Backscatter Transponder Based on Frequency Selective Surface for FMCW Radar Applications

This paper describes an actively-controlled frequency selective surface (FSS) to implement a backscatter transponder. The FSS is composed by dipoles loaded with switching PIN diodes. The transponder exploits the change in the radar cross section (RCS) of the FSS with the bias of the diodes to modulate the backscattered response of the tag to the FMCW radar. The basic operation theory of the system is explained here. An experimental setup based on a commercial X-band FMCW radar working as a reader is proposed to measure the transponders. The transponder response can be distinguished from the interference of non-modulated clutter, modulating the transponder’s RCS. Some FSS with different number of dipoles are studied, as a proof of concept. Experimental results at several distances are provided

Additively Manufactured RF Components, Packaging, Modules, and Flexible Modular Phased Arrays Enabling Widespread Massively Scalable mmWave/5G Applications

The 5G era is here and with it comes many challenges, particularily facing the high frequency mmWave adoption. This is because of the cost to implement such dense networks is much greater due to the high propagation losses of signals that range from 26 GHz to 40 GHz. Therefore there needs to be a way to utilize a method of fabrication that can change with the various environments that 5G will be deployed in, be it dense urban areas or suburban sprawl. In this research, the focus is on making these RF components utilized for 5G at low cost and modular with a focus on additive manufacturing. Since additive manufacturing is a rapid prototyping technique, the technology can be quickly adjusted and altered to meet certain specifications with negligible overhead. Several areas of research will be explored. Firstly, various RF passive components such as additively manufactured antennas and couplers with a combination hybrid inkjet and 3D printing will be discussed. Passive components are critical for evaluating the process of additive manufacturing for high frequency operation. Secondly, various structures will be evaluated specifically for packaging mmWave ICs, including interconnects, smart packaging and encapsulants for use in single or multichip modules. Thirdly, various antenna fabrication techniques will be explored which enables fully integrated ICs with antennas, called System on Antenna (SoA) which utilizes both inkjet and 3D printing to combine antennas and ICs into modules. These modules, can then be built into arrays in a modular fashion, allowing for large or smaller arrays to be assembled on the fly. Finally, a method of calibrating the arrays is introduced, utilizing inkjet printed sensors. This allows the sensor to actively detect bends and deformations in the array and restore optimal antenna array performance. Built for flexible phased arrays, the sensor is designed for implementation for ubiquitous use, meaning that its can be placed on any surface, which enables widespread use of 5G technologies.Ph.D

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

A Review: Substrate Integrated Waveguide Antennas and Arrays

This study aims to provide an overview and deployment of Substrate-Integrated Waveguide (SIW) based antenna and arrays, with different configurations, feeding mechanisms, and performances. Their performance improvement methods, including bandwidth enhancement, size reduction, and gain improvement are also discussed based on available literature. SIW technology, which acts as a bridge between planar and non-planar technology, is a very favorable candidate for the development of components operating at microwave and millimeter wave band. Due to this, SIW antennas and array take the advantages of both classical metallic waveguide, which includes high gain, high power capacity, low cross polarization, and high selectivity, and that of planar antennas which comprises low profile, light weight, low fabrication cost, conformability to planar or bent surfaces, and easy integration with planar circuits

