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

Ultra-Wideband Phased Arrays for Small Mobile Platforms

This dissertation presents the development of a new class of Ultra-Wideband (UWB) apertures for aerial applications by introducing designs with over 50:1 bandwidth and novel differential feeding approaches. Designs that enable vertical integration for flip-chip millimeter-wave (UWB) transceivers are presented for small aerial platforms. Specifically, a new scalable tightly coupled array is introduced with differential feeding for chip integration. This new class of beam-forming arrays are fabricated and experimentally tested for validation with operation from as low as 130 MHz up to 18 GHz. A major achievement is the study of millimeter wave beamforming designs that operate from 22-80 GHz, fabricated using low-cost printed circuit board (PCB) methods. This low-cost fabrication approach and associated testing of the beamforming arrays are unique and game-changing

Nanodevices for Microwave and Millimeter Wave Applications

The microwave and millimeter wave frequency range is nowadays widely exploited in a large variety of fields including (wireless) communications, security, radar, spectroscopy, but also astronomy and biomedical, to name a few. This Special Issue focuses on the interaction between the nanoscale dimensions and centimeter to millimeter wavelengths. This interaction has been proven to be efficient for the design and fabrication of devices showing enhanced performance. Novel contributions are welcome in the field of devices based on nanoscaled geometries and materials. Applications cover, but not are limited to, electronics, sensors, signal processing, imaging and metrology, all exploiting nanoscale/nanotechnology at microwave and millimeter waves. Contributions can take the form of short communications, regular or review papers

Planar Silicon Metamaterial Lenslet Arrays for Millimeter-wavelength Imaging

Large imaging arrays of detectors at millimeter and submillimeter wavelengths have applications that include measurements of the faint polarization signal in the Cosmic Microwave Background (CMB), and submillimeter astrophysics. We are developing planar lenslet arrays for millimeter-wavelength imaging using metamaterials microlithically fabricated using silicon wafers. This metamaterial technology has many potential advantages compared to conventional hemispherical lenslet arrays, including high precision and homogeneity, planar integrated anti-reflection layers, and a coefficient of thermal expansion matched to the silicon detector wafer. Here we describe the design process for a gradient-index (GRIN) metamaterial lenslet using metal-mesh patterned on silicon and a combination of metal-mesh and etched-hole metamaterial anti-reflection layers. We optimize the design using a bulk-material model to rapidly simulate and iterate on the lenslet design. We fabricated prototype GRIN metamaterial lenslet array and mounted it on a Polarbear/Simons Array 90/150~GHz band transition edge sensor (TES) bolometer detector array with sinuous planar antennas. Beam measurements of a prototype lenslet array agree reasonably well with the model simulations. We plan to further optimize the design and combine it with a broadband anti-reflection coating to achieve operation over 70--350~GHz bandwidth.Comment: Presented at SPIE Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy X, December 13-18, 202

On-Chip-antenna for millimeterwave technology

Dissertação para obtenção do Grau de Mestre em Engenharia Eletrónica e de TelecomunicaçõesRecentemente, as antenas em chip, para as tecnologias de ondas milimétricas e terahertz, têm sido um dos tópicos mais pesquisados na comunidade de antenas. A possibilidade de integração da antena com circuitos integrados num único chip e as potenciais taxas de dados elevadas (proporcionadas pelas altas frequências utilizadas) são duas das principais razões de interesse neste tipo de tecnologia. No entanto, existem alguns desafios associados com a combinação de antenas e circuitos integrados como os materiais utilizados que são benéficos para os circuitos integrados mas que prejudicam a performance da antenas. Neste trabalho, dois tipos de antenas são estudados como potenciais candidatos para integração, o complementar do dipolo dobrado e a antena impressa retangular. O complementar do dipolo dobrado foi dimensionada num substrato de fosfato de índio e mostrou ser uma possível solução atingindo uma largura de banda de 314 MHz, ganho máximo de 8.5 dBi, largura de feixe a meia potência de 25.3º e 46.8º nos dois planos principais e uma eficiência de 51%. A antena impressa retangular também dimensionada num substrate de fosfato de índio atingiu uma largura de banda de 1.38 GHz, com um ganho máximo de 5.45 dBi, uma largura de feixe a meia potência de 123.9º e 92.1º nos dois planos principais e uma eficiência de 95.5%. As simulações começaram com o substrato de fosfato de índio, no entanto, como o calendário de fabrico deste substrato está fora do calendário de entrega da dissertação o estudo continuo com o substrato de silício. A antena impressa no substrato de silício atingiu uma largura de banda de 2.18 GHz, ganho máximo de 5.28 dBi. uma largura de feixe a meia potência de 124.1º e 107.9º nos dois planos principais e uma eficiência de 89%. De forma a melhor a diretividade da antena, um agregado 2x2 foi dimensionado assim com a sua rede de alimentação que consiste em linhas impressas com uma transição para guia de onda coplanar. No fim, o agregado ocupou uma área de 5x6 mm2, apresentou uma largura de banda de 5.78 GHz, um ganho de 8.5 dBi com 42.7º e 42.6º largura de feixe a meia potência nos planos principais, e uma eficiência de 85.5%, melhorando o desempenho em termos de ganho e diretividade em comparação com um único elemento. Por fim, quatro agregados 2x2 foram construídos e o seu coeficiente de refleção foi medido recorrendo à utilização de uma probe station e um VNA, onde se verificou um comportamento semelhante ao simulado.Recently, On-Chip-Antennas, for both millimeter wave and terahertz technologies, have been one of the most researched topics in the antenna community. The possibility of integrating the antenna with the remaining circuitry in a single chip and possible large data rates (provided by the high frequencies used) are two of the main reasons for interest in this type of technology. However, there are some challenges associated with combining antennas and integrated circuits such as the materials used which are beneficial for integrated circuits but bad for On-Chip-Antennas design. In this work, two types of antennas were studied, the folded slot antenna and the microstrip patch antenna as potential options for antenna integration. The folded slot antenna on an indium phosphide substrate showed to be a possible solution achieving a bandwidth of 314 MHz, with a maximum gain of 8.5 dBi, half-power beamwidths of 25.3º and 46.8º in the two principal planes, and an efficiency of 51%. The microstrip patch antenna was designed as well on the indium phosphide substrate and achieved a bandwidth of 1.39 GHz with a maximum gain of 5.45 dBi, half power beamwidth of 123.9º and 92.1º in the two principal planes, and an efficiency of 95.5%. The simulations started with an indium phosphide substrate, however, the indium phosphide substrate manufacture calendar is out of the scope of this dissertation calendar,so, the study continued with the silicon substrate. The microstrip patch antenna on silicon substrate achieved a 2.18 GHz bandwidth, 5.28 dBi maximum gain, a half power beamwidth of 124.1º and 107.9º in the two principal planes, and an efficiency of 89%. To achieve a more directive radiation pattern, a 2x2 microstrip array was designed. A feeding network was studied and designed consisting of a microstrip line and a microstrip to coplanar waveguide transition. The array, occupying an area of 5x6 mm2 presented a bandwidth of 5.78 GHz, a gain of 8.5 dBi with 42.7º and 42.6º half power beamwidth on the principal planes, and an efficiency of 85.5% improving the performance in terms of gain and directivity compared with a single element. In the end, four 2x2 microstrip arrays were built and their input match was measured using a probe station and a VNA where it was observed similar behavior to the simulations.N/

Terahertz Communications and Sensing for 6G and Beyond: A Comprehensive View

The next-generation wireless technologies, commonly referred to as the sixth generation (6G), are envisioned to support extreme communications capacity and in particular disruption in the network sensing capabilities. The terahertz (THz) band is one potential enabler for those due to the enormous unused frequency bands and the high spatial resolution enabled by both short wavelengths and bandwidths. Different from earlier surveys, this paper presents a comprehensive treatment and technology survey on THz communications and sensing in terms of the advantages, applications, propagation characterization, channel modeling, measurement campaigns, antennas, transceiver devices, beamforming, networking, the integration of communications and sensing, and experimental testbeds. Starting from the motivation and use cases, we survey the development and historical perspective of THz communications and sensing with the anticipated 6G requirements. We explore the radio propagation, channel modeling, and measurements for THz band. The transceiver requirements, architectures, technological challenges, and approaches together with means to compensate for the high propagation losses by appropriate antenna and beamforming solutions. We survey also several system technologies required by or beneficial for THz systems. The synergistic design of sensing and communications is explored with depth. Practical trials, demonstrations, and experiments are also summarized. The paper gives a holistic view of the current state of the art and highlights the issues and challenges that are open for further research towards 6G.Comment: 55 pages, 10 figures, 8 tables, submitted to IEEE Communications Surveys & Tutorial

Statistical Review Evaluation of 5G Antenna Design Models from a Pragmatic Perspective under Multi-Domain Application Scenarios

Antenna design for the 5G spectrum requires analysis of contextual frequency bands, design of miniaturization techniques, gain improvement models, polarization techniques, standard radiation pattern designs, metamaterial integration, and substrate selection. Most of these models also vary in terms of qualitative & and quantitative parameters, which include forward gain levels, reverse gain, frequency response, substrate types, antenna shape, feeding levels, etc. Due to such a wide variety in performance, it is ambiguous for researchers to identify the optimum models for their application-specific use cases. This ambiguity results in validating these models on multiple simulation tools, which increases design delays and the cost of deployments. To reduce this ambiguity, a survey of recently proposed antenna design models is discussed in this text. This discussion recommended that polarization optimization and gain maximization are the major impact factors that must be considered while designing antennas. It is also recommended that collocated microstrip slot antennas, fully planar dual-polarized broadband antennas, and real-time deployments of combined slot antenna pairs with wide-band decoupling are very advantageous. Based on this discussion, researchers will be able to identify optimal performance-specific models for different applications. This discussion also compares underlying models in terms of their quantitative parameters, which include forward gain levels, bandwidth, complexity of deployment, scalability, and cost metrics. Upon referring to this comparison, researchers will be able to identify the optimum models for their performance-specific use cases. This review also formulates a novel Antenna Design Rank Metric (ADRM) that combines the evaluated parameters, thereby allowing readers to identify antenna design models that are optimized for multiple parameters and can be used for large-scale 5G communication scenarios

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

Design and characterization of terahertz CORPS beam forming networks

This work reviews the design and applicability of beam-forming networks based on Coherently Radiating Periodic Structures (CORPS-BFN) at Terahertz (THz) frequency bands. These versatile networks offer two operation modes: a continuous beam steering – feeding an antenna array with a linearly progressive phase distribution – using a reduced number of phase controls; or a multi-beam operation, generating independent, overlapped beams. These networks are built upon the concatenation of power combiners/dividers (PCDs) with isolated outputs. The isolation is provided by monolithically integrated resistors, implemented with Ti/TiO thin films for the first time. In this work, a planar prototype of a (inputs/outputs) microstrip CORPS-BFN for operation in the WR3.4/WM-864 band (220–330 GHz) on a thin 50 m Indium Phosphide (InP) substrate is designed, fabricated, and characterized. The measured S-parameters show a reflection coefficient better than -15 dB and an insertion loss between 1.6 and 3.2 dB in the whole band. In addition, an isolation better than 20 dB between the input ports has been measured. An overall remarkable agreement is observed between the measurements and the simulations. Last, the applications, scalability and efficiency of this type of networks at the targeted band are discussed in detail.This research was funded partially by the FPU Program from the Spanish Ministry of Science and Innovation, grant No. FPU18/00013, and project PID2019-109984RB-C43 (FRONT-MiliRAD); by the Deutsche Forschungs-Gemeinschaft (DFG, German Research Foundation) under Project 287022738-CRC/TRR 196 MARIE (Projects C02, C05, C06, C07 and S03); by BMBF (smartBeam, 6GEM grant No. EFRE-0400215, grant No.16KISK017 and grant No.16KISK039) and by the NRW/EFRE Terahertz-Integrationszentrum (Open6GHub and THz.NRW). Open Access funding provided by Universidad Pública de Navarra