This PDF file contains the front matter associated with SPIE Proceedings Volume 8188, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The actual and continuous threat by international terrorism and the increasing number of terroristic attacks raise the danger to the public and create a new and more complex dimension of threat. This evolution must and can only be combat by the application of new counter-measures like advanced imaging technologies for wide-area surveillance and the detection of concealed dangerous objects. Passive microwave remote sensing allows a daytime independent non-destructive observation and examination of the objects of interest under nearly all weather conditions without artificial exposure of persons and observation areas, hence fully avoiding health risks. Furthermore the acquisition of polarimetric object characteristics can increase the detection capability by gathering complementary object information. The recent development and construction of a fullypolarimetric receiver at W band allows the acquisition of a new dimension of information compared to former imaging capabilities. The new receiver can be part of various imaging systems used at DLR over the years. This paper will show some imaging results recorded recently from different sceneries.

Single sensor passive millimetre wave (PMMW) imaging systems typically suffer from long acquisition times, which inhibit their utilization in some security applications (i.e. concealed weapons detection systems) where real time operation is required. This is inherent to the physical principle behind the system, where the achievable temperature resolution and the integration time are inversely proportional to each other. The longer the sensor can collect (and integrate) energy radiated by the scene at each position, the finer the temperature resolution becomes. Reducing the integration time without degrading the temperature resolution can be achieved by increasing the bandwidth of the radiometer, but this is possible only up to certain limits. We propose to reduce the acquisition time in such a single sensor, by combining the recent theory of compressive sensing with special sparse trajectories, designed to achieve the level of incoherence that the theory of compressive sensing requires to successfully recover the image. Another alternative proposal is to sample all the pixels in the scene, but for each pixel, the integration time is randomly selected from a pool of discrete possible values. The radiometric image is then reconstructed by combining the images obtained from the individual application of compressive sensing to each group of pixels having the same integration time. For demonstration purposes, a single pixel PMMW imaging simulator has been implemented in Matlab/Simulink, which includes a configurable radiometric scene generator. The paper presents results from simulated radiometric scenes at 140GHz acquired with the proposed sparse trajectories and recovered using compressive sensing. The results show that savings in acquisition times between 50% and 70% are possible while maintaining the required temperature resolution.

The first video rate imagery from a proof-of-concept 32-channel 22 GHz aperture synthesis imager is reported. This imager has been brought into operation over the first half of year 2011. Receiver noise temperatures have been measured to be ~453 K, close to original specifications, and the measured radiometric sensitivity agrees with the theoretical predictions for aperture synthesis imagers (2 K for a 40 ms integration time). The short term (few seconds) magnitude stability in the cross-correlations expressed as a fraction was measured to have a mean of 3.45×10^-4 with a standard deviation of ~2.30×10^-4, whilst the figure for the phase was found to have a mean of essentially zero with a standard deviation of 0.0181°. The susceptibility of the system to aliasing for point sources in the scene was examined and found to be well understood. The system was calibrated and security-relevant indoor near-field and out-door far-field imagery was created, at frame rates ranging from 1 to 200 frames per second. The results prove that an aperture synthesis imager can generate imagery in the near-field regime, successfully coping with the curved wave-fronts. The original objective of the project, to deliver a Technology Readiness Level (TRL) 4 laboratory demonstrator for aperture synthesis passive millimetre wave (PMMW) imaging, has been achieved. The project was co-funded by the Technology Strategy Board and the Royal Society of the United Kingdom.

The demand for all-weather, day-night imaging systems has been spurred by calls for persistent surveillance in security and defense applications, and increased safety in military aviation, such as carrier landings in fog and helicopter landings in sand and dust. To meet these demands requires systems that offer robust imaging capabilities. Whereas visible and infrared systems can provide high resolution imagery in a small-sized package, they are hindered by atmospheric obscurants, such as cloud cover, fog, smoke, rain, sand, and dust storms. Millimeter wavelengths, on the other hand, are not and passive millimeter wave imaging may be one method to reduce, or perhaps even eliminate, the impact of low visibility atmospheric conditions. In this paper we examine the scattering from rotorcraft induced dust clouds using Sandblaster dust particle density data. We examine the effect of Mie scattering as a function of particle size and operating wavelength and conclude that W-band operation yields the highest resolution imaging while still maintaining "see-through" imaging capability.

