Tamer M. Abuelfadl

REALIZATION OF COMPOSITE RIGHT/LEFT-HANDED TRANSMISSION LINE USING COUPLED LINES

This paper presents a method to construct composite right/left-handed transmission line using coupled lines. A general procedure to design a composite right/left-handed unit cell is presented. The procedure was used on a specific coupled line configuration, which is the coupled microstrip lines with slotted ground. It is shown that by proper design of the slotted ground, the coupling between the two microstrip lines can be increased dramatically keeping practical dimensions for the coupled line width and spacing. Moreover, with accurate slotted ground design, equal even and odd electrical lengths can be achieved. The performance of this composite right/left-handed line, which is characterized by backward waves with phase advance, is demonstrated by both simulated and measured results and they show good agreement. The realized composite right/left-handed transmission line has a broad bandwidth and small size.

Leaky Wave Antenna Realization by Composite Right/Left-Handed Transmission Line

This paper presents a realization of composite right/left handed transmission lines using coupled microstrip lines. This structure exploits the advantages of the microstrip lines, while increases the coupling by a ∞oating conductor at the ground plane. The performance of this composite right/left-handed line is demonstrated by both simulated and measured results, and they show good agreement. The designed line has broad bandwidth with low losses and small size. A novel dominant mode leaky wave antenna design, using the previous structure, is presented with backward to forward scanning capability.

COUPLED LINES FROM FILTER TO COMPOSITE RIGHT/LEFT HANDED-CELLS

This paper studies the left-handed behavior in conven- tional 2-port coupled line networks. The propagation parameters of 12 periodic structures, each has a difierent coupled line conflguration, have been derived and the left-handed bands have been determined. Two structures were fabricated and measured to conflrm the compos- ite right/left handed (CRLH) characteristics. Measurements and EM simulations were in a very good agreement with the developed theory. In the light of the proposed theory, a geometrical circuit model was also proposed for split ring resonator (SRR). The model is capable to predict its performance over a wide band.

Dual and Wide-Band Inductively-Loaded Dipole-Based Antennas for WLAN/UMTS Applications

Electrically-small antennas can be designed using inductively-loaded dipoles. A simplified design procedure is carried out, using circuit models and EM simulations, to implement efficient dual and wide-band antennas with omni-directional radiation patterns. Measured performance agrees with simulations, and the proposed designs are employed for the UMTS 1.8/1.9/2.1/2.6-GHz and WLAN 2.4/3.6-GHz frequencies. A USB dongle antenna is prototyped to cover these frequency bands with impedance bandwidth reflection coefficient better than -10 dB.

Analysis of microwave cavities using an eigenmode projection approach

The resonance frequencies for an arbitrary-shaped cavity are determined using an approach whereby the known eigenmodes of a canonical cavity are employed to formulate the eigenvalue problem. Although the approach is originally developed for three-dimensional problems, using it for two-dimensional geometries will result in accurate estimation of the cut-off frequencies of waveguides with arbitrary-shaped cross-section.

Realization of composite right/left-handed transmission line using broadside coupled coplanar waveguides

Broadside coupled coplanar waveguides are used to realize a composite right/left-handed transmission line, which is characterized by antiparallel group and phase velocities. The transmission line design depends on the electromagnetic coupling between coupled lines. The broadside coupled coplanar waveguides was chosen to achieve tight coupling with practical dimensions, which reflects an enhancement in the bandwidth. Experimental verification for the design is demonstrated with good agreement to the simulated values. The proposed composite right/left-handed transmission line has a broad bandwidth.

Analysis of waveguide discontinuities using eigenmode expansion

A novel semi-analytical modal formalism is developed utilizing known solenoidal and irrotational cavity eigenmodes to solve electromagnetic scattering inside waveguides. The proposed approach is based on the use of modal expansion of fields to solve Maxwells equations, in conjunction with a convenient choice of port boundary conditions, which results in an eigenmode projection problem. With the help of the generalized scattering matrix (GSM) approach, waveguides discontinuities loaded with arbitrary dielectric profiles can easily be analyzed. Convergence studies show consistent solutions for a small number of expansion modes.

Solution of electromagnetic scattering problems using an eigenmode projection technique

Dielectric objects illuminated by uniform plane waves are analyzed using an eigenmode projection technique. A fictitious canonical cavity is chosen to enclose the scatterer, and the fields are expanded in terms of the cavity solenoidal and irrotational eigenmodes. The fictitious cavity surface is regarded as a port excited by the uniform plane wave, and the total cavity fields and the port fields are then matched on the surface resulting in the field coefficients. Results obtained using the proposed method are compared with results obtained for problems of known analytical solution and results obtained using other numerical techniques.

RF cavity design exploiting a new derivative-free trust region optimization approach

In this article, a novel derivative-free (DF) surrogate-based trust region optimization approach is proposed. In the proposed approach, quadratic surrogate models are constructed and successively updated. The generated surrogate model is then optimized instead of the underlined objective function over trust regions. Truncated conjugate gradients are employed to find the optimal point within each trust region. The approach constructs the initial quadratic surrogate model using few data points of order O(n), where n is the number of design variables. The proposed approach adopts weighted least squares fitting for updating the surrogate model instead of interpolation which is commonly used in DF optimization. This makes the approach more suitable for stochastic optimization and for functions subject to numerical error. The weights are assigned to give more emphasis to points close to the current center point. The accuracy and efficiency of the proposed approach are demonstrated by applying it to a set of classical bench-mark test problems. It is also employed to find the optimal design of RF cavity linear accelerator with a comparison analysis with a recent optimization technique.

Electromagnetic Scattering from Dielectric Objects Using the Eigenmode Projection Technique

Electromagnetic scattering by dielectric objects is analyzed using an eigenmode projection technique. A fictitious canonical cavity is chosen to enclose the illuminated scatterer, and the fields are expanded in terms of the cavity solenoidal and irrotational eigenmodes. The surface of fictitious cavity is regarded as a port excited by the incident wave, and the cavity fields and the port fields are then matched on the surface resulting in the cavity mode and port field coefficients. The frequency independent feature of the generated matrices is exploited to provide an efficient solution over a wide range of frequencies without the need of filling and inverting all the system of matrices and the numerical integrations are only evaluated once, with their values used at all frequencies. The technique also lends itself to problems, where variations of the same structure are to be analyzed, with the perturbations not necessarily small as long as they are bound by the same canonical cavity. Results are presented to validate the method and illustrate the speed up of the technique in wideband and perturbation analysis.