Tunable antenna design by metamaterial structures operating at S band

Un “metamaterial” por su definición ampliamente aceptada es una estructura construida artificialmente que obtiene sus propiedades materiales de su estructura en lugar de la composición de su material intrínseco. El ámbito de los materiales ha ganado mucha atención dentro de la comunidad científica en la última década. Con los continuos avances y descubrimientos conducen al camino de las aplicaciones prácticas; los metamateriales han ganado la atención de las empresas de base tecnológica y los organismos de defensa interesados en el uso de dispositivos de próxima generación. Las superficies selectivas en frecuencia (FSS) son una variedad potente de metamateriales que, dependiendo de la geometría de la superficie, se pueden utilizar para diseñar propiedades de radiación específicas tales como la emisión direccional, emisión polarizada circular y lineal, y la selectividad espectral. Los elementos de la FSS pueden ser tanto elementos metálicos sólidos como elementos metálicos con aberturas, y en los diseños tradicionales, la superficie selectiva en frecuencia (FSS) normalmente opera en torno a la resonancia de media longitud de onda de los elementos. En este proyecto se va a utilizar una superficie selectiva de frecuencia (FSS) con el fin de realizar metamateriales sintonizables -una amplia clase de metamateriales controlables diseñados artificialmente, y desarrollar una antena sintonizable que trabaje a 2.4 GHz. La FSS consiste en una serie de elementos rectángulos cargados con varactores y capacitores con una película delgada de material ferroeléctrico sintonizable (BST) para el ajuste externo de los parámetros de medio efectivo. Por lo tanto se diseñan unos varactores BST que son colocados entre los elementos metálicos que conforman la FSS. El efecto de la superficie selectiva en frecuencia es estudiado en dos antenas diferentes – antena ELPOSD (End-Loaded Planar Open-Sleeve Dipole) y una antena de parche microstrip. La antena ELPOSD consiste en un dipolo plano convencional con dos elementos parásitos muy juntos, y una carga en cada extremo del dipolo. Los beneficios principales de este tipo de antenas es que, además del rendimiento similar de la antena POSD (Planar Open-Sleeve Dipole) convencional, las antenas ELPOSD pueden ser miniaturizadas. La antena parche utilizada en este trabajo es un elemento metálico cuadrado plano alimentado a través de una línea microstrip. El material ferroeléctrico Barium Strontium Titanate (BST) es un material muy bien conocido hasta el momento. Para diseñar los varactores se utiliza una película delgada de BST, junto con los capacitores interdigitales (IDCs) que se utilizan en la capa del metal. La antena general consiste en un sustrato de múltiples capas donde en una capa se encuentra la Superficie selectiva en frecuencia (FSS) sintonizable y en otra la antena dipolo o antena de parche. La capacidad de la FSS completa varía introduciendo el material ferroeléctrico BST en el varactor. Como puede verse en los resultados, variando la permitividad del material BST de 200 a 300 se consigue una variación en frecuencia de 4.15 GHz a 3.5 GHz con una distancia alrededor de 100 MHz entre frecuencias resonantes. Esto equivale a una variación de la frecuencia alrededor del 8% entre los valores de permitividad adyacentes.A “metamaterial” by its widely accepted definition is an artificially engineered structure that gains its material properties from its structure as opposed to its intrinsic material composition. The field of metamaterials has gained much attention within the scientific community over the past decade. With continuing advances and discoveries leading the way to practical applications, metamaterials have earned the attention of technology-based corporations and defense agencies interested in their use for next generation devices. Frequency Selective Surfaces (FSS) are a potent variety of metamaterials that, depending on the surface geometry, can be used to engineer specific radiation properties such as directional emission, linear and circular polarized emission, and spectral selectivity. The elements of the FSS can either be patches or apertures, and in traditional designs, the FSS usually operates around the half-wavelength resonance of the elements. In this project a Frequency Selective Surface (FSS) is used in order to realize tunable metamaterials –a broad class of controllable artificially engineered metamaterials, and develop a tunable antenna operating at 2.4 GHz. The FSS consist of an array of square patches loaded with varactors and tunable ferroelectric thin film capacitors (BST) for external tuning of the effective medium parameters. Therefore a BST varactor is designed and located between the patches of the FSS. The effect of the Frequency Selective Surface is studied in two different antennas –an End-Loaded Planar Open-Sleeve Dipole (ELPOSD) and a Square Patch. An End-Loaded Planar Open-Sleeve Dipole consist of a conventional planar dipole with two closely spaced parasitic elements, or sleeves, and loaded stubs at the end of the dipole. The main benefits of this type of antennas is that in addition to retaining similar performance to that of conventional planar open-sleeve dipole, end-loaded planar opensleeve dipole (ELPOSD) antennas can be miniaturized. The Square Patch antenna used in this work is a conventional planar square patch feed with a microstrip line. Barium Strontium Titanate (BST) is a well-known ferroelectric material and up to now. A BST thin film is used to design the varactors, along with the Interdigital Capacitors (IDCs) geometry used in the metal layer. The overall antenna consists of a multilayer substrate with tunable FSS layer and dipole or patch antenna. The capacitance of the whole FSS changes introducing the BST ferroelectric material into the varactor. As can be seen in the results, by varying the BST permittivity from 200 to 300, a variation in frequency is achieved from 1.98 GHz to 1.717 GHz with a distance around 100 MHz between resonance frequencies, which equals a variation of the frequency about 8% in the adjacent permittivity values.Ingeniería de TelecomunicaciónTelekomunikazio Ingeniaritz

Additively Manufactured Shape-changing RF Devices Enabled by Origami-inspired Structures

The work to be presented in this dissertation explores the possibility of implementing origami-inspired shape-changing structures into RF designs to enable continuous performance tunability as well as deployability. The research not only experimented novel structures that have unique mechanical behaviour, but also developed automated additive manufacturing (AM) fabrication process that pushes the boundary of realizable frequency from Sub-6 GHz to mm-wave. High-performance origami-inspired reconfigurable frequency selective surfaces (FSSs) and reflectarray antennas are realized for the first time at mm-wave frequencies via AM techniques. The research also investigated the idea of combining mechanical tuning and active tuning methods in a hybrid manner to realize the first truly conformal beam-forming phased array antenna that can be applied onto any arbitrary surface and can be re-calibrated with a 3D depth camera.Ph.D

