This PDF file contains the front matter associated with SPIE Proceedings Volume 8362, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Heterodyne terahertz (0.3 - 3THz) imaging systems are currently limited to single or a low number of pixels. Drastic improvements in imaging sensitivity and speed can be achieved by replacing single pixel systems with an array of detectors. This paper presents an array topology that is being developed at the Jet Propulsion Laboratory based on the micromachining of silicon. This technique fabricates the array's package and waveguide components by plasma etching of silicon, resulting in devices with precision surpassing that of current metal machining techniques. Using silicon increases the versatility of the packaging, enabling a variety of orientations of circuitry within the device which increases circuit density and design options. The design of a two-pixel transceiver utilizing a stacked architecture is presented that achieves a pixel spacing of 10mm. By only allowing coupling from the top and bottom of the package the design can readily be arrayed in two dimensions with a spacing of 10mm x 18mm.

The development of millimeter-wave scanning reflectarrays and phased arrays provides an important path to enabling electronic scanning capabilities at high frequencies. This technology could be used to eliminate the mechanical scanners that are currently used with radar imaging systems. In this work, we analyze properties of wafer-scale two-dimensional rectangular lattice arrays that can be used with a confocal imager for 220 GHz electronic scanning of meter-sized fields of regard at 50 m. Applications include covert imaging of hidden anomalies. We examine tradeoffs between overall system size and array complexity and analyze properties of reflectarrays compatible with a system design that was chosen based on these considerations. The effects of phase quantization are considered in detail for arrays with 1- and 2- bit phase shifters and the results are compared in terms of impacts to image quality. Beam pointing accuracy, main beam energy fraction, and the number and intensity of quantization lobes that appear over the scan ranges of interest are compared. Our results indicate that arrays with 1- and 2-bit phase quantization achieve similar main beam energy efficiencies over the desired scan range. Without restricting the scan range, 1-bit phase quantization is insufficient, resulting in maximum errors that are comparable to the required minimum scan angle. Two-bit phase quantization is preferable, resulting in pointing angle errors of at most 15 % of the diffraction-limited beam-size. Both 1- and 2-bit phase quantization cases result in lobes appearing above our threshold, indicating that spurious returns are a problem that will require further attention.

We present results for a rapid, precise and wide field-of-view scanning antenna for use at millimeter and submillimeter wavelengths, based on the photo-injected Fresnel zone plate antenna (piFZPA) method. Our work demonstrates the potential of this technology as a viable solution to a range of applications demanding video rate imagery at these frequencies. This technique is based on optically exciting free carriers in a semiconductor substrate, to form a plasma-based Fresnel zone plate antenna, which focuses and steers incident millimeter-wave beams. By reconfiguring the optically projected pattern, it is possible to dynamically, and rapidly, manipulate (sub) millimeter-wave beams within a 3D volume. It is believed that the little attention devoted to this method since it was first demonstrated 20 years ago has been due to the high illumination densities required for sufficient plasma injection. Our work has made significant improvements in addressing this requirement and the technique is demonstrated using simple, commercially available hardware. We present proof-of-principle experiments at 94GHz incorporating a commercial data projector. The 100mm diameter piFZPA achieves 37dBi directivity, excellent beam symmetry, beam steering in two dimensions over a ±30° field-of-view, and precise beam control and repeatability. Whilst current demonstrations are restricted to less than 20 beams per second with the current implementation, the technique is capable of achieving beam scanning rates of more than 10,000 beams per second, suitable for video-rate imagery. We also present, believed to be for the first time, results of a piFZPA integrated into a short range, 94GHz, 3D imaging radar.

