This PDF file contains the front matter associated with SPIE Proceedings Volume 7309, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Passive millimeter-wave (mmW) imaging has many specific defense, security and safety applications, due to the fact that all terrestrial bodies above absolute zero are emissive, and these wavelengths are not scattered by normal obscurants such as haze, fog, smoke, dust, sandstorms, clouds, or fabrics. We have previously demonstrated results from the construction of a 94 GHz passive mmW far-field imaging system utilizing optical upconversion, which imaged in only horizontal polarization. The effective radiometric temperature of an object is a combination of the object's surface and scattered radiometric temperatures. The surface radiometric temperature is a function of the object's emissivity, which is polarization dependent. Imaging with radiometric temperature data from both polarizations will allow a greater identification of the scene being imaged, and allow the recognition of subtle features which were not previously observable. This additional functionality is accomplished through the installation of added equipment and programming on our system, thus allowing the simultaneous data collection of imagery in both polarizations. Herein, we present our experimental procedures, results and passive mmW images obtained by using our far-field imaging system, a brief discussion of the phenomenology observed through the application of these techniques, as well as the preliminary details regarding our work on a 3-D passive mmW simulator capable of true physical polarization dependent effective emissivity and reflectivity rendering, based on the open-source Blender engine.

Polarimetric signatures of terrain features and man-made objects have been measured using unique Direct Detection Polarimetric Radiometers (DDPR). The DDPRs are lightweight inexpensive systems operating at 35 and 94 GHz. Each system consists of a single antenna, amplifier, and a truncated cylindrical waveguide that directly measures Q, U, and V. The highly portable DDPRs are ideal for obtaining the Stokes vectors needed to study the physical characteristics of natural and man-made features. Field evaluations using the DDPR systems include measurements from an airborne platform over different terrain features and water, and ground based measurements of the polarimetric signature of grass, asphalt, buildings, and concealed munitions. The DDPR can function as a bistatic system by using an active source of polarization. Using this configuration and a soil chamber, we have investigated the effect of soil type and soil moisture on linear and circular polarization. This report will describe the DDPR and present the analysis of the airborne and ground based measurements, including the effects of soil type and soil moisture on sources of linear and circular polarization.

Results are presented from a trial in which a real-time passive millimetre-wave camera was mounted on a landing craft. The vessel was operated on rivers in the UK, and imagery of surrounding terrain, structures, obstacles and other vessels was obtained. An IR camera was also used, and the differences in signatures of various features are discussed. Opportunities for image fusion are highlighted.

This paper describes the modeling of human task performance using a passive interferometric millimeter wave (MMW) imaging sensor. The model is based on a previous model developed for concealed weapon identification using an active terahertz imager. Both models leverage the task performance modeling approach developed by the US Army Night Vision and Electronic Sensors Directorate. Key developments for this model include modeling of the effects of an interferometric antenna array, including sparse arrays, and a novel optical upconversion and processing stage being developed by the University of Delaware. Sparse interferometric arrays do not fully sample the spatial frequency extent of the image and as a result, can have degraded spatial frequency response over a fully populated array. The spatial frequency response of the sparse array can have a dramatic effect on image quality. Image quality is empirically related to task performance through the use of perception experiments. Possible applications of this model include system trade studies, concealed weapon identification, and navigation in fog and brown out conditions.

Passive Millimeter Wave Systems often have low spatial resolution which limits the size of detectable objects. However, there are some special cases in which objects that do not completely fill a pixel may be readily detected. The geometry of wires and pipes make them particularly visible, although the contrast can vary rapidly with detector - target geometry. In this paper a model is developed for the contrast of a reflective cylinder against an arbitrary background. Experimental data is presented from a high clutter environment that shows sub pixel detection in practical environments.

The Army has identified a need to rapidly identify, map, and classify natural and manmade features to aid situational awareness as well as mission and tactical planning. To address these needs, Digital Fusion and Trex Enterprises have designed a full Stokes, passive MMW imaging polarimeter that is capable of being deployed on an unmanned aerial vehicle. Results of a detailed trade study are presented, where an architecture, waveband and target platform are selected. The selected architecture is a pushbroom phased-array system, which allows the system to collect a wide fieldof- view image with minimal components and weight. W band is chosen as a trade-off between spatial resolution, weather penetration, and component availability. The trade study considers several unmanned aerial system (UAS) platforms that are capable of low-level flight and that can support the MMW antenna. The utility of the passive Stokes imager is demonstrated through W band phenomenology data collections at horizontal and vertical polarization using a variety of natural and manmade materials. The concept design is detailed, along with hardware and procedures for both radiometric and polarimetric calibration. Finally, a scaled version of the concept design is presented, which is being fabricated for an upcoming demonstration on a small, manned aircraft.

