Additive manufacturing of rectangular waveguide devices for teaching microwave laboratory

In this paper the outline of using of low-cost additive manufacturing FDM/FFF technology to build waveguide devices is presented. The focus is set in a full design from specifications to final measurements in a microwave teaching laboratory. Final results obtained asses that this experience is an extraordinary opportunity for students to get involved in waveguide technology. In addition, the use of 3D design software enriches the curricula of electronic engineering students.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Small Size Dual-band Bandpass Filters with Multiconductor Transmission Lines and Shunt Open Stubs

A dual-band bandpass filter consisting of multiconductor transmission lines (MTL) and shunt stubs has been designed. The used topology, based on the interconnection of two identical MTL and a shunt open stub, has a frequency response that can be modelled by using the generalized Chebyshev functions. A prototype of a 4 fingers-MTL is manufactured and measured and a good agreement between analytical and measured results is obtained. Furthermore, it is easy to get a design criterion that enables getting good responses varying just a few parameters.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Miniaturized top-metallized rectangular dielectric resonator antenna

In this paper, a modal analysis of a rectangular dielectric resonator antenna (DRA), with unconventional boundary conditions, is carried out. Analytical equations of the fields inside the resonator and simulations are presented, showing that if a resonator is mounted over a ground plane and loaded by a top metallic sheet, there is a miniaturization of the electric size of the new antenna, without significant deterioration of performance. Furthermore, dual-band responses can be achieved with this configuration.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Random Errors in Broadband Characterization of the Propagation Constant of Transmission Lines Using Multiple Two-Port Measurements

In this work, a comparison between three broadband methods used to estimate the propagation constant of planar transmission lines is presented. The goal of this comparison is to study how possible random measurement errors can affect the use of the aforementioned methods commonly used, since in ideal conditions the same solution is obtained from all of them. For this purpose, a sensitivity analysis is carried out in order to study the similarities and differences and how errors in measured Sparameters and in line lengths affect the attenuation and the phase constant obtained from each method. Subsequently, a minimization approach that consists of a least-square estimation using a criteria to choose the optimal line lengths is proposed to minimize measurement errors. Finally, an experiment has been designed, manufactured using microstrip transmission lines, and measured to validate the developed theory. Results corroborate the proposed theory and show an excellent agreement with electromagnetic simulations in the 0.1- to 50-GHz frequency band, therefore assessing the suitability of the proposed error analysis.This work was supported in part by the Spanish Ministerio de Economía, Industria y Competitividad, under Project ADDMATE TEC2016-76070-C3-3-R (AEI/FEDER, UE), in part by the Spanish Ministerio de Educación, Cultura y Deporte, under Grant FPU16/00246, and in part by Universidad de Málaga, under I Plan Propio de Investigación y Transferencia (C.1)

Caracterización en banda ancha de la constante de propagación de materiales de impresión 3D

In this work, a method for the characterization of the relative permittivity in broadband of 3D printing materials is proposed. It uses microstrip lines of different lengths covered with the material to be characterized. Once S-parameters of the structure are obtained, some transformations are performed, using transmission parameters and the line length differences, in order to obtain the propagation constant of the lines, from which it is possible to extract the characteristics of the material to be studied. The method has been tested by manufacturing and measuring lines covered with ABS material, showing results very close to those of electromagnetic simulation and those shown in the literature for this material.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Fuentes de error aleatorio en la estimación de la constante de propagación de líneas de transmisión usando medidas de dos puertos

In this contribution, we study different error sources that affect the estimation of the propagation constant in broadband methods. For this purpose, a study on the state-of-the-art has been made. The behavior of different error sources was examined separately: errors in the vector network analyzer, in the line lengths, in the inhomogeneity of the substrate, and the repeatability of the launchers. It has been shown that, depending on the method used, the behavior of the random errors can be different. In this sense, an excellent strategy to reduce the errors is to increase the number of lines, choosing their length reasonably. On the other hand, it has been seen that both the errors in the length of the lines and in the inhomogeneities of the substrates will work as a bias in the solution of the estimated propagation constant. The bias will depend on the difference between lengths or substrates. Finally, it has been studied how the repeatability of transitions and connectors affects the methods. To improve this problem, it has been demonstrated that always using the same pair of connectors is an efficient way to reduce the uncertainty of the results.Este proyecto ha sido financiado por el Ministerio de Ciencia e Innovación del Gobierno de España, con fondos de los proyectos PID2020-116968RB-C31/AEI/10.13039/501100011033 y MCIU/AEI/FEDER (Programa Estatal de I+D+i Orientada a los Retos de la Sociedad), por la Junta de Andalucía, con el proyecto PAIDI2020-PY20\_00452, por el Ministerio de Educación, Cultura y Deporte del Gobierno de España, con la beca FPU16/00246 y por la Universidad de Málaga, con un Contrato Puente del I Plan Propio de Investigación y Transferencia. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

End-launcher repeatability in broadband methods for characterization of the propagation constant of transmission lines using two-port measurements.

This work presents an analysis of the influence of connector repeatability in three different methods for estimating the propagation constant of transmission lines from two-port measurements. For this purpose, the repeatability of 16 transitions using 1.85 mm coaxial-to-microstrip end-launcher connectors has been tested. It has shown that using the same pair of connectors instead of the whole set significantly reduces the standard deviation of the transition S-parameters that affects the final estimation of the propagation constant, and especially the attenuation constant. In addition, the hypothesis that the measured data have a normal probability distribution has been validated by performing an Anderson-Darling test on the estimated S-parameters of the transition. The obtained standard deviation has been included in a sensitivity analysis, generating S-parameters from normal distribution and performing a Monte Carlo simulation. The objective is to study the standard deviation of the propagation constant obtained using the proposed methods when there are errors related to connector repeatability. In this case, unlike random errors of the analyzer, it has been found that all the compared strategies for the estimation of the propagation constant (traces, eigenvalues, and determinants) work in the same way concerning launcher repeatability errors. Furthermore, it has been seen that the propagation constant obtained also follows a normal distribution. Finally, to validate the presented theory, methods have been applied to several measurements of two lines in the 0.01- to 67-GHz frequency range, using the same kit and different combinations of different connectors. Results show that higher accuracy is obtained when using the same pair of connectors, considerably reducing attenuation constant ripple, which assesses the suitability of the proposed error analysis

Performance Evaluation of Broadband Characterization of Coupled Transmission Lines Even- and Odd-Mode Propagation Constants Using Differential and Common Mode S-Parameters

This work encompasses some relevant issues that arise when using a broadband method to characterize the even and odd mode propagation constants of symmetric microstrip coupled lines using four-port pure-mode differential and common mode S-Parameters. Correct excitations of differential and common modes play a significant role in experimental results. From these 4-port measurements, parameters corresponding to the even and odd modes can be extracted from the multi-mode generalized S-parameters obtained by the vector network analyzer. Differential and common mode sub-matrices are considered as two independent equivalent 2-port transmission lines. The method will be applied to extract the propagation constants of even and odd modes of coupled microstrip transmission lines. A discussion is included on ensuring the correct excitation of the modes in the structure and avoiding possible unwanted effects such as radiation, that negatively affects the final estimation, both in phase and attenuation. Two figures of merit are defined to evaluate how transitions affect the performance of the method. These figures of merit allow a reasonable estimation of how the final experiment is affected by selected excitation of modes. To assess the theory presented, two sets of seven lines of different lengths are manufactured. The experimental results show an excellent agreement, both with electromagnetic simulations and with the analytical model used, for the phase constant in the improved case of 30° bends, and an improvement in the useful bandwidth of the attenuation constant. This fact verifies the correct functioning of the method. In addition, the measurements are presented in the range of 0.01–67 GHz, which represents a significant advance in bandwidth for this type of structure

Parameters characterization of dielectric materials samples in microwave and millimeter-wave bands

In this work, an optimized broadband method using multilayer transmission lines to characterize dielectric permittivity and loss tangent of material samples is presented. For this purpose, a microstrip line loaded with a piece of the selected dielectric to be characterized is used. From two-port measurements, and using different length lines, the propagation constant can be obtained. To minimize random errors and to improve the accuracy, an overdetermination of the method increasing the number of lines measured and a criterion to choose the optimal line lengths is considered. First, the measurement method itself is applied to uncovered microstrip lines and an accurate model of the substrate is obtained. Second, the lines are covered with several materials, made by fused deposition modeling (FDM) additive manufacturing technique, such as acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), high impact polystyrene (HIPS), thermoplastic polyurethane (TPU), copolyester (CPE), FLEX, polyethylene terephthalate glycol (PETG), and nylon. A model of the transmission line considering the cover is developed, and an electromagnetic (EM) simulator is used to indirectly determine the cover material electrical parameters. Results show excellent agreement with EM simulations in the 0.1–67-GHz frequency band, so they assess the suitability of the proposed method

Miniaturized Top-Metalized 3D-printed Rectangular Dielectric Resonator Antenna.

This paper introduces a novel top-metalized Dielectric Resonator Antenna (DRA). The inclusion of top metallization induces a modification in the boundary conditions, resulting in a frequency reduction in the fundamental mode of the DRA. A prototype is designed for the 2.45-GHz WiFi band with a --10-dB bandwidth from 2.40 to 2.51 GHz. The radiation maxima occur in the top and bottom directions, with a gain of 1.81 dBi at 2.45 GHz. The proposed DRA is specifically designed for manufacturing using commercially available materials and additive manufacturing techniques.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech