H. Esteban

Efficient modal analysis of arbitrarily shaped waveguides composed of linear, circular, and elliptical arcs using the BI-RME method

This paper deals with the accurate and efficient modal analysis of arbitrarily shaped waveguides whose cross section is defined by a combination of straight, circular, and/or elliptical arcs. A novel technique for considering the presence of circular and/or elliptical segments within the frame of the well-known boundary integral-resonant mode expansion (BI-RME) method is proposed. This new extended BI-RME method will allow a more accurate solution of a wider number of hollow conducting waveguides with arbitrary profiles, which are usually present in most modern passive waveguide components. To show the advantages of this new extended technique, the modal chart of canonical (circular and elliptical) waveguides, as well as of irises with great practical interest (i.e., cross-shaped irises with rounded corners) has been first successfully solved. Next, a computer-aided-design software package based on such a novel modal analysis tool has first been validated with the accurate analysis of a referenced complex dual-mode filter, and then applied to the complete design of a novel twist component for K-band application based on circular and elliptical waveguides. A prototype of this novel device has been manufactured and measured for verification purposes.

A new hybrid mode-matching/numerical method for the analysis of arbitrarily shaped inductive obstacles and discontinuities in rectangular waveguides

A new and efficient hybrid mode-matching method is presented for the analysis of arbitrarily shaped inductive obstacles and/or discontinuities in a rectangular waveguide. The irregular region with obstacles and/or discontinuities is characterized using a full-wave hybrid spectral/numerical open-space technique expanding the fields in cylindrical wave functions. Next, a full-wave mode-matching procedure is used to match the cylindrical wave functions to guided modes in all ports and a generalized scattering matrix for the structure is finally obtained. The obstacles can be metallic or dielectric with complex permittivities and arbitrary geometries. The structure presents an arbitrary number of ports, each one with different orientation and dimensions. The accuracy of the method is validated comparing with results for several complex problems found in the literature. CPU times are also included to show the efficiency of the new method.

Novel Empty Substrate Integrated Waveguide for High-Performance Microwave Integrated Circuits

Over the last years, a great number of substrate integrated circuits has been developed. These new circuits are a compromise between the advantages of classical waveguide technologies, such as high quality factor and low losses, and the advantages of planar circuits, such as low cost and easy compact integration. Although their quality factor and losses are better than for planar circuits, these characteristics are worse than in the case of waveguides, mainly due to the presence of the dielectric substrate. In order to improve the performance of the integrated circuits, a new methodology for manufacturing empty waveguides, without a dielectric substrate, but at the same time completely integrated in a planar substrate, is proposed in this work. A wideband transition with return losses greater than 20 dB in the whole bandwith of the waveguide allows the integration of the empty waveguide into the planar substrate so that the waveguide can be directly accessed with a microstrip line. Therefore, a microwave circuit integrated in a planar substrate, but at the same time with a very high quality factor (measured quality factor is 4.5 times higher than for the same filter in the substrate integrated waveguide), and very low losses is successfully achieved.

Efficient Analysis of Substrate Integrated Waveguide Devices Using Hybrid Mode Matching Between Cylindrical and Guided Modes

In this paper, a new method to efficiently analyze substrate integrated waveguide (SIW) based devices with multiple accessing ports is presented. The problem is considered as a 2-D electromagnetic problem assuming no field variation normal to the dielectric substrate. The incident and scattered fields from each circular cylinder are expanded with cylindrical modes, and the fields in the waveguide ports are expanded using progressive and regressive modal summations. The addition theorems of Bessel and Hankel functions are used to analyze the full-wave behavior of the SIW device. In order to extract the circuital parameters, the hybrid mode-matching between guided and cylindrical modes is done by projecting continuity equations in a circular boundary containing the whole SIW structure over the inner modes of each region. Applying this new technique, it is possible to analyze multiple port devices by solving a set of integrals that can be easily approached analytically or by using the inverse fast Fourier transform, avoiding the use of non efficient numerical methods. It is shown that the new method runs faster than commercial software packages and other techniques recently published.

Hybrid Technique Plus Fast Frequency Sweep for the Efficient and Accurate Analysis of Substrate Integrated Waveguide Devices

In this paper, we adapt a novel mode-matching and method-of-moments hybrid technique to efficiently analyze substrate integrated waveguide (SIW) based devices. The hybrid technique is formulated in terms of a single equivalent current. This fact is used to include the emergent modal weights, i.e., the scattering parameters, as unknowns of the method-of-moments system of equations. In this case, it is relatively easy to develop fast frequency sweep schemes that can be used to highly accelerate the solution of an arbitrary device and, as a result, a very efficient technique is obtained. This technique can be applied to the analysis and design of SIW devices, and it is highly competitive when compared to other method-of-moments and mode-matching hybrid formulations or when compared to reference commercial software.