Passive imaging using millimeter waves (mmWs) has many advantages and applications in the defense and security markets. All terrestrial bodies emit mmW radiation and these wavelengths are able to penetrate smoke, blowing dust or sand, fog/clouds/marine layers, and even clothing. One primary obstacle to imaging in this spectrum is that longer wavelengths require larger apertures to achieve the resolutions typically desired in surveillance applications. As a result, lens-based focal plane systems tend to require large aperture optics, which severely limit the minimum achievable volume and weight of such systems. To overcome this limitation, a distributed aperture detection scheme is used in which the effective aperture size can be increased without the associated volumetric increase in imager size. However, such systems typically require high frequency (~ 30 - 300 GHz) signal routing and down conversion as well as large correlator banks. Herein, we describe an alternate approach to distributed aperture mmW imaging using optical upconversion of the mmW signal onto an optical carrier. This conversion serves, in essence, to scale the mmW sparse aperture array signals onto a complementary optical array. The optical side bands are subsequently stripped from the optical carrier and optically recombined to provide a real-time snapshot of the mmW signal. In this paper, the design tradeoffs of resolution, bandwidth, number of elements, and field of view inherent in this type of system will be discussed. We also will present the performance of a 30 element distributed aperture proof of concept imaging system operating at 35 GHz.

The design of a millimeter-wave (MMW) camera is presented. The camera is meant to serve as a demonstration platform for a new 32-channel MMW detector array that requires no pre-amplification prior to detection. The Army Research Laboratory (ARL) and National Institute of Standards and Technology (NIST) have worked with the Defense Advanced Research Projects Agency and several contractors for four years to develop an affordable MMW detector array technology suitable for use in a large staring array. The camera described uses one particular embodiment of detector array that resulted from the program. This paper reviews the design of the MMW optics that will be used to form imagery with the linear array and the tradeoffs made in that design. Also presented are the results of laboratory tests of the detector array that were made at both ARL and NIST.

Ground vehicle tests have been performed to evaluate the performance of a Passive Millimeter Wave (PMMW) imager in reduced visibility conditions and in particular, the ability to detect power lines and cables. A PMMW imager was compared with Long Wave Infrared (LWIR) and visible imaging cameras. The three sensors were mounted on a Land Rover, together with GPS and digital recording system. All three sensors plus the GPS data were recorded simultaneously in order to provide direct comparisons. The vehicle collected imagery from a number of sites in the vicinity of Malvern, UK, in January, 2008. Imagery was collected both while the vehicle was stationary at specific sites and while it was moving. Weather conditions during the data collection included clear, drizzle, rain and fog. Imagery was collected during the day, at night, and during dusk/dawn transition periods. The PMMW imager was a prototype which operated at 94 GHz and was based on a conically scanned folded Schmidt camera and the LWIR and visible sensors were commercial off the shelf items.

We discuss the methods and design considerations required in engineering a high-resolution camera for use at 94 GHz (~3mm wavelength) to yield the best compromise between optical resolution, field of view, object distance, depth of focus, image acquisition time, and system cost. This application is one in which only the blackbody radiation emitted by the body is a light source, i.e., a passive system. Several critical design parameters were optimized in this design, including, the point spread function size upon the detector array, optical losses, and depth of focus. The metric for characterization of the optical design was the Huygen's wavelet calculation that correlated well with measured performance. Measurements of the PSF and MTF agreed with the model within measurement error. Sample imagery of hidden objects demonstrate that this prototype design is capable of resolving objects with feature sizes as small as 0.50 inch and further show the utility of this millimeter wavelength camera.

Passive microwave imaging allows a daytime independent observation and examination of objects and persons without artificial exposure under nearly all weather conditions. The penetration capability of microwaves allows the detection of hidden objects like weapons and explosive devices under the clothing. In August/September 2008 a comprehensive military experiment was conducted by the German armed forces at the naval base Eckernfoerde, Germany. One activity in the Eckernfoerde trial was the simulation of a military entrance portal by a tent including various imaging and a chemical sensor suite. Besides commercial optical and infrared cameras various passive millimeter-wave imagers have been used from different German research institutions. The DLR Microwaves and Radar Institute, Department for Reconnaissance and Security (HR-AS), provided an imaging radiometer scanner operating at W band. A multitude of situations have been simulated and many persons carrying hidden objects under their clothing have been scanned. Some exemplary results from the trial are shown and discussed in the paper.

