Bijan Zakeri

Evaluation of Different Approximations for Correlation Coefficients in Stochastic FDTD to Estimate SAR Variance in a Human Head Model

In this paper, the stochastic finite-difference time domain (S-FDTD) method is employed to calculate the standard deviation of specific absorption rate (SAR) in a two-dimensional (2-D) slice of human head. S-FDTD calculates both the mean and standard deviation of SAR caused by variability or uncertainty in the electrical properties of the human head tissues. The accuracy of the S-FDTD result is controlled by the approximations for correlation coefficients between the electrical properties of the tissues and the fields propagating in them. Hence, different approximations for correlation coefficients are tested in order to evaluate their effect on the standard deviation of SAR. The 1-D Monte Carlo correlation coefficient (MC-CC) approximation reported in our previous work is successfully extended to 2-D and also tested for the head model. Then, all the results are compared with that of full-fledged Monte Carlo method (considered as gold standard in statistical simulations). In order to accelerate the simulations, the proposed algorithm is run on graphics processing unit by exploiting OpenACC application program interface. Using different correlation coefficients shows that the extended 2-D MC-CC S-FDTD results are very close to that of Monte Carlo and yield more accurate results than other approximations in SAR calculations.

SAR of the human's head due to electromagnetic radiation of a mobile antenna

In this paper, the influence rate of mobile phone radiation on the human head near the mobile antenna that is in various angles relating to the human head will be presented. To compare the results, we use SAR (Specific Absorption Rate) that is the indicator of the amount of absorbed RF waves energy by humans tissues. In order to observe the effect of changing the angle of mobile antenna relating to the human head, we continued the simulation, at first being parallel the antenna with the neck that indicate 0° and after that by increasing 10° the angle of antenna relating to human head in each step, to 90° angle that the antenna is along the neck.

A novel frog-eye band-notched ultra-wideband antenna

This paper presents a microstrip-fed planar antenna, which satisfies “band-notch characteristic”. Antennas dimensions are 24 mm × 20 mm and its simulated impedance bandwidth spreads across more than approximately 7.5 GHz, between 3.5 GHz and 11.3 GHz. The notched band covers the frequency range between 5.31 GHz and 5.78 GHz. Its radiation pattern is roughly steady across its bandwidth. The antenna exhibits UWB behavior with near directional characteristic. Additional features of the antenna are its low profile and compactness.

Linear antenna array design for UWB radar

This paper presents a compact microstrip-fed ultra-wideband (UWB) antenna and its four-element array design for target detection applications. A prototype was fabricated and then measured based on optimal parameters. There is good consistency between the simulated S11 and the measured one. In addition, a 1 × 4 linear array design with the size of 100 mm × 34 mm has been proposed to achieve a higher gain. Simulation shows that the array gain is increased about 6 dBi in comparison to the single element through the whole UWB frequency range of 3.1 GHz to 10.6 GHz. The proposed array has an average of -15 dB side lobe level (SLL) in the mentioned range. And also, a -23 dB SLL has been achieved by applying Dolph-Chebyshev amplitude distribution at 6 GHz. Simulation results confirm that the antenna exhibits a constant bidirectional radiation pattern with a high and flat gain in case of the array design.

Synthesis of aperiodic linear antenna arrays based on competition over resources optimization

In the recent years, many heuristic optimization algorithms derived from the behavior of biological or physical systems in nature have been developed. In this paper, we propose a new optimization algorithm based on competitive behavior of group animals. The competition gradually results in an increase in population of wealthy group which gives a fast convergence to the optimization algorithm. In the following, after a detailed explanation of the algorithm and pseudo code, we compare it with particle swarm optimizations as a famous heuristic algorithm. The proposed method is used to determine an optimal set of amplitude weights of antennas and element spacing that satisfy the optimal goal during constant first null beamwidth (FNBW) for aperiodic linear array. It is to be noted that the desired prescribed nulls depth and side lobes level is achieved simultaneously with the narrowest possible FNBW. The proposed algorithm on known array antenna synthesis, shows faster and superior results compared to other optimization algorithms.

An excellent reduction in sidelobe level for P4 code by using of a new pulse compression scheme

P4 polyphase code is well known in pulse compression technique. For P4 code with length 1000, peak sidelobe level (PSL) and integrated sidelobe level (ISL) are −36dB and −16dB, respectively. In order to increase the performance, there are different reduction techniques to reduce the sidelobes of P4 code. This paper presents a novel sidelobe reduction technique that reduces the PSL and ISL to −127dB and −104dB, respectively. Also, other sidelobe reduction techniques such as Woo filter are investigated and compared with the novel proposed technique. Simulations and results show that the proposed technique produces a better peak side lobe ratio (PSL) and integrated side lobe ratio (ISL) than other techniques.

Driving point impedance restriction in synthesis of linear antenna arrays using competition over resources optimization algorithm

In the recent years, many heuristic optimization algorithms derived from the behavior of biological or physical systems in nature have been developed. In this paper, we propose a new optimization algorithm based on competitive behavior of group animals. The competition gradually results in an increase in population of wealthy group which gives a fast convergence to the optimization algorithm. In the following, after a detailed explanation of the algorithm and pseudo code, we compare it with particle swarm optimizations as a famous heuristic algorithm. The proposed method is used to determine an optimal set of amplitude weights of antennas and element spacing that satisfy the optimal goal during constant first null beamwidth (FNBW) for aperiodic linear array. It is to be noted that the desired prescribed nulls depth and side lobes level (SLL) is achieved simultaneously with the narrowest possible FNBW. In addition, because of practical consideration in array antennas, restriction of driving-point impedance (DPI) of each element is proposed during pattern synthesis. Final array factor without and with impedance optimization are compared with uniform amplitude excitation and equal element spacing array factor as reference. The proposed algorithm on known array antenna synthesis, shows faster and superior results compared to other optimization algorithms.

Design and analysis of a multiband Sierpinski type monopole fractal antenna

Fractal antennas are one of the most important and useful types which exhibit wide band and multiband behavior. In this paper a Sierpinski monopole fractal antenna is designed and analyzed with FDTD method. It has both multiband and wideband features and have stable radiation pattern in wide frequency ranges such as 3.3GHz to 4.1 GHz and 8.2 GHz to 9.2 GHz. The antenna is designed on a substrate with permittivity of 2.1, 1.5 mm thickness and fed with 50 ohm microstrip line. The antenna has a compact size of 89.9mm × 102.65 mm.

A new partially grounded slotted ultra-wideband antenna with WLAN band-rejection

In this paper, we propose a new ultra-wideband (UWB) antenna with frequency band-notch characteristic. The designed antenna has a small size of 16 mm ×18 mm and operates over the frequency band between 3.45 GHz and 10.4 GHz. The antenna is then modified not to have interference with Wireless Local Area Network (WLAN) band by adding one rectangular part to the ground resulting in the band rejection performance in the frequency band of 5.4 GHz to 5.95 GHz while covering the frequency span between 3.4 and 11.95 GHz.

Non-focal microwave lens design with optimization of phase errors and amplitude performance

A symmetry design model for 7×7 microstrip non-focal Rotman lens is presented with a precise behavior of phase errors and amplitude performance. Methods for optimizing show average phase errors of 2.1 degree and average amplitude errors of 1.8 dB along the input ports of array elements. Array factor of the lens shows less than 2 degree deviation along the 90 degree scanning and shows good amplitude tapering at all excitation ports.