Groove gap waveguide in metallized 3D-printed plastic and in mechanized aluminium in Ka band

This paper conducts a comparison between two different manufacturing technologies for a prototype in Groove Gap Waveguide. Both technologies are metallized 3D-printed plastic and mechanized aluminium. The prototype is a straight section with transitions to WR-28 that works in the frequency band from 28 to 30 GHz. The main properties of the technologies in terms of losses, weight and ease of manufacture are presented, as well as measurements for both prototypes together with simulations

Radial Line Slot Antenna Design with Groove Gap Waveguide Feed for Monopulse Radar Systems

Radial line slot arrays (RLSAs) are well suited to be used in monopulse radar systems. The excitation of the sum and difference patterns can be achieved by the design of simple feeds as shown in this paper. In this work, a feed system based on the use of a cavity made in groove gap waveguide technology (GGW) is presented. The design is made at 24 GHz but can be easily scaled to higher frequencies as the technology is contact-less and fully made in metal. A good isolation between the sum and difference ports together with a good matching of the two of them is obtained. The radiation patterns of the manufactured antenna are also in good agreement with the simulated ones.This work was supported in part by the Spanish Government, Ministry of Economy, National Program of Research, Development and Innovation under the projects TEC2016-79700-C2-2-R and TEC2017-85529-C3-1-R and by the Madrid Regional Government under the project SPADERADAR “Space Debris Radar” (S2013/ICE-3000) and the FPI grant with reference BES-2015-07523

Study of materials and manufacturing technologies for an antenna distribution network in Ka band

A study for selecting the technology and material manufacturing for the distribution network of a low profile antenna in Ka band in order to provide Internet connection in commercial aircrafts through satellite link. It is presented the general structure of the network focused in new printed technologies for high frequencies such as Substrate Integrated Waveguide or Ridge Gap Waveguide. Simulated results for different dielectric materials in terms of transmission losses are provided

Design proposal for ridge waveguide and comparison with other technologies in Ka to W bands

A design procedure of Ridge Gap Waveguide technology is proposed. The simulated results for Ka-band and above are compared with other technologies like Substrate Integrated Waveguide, microstrip or classical waveguide in terms of transmission losses

New antenna topologies for 5G communication systems

This paper presents new antenna topologies for 5G communication systems. The objective is the study of low losses distribution network technologies and the radiating elements for low profile antennas for 5G applications. Different technologies are considered as PCB technology, LTCC technology and metallized 3D printing in terms of design procedures, transmission losses and manufacturing processes in order to contribute to these types of technologies. Different designs and prototypes are done to validate these antennas for 5G communication system

Ka Band active array antenna for mobile satellite communications

This paper describes a modular active antenna for satellite communications in the K/Ka band. The application is thought for mobile satellite communications and internet links, mainly for commercial airplanes. The impossibility to build full active antennas, including amplifiers in all the elements, leads to a modular semi active antenna. Here the module is a small subarray with complete phase control in the elements. The phase control is made with ad-hoc phase shifters giving the minimum losses. Only two-bit control has been selected to perform phase shifters associated to a circular polarization radiating element. The feeding network has been selected to minimise the losses and the gap waveguide has been designed to perform the network. The radiating element is a circular double patch fed into two points to obtain circular polarization. The entire prototype has been designed in LTCC substrate to minimise the losses and stabilise the structure

Analytical Approach of Director Tilting in Nematic Liquid Crystals for Electronically Tunable Devices

This paper presents an analytical expression that models the tilt angle of directors in a nematic liquid crystal (LC), depending on its elastic properties, its dielectric anisotropy, and the quasi-static electric field applied. The analytical solution obtained is fast and easily computable in comparison with numerical estimations and is of special interest in radiofrequency; for instance, for the LC modeling in full-wave electromagnetic simulators in the design process of electronically tunable devices, such as microwave phase shifters or electronically steerable antennas for satellite communications. Subsequently, a comparison is made between numerical approaches (self-implemented shooting method) and the analytical formulas when varying the parameters of the LC, being demonstrated its usefulness. The average LC director is then obtained and used to form the full permittivity tensor that completely characterizes the electrical properties of the material. Finally, an electromagnetic simulation is carried out to show the capabilities of the LC as a tunable phase shifter. It is shown that only 5 cm of a commercial 200-mm LC mixture is necessary to achieve 360 of the maximum variable phase shift at the 30-GHz bandThis work was supported in part by the Spanish Research and Development National Program under Project TIN2016-75097-P, and in part by the Ministerio de Economía under Project TEC2017-85529-C3-1-R

Advances in Periodic Structures and Manufacturing Technologies for mm-Wave Antennas

The arrival of 5G services demands the use of an increasing bandwidth, which leads to better use of the electromagnetic spectrum. 5G mass deployment requires solutions for working in upper frequency bands with low cost manufacturing. Printed substrate technologies, as stripline or microstrip, exhibit high transmission losses at high frequencies due to the presence of dielectric. At high frequencies, printed technologies have been replaced by waveguide. This technology is based on the propagation of electromagnetic waves in a hollow metallic cavity, which supposes very low transmission losses. However, materials and manufacturing mechanisms are expensive and the resulting structures are heavy and bulky. This makes waveguides incompatible with the development and mass production of small and low-cost technology. In recent years, various technologies have been emerged, such as gap waveguide (GW), higher symmetries (HS) or additive manufacturing (AM), that present a solution for new millimetre-wave devices. These new technologies are becoming globally important because they offer good performance in terms of low weight, low profile and low losses, and a low-cost fabrication on a massive scale compared to other PCB technologies or classical waveguides. Gap waveguide technology is based on fully metal pieces with several rows of periodic pins that prevent leakage in a certain frequency band when a metal plate is placed above them a distance below a quarter wavelength. A groove or a ridge can be inserted between those pins to propagate fields in the same way that classic waveguides, with the advantage that GW do not need good electrical contact between plates. Higher symmetries consist of periodical structures with symmetry operations such as screw symmetry (a periodical rotation), or glide symmetry (a mirroring and displacement). Especially this last type of symmetry is of great interest because it can provide EGB (Electromagnetic Bandgap) properties or increase the refractive index in a multitude of different transmission lines. The fabrication of the resulting structures in a complex design based on GW or HS can be costly using traditional CNC machining methods. In millimetre-wave bands, GW pins tend to be small and with a reduced separation between them, which increases the price. For that reason, it is interesting to consider additive manufacturing or 3D-printing for this type of structures, given that the time and cost of manufacturing do not depend on the complexity of the part, but on its size. The increasing introduction of new materials with anisotropic properties that can be modified by applying a voltage has also been documented. Among these materials, liquid crystals (LC) stand out, which were studied in optical applications. LC can have a great importance in the creation of new electrically reconfigurable antennas or RF devices. The objective of this thesis is to study in depth these novel technologies and materials and apply them in real prototypes of antennas and RF devices in millimetre-wave bands. Specifically, in chapter I a detailed introduction of each of the technologies used during the development of the thesis is carried out. In Chapter II, a comparison between available technologies such as rectangular waveguide, substrate integrated waveguide, microstrip and gap waveguide technologies is carried out in terms of transmission losses between 10 GHz to 100 GHz. Chapter III shows a study of the properties of 3D printing and the effect of metallization of the resulting plastic parts at Ka-band. Different prototypes implemented in GW were designed, manufactured and experimentally validated. Chapter IV focuses on a more complex GW design for a Radial Line Slot Array (RLSA) antenna fed with a 3D-printed Butler matrix for a monopulse radar at 94 GHz. 3D printing technology, together with a liquid crystal mixture developed specifically for microwave frequencies, were used for the design and manufacturing of an electrically tunable phase shifter in chapter V. Chapter VI contains the validation of several prototypes based on higher symmetries that seek to enhance different aspects: stop-band and refractive index modifications and attenuation and phase shift mechanical reconfigurability. These higher symmetries are also applied in Chapter VII for enhanced gap waveguide EGB or increase of the beam steering variation with frequency in leaky-wave antennas for automotive applications. Finally, conclusion and future work are drawn in Chapter VIII. ----------RESUMEN---------- La llegada de los servicios 5G exige el uso de un ancho de banda cada vez mayor, lo que conduce a un mejor uso del espectro electromagnético. El despliegue masivo de 5G requiere soluciones para trabajar en bandas de frecuencias altas con un bajo coste de fabricación. Las tecnologías de sustratos impresos, como stripline o microstrip, presentan altas pérdidas de transmisión a altas frecuencias debido a la presencia de dieléctricos. A altas frecuencias, las tecnologías impresas han sido reemplazadas por guías de onda. Esta tecnología se basa en la propagación de ondas electromagnéticas en una cavidad