This PDF file contains the front matter associated with SPIE Proceedings Volume 7117, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

A review of the equipments developed between 1950 and 2008 is given. In the 1950s the first airborne 35 GHz radiometer was flight tested on a Lincoln bomber. Initial results were encouraging but radar and thermal imaging were becoming established and offered more general utility. The technology was based on valves and the equipment occupied a large part of the rear of the aircraft. As semiconductor technology matured and gave rise to low noise mixers and amplifiers, new equipments were developed. In 1992, MITRE, a 94 GHz data collection system based on superheterodyne receivers, provided non real time high quality imagery and stimulated interest in both surveillance and security, with images through fog and clothing being demonstrated. More recently real time imaging based on a folded conically scanned Schmidt camera has been developed for helicopter pilotage and surveillance.

A compact, solid state, zenith looking 94 GHz meteorological radar is described. Samples of the reflectivity data obtained from representative samples of hydrometeors, including cirrus cloud and fog, are presented. This bistatic FMCW radar delivers continuous information on the distribution and thickness of cloud layers, permitting accurate determination of the cloud base altitude and upper limit. The maximum range is 16 km, with a corresponding resolution of 30 m: both range and averaging time are user selectable in ranges 2-16 km and 5-60 s respectively. A radiated millimetre wave power of below 200 mW yields a dynamic range of over 60 dB in the received signal.

We report the use of a 160×120 pixel microbolometer camera, under illumination by a milliwatt-scale 3.6 THz quantum cascade laser, for real-time imaging of materials which are exclusively nonmetallic in character. By minimizing diffraction effects suffered by the camera system and operating the laser at bias currents approaching saturation values, an imaging scheme was developed in which overlapping samples of nonmetallic materials can be imaged with high fidelity and long persistence times. Furthermore, an examination of various security features embedded within domestic and foreign currency notes suggests that this imaging scheme could serve a future role in detection of assorted counterfeiting practices.

Millimeter-wave imaging is very interesting due to its unique transmission properties through a broad range of atmospheric obscurants such as cloud, dust, fog, sandstorms, and smoke, which thereby enables all-weather passive imaging. Unfortunately, the usefulness of millimeter-wave imagers is often limited by the large aperture sizes required to obtain images of sufficient resolution, as governed by the diffraction limit. To this end, we previously proposed a distributed aperture system for direct non-scan millimeter-wave imaging using an optical upconversion technique. In this proposed approach, an antenna array is employed to sample image signals in the millimeter-wave domain. The sampled millimeter-wave signals are then upconverted to the optical domain using electro-optic modulation techniques. These optical signals are mapped into a similar array on the entrance pupil of the following optical system for direct imaging. Although distributed aperture imaging is not new in both radio astronomy and conventional optical inteferometric imaging, the proposed approach is different in that it physically samples image in the millimeter-wave domain and directly forms the image in the optical domain. Therefore, specific analysis and evaluation techniques are required for the design and optimization of the proposed system. In this paper, we will address these issues, develop techniques to evaluate and enhance the system imaging performance and present methods to optimize the geometric configuration.

The effective detection of concealed handguns and knives in open spaces is a major challenge for police and security services round the world. Here an automated technique for the detection of concealed handguns that relies on active swept illumination of the target to induce both scattered fields and aspect independent responses from the concealed object is presented. The broad frequency sweep permits information about the object's size to be deduced from transformations into the time/distance domain. In our experiments we collect multiple sweeps across the frequency range at very high speed, which produces a time evolved response from the target, from both normal and cross polarized detectors. From this we extract characteristic signatures from the responses that allow those from innocent objects (e.g. mobile phones, keys etc) to be distinguished from handguns. Information about the optical depth separation of the scattering corners and the degree and shape of cross polarization allows a neural network to successfully concealed handguns. Finally this system utilizes a range of signal processing techniques ranging from correlation between cross and normally polarized scattering through to a neural network classifier to deduce whether a concealed weapon is present.

The paper describes different technological efforts to demonstrate the usefulness of millimeter wave sensors for security applications. The scope of the work covers a miniature radar in a portal geometry using a near field SAR approach for passenger control and the same radar hardware with a slightly modified scanning approach for luggage inspection employing a three dimensional SAR algorithm. Another approach to detect concealed weapons and explosives is by using radiometric systems. In principle, a scanner using this technique measures the thermal noise of the radiation reflected by the body. This is equivalent to the temperature on the surface of the body. The main difficulty with this technique is the realization of a fast scanning algorithm. The status of both approaches is surveyed and typical results are discussed.

This paper overviews the development of digital beam-forming passive millimetre wave (PMMW) imagers at the frequencies of 22.51 GHz, 91.65 GHz, and 183.31 GHz. These systems are demonstrators for imager architectures that can evolve into security screening products, all weather flying aids, satellite based imagers for planetary observation and test beds for future radio astronomy hardware. These are all areas where the common goal is to develop an imaging capability which is highly sensitive, has good angular resolution and has a minimal volume, typically a factor of 100 smaller than equivalent quasi-optical systems, and minimal weight. This paper describes the science behind electronic beam-forming for passive imaging, the objectives of the project, its risks, and the future of the technology.

