Millimetre wave imaging for concealed target detection

PhDConcealed weapon detection (CWD) has been a hot topic as the concern about pub- lic safety increases. A variety of approaches for the detection of concealed objects on the human body based on earth magnetic ¯eld distortion, inductive magnetic ¯eld, acoustic and ultrasonic, electromagnetic resonance, MMW (millimetre wave), THz, Infrared, x-ray technologies have been suggested and developed. Among all of them, MMW holographic imaging is considered as a promising approach due to the relatively high penetration and high resolution that it can o®er. Typical concealed target detection methods are classi¯ed into 2 categories, the ¯rst one is a resonance based target identi¯cation technique, and the second one is an imaging based system. For the former, the complex natural resonance (CNR) frequencies associated with a certain target are extracted and used for identi¯cation, but this technique has an issue of high false alarm rate. The microwave/millimetre wave imaging systems can be categorized into two types: passive systems and active sys- tems. For the active microwave/millimetre wave imaging systems, the microwave holographic imaging approach was adopted in this thesis. Such a system can oper- ate at either a single frequency or multiple frequencies (wide band). An active, coherent, single frequency operation millimetre wave imaging system based on the theory of microwave holography was developed. Based on literature surveys and ¯rst hand experimental results, this thesis aims to provide system level parame- ter determination to aid the development of a target detection imager. The goal is approached step by step in 7 chapters, with topics and issues addressed rang- ing from reviewing the past work, ¯nding out the best candidate technology, i.e. the MMW holographic imaging combined with the resonance based target recog- i nition technique, the construction of the 94 GHz MMW holographic prototype imager, experimental trade-o® investigation of system parameters, imager per- formance evaluation, low pro¯le components and image enhancement techniques, feasibility investigation of resonance based technique, to system implementation based on the parameters and results achieved. The task set forth in the beginning is completed by coming up with an entire system design in the end.

Application Of Antenna Synthesis And Digital Signal Processing Techniques For Active Millimeter-wave Imaging Systems

Millimeter-wave imaging has gathered attention in recent years for its ability to penetrate clothing, thin layers of soils, and certain construction materials. However, image quality remains a challenge that needs to be addressed. One way of improving image quality is by increasing the dimensions of the collecting aperture. A sparse array can be used to synthesize a larger aperture with a limited set of relatively small detectors. In this research we design, build, and test a test-bed having an active source at 94 GHz and an array of coherent detectors, mounted on arms that extend radially on a rotary table. Using this test bed a circular area with a maximum diameter of 900 mm can be scanned. The signal is down-converted using heterodyne receivers with digital in-phase and quadrature detection. Signal correlation is performed using the digitized data, which is stored for post-processing, electronic focusing, and image reconstruction. Near-field imaging using interferometric reconstructions is achieved using electronic focusing. Imaging tests show the ability of the system to generate imagery of concealed and unconcealed objects at distances between 400 and 700 mm. A study of the effects of redundant and nonredundant configurations on image quality for 4 common detector configurations is presented. In this document we show that an active sparse-aperture imaging system using digital correlators is a viable way to generate millimeter-wave images