Development of a 120-GHz FMCW radar with a reflectarray as focusing element is described. The reflectarray is realized on a 150-mm silicon wafer and it has 3700 phase-modulating elements on it. The phase shifters have four discrete values to cover full phase modulation with 90° steps. The reflectarray element is realized with a conductor-backed coplanar waveguide patch antenna with a phase shifter coupled to it. The required phase modulation for each reflectarray element is determined with an in-house physical optics simulation combined with genetic-algorithm-based optimization. The reflectarrays are developed in two stages. First, preliminary reflectarrays with static phase shifters have been manufactured and tested at 120-GHz antenna measurement range. The static reflectarrays are found to perform as designed in their capability to steer the beam to a desired direction and to a distance of 3 m. The reflectarrays have -3-dB beam width from 1.1° to 1.3° depending on the beam tilt. After the preliminary verification with the static phase shifters, the reflectarrays will be assembled together with actively controlled MEMS-based phase shifters. The MEMS switches are controlled with dedicated high-voltage CMOS electronics, forming a system-in-a-package (SiP). First, the MEMS phase shifters are modeled, are being fabricated, and will be measured separately to verify their phase-shifting capability.

We present a 340 GHz 3D radar imaging test bed with 10 Hz frame rate which enables the investigation of strategies for the detection of concealed threats in high risk public areas. The radar uses a wideband heterodyne scheme and fast-scanning optics to achieve moderate resolution volumetric data sets, over a limited field of view, of targets at moderate stand-off ranges. The high frame rate is achieved through the use of DDS chirp generation, fast galvanometer scanners and efficient processing which combines CPU multi-threading and GPU-based techniques, and is sufficiently fast to follow smoothly the natural motion of people.

As millimeter-wave arrays become available, off-axis imaging performance of the fore optics increases in importance due to the relatively large physical extent of the arrays. Typically, simple optical telescope designs are adapted to millimeter-wave imaging but single-mirror spherical or classic conic designs cannot deliver adequate image quality except near the optical axis. Since millimeter-wave designs are quasi-optical, optical ray tracing and commercial design software can be used to optimize designs to improve off-axis imaging as well as minimize cross-polarization. Methods that obey the Dragone-Mizuguchi condition for the design of reflective millimeter-wave telescopes with low cross-polarization also provide additional degrees of freedom that offer larger fields of view than possible with single-reflector designs. Dragone's graphical design method does not lend itself readily to computer-based optical design approaches, but subsequent authors expanded on Dragone's geometric design approach with analytic expressions that describe the location, shape, off-axis height and tilt of the telescope elements that satisfy Dragone's design rules and can be used as a first-order design for subsequent computer-based design and optimization. We investigate two design variants that obey the Dragone-Mizuguchi conditions that exhibit ultra-low cross-polarization and a large diffraction-limited field of view well suited to millimeter-wave imaging arrays.

We report on the development of an active stand-off imaging system operating in the 80 GHz - 110 GHz frequency range. 3D real-time imaging is enabled by a combination of a mechanically scanned one-dimensional conventional imaging projection with a rotating metallic reflector and a two-dimensional synthetic imaging reconstruction with a linear array of transmitter (Tx) and receiver (Rx) elements. The system is conceived, in order to allow a resolution better than 1cm both in lateral, as well as in range directions by using a multi-view imaging geometry with an aperture larger than 2 m x 2 m. The operation distance is 8.5 - 9 m. The 2D synthetically reconstructed imaging planes are derived from the correlation of 20 sources and 24 coherent detectors. Range information is obtained by operating in a frequency modulated continuous wave (FMCW) mode. Real-time imaging is enabled by implementing the synthetic image reconstruction algorithms on a general purpose graphics processing unit (GPGPU) system. A multi-view imaging geometry is implemented, in order to enhance the imaging resolution and to reduce the influence of specular reflections.

In the paper we present the performance of our new 128 -channel passive submillimeter-wave camera, capable of cm-scale resolution at 5 m standoff and frame rates up to 10 fps. The measured resolution metrics for the system will be presented.

A passive millimeter-wave sensor based on optical up-conversion that is sensitive to the polarization state of incident radiation is described. This system up-converts incident millimeter-wave radiation to an optical frequency and then recreates the polarization state of the millimeter-wave radiation in the optical signal. A division of time approach is then used to extract the Stokes information from the signal using optical techniques. Results are shown which verify the feasibility of this approach and demonstrate the ability to control the phase of the signal to enable the measurement of Stokes information.