The chance of suicide bomber attacks against troops in the Theatre of Operations is currently quite high. Most of the time checkpoints and compound gates are not equipped with the appropriate equipment to screen for potential suicide bombers. The ultimate solution would be to be able to perform stand-off screening under various weather conditions whilst avoiding contact between Force Protection personnel and potential suicide bombers. Radiation in the millimeterwave and the lower Terahertz range, having the useful property of being able to penetrate clothing in addition to fog and rain, makes it a clear candidate for imaging in this situation. A study has been made simulating real case scenarios to test practical detection performance and stand-off distances at a range of frequencies in this band, the results of which will be presented.

Security solutions with the purpose to detect hidden objects underneath the clothing of persons are desired in many environments. With the variety of application scenarios criteria like flexibility and mobility become more important. So, many developments trend to focus on cameras, which can image scenes from a distance. This new generation of tools will have the advantage of hidden operation, which is believed by experts to add to the security because of its unpredictability. Such stand-off cameras do have some divergent requirements compared to mm-wave portal scanners. They will benefit from shorter wavelengths because of the higher optical resolution. In contrast to that, the needed transmission properties might become impractical at higher frequencies. A commonly accepted compromise is the use of wavelengths around 0.5mm. However, for stand-off cameras without oversized optical apertures, a resolution around 1cm is a practical limit. For our security camera "Safe VISITOR" (Safe VISible, Infrared and Terhaertz Object recognition) we have chosen to combine images from three different camera modules: a CCD for visible light, a microbolometer for long infrared (14μm) and a superconducting bolometer for 870μm. This combines the highest optical resolution (visible), the unprecedented temperature resolution at infrared and the almost perfect transmission at terahertz. We have built a first prototype and tested it in a field trial. We will present experimental results and try to assess the false error rate of our system.

At present, the imaging of concealed weapons and contraband is primarily carried out at a relatively short stand-off range of a few meters mainly because of spatial resolution considerations. In order to maintain a reasonable aperture size, there is a desire to extend the operating frequency towards 1 THz. In this paper we report the progress on a video-rate THz camera demonstrator which utilizes broadband antenna-coupled microbolometers as detectors, operated within a turnkey commercial closed-cycle cryocooler. A full system has been integrated consisting of 64 parallel sensors and readout electronics, and reflective Schmidt camera optics incorporating a conical scanner for real time imaging.

The Transportation Security Administration (TSA) is presently deploying millimeter-wave whole body scanners at over 20 airports in the United States. Threats that may be concealed on a person are displayed to the security operator of this scanner. "Passenger privacy is ensured through the anonymity of the image. The officer attending the passenger cannot view the image, and the officer viewing the image is remotely located and cannot see the passenger. Additionally, the image cannot be stored, transmitted or printed and is deleted immediately after being viewed. Finally, the facial area of the image has been blurred to further ensure privacy." Pacific Northwest National Laboratory (PNNL) originated research into this novel security technology which has been independently commercialized by L-3 Communications, SafeView, Inc. PNNL continues to perform fundamental research into improved software techniques which are applicable to the field of holographic security screening technology. This includes performing significant research to remove human features from the imagery. Both physical and software imaging techniques have been employed. The physical imaging techniques include polarization diversity illumination and reception, dual frequency implementation, and high frequency imaging at 100 GHz. This paper will focus on a software privacy technique using a dual surface dielectric depth detector method.

Active millimetre wave systems, operating at frequencies up to 110 GHz have been used to detect the presence of both concealed dielectric and metallic objects at standoff distances. Co- and cross-polarized superheterodyne or direct detectors are used to differentiate between metallic and purely dielectric objects. The technique determines the thickness of a dielectric target and detects the presence of concealed handguns or fragmentation by utilising the pattern of the responses from both the co- and cross-polarized detectors. The returned signals are processed and analysed by an artificial neural network, which classifies the responses according to their correspondence to previous training data.

A prototype active wideband 350 GHz imaging system has been developed to address the urgent need for standoff concealed-weapon detection. This system is based on a wideband, heterodyne, frequency-multiplier-based transceiver system coupled to a quasi-optical focusing system and high-speed conical scanner. This system is able to quickly scan personnel for concealed weapons. Additionally, due to the wideband operation, this system provides accurate ranging information, and the images obtained are fully three-dimensional. Waves in the microwave, millimeter-wave, and terahertz (3 GHz to 1 THz) frequency bands are able to penetrate many optical obscurants, and can be used to form the basis of high-resolution imaging systems. Waves in the sub-millimeter-wave band (300 GHz to 1 THz) are particularly interesting for standoff concealed-weapon detection at ranges of 5 - 20+ meters, due to their unique combination of high resolution and clothing penetration. The Pacific Northwest National Laboratory (PNNL) has previously developed portal screening systems that operate at the lower end of the millimeter-wave frequency range around 30 GHz. These systems are well suited for screening within portals; however, increasing the range of these systems would dramatically reduce the resolution due to diffraction at their relatively long wavelength. In this paper, the standoff 350 GHz imaging system is described in detail and numerous imaging results are presented.