Water drop lens antenna for sub-THz imaging

La banda de frecuencias de ondas milimétricas (MMW), caracterizada por una elevada atenuación atmosférica y un gran ancho de banda disponible, se ha convertido de gran interés para aplicaciones de imágenes de radar de alta precisión. El desarrollo continuo de la tecnología de circuitos de microondas monolíticos integrados (MMIC) da lugar a la aparición de diferentes transceptores de radar comerciales (COTS) en esta banda de frecuencia, donde las antenas están totalmente integradas en el chip para evitar pérdidas en el sustrato. Las lentes se utilizan para corregir el frente de fase de estos chips mejorando la directividad y, por tanto, el rango de funcionamiento. Las lentes geodésicas, que pueden ser construidas utilizando sólo metales, ofrecen las propiedades atractivas de las lentes dieléctricas comunes sin sus pérdidas en el metarial. En este trabajo de fin de máster se ha diseñado una antena del tipo lente geodésica específica con propiedades de enfoque para mejorar las capacidades de imagen de radar del transceptor TRA-120-002 que trabaja en la banda ISM de 120 GHz. Se ha hecho un estudio de diferentes transiciones para los puntos singulares de la antena, minimizando reflexiones sin aumentar las aberraciones en la lente. En el trabajo se muestra un diseño optimizado de la apertura de la antena donde se utilizan corrugacions para mejorar el diagrama de radiación. Se ha diseñado también una pequeña antena de apertura con una metasuperfície de pines periódicos para maximizar la transmisión de energía entre el transceptor COTS y la lente. Finalmente, se ha añadido una metasuperfície basada en agujeros con simetría deslizada para evitar fugas entre las placas de la antena debido a posibles limitaciones en su fabricación. Los resultados muestran que se puede conseguir una antena de tipo lente de 5l de radio totalmente metálica con directividad superior a 19,5 dB y niveles de lóbulos secundários (SLL) entre -10,5 dB y -9,2 dB dentro de la banda de 119 GHz - 125,5 GHz mientras que la antena focaliza a 30 cm.La banda de freqüències d'ones mil·limètriques (mmW), caracteritzada per una elevada atenuació atmosfèrica i un gran ample de banda disponible, ha esdevingut de gran interès per a aplicacions d'imatges de radar d'alta precisió. El desenvolupament continu de la tecnologia de circuits de microones monolítics integrats (MMIC) dona lloc a l'aparició de diferents transceptors de radar comercials (COTS) en aquesta banda de freqüència, on les antenes estan totalment integrades al xip per evitar pèrdues en el substrat. Les lents s'utilitzen per corregir el front de fase d'aquests xips millorant la directivitat i, per tant, el rang de funcionament. Les lents geodèsiques, que poden ser construïdes utilitzant només metalls, ofereixen les propietats atractives de les lents dielèctriques comuns sense les seves pèrdues en el material. En aquest treball de fi de màster s'ha dissenyat una antena del tipus lent geodèsica específica amb propietats d'enfocament per millorar les capacitats d'imatge de radar del transceptor TRA-120-002 que treballa a la banda ISM de 120 GHz. S'ha fet un estudi de diferents transicions per als punts singulars de l'antena, minimitzant reflexions sense augmentar les aberracions a la lent. En el treball es mostra un disseny optimitzat de l'obertura de la antena on s'utilitzen corrugacions per millorar el diagrama de radiació. S'ha dissenyat també una petita antena d'obertura amb una metasuperfície de pins periòdics per maximitzar la transmissió d'energia entre el transceptor COTS i la lent. Finalment, s'ha afegit una metasuperfície basada en forats amb simetria lliscada per evitar pèrdues entre les plaques de l'antena a causa de possibles limitacions en la seva fabricació. Els resultats mostren que es pot aconseguir una antena de tipus lent de 5l de radi totalment metàl·lica amb directivitat superior a 19,5 dB i nivells de lòbuls secundaris (SLL) entre -10,5 dB i -9,2 dB dins de la banda de 119 GHz - 125,5 GHz mentre que l'antena focalitza a 30 cm.The Millimiter Wave (mmW) frequency band, characterized by a high atmospheric attenuation and wide available bandwidth has become of big interest for high accuracy radar imaging applications. The continuous development of the Monolithic Microwave Integrated Circuit (MMIC) technology yields to the appearance of different commercial-off-the-shelf (COTS) radar transceivers at that frequency band, where the antennas are fully integrated into the chip. Lenses are being used to correct the phase front of those MMIC improving the directivity and therefore the operating range. Fully metallic geodesic lenses offer the attractive properties of common dielectric lenses without their material losses. In this master thesis, a specific water-drop geodesic lens antenna with focusing properties has been designed to enhance the radar imaging capabilities of the theTRA-120-002 transceiver working at the 120 GHz Industrial, Scientific and Medical (ISM) band. Different transitions for the antenna singular points have been studied to minimize reflections without increasing aberrations in the lens. An optimized design of a radiating flare is shown where corrugations are used to improve the antenna radiation pattern. A small feeding horn antenna with a bed-of-nails Electromagnetic Band-Gap (EBG) metasurface has been designed to maximize the energy transmission between the COTS transceiver and the lens. Finally, a glide-symmetric holey metasurface has been added to prevent leakage between the antenna plates due to manufacturing limitations. The results show that a fully metallic folded lens antenna with 5l radius can achieve directivities higher than 19.5 dB and side-lobe levels (SLL) between -10.5 dB and -9.2dB within the 119 GHz - 125.5 GHz band while having an image point located at 30cm from the antenna

Analytic and Machine Learning Based Design of Monolithic Transistor-Antenna for Plasmonic Millimeter-Wave Detectors