Future submillimeter-wave and THz (300GHz-3THz) imaging applications will require low-cost portable systems operating at room-temperature with a video-rate speed and capable of delivering acceptable sensitivity at the very low-power consumption levels to become attractive for truly commercial applications. In particular, CMOS technologies are of interest due to their high integration level offered at a high yield that is capable of massive cost reduction of currently existing THz systems. It has been recently demonstrated that CMOS direct detectors achieve the performance comparable or even superior to the today's existing classical THz devices for active imaging operating at room-temperature. So far, however, only single pixels have been used, allowing only a raster-scan operation. To address this obstacle, we present the very initial work on a 1k-pixel camera chip with a completely integrated readout circuitry and with a full video-rate capability at a power consumption of 2.5μW/pixel. The chip is fully compliant with an industrial bulk CMOS technology and it is intended for active imaging applications. It exhibits a pixel pitch of 80μm, defined by a novel on-chip wire ring antenna, and is designed to accommodate silicon hyper-hemispherical lens for a wide operation bandwidth of at least 0.7-1.1 THz.

Trex Enterprises and US Army RDECOM CERDEC Night Vision Electronic Sensors Directorate developed and tested helicopter radar to aid in brown-out landing situations. A brown-out occurs when sand and dust kicked up by the helicopter rotors impair the pilot's vision. Millimeter-wave (MMW) radiation penetrates sand and dust with little loss or scattering, and radar at this frequency can provide a pilot with an image of the intended landing zone. The Brown-out Situational Awareness System (BSAS) is a frequency-modulated, continuous-wave radar that measures range to the ground across a conical field-of-view and uses that range information to create an image for the pilot. The BSAS collected imagery from a helicopter in a blowing sand environment with obstacles including ditches, hills, posts, poles, wires, buildings and vehicles. The BSAS proved the capability to form images of the ground through heavy blowing sand and resolve images of some obstacles. The BSAS also attempted to differentiate flat ground from bumpy ground with limited success at some viewing angles. The BSAS test imagery includes some artifacts formed by high radar cross-section targets in the field-of-view or sidelobes. The paper discusses future improvements that could limit these artifacts.

One of the emerging applications of the millimeter-wave imaging technology is its use in biometric recognition. This is mainly due to some properties of the millimeter-waves such as their ability to penetrate through clothing and other occlusions, their low obtrusiveness when collecting the image and the fact that they are harmless to health. In this work we first describe the generation of a database comprising 1200 synthetic images at 94 GHz obtained from the body of 50 people. Then we extract a small set of distance-based features from each image and select the best feature subsets for person recognition using the SFFS feature selection algorithm. Finally these features are used in body geometry authentication obtaining promising results.

This PhD programme is contributing to the development of Passive Millimetre-Wave Imagers (PMMWI) using the principles of interferometric aperture synthesis and digital signal processing. The principal applications are security screening, all-weather flight aids and earth observation. To enhance the cost-effectiveness of PMMWI systems the number of collecting elements must be minimised whilst maintaining adequate image fidelity. A wide range of techniques have been developed by the radio astronomy community for improving the fidelity of sparse interferometric array imagery. This paper brings to the attention of readers these techniques and discusses how they may be applied to imaging using software packages publicly available from the radio astronomy community. The intention of future work is to adapt these algorithms to process experimental data from a range of realistic simulations and real-world targets.

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. In the other hand, the resolution of MMW images is lower comparing to IR and visual due to longer wavelength. Furthermore, the diffraction effects are more noticeable in THz and MMW imaging systems. Thus the MMW images are blurred and unclear and thus it is difficult to see the details and small objects. In recent experimental work with 8X8 Glow Discharge Detector (GDD) Focal Plane Array (FPA) we were able to improve the resolution of MMW images by using oversampling methods with basic DSP algorithms. In this work a super resolution method with basic DSP algorithms will be demonstrated using the 2X18 double row camera. MMW images with sub wavelength resolution will be shown using those methods and small details and small objects will be observed.

