Sánchez-Marín, JR.; Bachiller Martin, MC.; Juliá Morte, M.; Nova-Giménez, V.; Esteban González, H.; Boria Esbert, VE. (2018). Microwave Filter based on Substrate Integrated Waveguide with Alternating Dielectric Line Sections. IEEE Microwave and Wireless Components Letters. 28(11):990-992. https://doi.Abstract-A new topology of microwave filter based on Substrate Integrated Waveguide (SIW) with alternating dielectric line sections is presented in this paper. The two alternating sections are waveguides without and with dielectric material acting, respectively, as the inverters and the resonant sections of the proposed filter. This topology allows to easily design and manufacture compact filters with lower losses and higher rejection band than other available SIW realizations. For validation purposes, a prototype of a 4-pole bandpass filter, based on alternating dielectric line sections, has been designed and manufactured, including successful experimental results.Index Terms-Substrate Integrated Waveguide (SIW), planar structure, filter, alternating dielectric line sections.
Substrate integrated waveguides are increasingly being used due to their capability of combining the advantages of planar circuits and traditional waveguides. The development of empty substrate integrated waveguides has substantially reduced the related insertion losses, since waves propagate through air instead of propagating through a lossy dielectric medium. Recently, a new empty coaxial structure, completely built with printed circuit boards and integrated in a substrate, has been proposed. It has been named empty substrate integrated coaxial Line (ESICL). The resulting coaxial line has low cost, easy manufacturing, low radiation, low losses, high-quality factor, and is non dispersive. A transition from grounded coplanar waveguide to ESICL already exists. In this work, a transition from microstrip to ESICL is presented for the first time. In order to demonstrate its feasibility, a back-to-back structure and a bandpass filter have been manufactured and measured. Index Terms-Substrate integrated waveguide (SIW), empty substrate integrated waveguide (ESIW), transition, bandpass filter, empty substrate-integrated coaxial line (ESICL).
This work presents the practical realization of a power divider and a 90 • hybrid directional coupler in Empty Substrate Integrated Coaxial Line (ESICL) for C-band frequency applications. This new type of transmission line is very promising in terms of electric performance, bandwidth, integration with other planar circuits and manufacturing simplicity. The ESICL has been designed for obtaining a wide monomode bandwidth with a characteristic impedance of 50 ohms. Furthermore, an improvement of the efficient transition between the ESICL and the Grounded Coplanar Waveguide (GCPW), used as feeding line, has been also proposed. The passive devices built using this technology are reduced in mass and volume, keeping robustness and providing a well balanced power division, as well as reduced losses and high isolation in the whole operational bandwidth. Two prototypes have been manufactured and the experimental results are in good agreement with the simulated designs. Index Terms-C-band, empty substrate integrated coaxial line (ESICL), ESICL broadband transition, power divider, hybrid directional coupler.
The use of nematic liquid crystal (LC) mixtures for microwave frequency applications presents a fundamental drawback: many of these mixtures have not been properly characterized at these frequencies, and researchers do not have an a priori clear idea of which behavior they can expect. This work is focused on developing a new procedure for the extraction of the main parameters of a nematic liquid crystal: dielectric permittivity and loss tangent at 11 GHz under different polarization voltages; splay elastic constant K11, which allows calculation of the threshold voltage (Vth); and rotational viscosity γ11, which allows calculating the response time of any arbitrary device. These properties will be calculated by using a resonator-based method, which is implemented with a new topology of substrate integrated transmission line. The LC molecules should be rotated (polarized) by applying an electric field in order to extract the characteristic parameters; thus, the transmission line needs to have two conductors and low electric losses in order to preserve the integrity of the measurements. This method was applied to a well-known liquid crystal mixture (GT3-23002 from MERCK) obtaining the permittivity and loss tangent versus bias voltage curves, the splay elastic constant, and the rotational viscosity of the mixture. The results validate the viability of the proposed method.
Liquid Crystal (LC) is an anisotropic liquid material which flows like a liquid, but at the same time its molecules have an orientational order like in the solid state. Thus, LC is a promising dielectric material for designing reconfigurable devices at microwave frequencies. In order to optimize the design of reconfigurable microwave devices, accurate values of the dielectric permittivity and the loss tangent of LCs are needed. However, new LCs are not well characterized at these frequencies because of its recent use for microwave applications. Therefore, the characterization in this frequency range is required for its practical use within microwave components and devices.In this work, a split-cylinder resonator method is used for the characterization of four different nematic LCs at two frequency points, i.e. 5 and 11 GHz. This characterization includes the extraction of their complex dielectric permittivity values at these frequencies. The employed method allows to obtain the two extreme permittivity values without applying any external electric or magnetic field to polarize the LC molecules. Two different approaches, a modal analysis method and a full-wave numerical technique have been used for determining the LC parameters obtaining similar results in both cases.
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