Department of Electrical EngineeringThis thesis reports an advanced analysis on a monolithic transistor-antenna by designing a ring-type asymmetric FET itself as a receiving antenna element which receives millimeter-waves in a loss-less manner with a plasmonic ampli fication for millimeter-wave (mmW) detectors. The proposed transistor-antenna device combines the plasmonic and the electromagnetic (EM) aspects in a single place. As a result, it can absorb the incoming mmW and transfer power directly to the ring-type asymmetric channel without any feeding line and a separate antenna element. Both the charge asymmetry in the device channel and the antenna coupling are contributing to the enhanced photoresponse. Among the two factors, the improved antenna coupling is more dominant in the performance enhancement of our proposed design. Also, our transistor-antenna device have enhanced performance with a uniformly enhanced responsivity of every pixel by characterizing its impedance exactly pursuing real-time mmW imaging. Operation principle of the proposed device is discussed, focusing on how signal transmission through the ring-type structure is available without any feeding line between the antenna and the detector. To determine the antenna geometry aiming for a desired resonant frequency, we present an efficient design procedure based on periodic bandgap analysis combined with parametric electromagnetic simulations. From a fabricated ring-type FET-based monolithic antenna device, we demonstrated the highly enhanced optical responsivity and the reduced optical noise-equivalent power, which are in comparable order with the reported state-of-the-art CMOS-based antenna integrated direct detectors. Another part of the thesis focuses on developing machine learning models to enable fast, accurate design and veri fication of electromagnetic structures. We proposed a novel Bayesian learning algorithm named as Bayesian clique learning, for searching the optimal electromagnetic design parameter by using the structural property of EM simulation data set. Along with this, we also given an inverse problem approach for designing the electromagnetic structures which suggest going in the opposite direction to determine the design parameters from characteristics of the desired output.clos

A Technique for Time-Resolved Imaging of Millimeter Waves Based on Visible Continuum Radiation from a Cs-Xe DC Discharge — Fundamentals and Applications

The chapter presents a review of a highly sensitive technique for time-resolved imaging and measurement of the 2D intensity profiles of millimeter waves (MMW) based on the use of visible continuum radiation (VCR) from the positive column (PC) of a medium pressure Cs-Xe DC discharge (VCRD technique). The review focuses on the operating principles, fundamentals, and applications of this new technique. The design of a discharge tube and an experimental setup which were used to create a wide homogeneous PC plasma slab are described. The MMW effects on the plasma slab are studied. The mechanism of microwave-induced variations in the VCR intensity and the causes of violation of the local relation between the visible continuum emissivity and the MMW intensity are discussed. The main characteristics, e.g., spatial and temporal resolution, and sensitivity of the VCRD technique have been evaluated. Experiments on imaging of the field patterns of horn antennas and quasioptical beams demonstrated that the VCRD technique can be used for a good-quality imaging of the MMW beams in the entire MM-wavelength band. The VCRD technique was applied for imaging of output field patterns of the MMW electron tubes and determination of some of their characteristics, as well as for active real-time imaging and nondestructive testing using MM waves

Far-infrared/millimeter Wave Source And Component Development For Imaging And Spectroscopy

The far-infrared and millimeter wave (FIR/mmW) (wavelength 75 micrometer to 10 mm) portion of the electromagnetic spectrum is fairly underdeveloped technologically, owing to the large amount of atmospheric attenuation in that range. At present, the FIR/mmW region is lacking in compact, high-brightness radiation sources and practical imaging systems. This dissertation focuses on development of two complementary technologies in this area - an active mmW imaging system and high-reflectivity Bragg mirrors for the FIR p-Ge laser. The imaging system uses a vector network analyzer in the frequency range of 90-140 GHz as the radiation source and receiver. Raster scanning is used to map a two-dimensional field of view, demonstrating the detection and imaging of buried plastic landmines. Principal components analysis is used for hyperspectral signal processing, where a series of images is taken at discrete frequencies. Results are obtained as a function of depth and disturbance of the soil surface. In support of this study, various types of soils were characterized for scattering loss across the mmW/FIR region, with measured results compared to theory. This mmW imaging system was also used to demonstrate imaging through walls and other obscuring materials, as well as for imaging of rocks beneath volcanic sand, simulating the conditions encountered by an imaging system on a Mars rover vehicle. Furthermore, a high-reflectivity Si-etalon FIR mirror design was developed and demonstrated as a cavity mirror for the p-Ge laser. These components stand to have a number of systems-level impacts on FIR imagers. In the context of an active illuminator, they may allow narrowband selection from the broad emission spectrum of the p-Ge laser source. These mirrors can also be used in a Fabry-Perot FIR scanning spectrometer, where the resulting high finesse would give discrimination advantages in chemical sensing and astrophysical spectroscopy applications

