A fast mode analysis for waveguides of arbitrary cross section with multiple regions by using a spectrum of two-dimensional solutions and asymptotic waveform evaluation

A fast mode analysis for waveguides of arbitrary cross section with multiple regions is presented in this paper. The analysis is based on a spectrum of two-dimensional (2-D) solutions with application of asymptotic waveform evaluation, which requires only several 2-D solutions in searching for the propagation modes and calculating the field distribution of the modes in waveguides. The boundaries of waveguides can be modeled by perfect electric conductors, perfect magnetic conductors, dielectric materials, and asymptotic strip boundary conditions. By this modeling, one can also analyze the waveguides with the soft and hard surfaces. The method is excitation dependent, which provides a tool to analyze the response of different modes to different excitations. No existence of spurious modes is experienced by using this method. The verification and comparison of the numerical results with analytical, published data, and measurements are also presented in this paper.     

Split-ring resonator loaded waveguides with multiple stopbands

The use of split-ring resonators (SRR) to realise novel waveguide filters with multiple stopbands is reported. Dielectric slabs printed with arrays of metallic SRR elements are attached to the two sidewalls of a rectangular waveguide. Arrays of differently sized SRRs are interlaced over the shared surface of a dielectric slab to achieve multiple stopbands. Numerical and experimental results are presented.     

Numerical and experimental studies of split ring resonators loaded on the sidewalls of rectangular waveguides

This work investigates the use of a lattice comprising split ring resonators (SRRs) as a negative permeability medium to achieve backward travelling modes within a rectangular waveguide. The loadings of such SRR-type periodic structures into a waveguide can be tailored such that the backward mode exists in a passband below the ordinary basic modal cutoff frequency, thus affording filtering capabilities and miniaturisation. Theoretical studies by two approaches are performed here, a moment method spectral domain analysis, and a commercial simulation tool. Parametric studies that characterise the effects of various dimensional and electrical properties on the dispersion behaviour of the SRR-loaded waveguide shall also be conducted. The SRR parameters are then optimised using the ant colony optimisation (ACO) algorithm to achieve a low backward passband, for a high degree of miniaturisation and isolation. Experimental results of measurements performed on a manufactured prototype of the optimised SRR-loaded waveguide will also be presented.     

Permittivity measurement of disk and annular dielectric samples using coaxial transmission line fixtures. part II: experimentation and accuracy analyses

An improved permittivity measurement technique for dielectric disks involving S-parameter measurement of a two-port coaxial transmission line fixture is presented. The previous form of the method suffers from variation of the retrieved permittivity with frequency, which leads to inaccuracies that may be severe at some frequencies. An extension of the method that reduces these errors is devised. In addition, an independently developed new technique for measuring the permittivity of annular samples via quadratic curve fitting is presented. This technique also involves S-parameter measurement of a coaxial fixture and requires measurement of only three known materials (one of them may be free space, in which case the requirement is reduced to only two solid dielectrics). The permittivity of any unknown dielectric may subsequently be determined with high accuracy over a wide frequency range. The method is based on the premise that the variation of the reflection characteristics of the two-port coaxial transmission line fixture with the permittivity of the sample displays a strongly quadratic behaviour. This paper constitutes the second of two parts of this work. Part I, also appearing in this issue, presents the theoretical formulation for the moment method mode-matching treatment of the coaxial fixture for treating annular samples. In the present paper, the measurement techniques are described, and numerical simulations of the experimental procedure based on the theory of Part I are presented. In addition, comparative results of accuracy for these two approaches are given. Sensitivity analyses are also presented, along with preliminary experimental results.     

Permittivity measurement of disk and annular dielectric samples using coaxial transmission line fixtures. part I: theory and formulation

One way of measuring the permittivity of circularly shaped dielectric samples is to measure the S-parameters of a two-port coaxial transmission line fixture into which the samples are placed. Among the sample forms that can be fitted into coaxial waveguides are (1) circular disks and (2) annular rings. The former type is sandwiched between two disjointed inner conductors of the coaxial line, whereas the latter dielectric form is snug-fitted to become the insulation layer of an intermediate coaxial section. Each type of sample requires a different coaxial configuration; this work studies both fixtures. The investigation of the first type is based on a previously studied technique that treats the sandwiched circular disk as a parallel-plate capacitor. Because of inaccuracies in the original form of that method, a modified version that offers improved accuracy is devised here. In addition, a new, independently developed technique for accurately characterizing dielectrics of the second form (annular-ring samples) using quadratic curve fitting is proposed. The experimental fixture, comprising a connected series of coaxial waveguide sections, is numerically treated with the method of moments and mode-matching technique. Details of the theoretical groundwork are presented in this paper, which constitutes the first of two parts of this work. Part II, also appearing in this issue, describes the measurement technique in detail and presents simulation results of the experimental procedure based on the formulation presented herein. In addition, the method that treats circular disks is also investigated in Part II and is used to make comparative performance studies.     

Analysis of dispersion in dipole-FSS loaded hard rectangular waveguide

We investigate the properties of the dipole frequency selective surfaces-loaded rectangular waveguide. The analysis is carried out by using the method of moments together with an algorithm that solves for a multilayer structure in the spectral domain. The eigenmodes are determined by searching for resonant solutions. Dispersion diagrams obtained from this approach are compared with those generated by commercial software simulations. Experimental validation is also performed     

Proper interpretation of source excitations for resolving ostensible excessive power gains of metamaterial resonances

The aim of this communication is to resolve the anomalous phenomenon of extremely large radiated powers of antennas embedded within metamaterial layers apparently achievable under resonances. The essence of the discussion rests on the law of power conservation and causality conditions. A slotted spherical dipole coated with two layers of homogeneous materials is chosen to illustrate the concepts, and the classical approach for solving boundary-value problems via separation of variables is used to treat the structure.