Impedance Matched Absorptive Thermal Blocking Filters

We have designed, fabricated and characterized absorptive thermal blocking filters for cryogenic microwave applications. The transmission line filter's input characteristic impedance is designed to match $50\,\Omega$ and its response has been validated from 0-to-50\,GHz. The observed return loss in the 0-to-20\,GHz design band is greater than $20\,$dB and shows graceful degradation with frequency. Design considerations and equations are provided that enable this approach to be scaled and modified for use in other applications

A New Stand-Alone Microwave Instrument for Measuring the Complex Permittivity of Materials at Microwave Frequencies

"© 2020 IEEE. Personal use of this material is permitted. Permissíon from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertisíng or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works."[EN] This paper reports the development of a stand-alone and portable instrument designed to measure the complex permittivity of dielectric materials at microwave frequencies. The equipment consists of an in-house single-port vectorial reflectometer and a resonant coaxial bi-reentrant microwave cavity where the material under test is placed inside a Pyrex vial, making the device appropriate for measuring liquids, semi-solids, powders and granular materials. The relation between the dielectric properties of the involved materials and the cavity resonance has been solved by numerical methods based on mode-matching and circuit analysis. In order to increase the measurement range, so that low to high loss materials can be characterized in the same cavity, the effect of the coupling network is de-embedded from the resonance measurements. The performance of the newly devised instrument is evaluated by error/uncertainty analysis and comparative studies with other well-established instruments and methods. Errors lower than 2% in the dielectric constant, and 5% in the loss factor, are found. This simple, portable, affordable and robust device could help non-specialized personnel to accurately measure dielectric properties of materials used in a wide range of microwave applications.This paper has been financially supported through the grant reference BES-2016-077296 of the call Convocatoria de las ayudas para contratos predoctorales para la formacion de doctores de 2016 by Ministerio de Economia y Competitividad (MINECO) and by European Social Funds (ESF) of European Union and the project SEDMICRON TEC2015-70272-R (MINECO/FEDER) supported by Ministerio de Economia y Competitividad (MINECO) and by European Regional Development Funds (ERDF) of European Union. The Associate Editor coordinating the review process was Samir Trabelsi.Gutiérrez Cano, JD.; Plaza González, PJ.; Canós Marín, AJ.; García-Baños, B.; Catalá Civera, JM.; Penaranda-Foix, FL. (2020). A New Stand-Alone Microwave Instrument for Measuring the Complex Permittivity of Materials at Microwave Frequencies. IEEE Transactions on Instrumentation and Measurement. 69(6):3595-3605. https://doi.org/10.1109/TIM.2019.2941038S3595360569

Full-wave analysis of dielectric-loaded cylindrical waveguides and cavities using a new four-port ring network

“© 2012 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.”In this paper, a full-wave method for the electromagnetic analysis of dielectric-loaded cylindrical and coaxial waveguides and cavities is developed. For this purpose, a new four-port ring network is proposed, and the mode-matching method is applied to calculate the generalized admittance matrix of this new structure. A number of analyses on dielectric-loaded waveguide structures and cavities have been conducted in order to validate and to assess the accuracy of the new approach. The results have been compared with theoretical values, numerical modeling from the literature, and data from commercial electromagnetic simulators. The method has been also applied to the accurate determination of dielectric properties, and we provide an example of these measurements as another way to validate this new method. © 1963-2012 IEEE.This work was supported by the Ministry of Science and Innovation of Spain under Project MONIDIEL (TEC2008-04109). The work of F. L. Penarada-Foix was supported by the Conselleria de Educacion of the Generalitat Valenciana for economic support (BEST/2010/210).Penaranda-Foix, FL.; Janezic, MD.; Catalá Civera, JM.; Canós Marín, AJ. (2012). Full-wave analysis of dielectric-loaded cylindrical waveguides and cavities using a new four-port ring network. IEEE Transactions on Microwave Theory and Techniques. 60(9):2730-2740. https://doi.org/10.1109/TMTT.2012.2206048S2730274060