Imaging Technology and Systems

Presents a review of various imaging techniques used in the ground-based airborne and spaceborne systems. It mainly covers the subject on electromagnetic spectrum extending from ultraviolet to microwave region. Discusses various imaging techniques, including their advantages/limitations and available systems and highlights visible, near infrared, thermal infrared and millimeter wave band imaging system developed by the Defence Electronics Applications Laboratory, Dehradun

Design and Implementation of High Gain 60 GHz Antennas for Imaging/Detection Systems

Recently, millimeter wave (MMW) imaging detection systems are drawing attention for their relative safety and detection of concealed objects. Such systems use safe non-ionizing radiation and have great potential to be used in several applications such as security scanning and medical screening. Antenna probes, which enhance system performance and increase image resolution contrast, are primarily used in MMW imaging sensors. The unlicensed 60 GHz band is a promising band, due to its wide bandwidth, about 7 GHz (57 - 64 GHz), and lack of cost. However, at 60 GHz the propagation loss is relatively high, creating design challenges for operating this band in MMW screening. A high gain, low profile, affordable, and efficient probe is essential for such applications at 60 GHz. This thesis’s focus is on design and implementation of high gain MMW probes to optimize the performance of detection/imaging systems. First, single-element broadside radiation microstrip antennas and novel probes of endfire tapered slot high efficient antennas are presented. Second, a 57-64 GHz, 1 × 16-element beam steering antenna array with a low-cost piezoelectric transducer controlled phase shifter is presented. Then, a mechanical scanner is designed specifically to test proposed antenna probes utilizing low-power 60 GHz active monostatic transceivers. The results for utilizing proposed 60 GHz probes show success in detecting and identifying concealed weapons and explosives in liquids or plastics. As part of the first research theme, a 60 GHz circular patch-fed high gain dielectric lens antenna is presented, where the prototype’s measured impedance bandwidth reaches 3 GHz and a gain of 20 dB. A low cost, 60 GHz printed Yagi antenna array was designed, optimized, fabricated and tested. New models of the antipodal Fermi tapered slot antenna (AFTSA) with a novel sine corrugated (SC) shape are designed, and their measured results are validated with simulated ones. The AFTSA-SC produces a broadband and high efficiency pattern with the capacity for high directivity for all ISM-band. Another new contribution is a novel dual-polarized design for AFTSA-CS, using a single feed with a pair of linearly polarized antennas aligned orthogonally in a cross-shape. Furthermore, a novel 60 GHz single feed circularly polarized (CP) AFTSA-SC is modeled to radiate in the right-hand circularly polarized antenna (RHCP). A RHCP axial ratio bandwidth of < 3dB is maintained from 59 to 63 GHz. In addition, a high gain, low cost 60 GHz Multi Sin-Corrugations AFTSA loaded with a grooved spherical lens and in the form of three elements to operate as the beam steering antenna is presented. These probes show a return loss reduction and sidelobes and backlobe suppression and are optimized for a 20 dB or higher gain and radiation efficiency of ~90% at 60 GHz. The second research theme is implementing a 1 × 16-element beam steering antenna array with a low-cost piezoelectric transducer (PET) controlled phase shifter. A power divider with a triangular feed which reduces discontinuity from feed lines corners is introduced. A 1 × 16-element array is fabricated using 60 GHz AFTSA-SC antenna elements and showed symmetric E-plane and H-plane radiation patterns. The feed network design is surrounded by electromagnetic band-gap (EBG) structures to reduce surface waves and coupling between feed lines. The design of a circularly polarized 1 × 16-element beam steering phased array with and without EBG structures also investigated. A target detection investigation was carried out utilizing the proposed 60GHz antennas and their detection results are compared to those of V-band standard gain horn (SGH). System setup and signal pre-processing principle are introduced. The multi-corrugated MCAFTSA-SC probe is evaluated with the imaging/detection system for weapons and liquids concealed by clothing, plywood, and plastics. Results show that these items are detectable in clear 2D image resolution. It is believed that the 60 GHz imaging/detection system results using the developed probes show potential of detecting threatening objects through screening of materials and public