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.INDEX TERMS Attenuation constant, broadband measurements, characterization, error analysis, microstrip line, phase constant, propagation constant, random errors, transmission line measurements.
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 over determination of the method increasing the number of lines measured and a criteria to choose the optimal line lengths is considered. Firstly, the measurement method itself is applied to uncovered microstrip lines and an accurate model of the substrate is obtained. Secondly, the lines are covered with several materials, made by 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 simulator is used to indirectly determine the cover material electrical parameters. Results show excellent agreement with electromagnetic simulations in the 0.1-to 67-GHz frequency band, so they assess the suitability of the proposed method.
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.
The design of dual-band bandpass filters consisting of series short-circuited wire-bonded multiconductor transmission lines and shunt open stubs is thoroughly carried out in this paper. Two different configurations are studied, and closed-form analytical design equations are derived to synthesize Chebyshev filtering functions. A novel, simplified, and time-saving synthesis procedure to design dual-band filters with narrow or moderate broad bandwidths is finally presented, attending to the required final specifications and the physical and manufacturing limitations. The usefulness and validity of the proposed analytical equations are illustrated by designing, manufacturing, and measuring three different prototypes, showing an excellent agreement between analytical and measured results. INDEX TERMS Bandpass filter, Chebyshev response, coupled lines, dual-band, multiconductor transmission lines (MTLs), shunt stubs.
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