Polymer-Based Micromachining for Scalable and Cost-Effective Fabrication of Gap Waveguide Devices Beyond 100 GHz

The terahertz (THz) frequency bands have gained attention over the past few years due to the growing number of applications in fields like communication, healthcare, imaging, and spectroscopy. Above 100 GHz transmission line losses become dominating, and waveguides are typically used for transmission. As the operating frequency approaches higher frequencies, the dimensions of the waveguide-based components continue to decrease. This makes the traditional machine-based (computer numerical control, CNC) fabrication method increasingly challenging in terms of time, cost, and volume production. Micromachining has the potential of addressing the manufacturing issues of THz waveguide components. However, the current microfabrication techniques either suffer from technological immaturity, are time-consuming, or lack sufficient cost-efficiency. A straightforward, fast, and low-cost fabrication method that can offer batch fabrication of waveguide components operating at THz frequency range is needed to address the requirements.A gap waveguide is a planar waveguide technology which does not suffer from the dielectric loss of planar waveguides, and which does not require any electrical connections between the metal walls. It therefore offers competitive loss performance together with providing several benefits in terms of assembly and integration of active components. This thesis demonstrates the realization of gap waveguide components operating above 100 GHz, in a low-cost and time-efficient way employing the development of new polymer-based fabrication methods.A template-based injection molding process has been designed to realize a high gain antenna operating at D band (110 - 170 GHz). The injection molding of OSTEMER is an uncomplicated and fast device fabrication method. In the proposed method, the time-consuming and complicated parts need to be fabricated only once and can later be reused.A dry film photoresist-based method is also presented for the fabrication of waveguide components operating above 100 GHz. Dry film photoresist offers rapid fabrication of waveguide components without using complex and advanced machinery. For the integration of active circuits and passive waveguides section a straightforward solution has been demonstrated. By utilizing dry film photoresist, a periodic metal pin array has been fabricated and incorporated in a waveguide to microstrip transition that can be an effective and low-cost way of integrating MMIC of arbitrary size to waveguide blocks

An Overview of Recent Development of the Gap-Waveguide Technology for mmWave and Sub-THz Applications

The millimeter-wave (mmWave) and sub-terahertz (sub-THz) bands have received much attention in recent years for wireless communication and high-resolution imaging radar applications. The objective of this paper is to provide an overview of recent developments in the design and technical implementation of GW-based antenna systems and components. This paper begins by comparing the GW-transmission line to other widely used transmission lines for the mmWave and sub-THz bands. Furthermore, the basic operating principle and possible implementation technique of the GW-technology are briefly discussed. In addition, various antennas and passive components have been developed based on the GW-technology. Despite its advantages in controlling electromagnetic wave propagation, it is also widely used for the packaging of electronic components such as transceivers and power amplifiers. This article also provided an overview of the current manufacturing technologies that are commonly used for the fabrication of GW-components. Finally, the practical applications and industry interest in GW technology developments for mmWave and sub-THz applications have been scrutinized.Funding Agencies|European Union - Marie Sklodowska-Curie [766231WAVECOMBEH2020-MSCA-ITN-2017]</p

Low-Dispersive Leaky-Wave Antenna Integrated in Groove Gap Waveguide Technology

In this paper, the use of a dispersive prism with a triangular shape is proposed to reduce the dispersive radiation nature of a leaky-wave antenna (LWA) in groove-gap waveguide technology. The operation of gap waveguide technology is based on the use of metallic pins that act as an artificial magnetic conductor, so the electromagnetic fields are confined and guided in the desired directions. To control a leaky-wave radiation of these confined fields is possible by tailoring the height of the pins, its periodicity, and the waveguide width. This radiation, as in any conventional LWA, is dispersive, leading to beam squint as the frequency is varied. Here, we mitigate this beam squint by using a prism made of dispersive pins and choosing appropriately their periodicity and height. With this prism, the leaky-wave radiation is focused into one single direction in a wide frequency band. This concept is demonstrated with a prototype designed to radiate at phi = 41 degrees with a central frequency of 12 GHz and the high gain of 16.5 dBi. A 22% frequency bandwidth for the 3 dB realized gain at phi = 41 degrees is achieved, and the main radiating direction, with half-power beamwidth of 5 degrees, steers only +/- 0.5 degrees from 11.4 to 13.4 GHz.This work was supported in part by the Alexander von Humboldt Foundation, in part by the Spanish Government under Project TEC2016-79700-C2-2-R, and in part by the Madrid Regional Government under Project S2013/ICE-3000

Enhancement of Millimeter-Band Transceivers with Gap Waveguide Technology

Mención Internacional en el título de doctorIt is known to all that year after year in modern society there is an urgent demand to consume wirelessly, and even stream ever larger multimedia content. High-frequency technologies have made it possible to go from transmitting analog voice and SMS text messages, to now transmitting live video in 4K quality from a mid-range smartphone. The way to measure these advances is by the bandwidth (Mb/s) reserved for each network user and the cost required to achieve it. To achieve even higher bandwidths, it is essential to improve signal coding techniques or increase the frequency of the signal, for example: to the mmWave bands (25GHz - 100 GHz), where these high-frequency techniques come into play. However, there is a frequency limit where current planar technology materials - such as the printed circuit boards used to build RF devices - are so lossy that they are not suitable at these mmWave frequencies. Current commercial solutions consist of guiding the electromagnetic energy with hollow metallic waveguides, but they suffer from the problem that as the frequency increases the diameter of these waveguides gets smaller and smaller, so manufacturing tolerances increase exorbitantly. Not to mention that they are usually manufactured in two parts, one upper and one lower, whose joints are not always perfect and produce energy losses. With these issues in mind, in 2009 the theory and basic science of a new electromagnetic energy guidance technology called Gap Waveguide was proposed, which is based on the use of metasurfaces constructed with periodic elements similar to a bed of nails. There are several implementations of this technology, but the three main ones are: Ridge, Groove and Inverted Microstrip Gap Waveguide. The latter is the most compatible with conventional planar manufacturing technologies and therefore the most cost-effective, although it also has drawbacks mainly in terms of losses when compared to the other versions. This thesis aims to deepen the study of the Inverted Microstrip guidance technology, its limitations and to develop with it some of the needed components in RF systems such as filters, diplexers, amplifiers, antennas, etc. Regarding the methodology for this thesis, a commercial simulation software for the analysis of antennas and components, CST Microwave Studio [1], has been used. AWR Microwave Office [2], a circuit simulator, has also been used to complement the simulations. On the other hand, there is a laboratory for the manufacture of prototypes in printed technology (with some limitations in terms of resolution) and the corresponding measurement laboratory, which includes network analyzers up to 40 GHz, spectrum analyzers and an anechoic chamber.This thesis arose under the Spanish Ministry of Science and Innovation (MINECO) and European Regional Development Fund (ERDF) project, called "Antenna for Mobile Satellite Communications (SATCOM) in Ka-Band by means of metasurfaces (2016-2019)", with reference TEC2016-79700-C2-2-R. Under this contract, the author signed an FPI research contract.Programa de Doctorado en Multimedia y Comunicaciones por la Universidad Carlos III de Madrid y la Universidad Rey Juan CarlosPresidente: Íñigo Cuiñas Gómez.- Secretario: Ángela María Coves Soler.- Vocal: Astrid Algaba Brazále

High gain V-band planar array antenna using half-height pin gap waveguide

With growing demand for mm-Wave applications, gap waveguide technology introduced many advantageous features compared to hollow waveguides or SIW. Till now several wideband, high-efficiency and highly directive planar gap waveguide antennas have been proposed. Recently, a new form of pins, the so called half-height pin, is proposed for realizing gap waveguide technology. In this paper, a wide-band, high gain, and high efficiency 8 78-element slot array antenna for 60 GHz band based on the new form of pins is introduced. The simulation shows a very good performance of the antenna, with 14% bandwidth of the 10 dB return loss, 26 dBi realized gain and close to 80% aperture efficiency. The antenna has less difficulty in manufacturing because of new pin form and therefore is suitable for the low cost mass production of mm-Wave antennas

Analytical Design Procedures for the Odd Mode of Ridge Gap Waveguide Devices and Antennas

The millimeter-wave (mm-wave) band has attracted attention due to its wideband characteristics that make it able to support multi-gigabit per second data rate. Nevertheless, the performance of mm-wave wireless communication systems is restricted due to attenuation loss. Design of mm-wave components and antennas is rapidly growing with the current evolution in the wireless communication systems. However, the traditional waveguide structures such as microstrip, coplanar, substrate integrated waveguide, and rectangular waveguide either suffer from high losses or difficulty in manufacturing at mm-wave band. The ridge gap waveguide (RGW) technology is considered as a promising waveguide technology for the mm-wave band. RGW technology overcomes the conventional guiding structure problems as the wave propagates in an air gap region which eliminates the dielectric loss. Moreover, RGW does not need any electrical contacts, unlike traditional rectangular waveguides. Also, the RGW can be implemented in the printed form (PRGW) for easy integration with other planer system components. In this thesis, the use of the odd mode (TE10 (RGW)) RGW to design mm-wave components and antennas is presented. First, a systematic design methodology for the RGW using hybrid PEC/PMC waveguide approximation is presented. This reduces the design time using full wave simulators. The concept has been verified by simulation and experimental measurements. Second, two different methods to excite the odd mode in RGW are studied and investigated. In the first method, a planar L-shape RGW is used where less than -10 dB reflection coefficient is achieved, from 28 to 36 GHz, and more than 93% of the input power has been converted into the odd mode at the output port. The second method uses a magic tee with a shorted sum port and provides a wideband pure odd mode at the output port with reflection coefficient less than -10 dB from 28 GHz to 39 GHz. Other mm-wave components based on odd mode TE10 RGW are designed and presented including a Y-junction power divider and 3 dB forward coupler are designed for the first time in RGW technology. The Y-junction has a wideband matching from 28 to 34 GHz with a reflection coefficient less than -15 dB and the transmission output levels are about -3.3 dB. The usefulness of the odd mode RGW lies in the ability to increase the channel bandwidth that has been achieved by designing a dual-mode RGW. A magic tee is used to simultaneously excite the fundamental mode Q-TEM and the odd mode TE10 (RGW) on the ridgeline. The proposed dual-mode RGW performance is verified through simulation and measurement of a back-to-back configuration. The proposed design achieves a matching level less than -10 dB for the two modes over the frequency range from 29 GHz to 34.5 GHz with isolation better than 23 dB. The dual-mode RGW is then used to feed a reconfigurable Vivaldi horn antenna where two different radiation patterns can be obtained depending on the excited mode. The Q-TEM generates a single beam pattern, while the odd mode TE10 (RGW) generates a dual-beam pattern. The maximum gain for the single beam radiation is 12.1 dBi, while it is 10.43 dBi for the dual-beam pattern. The bandwidth of the dual-mode antenna is 25% at 32 GHz with impedance matching less than -10 dB and isolation better than 20 dB. Finally, several antennas are presented in this thesis based on the odd mode RGW. A novel differential feeding cavity antenna using the odd mode of RGW is presented. The measured results show good performance in terms of gain, bandwidth, sidelobe level, and cross-polarization. The maximum gain is 16.5 dBi, and the sidelobe level is -17 dB and -13.8 dB, for the E-plane and H-plane, respectively. Moreover, the proposed antenna has low cross-polarization levels of -35 dB in the E-plane and -27 dB in the H-plane. In addition, two 2x1 linear frequency scanning array antennas are designed and implemented using the proposed Y-junction to generate single beam and dual-beam patterns. The beam scan is from -11(degree) to -40(degree) at 28 GHz and 32 GHz, respectively

Compact RF Integration and Packaging Solutions Based on Metasurfaces for Millimeter-Wave Applications

The millimeter-wave frequency range has got a lot of attention over the past few years because it contains unused frequency spectrum resources that are suitable for delivering Gbit/s end-user access in areas with high user density. Due to the limited output power that the current RF active components can deliver in millimeter-wave frequencies, antennas with the features of low profile, high gain, high efficiency and low cost are needed to compensate free space path loss and increase the communication distance for the emerging high data rate wireless systems. Moreover, it is desired to have a compact system by integration of the antenna with passive and active components at high frequencies.In order to move towards millimeter-wave frequencies we need to face significant hardware challenges, such as active and passive components integration, packaging problems, and cost-effective manufacturing techniques. The gap waveguide technology shows interesting characteristics as a new waveguide structure. The main goal of this thesis is to demonstrate the advantages of gap waveguide technology as an alternative to the traditional guiding structures to overcome the problem of good electrical contact due to mechanical assembly with low loss. This thesis mainly focuses on high-gain planar array antenna design, integration with passive and active components, and packaging based on gap waveguide technology. \ua0We introduce several low-profile multilayer corporate-fed slot array antennas with high gain, high efficiency and wide impedance bandwidth operating at the millimeter-wave frequency band. A system demonstration consisting of two compact integrated antenna-diplexer and Tx/Rx MMICs for Frequency-division duplex (FDD) low latency wireless backhaul links at E-band is presented to show the advantages of gap waveguide technology in building a complete radio front-end. Moreover, the use of several new manufacturing methods, such as die-sink Electric Discharge Machining (EDM), direct metal 3-D printing, and micro-molding are evaluated to fabricate gap waveguide components in a more effective way.Furthermore, a novel air-filled transmission line, so-called multi-layer waveguide (MLW), that exhibits great advantages such as low-cost, simple fabrication, and low loss, even for frequencies beyond 100 GHz, is presented for the first time. To constitute an MLW structure, a rectangular waveguide transmission line is formed by stacking several thin metal layers without any electrical and galvanic contact requirement among the layers. The proposed concept could become a suitable approach to design millimeter-wave high-performance passive waveguide components, and to be used in active and passive components integration ensuring mass production at the same time

Rotated Half-Mode Substrate Integrated Waveguide and other Planar Integrated Structures

