Majeed A. S. Alkanhal

A NOVEL DUAL-BAND RECONFIGURABLE SQUARE-RING MICROSTRIP ANTENNA

A novel compact dual-band reconfigurable square-ring microstrip antenna is presented. The tuning is achieved using a single varactor diode connected to a small square patch attached to an inner corner of the square-ring. The square patch perturbs the symmetry and splits the two degenerate modes to create dual-band operation. The frequency ratio in the range of 1.04 to 1.4 can be achieved by the proper selection of the square patch size. The lower resonance frequency can be further decreased by loading the square patch at its corner by a reverse biased varactor diode. The diode has almost no effect on the upper resonance frequency. This technique is used to implement an electronically tunable dual-band antenna on FR4 material with er =4 .5 and 1.5 mm thickness. The size of the ring,the square patch,and the varactor used,are selected to yield a fixed upper resonance frequency at about 1.93 GHz. The resulting lower resonance frequency is tuned from 1.37 to 1.7 GHz in the voltage range from 0 to 30 V,respectively. The measurements agree well with simulation results.

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.

COMPOSITE COMPACT TRIPLE-BAND MICROSTRIP ANTENNAS

Two new triple band small size composite-resonator microstrip antenna conflgurations for wireless communications are presented in this paper. The proposed antennas, each is built of three resonant elements. Two types of compact short-circuited resonators are used; stepped impedance and quarter-wave resonators. The design procedure based on composing the antenna resonators is straightforward and can be applied to design any triple band antenna at three pre-specifled bands using simple relations and design curves. The resonator integration has been performed to maintain single feed, reduce the overall antenna size, and preserve the quality-performance at each band. The two designed antennas are simulated, optimized, and realized on RT/Duroid substrate to verify the concept. Simulation and experimental results are in good agreement and demonstrate the performance of both triple band compact antennas.

Electromagnetic scattering from a chiral cylinder of arbitrary cross section

A simple moment solution is presented to the problem of electromagnetic scattering from a homogeneous chiral cylinder of arbitrary cross-section. The cylinder is assumed to be illuminated by either a TE or a TM wave. The surface equivalence principle is used to replace the cylinder by equivalent and magnetic-surface currents. These currents radiating in unbounded external medium produce the correct scattered field outside. When radiating in an unbounded chiral medium, they produce the correct total internal field. By enforcing the continuity of the tangential components of the total electric field on the surface of the cylinder, a set of coupled integral equations is obtained for the equivalent surface currents. Unlike a regular dielectric, the chiral scatterer produces both copolarized and cross-polarized scattered fields. Hence, both the electric and magnetic current each have a longitudinal and a circumferential component. These four components of the currents are obtained by using the method of moments (MoM) to solve the coupled set of integral equations. Pulses are used as expansion functions and point matching is used. The Greens dyads are used to develop explicit expressions for the electric field produced by two-dimensional surface currents radiating in an unbounded chiral medium. Some of the advantages and limitations of the method are discussed. The computed results include the internal field and the bistatic and monostatic echo widths. The results for a circular cylinder are in very good agreement with the exact eigenfunction solution.

Electromagnetic Wave Scattering by Elliptic Chiral Cylinder

An exact boundary value solution for the scattering of transverse magnetic (TM) wave by an elliptic chiral cylinder is developed and presented in this paper. The solution is based on the separation of variable technique in the elliptic cylinder coordinates system and expressed in terms of Mathieu and modified Mathieu functions. The incident, transmitted and scattered electromagnetic waves are expressed in terms of infinite series of wave functions. The matrix form of the expansion coefficients is found by applying the boundary conditions and orthogonality of the Mathieu functions. Numerical results of the forward and back scattered echo widths for co- and cross-polarized waves with TM and TE polarized incident fields, for various cases are presented and discussed.

Dual-band Bandpass Filters using Inverted Stepped-Impedance Resonators

This paper presents a new dual-band bandpass filter (BPF) using inverted stepped impedance resonators. In the proposed filter configuration, the conventional half-wavelength open-circuited stub single-frequency resonators are replaced with dual-band simple two-section stepped impedance configurations. Simple equations to design the dual-band stepped impedance resonators are derived using transmission line analysis. The filter structure is investigated using a full wave electromagnetic (EM) simulator and then realized at 2.5 GHz and 3.55 GHz bands. Experiments have also been done to validate the design concept. The distinguished dual-band performance of the proposed design is verified by the simulation and measurement results.

Excitation requirements of three phase self-excited induction generator under single phase loading with minimum unbalance

This paper presents an optimization method to determine the excitation requirements of three phase self-excited induction generator under single phase mode of operation. A single phase load is connected to the generator through two excitation capacitors. The values of these capacitors are chosen to ensure minimum self-excitation of the machine in addition to minimization of the unbalance between the stator voltages. The problem is formulated as a multi-dimensional optimization problem. A sequential genetic (GA)/gradient optimizer is used to minimize a cost function of the summation of the equivalent impedance of the generator plus the ratio of the negative to the positive sequence voltages, to obtain the values of the frequency and the excitation reactances. These values are then used to determine the other performance of the machine. A classic gradient solver initialized by a simple GA is used to solve for the unknown parameters in the formulated optimization problem.

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.

Compact bandstop filter using defected ground structure (DGS)

This paper presents a new structure to implement compact bandstop filters by employing coupled DGS resonators etched in the ground plane. The proposed bandstop filter consists of symmetrical DGS resonators with a microstrip excitation to obtain a bandstop filter response. By adjusting space S between the two DGS coupled resonators, the bandwith of the bandstop filter can be easily controlled. A bandstop filter is designed, analyzed and implemented on FR4 dielectric substrate to operate at 2GHz. The measured results are in good agreement with simulations.

A Novel Reconfigurable Dual-Mode Microstrip Meander Loop Filter

A novel dual-mode reconfigurable band pass filter is proposed. A meander loop compact structure is used, where its four arms are brought inside the loop. Structures perturbation is designed by filling the gap between the two arms at the top right corner. The loop is loaded by four varactor diodes connected between each arm and a small square patch located at the centre. Varactors are shorted through a via at the centre of the small square patch to control the centre frequency of the filter. This structure is compact, simple in fabrication, and has a wide tuning range. A tunable bandpass filter is designed and implemented to tune over the range from 1.47 GHz to 2.40 GHz (relative tuneable bandwidth ~48%). The fractional bandwidth (FBW) changes from 6.9% at 2.4 GHz to 3.1% at 1.47 GHz.