Full-3D Printed Electronics Fabrication of Radiofrequency Circuits and Passive Components

[eng] This doctoral thesis raises the idea that 3D printing can change the paradigm of radio- frequency electronics, which has been traditionally developed mainly conceiving planar topologies. A review on additive manufacturing and the different existing technologies is reported. To focus on the concerning topic, several applications of 3D-printed electronics in the RF field are collected to elaborate the State-of-the-Art. The main objectives of this project is to develop a 3D manufacturing technology for RF electronics passive components and circuits and to generate innovative research about the possibilities of AM in this area. Once the context is exposed, the manufacturing process for 3D-printed electronics developed within the frame of this project is described and characterized. This technology consists of three different steps. First of all, the 3D model of the prototype is designed using a CAD environment with electromagnetic simulation features, hence size parameters are adjusted to fit the specifications. Hereon, the 3D polymer substrate is printed by using either stereolithography or material jetting techniques. Stereolithography is found to be a cheaper AM technology while material jetting offers a better printing resolution and softer surface endings. Finally the object is partially metallized to obtain the conductive layer of the component or circuit using an electrolytic process, such as electroless plating or electroplating. The characterization includes the electromagnetic specifications of the dielectric substrates (i.e. the dielectric constant and the loss tangent) and the quality of the metallization (i.e. the resistivity and the layer thickness). The results of the plating resitivity are found to be competitive compared to the SoA. In order to demonstrate the possibilities of the developed technology, several devices are designed and tested. The key factor of these prototypes is that they would be very difficult, costly or impossible to manufacture using conventional technologies. As a preliminary demonstration, a hello-world circuit to turn on a LED proves that almost any kind of shape can be plated, including vias; both through hole and SMD components can be soldered and that mechanical stress such as USB plugging is resisted by the metal layer. In addition, a study on conical inductors is carried out showing the advantages of these components for broadband applications with compact devices. They offer a larger bandwidth cylindrical solenoids and are more compact than planar coils. As an application example, they are used in the manufacturing of 3D passive filters. The prototypes present agreement with simulations and the ideal response. Slight discrepancies are caused by the manufacturing tolerances. Moreover, 3D filters are also designed as one single-printed part, a new technique for 3D discrete component integration. That permits to reduce the number of components to assembly so that it does not increase with the order of the filter. These single 3D-printed prototypes present improvement in performance and compactness as well. In addition to the lumped circuits, a whole chapter is dedicated to distributed-element devices. A study on helical-microstrip transmission lines is carried out showing an important enhancement for line segment miniaturization. Hereon, they are implemented on the design of impedance transformers, which also benefit from bandwidth broadening. Another proposed device is the hybrid branch-line coupler, which, besides the implementation of helical lines, it has been designed conceiving a capacitively loaded folded structure. This coupler gives very interesting results in compactness improvement, without significant reduction of the bandwidth. The prototypes have been compared to the conventional topology as well as to other designs found within the SoA. Finally, helical-microstrip coupled-line couplers have also been designed, fabricated and studied. They offer a good enhancement in terms of compactness though it goes in slight detriment of the coupling factor due to the manufacturing tolerances.[cat] Aquesta tesi doctoral proposa la idea que la impressió 3D pot canviar el paradigma de l’electrònica de radiofreqüència. S’hi anomenen i expliquen les tecnologies de manufactura additiva existents. Per centrar-se en el principal tema d’interès, s’exposa un compendi d’aplicacions d’electrònica impresa en 3D en el camp de la RF amb el qual s’ha confeccionat l’estat de la qüestió. Un cop exposat el context, el procés de manufactura per a electrònica impresa en 3D que s’ha desenvolupat en el marc d’aquest projecte és descrit i caracteritzat. Aquesta tecnologia consisteix en la impressió en 3D d’un substrat de polímer utilitzant tècniques basades, o bé en estereolitografia, o bé en material jetting. Posteriorment, el component o circuit es metal·litza parcialment mitjançant un procés electrolític ja sigui electroless plating o electroplating. La caracterització inclou les especificacions electromagnètiques del substrat dielèctric i la qualitat de metal·lització, que s’han resultat ser competitives relació amb l’estat de la qüestió. Amb l’objectiu de demostrar les possibilitats de la tecnologia desenvolupada, s’han dissenyat i testejat dispositius electrònics de RF, concebent-los en l’espai tridimensional. El punt clau és que els dispositius dissenyats serien molt difícils, costosos o directament impossibles de fabricar usant tecnologies convencionals. A remarcar, s’ha dut a terme un estudi sobre inductors cònics, mostrant els avantatges d’aquests components per a aplicacions de banda ampla amb dispositius compactes. Aquests inductors shan fet servir per a la fabricació de filtres passius en 3D. A més, a més, s’han dissenyat filtres 3D per ser impresos en una sola part, una tècnica nova que per produir circuits 3D amb components discrets integrats. A part dels circuits d’elements discrets, s’ha dedicat un capítol sencer als dispositius d’elements distribuïts. S’ha dut a terme un estudi sobre línies de transmissió microstrip helicoidals, les quals aporten una millora important de miniaturització dels segments de línia. Partint d’aquí, aquestes línies s’han implementat en el disseny de transformadors d’impedància, que també milloren en termes d’ample de banda, acobladors híbrids de tipus branch-line i acobladors basats en línies acoblades. Aquests dispositius han resultat tenir millores importants de compacitat respecte els dissenys convencionals fabricats en estructures planars