This paper examines the sourcing of low cost components for next generation passive millimetre wave (PMMW) aperture synthesis imagers. Splitting the elements of the imager into antennas/receivers, analogue to digital converters (ADCs), digital signal processors (DSP) and a host computer, technologies are identified that can minimise the cost of these in future systems. It is established that the follow-on aperture PMMW imagers can be constructed at relatively low cost, using a combination of low frequency (< 30 GHz) satellite receiver technology, high-speed clocked comparators, DSP (both Field Programmable Gate Arrays (FPGAs) and Graphical Processor Units (GPUs)) and the latest personal computers that use high-speed high lane count PCI Express Bus technology.

This paper presents an exploratory attempt to use high-resolution radar measurements for face identification in forensic applications. An imaging radar system developed by JPL was used to measure a human face at 670 GHz. Frontal views of the face were measured both with and without a ski mask at a range of 25 m. The realized spatial resolution was roughly 1 cm in all three dimensions. The surfaces of the ski mask and the face were detected by using the two dominating reflections from amplitude data. Various methods for visualization of these surfaces are presented. The possibility to use radar data to determine certain face distance measures between well-defined face landmarks, typically used for anthropometric statistics, was explored. The measures used here were face length, frontal breadth and interpupillary distance. In many cases the radar system seems to provide sufficient information to exclude an innocent subject from suspicion. For an accurate identification it is believed that a system must provide significantly more information.

The properties of terahertz (THz) radiation are well known. They penetrate well most non-conducting media; there are no known biological hazards, and atmospheric attenuation and scattering is lower than visual and IR radiation. Thus THz imaging is very attractive for homeland security, biological, space, and industrial applications Recently we have found experimentally that inexpensive miniature neon indicator lamp Glow Discharge Detectors (GDD) can be used as THz detectors. Based on the GDD we designed, constructed, and experimentally tested an 8×8 GDD array. In order to improve the performance and the resolution of the THz images a larger array is required. In this work we use a special double row 2×18 moving array detector. The 2×18 GDD array enables us to employ scanning method in order to obtain 36×36 pixel THz images. Furthermore, using this double row array it will be possible to employ super resolution methods. Optical properties such as optical transfer function and measurement of point spread function are presented, as well as first results for the 2×18 GDD array.

Quality control systems in industry can benefit from the new possibilities offered by the THz frequency range. THz imaging systems can complement actual quality control systems and at the same time offer new information about products, improving quality and reducing costs. In this case we have implemented an imaging system to control the evolution of water content in leaves. The work presented in this paper shows the water content evolution of leaves in the range from 0.14 THz to 0.22 THz. Transmission and reflection parameters have been measured obtaining frequency and time domain information. While in the visible region the leaf is still green after 48 hours of cutting, and no appreciable change can be seen, in the THz image more than 5dB variation can be obtained due to the loss of water in the leaf. As a conclusion, it can be said that imaging in active THz technology can be used to measure the evolution of water content in leafs at the early stage of drying, where no changes are noticeable in the visible region. Agriculture quality control systems could benefit from this technology.

The use of millimeter-waves for imaging purposes is becoming increasingly important, as millimeter-waves can penetrate most clothing and packaging materials, so that the detector does not require physical contact with the object. This will offer a view to the hidden content of e.g. packets or bags without the need to open them, whereby packaging and content will not be damaged. Nowadays X-ray is used, but as the millimeter-wave quantum energy is far below the ionization energy, it is less harmful for the human health. In this paper we report an active millimeter-wave imaging tomograph for material analysis and concealed object detection purposes. The system is build using in-house W-band components. The object is illuminated with low-power millimeter-waves in the frequency range between 89 and 96GHz; mirrors are used to guide and focus the beam. The object is moved through the focus point to scan the object pixel by pixel. Depending on the actual material some parts of the waves are reflected, the other parts penetrate the object. A single-antenna transmit and receive module is used for illumination and measurement of the material-specific reflected power. A second receiver module is used to measure the transmitted wave. All information is processed for amplitude and phase images by a computer algorithm. The system can be used for security, such as detecting concealed weapons, explosives or contrabands at airports and other safety areas, but also quality assurance applications, e.g. during production to detect defects. Some imaging results will be presented in this paper.

Lithium niobate (LN) modulators have been for years the devices of choice for the telecommunication market due to their high modulation rate and their robustness. Matching RF and optical velocities has been the most critical factor that limited this technology to 40 Gb/s since the early 2000's. However, recent interest in millimeter-wave (mmW) imaging, which requires good resolution images for object recognition, has led to significant progress in modulator's design and fabrication techniques [1]. 100 GHz modulation bandwidth has been reported [2]. For passive mmW imaging purpose at 77 GHz and beyond, we have developed an electro-optic phase modulator that can work up to 220 GHz. Modulator design and fabrication techniques are presented, supported by experimental measurements of optical response. We demonstrate optical upconversion up to 220 GHz by achieving RF and optical index matching combined with substrate modes elimination and low dielectric and conduction losses. The RF index is matched to the optical group velocity at 2.19 through CPW ridged structure and silicon dioxide layer deposition. Accurate index matching is obtained by controlling the thickness and the topology of the silicon dioxide layer, whereas substrate modes are reduced by thinning the LN substrate down to 50 μm. A fiber-modulator-fiber optical insertion loss of 4.5 dB also ensures good optical upconversion efficiency. We have applied the phase modulator to our mmW imaging system and obtained high quality mmW images in W-band.

