C. Bachiller

Efficient Technique for the Cascade Connection of Multiple Two-Port Scattering Matrices

There are several practical applications in microwave engineering that require the cascade connection of multiple two-port scattering matrices. Many microwave devices are analyzed by segmenting the structure into small building blocks (steps, resonators, lines, etc.) that are characterized by means of the generalized scattering matrix. In order to obtain the reflection and transmission parameters of the entire structure, the scattering matrices of all the building blocks must be cascaded. Traditionally, the conversion of the scattering matrices to ABCD or T matrices has been used in order to perform the cascade connection. An alternative to this procedure is to perform a recursive connection by pairs of the scattering matrices. In this paper, we present a new technique for the efficient cascade connection of N monomodal or multimodal scattering matrices that reduces the computation time by 35% when compared to the cascading by pairs, and by 75% when compared with the use of ABCD matrices.

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.

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.

Efficient CAD tool of direct-coupled-cavities filters with dielectric resonators

This article describes a new CAD tool of directly coupled cavities filters with dielectric resonators based on a very efficient hybrid analysis method. The CAD tool efficiently combines two accurate analysis techniques: a first one, based on the integral equation method, for the analysis of the standard rectangular waveguide filter steps, and a second one, based on mode matching and spectral methods, for solving the dielectric resonators. The suitable combination of these two analysis techniques provides high improvements in the CPU time required in the CAD of these filters. The CAD tool is based in ASM with a hybridization of several optimization algorithms, including a continuous-time genetic algorithm. A band-pass filter with dielectric resonators has been successfully designed making use of this novel CAD tool

Hybrid Mode Matching Method for the Efficient Analysis of Metal and Dielectric Rods in H Plane Rectangular Waveguide Devices

The paper presents a new accurate and efficient technique for the analysis of H-plane single or multiple rods in rectangular waveguides. The new method is based on a mode matching procedure that matches open space and guided modes along a circular boundary that encloses the rods. Since the EM fields around the obstacles are expanded using open space cylindrical modes, a full analytical (and highly efficient) solution can be obtained for dielectric or metallic circular posts. However, this technique can also cope with any arbitrary geometry of the H plane obstacles. In such a case, a numerical method should be used to characterize geometries other than circular in terms of cylindrical modes, and therefore the efficiency would be reduced. The method has been successfully applied to the analysis and design of several H plane filters with different topologies involving single centered and off-centered posts, as well as double post geometries.

Teaching of advanced wave-propagation phenomena in open-space problems and waveguide devices using MATLAB GUIs

Interactive graphics and animations are fundamental tools for teaching electromagnetic concepts, especially to explain propagation phenomena. For this reason, the study of these phenomena needs advanced analysis tools. This article presents an accurate and efficient hybrid mode-matching method for the analysis of arbitrarily shaped structures with H-plane obstacles and discontinuities. An open-space spectral method is used to model the electric behavior of the H-plane problem. Next, the open-space modes are matched to guided modes, in order to obtain a multimode scattering-matrix representation of the structure. This new method is used to analyze the propagation in passive complex radio-frequency structures. The results from the analysis are integrated into a MATLAB graphical user interface (GUI), which has been designed to improve the teaching/learning process at the Universidad Politecnica of Valencia in Spain. These GUIs are thoroughly explained in the paper, and the improvements in the teaching/learning process are also discussed.

Efficient automated design of H plane filters with rounded corners using ASM with a segmentation strategy and hybrid optimization techniques

An efficient and accurate CAD tool for the automated design of H-plane filters with rounded corners has been presented in this paper. These rounded corners are a consequence of the use of low-cost fabrication techniques. The well known ASM technique has been used in conjunction with an efficient simulator that does not take into account the presence of rounded corners and a general purpose full-wave simulator. A new segmentation procedure and a suitable hybridization of several optimization algorithms are used to increase the robustness and efficiency of ASM. Several H-plane filters have been successfully designed with this CAD tool. The time required to perform the designs has proved to be lower than in other design procedures found in the literature. The CPU cost could be drastically reduced if a more specific and efficient simulator was used for the fine model. The CAD tool does not require human intervention for performing the design.

Online application for representation of the radiation pattern of antenna arrays

Students should learn how to plot the radiation patterns of arrays of antennas in undergraduate and graduate courses on antennas. Simple chalk plots do not provide a good idea of the radiation patterns, especially for three dimensions. The authors began to work with MATLAB GUIs in order to provide an application that achieved high-quality radiation-pattern graphics and good interaction with the students, allowing them to change the different parameters of the array and to visualize the whole process of pattern plotting. Nevertheless, we found that the students wanted to have the same application for testing and studying at home, but many of them did not have copies of the MATLAB environment. The authors then looked for a solution that was portable, free, and that did not require any specific software in order to run. In order to give access to the application via the Internet, we imported our functions in MATLAB to GNU Octave, an open-source software package with characteristics similar to MATLAB but freely redistributable under the terms of the GNU General Public License (GPL).

Improved Low Reflection Transition From Microstrip Line to Empty Substrate-Integrated Waveguide

Substrate-integrated waveguides (SIWs) maintain the advantages of planar circuits (low loss, low profile, easy manufacturing, and integration in a planar circuit board) and improve the quality factor of filter resonators. Empty substrate-integrated waveguides (ESIWs) substantially reduce the insertion losses, because waves propagate through air instead of a lossy dielectric. The first ESIW used a simple tapering transition that cannot be used for thin substrates. A new transition has recently been proposed, which includes a taper also in the microstrip line, not only inside the ESIW, and so it can be used for all substrates, although measured return losses are only 13 dB. In this letter, the cited transition is improved by placing via holes that prevent undesired radiation, as well as two holes that help to ensure good accuracy in the mechanization of the input iris, thus allowing very good return losses (over 20 dB) in the measured results. A design procedure that allows the successful design of the proposed new transition is also provided. A back-to-back configuration of the improved new transition has been successfully manufactured and measured.