bands of 0.9GHz and 1.8GHz. The chassis current is reduced using a metallic shim-layer inserted between the patch and chassis. This shim-layer is connected to the handset chassis through posts whose number and positions are determined using optimization techniques. Sidewalls are attached to increase the gain of the antenna and reduce the radiation towards human head. Simulations in the cheek mode show that the SAR reduction factor (SRF) of the proposed structure averaged over 10-g is more than 75% at 0.9GHz and 46% at 1.8GHz. The SRF values obtained using simulations and measurements are found to be better than 51% and 76% at 0.9GHz and 1.8GHz, respectively.

New miniature broadband CPW-to-slotline transitions

This paper proposes a novel class of uniplanar coplanar waveguide (CPW)-to-slotline transitions, which is particularly suitable for monolithic millimeter-wave integrated circuits. Instead of using CPW series stub printed in the ground plane, as is the case in classical CPW-to-slotline transition, this paper shows the capability to use a CPW series stub printed in the center conductor of the CPW. Compared to classical CPW-to-slotline transitions, the proposed transitions have the following advantages: additional degrees of freedom, lower radiation loss, larger bandwidth, higher compactness, and a major reduction of the number of air bridges that are potentially expensive to build. One alternative configuration that appears to have some merit involves the use of the slotline ring resonator, which does not suffer from open-end or short-end effects and, therefore, gives more accurate resonance frequency, provides an accurate localized zero or infinite impedance point, and maintains low- or high-input impedance values over a wide frequency range, depending on the feed type. A principle of achieving such high-quality transitions is detailed and also confirmed by experimental and theoretical results, which are in good agreement up to 50 GHz. A maximum fractional bandwidth of 160% is achieved for a 10-dB return loss, and the corresponding insertion loss is less than or equal to 2 dB.

MULTIBAND FRACTAL-LIKE ANTENNAS

In this paper, new multiband fractal-like antennas are proposed. The proposed multiband antenna design is based on a methodology that utilizes the self transformation principle of fractal- like rectangular proflles to generate multiband operation. The proposed monopole-type antennas are built on a partial ground plane and fed through a microstrip feed line. The analytical design procedures are straightforward and can be applied to any practical antenna structure to operate at multiple preselected bands. The developed methodology has been used to design antennas operating at three, four, and flve preselected practical bands. Numerical simulations are utilized to verify the simple design procedures of the proposed multiband antenna structures. The triple-band and the quad- band structures have been realized on FR4 substrate to prove the concept. Simulation and experimental results are in good agreement and demonstrate the performance of the design methodology and the proposed antenna structures.

Design and analysis of a 3-way unequal split ultra-wideband Wilkinson power divider

In this article, a 3-way ultra-wideband (UWB) unequal split Wilkinson power divider (WPD) using tapered line transformers is presented. Three tapered lines are designed through the even-mode analysis, and used instead of the conventional 3-way WPD arms. In addition to the three main arms, three additional tapered transformers are used to match the output ports to the 50u2009Ω connectors. To achieve an acceptable output ports matching and isolation, multiple resistors are uniformly distributed and mounted between the three tapered arms of the WPD. An optimisation process is carried out to obtain the values of these resistors considering the odd-mode analysis. The proposed WPD is designed to operate over the frequency band of 2–12u2009GHz, and simulated using two full-wave EM simulators. Full-wave simulation and experimental results verify the design procedure.

Optimization of UWB applicator for hyperthermia treatment of human head

An Ultra-Wideband (UWB) applicator for hyperthermia treatment of human head is developed. The system depends on the design of an array of small foot-print horn elements to allow the construction of large sized-array to surround the human-head. A waveform optimization tool is developed based on genetic algorithms to localize the energy into the tumor location. Computational analysis is performed using CST and experimental measurements are obtained using DASY5 system. Results of the field and SAR image distributions within the human head phantom illustrate the promising performance of this applicator design.

Analysis and Design of Ultra-Wideband 3-Way Bagley Power Divider Using Tapered Lines Transformers

An ultra-wideband (UWB) modified 3-way Bagley polygon power divider (BPD) that operates over a frequency range of 2–16u2009GHz is presented. To achieve the UWB operation, the conventional quarter-wave transformers in the BPD are substituted by two tapered line transformers. For verification purposes, the proposed divider is simulated, fabricated, and measured. The agreement between the full-wave simulation results and the measurement ones validates the design procedure.

Design and analysis of unequal split Bagley power dividers

In this article, we propose a general design procedure to develop unequal split Bagley power dividers (BPDs). Based on the mathematical approach carried out in the insight of simple circuit and transmission line theories, exact design equations for 3-way and 5-way BPDs are derived. Utilising the developed equations leads to power dividers with the ability of offering different output power ratios through a suitable choice of the characteristic impedances of the interconnecting transmission lines. For verification purposes, a 1:2:1 3-way, 1:2:1:2:1 5-way and 1:3:1:3:1 5-way BPDs are designed and fabricated. The experimental and full-wave simulation results prove the validity of the designed unequal split BPDs.

Ultra-wideband applicator for brain-tumor ablation and imaging system

An Ultra-Wideband (UWB) applicator for microwave imaging and hyperthermia or thermal ablation of brain tumors is developed. The system depends on the design of a MIMO array of UWB applicator to be mounted on the head. The applicator is based upon Vivaldi antenna structure, which is designed to increase the power radiated toward the human head to enhance power absorption within the tumor region. Based on the traveling-wave performance, the antenna radiates in the end fire beam, and each applicator touches the head in a slim area of the size of the substrate thickness (1.57 mm) and the antenna width (64 mm). This structure is thus attractive for use as small foot-print elements that allow the construction of large sized-array to surround the human-head. Analysis is performed using the IE3D and SEMCAD-X simulators, and the S-parameters illustrate the UWB characteristics of the antenna. Results of the field and SAR image distributions within the human head illustrate the promising performance of this applicator design.

A novel low SAR PIFA for mobile terminal

This paper proposes a novel low SAR PIFA structure to reduce exposure of the human head to mobile-set antenna radiation. Dual-band PIFA structures operating at 0.9 GHz and 1.8 GHz bands are considered. SAR is decreased by reducing the back-radiation coming from the patch and the ground plane. This SAR reduction is accomplished by inserting a thin metallic layer between the patch and the ground plane to reduce the current flowing in the ground plane. This layer is connected to the ground plane through few posts located at selected optimum positions. Additionally, three vertical sidewalls are used to reduce radiation from the patch to the human head. Results show that the proposed structure can reduce SAR by up to 76%.

Multiobjective optimization for low SAR antenna design

With the widespread use of wireless communication systems, efforts are directed to reduce the human exposure to RF radiation. Multiobjective optimization is becoming essential to achieve satisfactory antenna performance whilst minimizing the radiation level in the human body. A technique based on the genetic algorithm is proposed to optimize a multiobjective function involving weighted goals related to the antenna performance and the near-field radiation pattern inside the human body. Electromagnetic simulation based on FDTD formulation is performed using SEMCAD X. Dispersive material characteristic is chosen for the human head phantom. Results illustrate the enhancement introduced by this technique of antenna design that could be used in multifunction communication systems.