Analysis and Design of Low-Cost Waveguide Filters for Wireless Communications

The area of research of this thesis is built around advanced waveguide filter structures. Waveguide filters and the waveguide technology in general are renowned for high power capacity, low losses and excellent electromagnetic shielding. Waveguide filters are important components in fixed wireless communications as well as in satellite and radar systems. Furthermore, their advantages and utilization become even greater with increase in frequency, which is a trend in modern communication systems because upper frequency bands offer larger channel capacities. However, waveguide filters are relatively bulky and expensive. To comply with more and more demanding miniaturization and cost-cutting requirements, compactness and economical design represent some of the main contemporary focuses of interest. Approaches that are used to achieve this include use of planar inserts to build waveguide discontinuities, additive manufacturing and substrate integration. At the same time, waveguide filters still need to satisfy opposed stringent requirements like small insertion loss, high selectivity and multiband operation. Another difficulty that metal waveguide components face is integration with other circuitry, especially important when solid-state active devices are included. Thus, improvements of interconnections between waveguide and other transmission interfaces are addressed too. The thesis elaborates the following aspects of work: Further analysis and improved explanations regarding advanced waveguide filters with E-plane inserts developed by the Wireless Communications Research Group, using both cross coupled resonators and extracted pole sections (Experiments with higher filter orders, use of tuning screws, degrees of freedom in design, etc. Thorough performance comparison with competing filter technologies) - Proposing novel E-plane filter sections with I-shaped insets - Extension of the E-plane filtering structures with metal fins to new compact dual band filters with high frequency selectivity and miniaturized diplexers. - Introduction of easy-to-build waveguide filters with polymer insert frames and high-performance low-profile cavity filters, taking advantage of enhanced fabrication capabilities when using additive manufacturing - Developing new substrate integrated filters, as well as circuits used to transfer signals between different interfaces Namely, these are substrate integrated waveguide to metal waveguide planar transitions that do not require any modifications of the metal waveguides. Such novel transitions have been designed both for single and orthogonal signal polarizations

Millikelvin thermal and electrical performance of lossy transmission line filters

We report on the scattering parameters and Johnson noise emission of low-pass stripline filters employing a magnetically loaded silicone dielectric down to 25 mK. The transmission characteristic of a device with $f_{-3dB}$=1.3 GHz remains essentially unchanged upon cooling. Another device with $f_{-3dB}$=0.4 GHz, measured in its stopband, exhibits a steady state noise power emission consistent with a temperature difference of a few mK relative to a well-anchored cryogenic microwave attenuator at temperatures down to 25 mK, thus presenting a matched thermal load.Comment: 4 pages, 4 figure

3-D Printed microwave and tetrahertz passive components

This thesis presents the design of microwave and terahertz filters, fabricated using different types of 3-D printing technology. The work demonstrates the potential of using 3-D printing in the fabrication of microwave and terahertz passive components. The first project introduces a compact coaxial cavity resonator filter which was fabricated using stereolithography 3 D printing process. The size and volume of this filter reduced by almost half, by fitting one resonator inside another resonator. This filter is ideal for fabrication by 3 D printing, as such a complex structure cannot be made easily by other methods. This project demonstrates the advantage of using 3-D printing in fabrication of components with complex structures. The second project introduces three waveguide bandpass filters operating at centre frequency of 90 GHz, which were fabricated using the micro laser sintering process. The filters were the highest frequency metal 3-D printed filters reported at the time of publication. The third project introduces two waveguide filters operating at centre frequency of 180 GHz, which were also fabricated using the micro laser sintering process. These are the world highest frequency waveguide filters fabricated by a metal 3-D printing process. The capability of reproducibility of the micro laser sintering process is also discussed in this thesis. The fourth project introduces a hybrid coaxial bandpass filter with two symmetrical transmission zeros, which was fabricated using stereolithography 3-D printing process. In this project the main-line couplings and input/ output coupling were realized using PCB lines, the idea of using PCB lines instead of coupling irises or probes is to allow different topologies to be designed easily by altering the PCB layout. Finally, the fifth project introduces a terahertz waveguide bandpass filter with embedded H plane waveguide bends. This filter is being fabricated using 3-D screen printing

Microwave Response of Coaxial Cavities Made of Bulk Magnesium Diboride

We report on the microwave properties of coaxial cavities built by using bulk MgB2 superconductor prepared by reactive liquid Mg infiltration technology. We have assembled a homogeneous cavity by using an outer MgB2 cylinder and an inner MgB2 rod and a hybrid cavity by using an outer copper cylinder and the same MgB2 rod as inner conductor. By the analysis of the resonance curves, in the different resonant modes, we have determined the microwave surface resistance Rs of the MgB2 materials as a function of the temperature and the frequency, in the absence of dc magnetic fields. At T=4.2 K and f ≈ 2.5 GHz, by an mw pulsed technique, we have determined the quality factor of the homogeneous cavity as a function of the input power up to a maximum level of about 40 dBm (corresponding to a maximum peak magnetic field of about 100 Oe). Contrary to what occurs in many films, Rs of the MgB2 material used does not exhibit visible variations up to an input power level of about 10 dBm and varies less than a factor of 2 on further increasing the input power of 30 dB

A Laboratory Test Setup for in Situ Measurements of the Dielectric Properties of Catalyst Powder Samples under Reaction Conditions by Microwave Cavity Perturbation : Set up and Initial Tests

The catalytic behavior of zeolite catalysts for the ammonia-based selective catalytic reduction (SCR) of nitrogen oxides (NOX) depends strongly on the type of zeolite material. An essential precondition for SCR is a previous ammonia gas adsorption that occurs on acidic sites of the zeolite. In order to understand and develop SCR active materials, it is crucial to know the amount of sorbed ammonia under reaction conditions. To support classical temperature-programmed desorption (TPD) experiments, a correlation of the dielectric properties with the catalytic properties and the ammonia sorption under reaction conditions appears promising. In this work, a laboratory test setup, which enables direct measurements of the dielectric properties of catalytic powder samples under a defined gas atmosphere and temperature by microwave cavity perturbation, has been developed. Based on previous investigations and computational simulations, a resonator cavity and a heating system were designed, installed and characterized. The resonator cavity is designed to operate in its TM010 mode at 1.2 GHz. The first measurement of the ammonia loading of an H-ZSM-5 zeolite confirmed the operating performance of the test setup at constant temperatures of up to 300 °C. It showed how both real and imaginary parts of the relative complex permittivity are strongly correlated with the mass of stored ammonia