metálica hueca lo que supone unas pérdidas de transmisión muy bajas. Sin embargo, los materiales y los métodos de fabricación son caros y las estructuras resultantes son pesadas y voluminosas. Esto hace que las guías de onda sean incompatibles con el desarrollo y la producción en masa de tecnología de pequeño tamaño y bajo coste. En los últimos años han surgido diversas tecnologías, como gap waveguide (GW), simetrías superiores (HS) o la fabricación aditiva (AM), que presentan una solución para nuevos dispositivos de ondas milimétricas. Estas nuevas tecnologías están adquiriendo importancia mundial porque ofrecen un buen rendimiento en términos de bajo peso, bajo perfil y bajas pérdidas, y un bajo coste de fabricación a gran escala en comparación con otras tecnologías de circuitos impresos o guías de onda clásicas. La tecnología gap waveguide se basa en piezas totalmente metálicas con varias filas de pines periódicos que evitan las fugas en una banda de frecuencia determinada cuando se coloca una placa de metal por encima de ellos a una distancia inferior a un cuarto de longitud de onda. Se puede insertar una ranura (groove) o una cresta (ridge) entre esos pines para propagar los campos de forma similar a las guías de onda clásicas, con la ventaja de que GW no necesita un buen contacto eléctrico entre las placas. Las simetrías superiores consisten en estructuras periódicas con operaciones de simetría tales como simetría de tornillo (una rotación periódica), o simetría de deslizamiento (un reflejo y desplazamiento). Especialmente este último tipo de simetría es de gran interés debido a puede proporcionar propiedades EGB (Electromagnetic Bandgap), o aumentar el índice de refracción en una multitud de líneas de transmisión diferentes de forma sencilla. La fabricación de las estructuras resultantes en un diseño complejo basado en GW o HS puede ser costosa utilizando métodos tradicionales de mecanizado CNC. En las bandas de ondas milimétricas, los pines GW tienden a ser pequeños y con una separación reducida entre ellos, lo que aumenta el precio. Por ello, es interesante considerar la fabricación aditiva o impresión 3D para este tipo de estructuras, ya que el tiempo y el coste de fabricación no dependen de la complejidad de la pieza, sino de su tamaño. También se ha documentado la creciente introducción de nuevos materiales con propiedades anisotrópicas que pueden modificarse aplicando una tensión. Entre estos materiales destacan los cristales líquidos (LC), que fueron estudiados en profundidad en aplicaciones ópticas. Los cristales líquidos pueden tener una gran importancia en la creación de nuevas antenas o dispositivos de RF reconfigurables eléctricamente. El objetivo de esta tesis es estudiar en profundidad estas nuevas tecnologías y materiales y aplicarlos en prototipos reales de antenas y dispositivos de RF en bandas de ondas milimétricas. Concretamente, en el capítulo I se realiza una introducción detallada de cada una de las tecnologías utilizadas durante el desarrollo de la tesis. En el capítulo II se efectúa una comparación entre las tecnologías disponibles, como la guía de ondas rectangular, la guía de ondas integrada en el sustrato, la microstrip y la guía de ondas gap waveguide, en lo que respecta a las pérdidas de transmisión entre 10 GHz y 100 GHz. El capítulo III muestra un estudio de las propiedades de la impresión en 3D y el efecto de la metalización de las piezas de plástico resultantes en la banda Ka. Se diseñaron, fabricaron y validaron experimentalmente diferentes prototipos implementados en GW. El capítulo IV se centra en un diseño basado en GW más complejo para una antena RLSA (Radial Line Slot Array) alimentada con una matriz de Butler impresa en 3D para un radar monopulso a 94 GHz. La impresión 3D, junto con un cristal líquido desarrollado específicamente para microondas, son empleados para el diseño y la fabricación de un desfasador eléctricamente sintonizable en el capítulo V. El capítulo VI contiene la validación de varios prototipos basados en simetrías superiores que buscan mejorar diferentes aspectos: modificaciones de la stop-band y del índice de refracción y reconfigurabilidad mecánica de atenuación y desfase. Estas simetrías superiores también se aplican en el capítulo VII para EBG mejorado en gap waveguide, o aumento de la variación de la dirección del haz con la frecuencia en antenas leaky-wave para aplicaciones de automoción. Finalmente, las conclusiones y trabajo futuro se describen en el capítulo VIII

Low losses printed distribution network technologies for planar antennas in Ka band

Study of Substrate Integrated Waveguide and Gap Waveguide technologies used to manufacture some demonstration prototypes at Ka band for a low losses distribution network in a low profile antenna. A transmission losses comparison is presented using lossy and lossless dielectric substrates in the simulations for the different technologies at 30 GHz. Various structures such as transitions from WR-28, bends, and power dividers have been designed and simulated. The simulations of different models are compared with the manufactured prototypes in metallized 3D-printed plastic technology and in RO4350B and FR-4 substrates for a band from 28 to 30 GHz