A Micromachined Millimeter-Wave Radar Technology for Indoor Navigation

A compact, light-weight, low-power MMW radar system operating at 240 GHz is introduced to enable autonomous navigation of micro robotic platforms in complex environments. The short wavelength at the operating frequency band (1.25mm @ 240 GHz) enables implementation of the radar front-end components on a silicon wafer stack using micromachining techniques. This work presents the design, fabrication technology, and measurement methodology of components for the micromachined MMW radar and the phenomenology of such radars in indoor environments. Novel passive structures are developed to realize a fully micromachined radar front-end. Low loss cavity-backed CPW (CBCPW) lines (0.12 dB/mm @ 240 GHz), broadband transitions from the CBCPW line to rectangular waveguide (IL13 dB; BW: 39%), MMIC chip integration transitions, and waveguide directional couplers are designed to fully integrate active and passive components of the radar. Also a membrane-supported miniaturized-element FSS image-reject filter (IL25 dB in the stopband) is developed for MMW radar applications. The structures are designed compatible with micromachining technology and optimized for minimum insertion loss. The designed components are then realized over a two layer stack of silicon wafers. Multi-step structures are realized on one of the wafers and the membrane-supported features are implemented on the other wafer. A novel multistep DRIE technique is utilized to enhance the profile quality of the fabricated structures. Measurement techniques are developed to enable accurate and repeatable characterization of the on-wafer components at MMW and higher frequency bands. A novel waveguide probe S-parameter measurement technique is introduced for non-contact characterization of the multi-port components using a two-port network analyzer. To examine the utilization of the proposed 240 GHz radar for collision avoidance and building interior mapping applications, the interaction of electromagnetic waves with objects in the indoor environments is investigated. An instrumentation radar is utilized to collect backscatter data from corridors in an indoor setting. The collected data is used to form radar images for obstacle detection. The radar images are co-registered in a global coordinate matrix to form a complete map of the interior layout. Image processing techniques are used to enhance the final layout map.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/107273/1/moallem_1.pd

Electromagnetic bandgap antennas and components for microwave and (Sub)millimeter wave applications

This paper reviews the primary application areas of electromagnetic bandgap (EBG) technology at microwave and (sub)millimeter wave frequencies. Examples of EBG configurations in the microwave region include array antennas, high precision GPS, mobile telephony, wearable antennas and diplexing antennas. In the submillimeter wave region a 500 GHz dipole configuration and a novel heterodyne mixer is shown for the first time. Some emphasis is also placed on EBG waveguides and filters. As most fundamental components will be available in EBG technology, a fully integrated receiver could be developed in order to take full advantage of this technology. True integration of passive and active components can now begin to materialise using EBG technology

High efficiency planar microwave antennas assembled using millimetre thick micromachine polymer structures

Communication systems at microwave and millimetre wave regimes require compact broadband high gain antenna devices for a variety of applications, ranging from simple telemetry antennas to sophisticated radar systems. High performance can usually be achieved by fabricating the antenna device onto a substrate with low dielectric constant or recently through micromachining techniques. This thesis presents the design, fabrication, assembly and characterisation of microstrip and CPW fed micromachined aperture coupled single and stacked patch antenna devices. It was found that the micromachining approach can be employed to achieve a low dielectric constant region under the patch which results in suppression of surface waves and hence increasing radiation efficiency and bandwidth. A micromachining method that employs photolithography and metal deposition techniques was developed to produce high efficiency antenna devices. The method is compatible with integration of CMOS chips and filters onto a common substrate. Micromachined polymer rims (SU8 photoresist) was used to create millimetre thick air gaps between the patch and the substrate. The effect of the substrate materials and the dimensions of the SU8 polymer rims on the performance of the antenna devices were studied by numerical simulation using Ansoft HFSS electromagnetic field simulation package. The antenna structures were fabricated in layers and assembled by bonding the micromachined polymer spacers together. Low cost materials like SU8, polyimide and liquid crystal polymer films were used for fabrication and assembly of the antenna devices. A perfect patch antenna device is introduced by replacing the substrate of a conventional patch antenna device with air in order to compare with the micromachined antenna devices. The best antenna parameters for a perfect patch antenna device with air as a substrate medium are ~20% for bandwidth and 9.75 dBi for antenna gain with a radiation efficiency of 99.8%. In comparison, the best antenna gain for the simple micromachined patch antenna device was determined to be ~8.6 dBi. The bandwidth was ~20 % for a microstrip fed device with a single patch; it was ~40 % for stacked patch devices. The best bandwidth and gain of 6.58 GHz (50.5%) and 11.2 dBi were obtained for a micromachined sub-array antenna device. The simulation results show that the efficiency of the antenna devices is above 95 %. Finally, a novel high gain planar antenna using a frequency selective surface (FSS) was studied for operation at ~60 GHz frequency. The simulation results show that the novel antenna device has a substantial directivity of around 25 dBi that is required for the emerging WLAN communications at the 60 GHz frequency band

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance