Rafal Lech

Rigorous modal analysis of structures containing inhomogeneous dielectric cylinders

The orthogonal expansion method and modified iterative scattering procedure is proposed to analyze structures containing asymmetrically located, partial-height, or multilayered inhomogeneous dielectric posts. The analysis is based on a novel concept called the hybrid impedance matrix (HIM), which describes the relation between the total scattered electric and magnetic fields obtained from all posts. As a result, the HIM can be easily applied to match it with other known incident fields and finds applications in closed (waveguide junctions, resonators) and open structures (posts in free space for plane-wave excitation). Additionally, a procedure for constructing eigenmode functions describing field components in the inhomogeneous dielectric cylinders is presented. The proposed method has been extensively verified for a rectangular waveguide junction by a finite-difference time-domain software package, as well as our own measurements and, in both cases, very good agreement can be observed.

Simulation and Experiment of a Compact Wideband 90

A compact wideband 90° differential phase shifter is developed by modifying ports termination in the Abbosh phase-shifter configuration. This novel phase-shifter arrangement consists of a 3-dB directional coupler with the coupled and transmission ports terminated with reactive loads. The proper reactance is found at the input of the coupled line section in which the remaining ports are open circuited. Both coupled sections utilize a multilayer broadside coupling microstrip-slot-microstrip tight coupler. A theoretical model is presented to explain the performance of the proposed phase shifter and design procedure. Further, the phase shifter was designed and manufactured. Results of calculation and measurement show that the developed circuit provides a 90° differential phase shift with deviation less than ±4° across the 3-7-GHz frequency band.

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A new hybrid method for analysis of scattering on configuration of cylindrical objects with arbitrary geometries is presented. In this approach each scatterer is treated as an effective circular cylinder represented by its impedance matrix. To obtain the impedance matrix representation of the arbitrary geometry post the combination of finite-difference frequency-domain (FDFD) and mode matching (MM) technique is applied. In the analysis of an arbitrary configuration of objects the iterative scattering procedure (ISP) is used. The error estimation of the method and numerical results are presented and discussed. A good agreement of the presented results with analytical approach and commercial finite-difference time-domain (FDTD) software is obtained.

Differential Phase Shifter

The analysis of propagation in periodically loaded waveguide structures is conducted. The eigenvalue equation is derived to determine the propagation constants of the Floquet modes. Theoretical and experimental investigations of semi-periodic structures and their scattering matrices are performed. The existence of passbands and stopbands, which are characteristic for periodic structures, is shown.

A New Hybrid Method for Analysis of Scattering From Arbitrary Configuration of Cylindrical Objects

A multipatch configuration of probe-fed rectangular microstrip antennas mounted on a cylindrical body, with electrically small radius, with an arbitrary number of substrate and superstrate layers is investigated in this paper. A full-wave analysis and a moment-method calculation are employed. A unified procedure for creating proper matrices for the investigated geometry of the structure is outlined here. Numerical results for the input impedances and radiation patterns are calculated and verified by comparing them with results from the literature and our own measurements of manufactured prototypes.

Propagation in rectangular waveguides periodically loaded with cylindrical posts

The theory of scattering in junction by posts consisting of a segment of conducting cylinder is developed using a combination of a modified iterative scattering procedure and an orthogonal expansion method. The multimode scattering matrix of the junction is obtained. The change of the posts configuration, as well as a simple rotation of the post, makes it possible to vary the electrical characteristic. The validity and accuracy of the method is verified by comparing the numerical results with those given in literature, received from finite-difference time-domain (FDTD) simulation and our own measurements. The proposed procedure is efficient and faster than alternative numerical solutions such as the FDTD method used for comparison.

An Analysis of Probe-Fed Rectangular Patch Antennas With Multilayer and Multipatch Configurations on Cylindrical Surfaces

In the paper, the analysis of electromagnetic wave scattering from multilayered frequency selective surfaces is presented. The surface is composed of periodically arranged posts with irregular shapes. The multimodal scattering matrix of such structure is derived and the transmission and re∞ection characteristic for the structure with arbitrary plane wave illumination are calculated. The exact full- wave theory based on the hybrid approach employing mode-matching method and flnite-difierence frequency-domain (FDFD) technique is applied to develop an e-cient theory to analyze such structures. The validity and accuracy of the approach are verifled by comparing the results with those obtained from alternative methods and own measurements of manufactured periodic structures.

Scattering in junction by posts consisting of a segment of conducting cylinder

A rigorous analysis of the resonance frequency problem of an elliptical-rectangular microstrip structure mounted on dielectric-coated elliptic conducting cylinder, with electrically small radius, is investigated in this paper. A full-wave analysis and a moment-method calculation are employed. The analysis is carried out considering the expansion of the field as a series of Mathieu functions. The complex resonance frequencies of the structure are studied. Modes suitable for antenna application are also investigated. Numerical results for the complex resonance frequency and radiation patterns are calculated and verified by comparing them with results from commercial software and our own measurements of manufactured prototypes. The difference between confocal and nonconfocal dielectric-coated elliptic cylinders is investigated.

HYBRID TECHNIQUE FOR THE ANALYSIS OF SCATTERING FROM PERIODIC STRUCTURES COMPOSED OF IRREGULAR OBJECTS

This letter presents the scattering and tunneling properties of multilayered periodic arrangement composed of frequency selective surfaces (FSS). Each surface is composed of a linear array of cylindrical metallodielectric posts. This arrangement constitutes a two-dimensional (2-D) electromagnetic band gap (EBG) structure. The electromagnetic curtain effect, realized by a rotation of the scatterers in the structure under investigation, is discussed in this letter. The effect of complete wave tunneling, which was previously observed in a structure composed of a pair of epsilon-negative and mu-negative medium, and also in a pair of different FSS stacks characterized by dual behaviors, is also discussed here for the wave propagating through the proposed structure.

An Analysis of Elliptical-Rectangular Multipatch Structure on Dielectric-Coated Confocal and Nonconfocal Elliptic Cylinders

This communication offers a rigorous analysis of the resonance frequency problem of a spherical microstrip structure mounted on a multilayer, dielectric-coated metallic sphere, with an electrically small radius. The structure consists of single or multiple metallic patches with arbitrary shapes. A full-wave analysis is employed with the use of proposed hybrid approach, combining the finite-difference technique with a spectral domain approach (SDA). In this approach, the finite-difference technique is applied in a cavity model to determine the current basis functions on the patch of an arbitrary shape. Then, the SDA is used to calculate the complex resonance frequencies of the structure. The numerical results concerning modes suitable for antenna applications are calculated. The presented results are verified by comparing them with the ones obtained from commercial software.