Zeyad Alhekail

Electromagnetic radiation from microwave ovens

Electromagnetic radiation from microwave ovens in Saudi Arabia was investigated by means of a field measurement survey. The survey was carried out for 106 ovens used in households and restaurants in Riyadh city. Ovens were between 1 month and 14 years old with operating power ranging from 0.5 to 4.4 kW. One oven was found to leak more than the 5 mW cm(-2) limit specified in the standard. Fifteen other ovens were found to leak 1 mW cm(-2) or more, with the remaining ovens leaking less than that. Based on the survey result, previous studies and the fast decay of radiated power density with distance from the oven, the conclusion was that user exposure to RF radiation from microwave ovens is much less than the general public exposure limit set by most international standards at 2450 MHz, i.e. 1 mW cm(-2), and that a detrimental effect on health is an unlikely result of exposure to radiation from microwave ovens.

Public safety assessment of electromagnetic radiation exposure from mobile base stations

Exposure of the general public to electromagnetic radiation originating from randomly selected GSM/WCDMA base stations in Riyadh, Kingdom of Saudi Arabia has been assessed in the context of the International Commission on Non-Ionising Radiation Protection (ICNIRP) guidelines. The purpose of the measurement was to record the maximum power density of signals to estimate possible worst case exposure at each measurement location. These power density measurements were carried out at 60 mobile base stations located in different regions of the city. For each of these sites, three sectors were operational, yielding a total of 180 sectors. Two positions were identified per site with the greatest power density values. Exposures from these base stations were generally found to be in the range of 0.313 to 0.00000149% of the ICNIRP general public reference level, and the greatest exposure near any of the base stations was 21.96 mW m(-2) for a wideband measurement in the 75-3000 MHz frequency range. Analysis of the measured data reveals several trends for different mobile bands with respect to maximum exposure in those locations. Additionally, a simplified calculation method for the electromagnetic fields was used to compare calculated and the measured data. It was determined, on the basis of both results of the measurements and calculations carried out for these selected base stations, that members of the public would not be exposed to in excess of a small fraction of the ICNIRP guidelines at any of those sites. These are first such measurements to be made in the Middle East and provide assurance that exposures in this region of the world do not seem to be any greater than elsewhere.

B4. Analysis and design of single section and three-section ultra-wideband quadrature hybrid couplers

This paper presents analysis and design of two different slot coupled ultra-wideband quadrature couplers, employing a single section and a three-section configuration. A design procedure based on analysis of different design parameters of both circuit configurations is proposed. The simulation results of the single section coupler shows an amplitude imbalance ± 1dB form 4.8-10.6-GHz. The return loss and the isolation are better than 19dB and 25dB, respectively. The manufactured single section can exhibit 6° phase imbalance from 3-8 GHz. An improved three-section slot coupled hybrid coupler is designed by adding strips and slots of elliptical shape on the both sides of the tapered hexagon. The final circuit of three section coupler can exhibit a coupling of 3dB ±0.75 dB from 3.1-10.6-GHz. The corresponding return loss and isolation is the order of 22 dB and 26 dB, respectively. A phase deviation of ±1.8° between the ports is confirmed.

FPGA IMPLEMENTATION OF SPACE-TIME ADAPTIVE PROCESSING (STAP) ALGORITHM FOR TARGET DETECTION IN PASSIVE RADARS

Space-Time Adaptive Processing (STAP) algorithm has recently been used in Passive Bi-static Radars (PBR) because it removes the clutter and non-cooperative transmitter efiectively making the target detection easy in harsh environments like air-ground. Real- time implementation of STAP is a very challenging task as it is computationally-intensive, time-critical and resource-hungry process. This paper focuses on the Field-Programmable Gate Array (FPGA) implementation of STAP algorithm for passive radar using FM radio as transmitter of opportunity. The signals of interest were collected using an eight-channel software-deflned radar with a uniform circular array (UCA). The STAP processing was simulated using MATLAB and hardware implementation was carried out on a Xilinx Virtex-6 FPGA. The system is tested using experimental radar data. Timing and Power analysis of hardware implementation justifles that FPGA provides a fast and reliable platform for STAP real-time radar processing.

A NOVEL SMALL PRINTED ULTRA‐WIDEBAND ANTENNA FOR NEAR‐FIELD IMAGING

Ultra‐wideband (UWB) antennas have been suggested recently for use in near field imaging systems. A small printed antenna is introduced with L‐shaped reduced ground‐plane to achieve UWB characteristics. The ground is optimized to allow reconfiguration of the inspection system to various operation sub‐bands. Design and optimization of antenna characteristics including matching and bandwidth are performed using FDTD computational modeling of the antenna in free space as well as in the proximity to human head phantom. Effect of tumor model is investigated on field map values. Experimental validation of antenna characteristics is studied using human brain simulating liquid, and implementing a six‐degree‐of‐freedom robot to control the scanning of the measurement sensors. Results of this research should help enhance UWB systems as promising nondestructive and noninvasive imaging tools.

Design of a slot-coupled Ultra-Wideband 180° hybrid coupler

In this paper a wideband microstrip 180° hybrid coupler is proposed. The coupler is designed using a double sided single layer substrate for Ultra-Wideband (UWB) applications. The device is constructed from Wilkinson Power Divider (WPD) employing microstrip line to slot transition for the construction of a delta (Δ) port. The input port (Σ port) of the WPD acts as the in phase power divider. The Σ and Δ ports are located opposite to each other, making the overall size compact and easy for measurements. The proposed method of design results in a 180° hybrid coupler with good UWB performance. The return loss of the sum port and delta port is less than 10 dB. The power imbalance and the phase imbalance between the output ports is less than 0.5 dB and 0.8°, respectively, for complete UWB frequency range. The isolation between sum and delta ports is more than 40 dB.

Parametric analysis of multi section slot coupled quadrature coupler

This paper presents a design procedure of an ultra wideband three section slot coupled hybrid coupler employing a parametric analysis of different design parameters. The coupler configuration is composed of a modified hexagonal shape at the top and bottom conductor plane along with a hexagonal slot at the common ground plane. The coupler performance for different design parameters is studied through full wave simulations. A final design providing a return loss and isolation better than 20dB, an amplitude imbalance between output ports of less than 0.9dB and a phase imbalance of ±1.9° across the 3.1-10.6 GHz band is confirmed.

A compact wideband tunable square ring microstrip antenna

Microstrip antennas are now extensively used in many applications such as mobile and satellite communications due to their compactness, lightweight, low profile and conformability to any structure. The size of the conventional microstrip antennas such as rectangular, circular, and triangular, patches is large and unsuitable to be used in many applications, especially at the lower microwave range. Various techniques have been investigated in the literature to reduce the size of conventional structures. One can cut slits or slots on the basic shapes which will result in new compact geometries like slotted L-shaped and ring microstrip antennas. The main disadvantage of the resulting compact structures is the associated bandwidth reduction. However, bandwidth can be increased by adding lossy elements in turn of lower antenna efficiencies. One possible solution to avoid the use of lossy elements is the use of tunable or reconfigurable antenna concept [1]. In this case the small size antenna would not cover all bands simultaneously. Instead, it will provide narrower instantaneous bandwidths in a wide tuning range with better antenna efficiencies.