Ashraf S. Mohra

Compact Lowpass Filter with Sharp Transition Band Based on Defected Ground Structures

A lowpass filter with a very sharp transition band using defected ground structures (DGS) is described. The lowpass filter was designed by using three dumbbell slots at the ground plane. Two of those dumbbell slots are the reshaped rectangular and the third dumbbell slot is an inverted triangle. The lowpass filter designed at cutoff frequency of 3.0 GHz, which is suitable for GSM900, GSM1800 and UMTS applications of the mobile communications. The equivalent circuits for the proposed lowpass filter and its corresponding LC parameters are given. The proposed lowpass filter provides a size of 33 × 30 mm 2 , and have good transition band with good performance in the passband and have wide rejection up to 9.25 GHz plus harmonic suppression in the stopband. Measurements results show good agreements with the simulated results.

Compact dual band Wilkinson power divider

This paper presents the design of a compact Wilkinson power divider for dual applications. The design is accomplished by transforming the length and impedance of the quarter wave sections of the conventional Wilkinson power divider into dual band Pi-shaped sections. Simple design equations for basic design geometry are given. The dual band power divider geometry is analyzed using EM simulator and then realized at 1.8 and 4.775 GHz.

GMR- AND GMI-BASED SYSTEMS FOR NONDESTRUCTIVE EVALUATION OF PRINTED CIRCUIT BOARD

Advances in magnetoresistive type sensors provide a new technique for nondestructive evaluation of metal structures. Giant magnetoresistive and giant magnetoimpedance sensors provide high sensitivity and reduced size with GMI sensors also adding capabilities of high frequency range of measurements. Being produced with thin film processing techniques, the manufacturing cost of these sensors is low. An example is considered of detecting defects in printed circuit boards. System details and experimental results are provided. Computational modeling validation is introduced based on finite element as well as method of moments analysis.

A Small Size 3 dB 0°/180° Microstrip Ring Couplers

New small size 3dB microstrip ring couplers suitable for microwave integrated circuits (MICs) and monolithic microwave integrated circuits (MMICs) are presented. Area saving more than 85% of that of the conventional ring coupler can be achieved using the proposed configurations. Small size couplers based on the proposed configurations and designed at 900MHz have been implemented on RT/duroid 5880 dielectric material. The theoretical and experimental results show favorable comparison.

Modified compact H-shaped microstrip antenna for tuning multi-band operation

Modified H-shaped microstrip antenna configurations are introduced. Additional stubs or etching slots can be properly used to tune the desired band and leave little effect on others. Using the proposed approach, some modes can be tuned over 20% frequency range. The technique improves the flexibility in the design approach that allows the pre-selection of the resonant frequencies of the antenna. The approach is validated by the design of different modified H-shaped antennas for operation in quad band. The designed antennas are simulated by IE3D software. Good agreement with experimental results is demonstrated.

Analysis and design of small size short circuited microstrip T-shaped antenna

A small size short-circuited microstrip T-shaped antenna is presented. The antenna is analyzed by placing electric and magnetic walls at the plane of symmetry. Design equations and curves are introduced. The proposed approach has been validated through the design and implementation of an antenna at 850 MHz. Significant size reduction has been achieved. The IE3D soft ware is used to simulate the designed antenna. The experimental results agree well with the theoretical prediction.

A compact antenna for microwave imaging and hyperthermia treatment of brain tumor

This paper presents a design of a small size antenna in the L-band for applications of microwave hyperthermia treatment and microwave imaging of the human head. The design is intended to provide an increase of the power radiated toward the human and concentrate the specific absorption rate (SAR) values in the tumor tissue. Size reduction is achieved here by adding a high dielectric layer just above the antenna, and the best suitable material for this application is found to be the fresh water. The design depends on a short circuit triangular slotted shaped on a thick foam substrate to enhance its bandwidth. Analysis is performed using the IE3D and SEMCAD-X simulators, and the obtained overall antenna size is 40×40×14 mm3. The resonance frequency in air is 2.35 GHz at free space, which is reduced near the head to 1.4 GHz, using a 5-mm water layer pad. Simulation analysis is provided of the SAR patterns associated with this antenna.

NEAR‐FIELD CHARACTERIZATION OF RECONFIGURABLE NARROWBAND ANTENNA IN THE PROXIMITY OF THE HUMAN BODY

Reconfigurable antennas have been suggested recently for use in various mobile systems. These systems are usually operated in the vicinity of human body, leading to mutual interaction with body tissues. A nondestructive evaluation method is developed to characterize a reconfigurable antenna designed to cover the GSM‐900/DCS‐1800 bands. Modeling based on FDTD is performed of the antenna in free space and in proximity to the human head. Results reveal frequency shift, and variations in the matching and bandwidth, depending on antenna orientation with respect to the head. Experimental setup is also used to characterize the SAR values in human head. A six‐degree‐of‐freedom robot is implemented to scan a head phantom using specialized sensors and head simulating liquids. The developed system provides a tool for guiding the design of the new category of reconfigurable antennas.

Development of Metal Inspection System Exploiting Magnetoresistive Sensors

Advances in magnetoresistive (MR) type sensors provide a new technique for nondestructive evaluation NDE of metal structures. MR sensors include high sensitivity and reduced size being produced by thin film processing techniques, the manufacturing cost of these sensors is low. This paper provides an attempt to develop an NDE system that depends on one type of MR sensors, namely the giant MR (GMR) elements. An example is considered of detecting defects in printed circuit boards. System details and experimental results are provided. Computational modeling validation is introduced based on finite element analysis

A small size 3-dB 0/spl deg//180/spl deg/ microstrip ring couplers

A new small size 3 dB microstrip ring couplers suitable for microwave integrated circuits (MICs) and monolithic microwave integrated circuits (MMICs) are presented. Area saving more than 85% of that of the conventional ring coupler can be achieved using the proposed configurations. Small size couplers based on the proposed configurations designed at 900 MHz have been implemented on RT/Duroid 5880 dielectric material. The theoretical and experimental results show favorable comparison.