Wideband Passband Transmission Line Based on Metamaterial-Inspired CPW Balanced Cells

In this letter, a balanced metamaterial-inspired coplanar waveguide transmission line with enhanced bandwidth is presented. The coplanar waveguide line is composed of a basic cell with two split-ring resonators, two series capacitances (interdigital capacitors), two wide shunt inductances (metallic strips), and four shunt capacitances (implemented through open-ended stubs). The use of split-ring resonators together with metallic shunt strips provides negative permeability and permittivity, respectively. Likewise, the employment of additional series and shunt capacitances permits to control both the left- and right-handed bands, thus achieving a balanced composite transmission line. The configuration exhibits a wide bandpass response as a result of this balance between advance and delay phase offsets. The interpretation is based on an equivalent circuit model, full-wave electromagnetic analysis, and measured responses of a prototype designed for microwave (C-band) frequency operation. Due to the small dimensions of the resonators employed, the resulting line is very compact. Potential use of these transmission lines can be foreseen in many applications concerning planar microwave devices with severe size restrictions and wide frequency bandpass responses.

A rigorous and efficient full-wave analysis of uniform bends in rectangular waveguide under arbitrary incidence

In this paper, a rigorous full-wave analysis of uniform bends in rectangular waveguides is performed. An accurate and efficient method-of-moments solution combined with the generalized-admittance-matrix (GAM) formulation is proposed in order to achieve a full-wave characterization of the analyzed structures. This full-wave modal solution turns out to be necessary for modeling complex microwave devices involving an arbitrary number of discontinuities between curved and straight waveguides, where all the modes of the involved guides are excited. The key feature of the presented method lies in the GAM representation of single and cascaded curved E- and H-plane uniform bends, which allows the construction of accurate models of the investigated discontinuities. To validate the theory, the convergence of the method is discussed and comparisons between our simulations and theoretical and experimental data are presented. The excellent behavior of our results, together with the computational efficiency of the proposed method, proves that the developed computer-aided-design tool can be successfully used in the design of complex microwave subsystems involving curved waveguides.

Permittivity and permeability measurement of microwave packaging materials

There has recently been a growing interest in using new packaging materials-dielectric and/or magnetic-in a wide variety of applications for controlling the microwave heating of food. The study of the thermal behavior of these products requires the accurate determination of the complex permittivity and permeability when the temperature varies, and when the materials are irradiated in specific conditions. One of the main challenges is to distinguish the dielectric losses from the magnetic ones. In this paper, a practical measurement method is proposed, which consists of irradiating a rod sample successively with a homogeneous electric-field distribution with a low magnetic field and with a homogeneous magnetic-field distribution with low electric field. An accurate and efficient electromagnetic analysis tool is used to generate a set of points, which allow the construction of several bilinear functions that relate the scattering parameters of the circuit to the complex values of /spl epsiv/ and /spl mu/ so that /spl epsiv/ and /spl mu/ can then be easily determined from experimental measurements in accordance to whatever the special irradiation conditions. Some results for test materials are presented and discussed.

Improvement for the design equations for tapered Microstrip-to-Substrate Integrated Waveguide transitions

This article describes a new design strategy for Microstrip-to-Substrate Integrated Waveguide (SIW) transitions with different geometries. This design strategy focuses in obtaining a good initial point for the length and the width of the transition. Later, these parameters are optimized together in order to calculate a low reflection transition in the desired bandwidth. With this method, different transitions have been designed, in which the impedance variation follows different mathematical expressions, some of them extracted from the classical theory.

Hybrid Mode Matching and Method of Moments Method for the Full-Wave Analysis of Arbitrarily Shaped Structures Fed Through Canonical Waveguides Using Only Electric Currents

A new hybrid mode matching and method of moments formulation based only on electric currents is presented in this paper. The use of only one equivalent current allows the introduction of a new set of unknowns. The chosen new unknowns are the weights related to the scattered modes that emerge from the ports to the waveguides that feed the problem. Applying this new formulation, the matrices that must be inverted are smaller and the generalized scattering matrix can be obtained directly from the solution of the resulting system of equations so that no additional projection is needed to obtain the scattering parameters, as happens with traditional approaches with two equivalent currents. As a result, certain efficiency improvement is obtained, as can be seen when this technique is applied to the solution of H-plane problems in rectangular waveguide.