TowerJazz has been offering the high volume commercial SiGe BiCMOS process technology platform, SBC18, for more than a decade. In this paper, we describe the TowerJazz SBC18H3 SiGe BiCMOS process which integrates a production ready 240GHz F_T / 270 GHz F_MAX SiGe HBT on a 1.8V/3.3V dual gate oxide CMOS process in the SBC18 technology platform. The high-speed NPNs in SBC18H3 process have demonstrated NF_MIN of ~2dB at 40GHz, a BV_ceo of 1.6V and a dc current gain of 1200. This state-of-the-art process also comes with P-I-N diodes with high isolation and low insertion losses, Schottky diodes capable of exceeding cut-off frequencies of 1THz, high density stacked MIM capacitors, MOS and high performance junction varactors characterized up to 50GHz, thick upper metal layers for inductors, and various resistors such as low value and high value unsilicided poly resistors, metal and nwell resistors. Applications of the SBC18H3 platform for millimeter-wave products for automotive radars, phased array radars and Wband imaging are presented.

We designed InAs/Ga_0.6In_0.4Sb superlattice (SL) material for terahertz-range photodetectors. Depending on the thicknesses of the InAs and Ga_0.6In_0.4Sb layers, the SL energy gap Eg can be adjusted to be between 8-25 meV, which corresponds to a cut-off frequency from 2 to 6 THz. Different designs were numerically evaluated by using the eightband k•p model. The calculations show that the SL energy gap is sensitive to monolayer (ML) scale variations in layer thickness, and that realization of the design parameters requires better than 1ML accuracy of epitaxial growth. A 40-period strained Ga_0.6In_0.4Sb SL with alternating InSb (1ML) and GaAs (1ML) interfaces was grown by a molecular beam epitaxy on a GaSb substrate; the target energy gap Eg was 9 meV. The SL samples were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence and absorption spectroscopy measurements. Despite the large lattice mismatch between InAs and Ga_0.6In_0.4Sb, the XRD and AFM measurements showed that the SL had good structural and surface quality and an accurate layer structure. The surface roughness was 0.22 nm.

Infrared and terahertz are two imaging technologies that differ fundamentally in numerous aspects. Infrared imaging is an efficient passive technology whereas terahertz technology is an active technology requiring some kind of illumination to be efficient. What's more, the detectors are also different and yield differences in the fundamental physics when integrated in a complete system. One of these differences lies in the size of the detectors. Infrared detectors are typically larger than the infrared wavelengths whereas terahertz detectors are typically smaller than the wavelength of illumination. This results in different constraints when designing these systems, constraints that are imposed by the resolution capabilities of the system. In the past INO has developed an infrared imaging camera core of 1024×768 pixels and tested some microscanning devices to improve its sampling frequency and ultimately its resolution. INO has also engineered detectors and camera cores specifically designed for active terahertz imaging with smaller dimensions (160×120 pixels). In this paper the evaluation of the resolution capabilities of a terahertz imager at the pixel level is performed. The resolution capabilities for the THz are evaluated in the sub-wavelength range, which is not actually possible in the infrared wavebands. Based on this evaluation, the comparison between the resolution limits of infrared detectors and the terahertz detectors at the pixel level is performed highlighting the differences between the wavebands and their impact on system design.

The U.S. Army Research Laboratory (ARL) and the U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) have developed a terahertz-band imaging system performance model/tool for detection and identification of concealed weaponry. The details of the MATLAB-based model which accounts for the effects of all critical sensor and display components, and for the effects of atmospheric attenuation, concealment material attenuation, and active illumination, were reported on at the 2005 SPIE Europe Security & Defence Symposium (Brugge). An advanced version of the base model that accounts for both the dramatic impact that target and background orientation can have on target observability as related to specular and Lambertian reflections captured by an active-illumination-based imaging system, and for the impact of target and background thermal emission, was reported on at the 2007 SPIE Defense and Security Symposium (Orlando). This paper will provide a comprehensive review of an enhanced, user-friendly, Windows-executable, terahertz-band imaging system performance analysis and design tool that now includes additional features such as a MODTRAN-based atmospheric attenuation calculator and advanced system architecture configuration inputs that allow for straightforward performance analysis of active or passive systems based on scanning (single- or line-array detector element(s)) or staring (focal-plane-array detector elements) imaging architectures. This newly enhanced THz imaging system design tool is an extension of the advanced THz imaging system performance model that was developed under the Defense Advanced Research Project Agency's (DARPA) Terahertz Imaging Focal-Plane Technology (TIFT) program. This paper will also provide example system component (active-illumination source and detector) trade-study analyses using the new features of this user-friendly THz imaging system performance analysis and design tool.

