Miguel A. Solano

Full-Wave Hybrid Technique for 3-D Isotropic-Chiral-Material Discontinuities in Rectangular Waveguides: Theory and Experiment

Numerical results obtained using a full-wave hybrid technique (comprising a new formulation of the coupled-mode method and the mode-matching method) for treating 3-D isotropic- chiral-material discontinuities in rectangular wave guides with perfect electrically conducting walls were compared with experimental data. For that purpose, samples of an isotropic chiral material were manufactured as composite materials. These samples were then fully characterized in the X-band. The measured constitutive parameters were used in the full-wave hybrid technique to predict the scattering parameters of three different structures-each a waveguide filled partially with the isotropic chiral material. The scattering parameters were also measured. The predicted and measured scattering parameters were in reasonably good agreement.

Modelling multiple discontinuities in rectangular waveguide partially filled with non-reciprocal ferrites

This work analyzes multiple 3D discontinuities between rectangular ferrite-loaded waveguides. Each uniform section of waveguide is analyzed by means of Schelkunoffs method with improved convergence. Combining this method with the mode matching method allows the analysis of multiple discontinuities to be simplified. The theoretical results obtained in this way agree quite well with measurements. >

On One- and Two-Dimensional Electromagnetic Band Gap Structures in Rectangular Waveguides at Microwave Frequencies

Electromagnetic band gap (EBG) structures of two different configurations implemented inside R120 rectangular waveguides (frequency range 10–15 GHz) are examined. The first configuration has a periodic, piecewise uniform variation of permittivity in the propagation direction. Two types of such one-dimensional (1D) EBG structures are analyzed, one with the unit cell comprising two dielectric layers, the other with three dielectric layers per unit cell. The second configuration is two-dimensional, with the unit cell along the propagation direction containing two sections, each of which is made of alternating pillars of two dielectric materials. The Bloch theorem is invoked for the ideal EBG structures, which are infinitely long in the propagation direction. The mode-matching method (MMM) is used for real 1D-EBG structures, which contain a finite number of unit cells, whereas a combination of the coupled-mode method (CMM) and the MMM is used for real 2D-EBG structures. Spectrums of the transmission coefficient of the fundamental mode for the 1D-EBG structures are computed and shown to compare favorably against experimental data. The effect of inserting a defect in 1D-EBG structures is demonstrated theoretically as well as experimentally. The band gaps computed for real and ideal 2D-EBG structures are compared as well.

X-band Gunn diode oscillator for a multiple-frequency continuous-wave radar for educational purposes

A low-cost, high-performance X-band Gunn diode oscillator for educational and research purposes has been developed. The cavities have been manufactured on a standard WR90 rectangular waveguide with UBR100 flange in order to make it compatible with the waveguide circuitry usually available in a basic microwave laboratory. The capability of sweeping the whole X band at constant output power and low phase noise, as well as the low cost of its components, make this device suitable for users at any level. As an example of its many educational applications, a multiple frequency continuous-wave (MFCW) radar has been developed, and the results of the laboratory implementation are shown.

Characterization of discontinuities in dielectric waveguides using Schelkunoff's method: application to tapers and transitions

Transitions, tapers and abrupt discontinuities are frequently used between different types of dielectric waveguides. This work presents a theoretical method to analyse the former structures. A modal matching method together with the generalized telegraphists’ equations are used. By using the generalized scattering matrix of two discontinuities, we can find the generalized scattering matrix of the cascaded set. Theoretical results of reflection and transmission coefficients, both module and phase, as well as some measurements are compared with those published by other authors.

Rigorous analysis of guided wave propagation of dielectric electromagnetic band-gaps in a rectangular waveguide

Guided wave propagation in a Ku-band rectangular waveguide filled with a series of cells of dielectric materials in the Kronig–Penney morphology is examined. Allowed and forbidden bands in these ideal electromagnetic band-gap (EBG) filters are obtained for the TE z and TM z propagation modes by invoking the Floquet theorem. Real EBG structures, with a finite number of unit cells, are also studied using the scattering matrix technique. As the number of unit cells in a real structure increases, its transmission characteristics converge to those of its ideal analogue.

Comments on "A comprehensive study of discontinuities in chirowaveguides"

For original article by T.X. Wu and D.L. Jaggard see ibid., vol.50, no.10, p.2320-30, Oct. 2002.

New formulation of the coupled mode method for the analysis of chirowaveguides

In this communication we present a formulation of the Coupled Mode Method (CMM) which is different from the one normally used in the literature for solving chirowaveguides. An essential step in the development of the CMM is the way in which the longitudinal components of the electromagnetic field are related to the transverse components of the electromagnetic field. An approach which involves some previous manipulation of the constitutive relations is normally used. This gives a slow convergence of the propagation constants. In previous works, involving isotropic and anisotropic dielectric guides, we have shown that a different way of using the constitutive relations produces faster convergence of the propagation constants to the correct results for the different modes. Following this approach, we show here how this formulation can be applied to a parallel plate waveguide partially filled with different slabs of chiral media. Our results show that the predictions are confirmed in the same way as for anisotropic media.

Reduction of losses in dielectric waveguide Y-junctions with wide aperture angles

In this work, symmetrical Y-junctions made of rectangular dielectric guides are studied theoretically and experimentally. Using the effective dielectric constant method (EDCM), the dielectric guides are transformed into equivalent slab guides; after that, the junction is analysed as a discrete discontinuity located in a single plane transverse to the propagation axis. The experimental results agree very well with the theoretical predictions which indicate that there should be dimensions of the dielectric guide of the junction which optimize the transmission coefficient for a given angle and frequency. If wide aperture angles are required and image guides are used in making the junction, high losses appear; to diminish the former losses we have used Π guides in which the dielectric inside the window has a greater permittivity than the rest of the guide; metallic shields were also employed for the same purpose. These modifications improve the transmission coefficient, in some cases by nearly 5 dB

Efficient Modal Analysis of Bianisotropic Waveguides by the Coupled Mode Method

A modal analysis based on the coupled mode method is performed for the resolution of partially filled waveguides with a general bianisotropic medium. The calculation of the generalized telegraphists equations can be made by using two different strategies: direct and indirect formulations. In this paper, the indirect formulation of the method is extended to bianisotropic materials and exposed in detail. The convergence of both formulations is compared and it is demonstrated that the indirect formulation converges much faster than the direct formulation, which means that fewer modes are required for a given precision. Results of some particular cases of the constitutive relationships, like dielectric, magnetic, ferrites, and omega materials are shown and compared with the bibliography or commercial electromagnetic simulators. Good agreement is found, which demonstrates the validity and reliability of the method