We present experimental results for an uncooled imaging focal plane array technology that consists of a polymer/metal/polymer layered membrane suspended over a micro-fabricated array of cavities. The device operation is Golay-like (heating of air in the cavity causes a detectable deflection of the membrane proportional to incident EM power), but potentially offers both greater sensitivity and more read-out options (optical or electrical) than a traditional Golay cell through tailoring of the membrane properties. The membrane is formed from a layer-by-layer deposition of polymer with one or more monolayers of gold nanoparticles (or other metal) that help control the membrane's elasticity and deformation-dependent optical reflectivity/electrical conductivity. Baseline capabilities of the device have been established through optical measurements of membrane deflection due to incident mm-wave radiation modulated at 30 Hz (corresponding to a video refresh rate). The device demonstrates an NEP of 300 nW/√Hz at 105 GHz for a 19-layer membrane (9 poly/1 Au/9 poly) suspended over an array of 80 μm diameter cavities (depth = 100 μm) etched in a 500 μm thick substrate of Si. Calculations of membrane sensitivity show that this NEP could be reduced to ~ 100 pW/√Hz with enlarged cavity diameters on the order of 600 μm.

In this paper a two dimensional electromagnetic analysis and numerical simulations for a structure consisting of a resistive sheet backed by a spatially non-uniform perfectly conducting reflector is presented. The analyzed nonuniformity is a dip or bump on the reflector surface. The analysis is aimed at the design and evaluation of this structure as a spatially selective mirror for use in a single pixel sub-millimeter wave imager. Scattered and absorbed powers as well as the scattered radiation intensity are calculated in the far field for illumination by a linearly polarized, tapered Gaussian beam. Simulations for normally incident radiation and radiation at obtuse angles are presented. The scattered field in the far region is measured (simulation) by a receiving antenna and the dependence of the simulated received power on the position of the non-uniformity is observed. The dependence of the simulated received power on the size of the non-uniformity on the reflector is also presented. We conclude with the description of a single pixel sub-millimeter wave imager that uses the analyzed structure.

Millimetre-wave (mmW) imaging has attracted significant research interests for the promises of allweather imaging and security scanning for military applications. Recently, we have developed a highsensitivity mmW imaging system based on photonic devices, which relies on optical up-conversion of the received mmW signal to generate detectable sidebands. For system with lower detector reponsivity, higher resolution and wider separation between sidebands and optical carrier, a high efficiency EO modulator that works in W-band is required. Since such system does not exist commercially, we were motivated to develop our own 94GHz phase modulator. In our previous publications, we have presented design, fabrication and preliminary characterization of Lithium Niobate (LN) based devices. We continue in this paper with our post-processing techniques, updated characterization results and the packaging method between antenna and modulator. Modulation efficiency >1W^-1 has been achieved over W-band. Using a fin-coupler for antenna integration, we have obtained insertion loss less than 3dB. The packaged modulator has been installed in our imager. Initial scanning showed high-quality images of various objects.

Narrow-gap direct detection mercury cadmium telluride (MCT) THz semiconductor hot electron bolometer (SHEB) is considered. Device operation takes into account the phenomena in semiconductor bipolar plasma and hot-carrier effect at uncooled or slightly cooled conditions. To examine the SHEB detector in the wide range of operation frequencies (ν=0.037-1.58 THz) the simplest dipole antennas were used in prototype arrays. The experiments were performed at T = 300 K at ν= 37, 50, 75 GHz, 0.89 and 1.58 THz with a MCT SHEB devices with intrinsic conductivity. At ν=1.58, 0.89, 0.078 and 0.037 THz the signal temperature dependencies were measured too. The sensitivity was S_v~2.5 V/W (estimated NEP~4×10^-10 W/Hz^1/2) at T=300 K; and S_v~2×10³ V/W (estimated NEP~3×10^-12 W/Hz^1/2) at T=78K and ν=37, and 78 GHz. The signal temperature dependences at ν=0.89 THz are different compared to those at ν=37 and 78 GHz. Temperature phase dependent signals are discussed with their dependence on energy relaxation time. A model of such a detector is developed. The radiation entrance through semiconductor surface and metal contacts are both modeled.