Millimeter wave (MMW) imaging is finding rapid adoption in security applications such as concealed object detection under clothing. A passive MMW imaging system can operate as a stand-off type sensor that scans people in both indoors and outdoors. However, the imaging system often suffers from the diffraction limit and the low signal level. This paper discusses real-time concealed object recognition based on geometric descriptors. The concealed object region is extracted by the multi-level segmentation method. A novel approach is proposed to measure similarity between a true object model and segmented binary objects. Principal component analysis (PCA) regularizes the shape in terms of translation and rotation. Size normalization provides scale-invariant property. A geometric feature vector is composed of several shape descriptors. The feature vector is invariant to scale, rotation, and translation, and tolerant to distortion. Classification is performed by means of measuring Euclidean distance between the mean feature vector of training models and the feature vector of the segmented object. Experiments confirm that the proposed method provides fast and reliable recognition of the concealed object carried by a moving human subject.

Passive millimeter wave (PMMW) imaging has shown distinct advantages for detection of terrestrial targets under optically obscuring conditions such as cloud, haze, snow, and light rain. The purpose of this paper is to evaluate the performance of a PMMW imager for terrestrial target recognition with respect to range of detection and climatic variables such as cloud, light rain, and snow. We used a dual polarization MMW radiometer in the frequency range of 70-100 GHz for the evaluation. We present experimental results and analyze the effect of weather conditions on the image quality and its polarization contrast. These results will be useful for quantitative prediction of PMMW system performance for long-range terrestrial imaging.

We demonstrate real-time computer code improving significantly the quality of images captured by the passive THz imaging system. The code is not only designed for a THz passive device: it can be applied to any kind of such devices and active THz imaging systems as well. We applied our code for computer processing of images captured by four passive THz imaging devices manufactured by different companies. It should be stressed that computer processing of images produced by different companies requires using the different spatial filters usually. The performance of current version of the computer code is greater than one image per second for a THz image having more than 5000 pixels and 24 bit number representation. Processing of THz single image produces about 20 images simultaneously corresponding to various spatial filters. The computer code allows increasing the number of pixels for processed images without noticeable reduction of image quality. The performance of the computer code can be increased many times using parallel algorithms for processing the image. We develop original spatial filters which allow one to see objects with sizes less than 2 cm. The imagery is produced by passive THz imaging devices which captured the images of objects hidden under opaque clothes. For images with high noise we develop an approach which results in suppression of the noise after using the computer processing and we obtain the good quality image. With the aim of illustrating the efficiency of the developed approach we demonstrate the detection of the liquid explosive, ordinary explosive, knife, pistol, metal plate, CD, ceramics, chocolate and other objects hidden under opaque clothes. The results demonstrate the high efficiency of our approach for the detection of hidden objects and they are a very promising solution for the security problem.

Screening cameras working in millimetre band gain more and more interest among security society mainly due to their capability of finding items hidden under clothes. Performance of commercially available passive cameras is still limited due to not sufficient resolution and contrast in comparison to other wavelengths (visible or infrared range). Testing of such cameras usually requires some persons carrying guns, bombs or knives. Such persons can have different clothes or body temperature, what makes the measurements even more ambiguous. To avoid such situations we built a moving phantom of human body. The phantom consists of a polystyrene manikin which is covered with a number of small pipes with water. Pipes were next coated with a silicone "skin". The veins (pipes) are filled with water heated up to 37 C degrees to obtain the same temperature as human body. The phantom is made of non-metallic materials and is placed on a moving wirelessly-controlled platform with four wheels. The phantom can be dressed with a set of ordinary clothes and can be equipped with some dangerous (guns, bombs) and non-dangerous items. For tests we used a passive commercially available camera TS4 from ThruVision Systems Ltd. operating at 250 GHz. We compared the images taken from phantom and a man and we obtained good similarity both for naked as well as dressed man/phantom case. We also tested the phantom with different sets of clothes and hidden items and we got good conformity with persons.