Range resolution enhancement techniques, or so called super-resolution ranging techniques, are a significant breakthrough in short-range radar imaging. Improving range resolution in a robust stable manner enables a target to be peeled in finer layers and/or the RF specifications of the radar system to be relaxed, which has clear effects on performance improvement and cost reduction. For a radar system using the frequency modulated continuous wave (FMCW) technique and traditional frequency domain techniques for reception, the range resolution is limited by the bandwidth of the transmitted wave. In this paper we propose and investigate a new super-resolution ranging technique. Multiple key performance characteristics including, minimum distinguishable distance between targets, accuracy in absolute positioning and stability in low SNR environments were evaluated using statistical simulations and real measured data. The presented results show that the proposed technique yields improved performance.

A millimetre wave (75 - 110 GHz) polarimetric RADAR system is demonstrated for the detection of threat objects concealed under clothing upon the human body at stand-off ranges of up to 25 metres. The system implements Swept Frequency Continuous Wave RADAR with low cost components to deliver a compact, UWB, high resolution (~ 1 cm) RADAR system capable of detecting, resolving and discriminating a wide spectrum of threat items concealed on the human body. Threat detection is autonomously rendered by application of a neural network to the scattered time domain polarimetric radar return, the system may be taught to alarm or reject certain classes of objects; allowing for highly specific through to broad spectrum threat detection. The authors present data for some simple envisaged threat scenarios at stand off ranges out to 25 metres.

Various schemes for active imaging require different allocations of source power and can result in different overall signal to noise ratios. At the University of Memphis we have developed an image-plane scanning device used with a single pixel detector to form video rate images of the scene. Imaging with this device requires flood illumination of the scene. Because sub-millimeter wave sources typically produce low power, it is a common belief that flood illumination results in low detected signal power and therefore low signal to noise ratios (SNR) at the detector. In this work we quantify the SNR at the detector for our system and compare it to conventional imaging systems, conjugate point imaging systems, and focal plane array imaging. Unlike the other two systems, imaging with our device requires an additional pixel formation step; therefore, the SNR at the detector is not the per-pixel SNR. We present the limits of the per-pixel SNR and discuss its dependence on various device components.

A Thz spectral characterization of the behaviour of different explosives is presented in this paper. This characterization will be done in the frequency range from 20 GHz to 4 THz using a Teraview Spectra 3000. This system has a capacity of measuring from 20 GHz to 4 THz fed by a laser source. With the Teraview Spectra 3000 equipment will be possible to calculate the refractive index, the absorbance and other important parameters of the explosive samples. With this study it will be possible to characterize some of the most common used explosives, i.e., gun explosive, gunpowder mine, pent, TNT, RDX, etc, and it will allow to determine their electromagnetic peculiarities in order to design a future imaging system that allow detecting them in security and defense sectors.

Recently, there has been a significant interest in employing Terahertz (THz) technology, spectroscopy and imaging for standoff detection. The main advantage of terahertz systems is the possibility for remote detect and identification of chemical compounds. Practical security system in reflection mode is desired. Unfortunately, reflection spectra for many compounds are very similar. Therefore, the simple correlation method is not sufficient to distinguish substances. In this paper we present the concept of using combined techniques of Short Time Fourier Transform (SFFT) and image processing with pattern recognition application in the area of automatic identification of explosives in THz range.

Terahertz (THz) radiation or millimeter wavelength detection and imaging don't have to be expensive. A miniature neon indicator lamp costing about 50 cents acting as a Glow Discharge Detector (GDD) is excellent as a low cost THz detector, but not as the most sensitive detector on the market. Experimental results show that a GDD can work as heterodyne detector, which improves the sensitivity. The experimental results show that sensitivity of heterodyne detection is improved by two orders of magnitude as compared to direct detection. We show here a proof of concept at low frequencies. In this work we compare the performance of GDDs in direct detection to the performance of GDDs in heterodyne detection at 10 GHz and at 300GHz with a low power source.