High data rate communication channels are becoming more and more integrated into our increasingly technological society. Substrate Integrated Waveguides (SIW) are one planar solution available to the microwave engineer, offering a low-loss and low dispersion means of propagating these high speed, high bandwidth signals. In this thesis, a brief synopsis of SIW structures and components is presented covering the basic waveguide propagating modes and cut-off frequencies. The main analysis techniques associated with SIWs including full wave electromagnetic modelling methods are overviewed, and the associated loss mechanisms of conduction, dielectric and radiation defined, leading to the design rules and guidelines on how best to mitigate them. SIW antennas as both leaky-wave and radiating slots are discussed and an example of a single and dual resonating slot antenna design is presented, along with a detailed review of a novel switch beam antenna developed for use within the current WiFi bands. The Slot SIW (or SSIW), which has a small longitudinal gap in one of the main conducting surfaces, allows easy integration of lumped elements or active devices, enabling the waveguide to be loaded with impedances or to be shorted. When the slot is shorted, the waveguide reverts back to the full SIW mode, and when partially loaded an intermediate state results. This is discussed, and the SSIW analysed with the transverse resonance technique, leading to the development of a travelling wave attenuator with the SSIW being periodically loaded with pin diodes. The application of the pin diodes required the use of a capacitive overlay, a development of flexi circuit design to allow capacitive coupling of impedances to connect to the waveguide. The overlay concept is extended further, to form novel passive bandpass filters, with the introduction of virtual vias. A limitation of the SSIW is that the majority of the field resides within the dielectric; this allows only a limited interaction with the field at the slot. The rotated Half Mode SIW (rHMSIW), a new variant of the SIW family, places the maximum of the electric field directly on the top dielectric surface, allowing for direct interaction. The waveguide width a is now defined by the dielectric thickness, allowing for the waveguide height b to be adjustable, in normal SIWs this is the other way round; the dielectric thickness fixing the waveguide height and the waveguide width being adjustable. The rHMSIW is characterised with regard to the height and width ratios b/a and the dielectric exposed width (which is adjustable). These parameters effect the modal cut-off frequency, this is investigated and a new equation describing the fundamental mode cut-off frequency is empirically derived. Finally a test coupon which spans the Ku band is designed and measured, which required the development of a novel waveguide transition

New solutions for directive antennas and components for millimeter wave-band applications

Mención Internacional en el título de doctorEn las últimas décadas se ha producido un avance tecnológico exponencial en el área de las telecomunicaciones. Cada pocos años surgen sistemas de comunicaciones de nueva generación, siendo el 5G el que, hoy en día, se va implementando y ofreciendo progresivamente a los usuarios de todo el mundo. Los sistemas de comunicaciones 5G permiten tasas de datos mucho más altas, una velocidad ultrarrápida y un mayor ancho de banda que el 4G no soportaba debido a las bandas excesivamente utilizadas por debajo de los 6 GHz. Sin embargo, este aumento de la frecuencia introduce retos que no existen en frecuencias inferiores, como la absorción ambiental. Además, los obstáculos físicos que se interponen en el trayecto entre el emisor y el receptor también son un problema a estas frecuencias y las pérdidas inherentes a la propagación en el espacio libre son muy elevadas. El objetivo de esta tesis ha sido desarrollar e introducir nuevos e innovadores diseños de antenas que puedan ser utilizados en las bandas de frecuencia de las comunicaciones 5G y superiores así como en otras aplicaciones de ondas milimétricas. Los diseños que se presentan tienen como principal objetivo conseguir una alta directividad, manteniendo bajas pérdidas. Estos diseños se pueden agrupar en dos categorías principales: antenas Fabry-Pérot, y antenas gap waveguide. En la primera parte de esta tesis se han desarrollado tres diseños de antena Fabry-Pérot, incluyendo una metodología innovadora para el diseño de una metasuperficie que permite un funcionamiento en doble banda con control de directividad y que también puede ser utilizada también para implementar arrays de antenas en bandas de ondas milimétricas. Además, se muestra que este concepto de antenas Fabry-Pérot, implementado en un rango de frecuencias mucho más bajas, puede utilizarse también en aplicaciones de sistemas radar. En la segunda parte, se han desarrollado e implementado diseños innovadores de antenas y arrays usando la tecnología gap waveguide en particular su versión groove. En ellos, se han diseñado novedosas redes de alimentación y sistemas de corrección de fase que proporcionan bajas pérdidas y alta eficiencia.Programa de Doctorado en Multimedia y Comunicaciones por la Universidad Carlos III de Madrid y la Universidad Rey Juan CarlosPresidente: José Luis Masa Campos.- Secretario: Óscar Quevedo Teruel.- Vocal: Guido Valeri