We report on recent measurements and analysis performed with a metal-dielectric near-field terahertz probe. The images obtained with the near-field probe have been decomposed using factor analysis. Components corresponding to the dielectric properties of investigated samples and to the distance of the probe and of the sample have been identified. We further employed the probe for investigation of local anisotropy in a BaTiO3 crystal.

Microwaves in the range of 1-300 GHz are used in many respects for remote sensing applications. Besides radar sensors particularly passive measurement methods are used for two-dimensional imaging. The imaging of persons and critical infrastructures for security purposes is of increasing interest particularly for transportation services or public events. Personnel inspection with respect to weapons and explosives becomes an important mean concerning terrorist attacks. Microwaves can penetrate clothing and a multitude of other materials and allow the detection of hidden objects by monitoring dielectric anomalies. 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 or areas. Some millimeter-wave radiometric imaging devices with respect to low cost are investigated. Measurement results of some typical personnel screening scenarios are discussed. Requirements for future operational systems are outlined.

A novel technique of NIR imaging is presented that gives access to most of the applications currently published as being solely suitable for Terahertz (THz) waves. The technique uses NIR beams wavelengths found in ordinary domestic remote controls (circa 850 nm) and various signal recovery techniques commonly found in astronomy. This alternative technique can be realised by very simple and inexpensive electronics and is inherently far more portable and easy to use and no special sources are required. Transmission imaging results from this technique are presented from several industrial examples and various security applications and are compared and contrasted directly with their THz-derived counterparts. It would appear possible to very cheaply and simply emulate the performance of commercial terahertz systems at a fraction of the cost and with greatly reduced processing times Another advantage is that apart from imaging, this technique affords the means to provide simultaneous in-situ chemical-bond analysis for stand-off detection of certain chemical signatures - for example, those found in drugs and explosives (both molecular and oxidiser based). Also, unlike THz, this technique can penetrate bulk water and high humidity atmospheres and be used in transmission mode on biological and medical samples. Several results are presented of non-ionising X-ray type images that even differentiate between separate types of soft tissue

QinetiQ has used a suite of modelling tools to predict the millimetric plume signatures from a range of ballistic missile types, based on the accepted theory that Bremsstrahlung emission, generated by the collision of free electrons with neutral species in a rocket motor plume, is the dominant signature mechanism. Plume signatures in terms of radiation temperatures varied from a few hundred Kelvin to over one thousand Kelvin, and were predicted to be dependent on emission frequency, propellant type and missile thrust. Two types of platform were considered for the passive mmw imager launch detection system; a High Altitude Platform Station (HAPS) and a satellite based platform in low, mid and geosynchronous earth orbits. It was concluded that the optimum operating frequency for a HAPS based imager would be 35GHz with a 4.5m aperture and a sensitivity of 20mK providing visibility through 500 vertical feet of cloud. For a satellite based platform with a nadir view, the optimum frequency is 220 GHz. With such a system, in a low earth orbit at an altitude of 320km, with a sensitivity of 20mK, a 29cm aperture would be desirable.

The characterization of materials in the millimeter wave frequency range offer many new applications for quality control and security applications. This paper shows results for different applications with a real aperture scanning system in the frequency range between 75 GHz - 325 GHz in amplitude and phase.

The possibilities to support the interpretation of spatial 3D-radar data visually both with and without camera images are studied. Radar measurements and camera pictures of a person are analyzed. First, the received signal amplitudes distributed in three dimensions, spherical range and two angles, are fed to a selection procedure using amplitude and the scene volume of interest. A number of resolution cells will then form images based on a volume representation depending upon the amplitude and location. Projecting the images of all the cells upon an imaging plane then forms the total image. Different images of a radar data set are performed for different projecting planes. The images were studied to find efficient aspect angles to get the target information of most interest. Rotating the target data around a suitable axis may perform such search. In addition, a visualization method for presenting radar data merged with a camera picture has been developed. An aim in this part of the work has been to keep the high information content of the camera image in the merged image. From the 3D-radar measurements the radar data may be projected upon the imaging plane of a camera with an arbitrary viewing center. This possibility is presented in examples with one camera looking at the target scene from the radar location and another camera looking from an aspect angle differing 45° relative to the aspect angle of the radar.

The development of a 210 GHz radar system intended to study security applications such as personnel scanning is reported. The system is designed to operate with a transmit antenna floodlighting the target scene and a mechanically scanned antenna-integrated receiver module. For increased performance and potential future volume production the receiver front-end is based on highly integrated MMICs manufactured using the IAF 0.1 μm GaAs mHEMT process made available through a Swedish-German MoU. A single-chip MMIC solution is being developed containing feed antenna, LNA, mixer and an LO multiplier-chain. The transmitter part is based on a high-power HBV quintupler source-module.

The characteristics of continuous-wave millimeter-wave/terahertz radars make them candidates to remotely sense the physiological parameters of individuals, such as respiration and heart rates. The characteristics of these radars include transmission through the atmosphere and clothing, well-collimated beams, and sensitivity to small displacements. The directional Doppler velocity can be used to measure the movement of a subject's chest wall due to respiration and the more subtle motion of the body due to the cardiopulmonary system. We will present an overview of two systems that have been developed along with representative data from each.

Millimetre waves in the range 20 to 110 GHz have been used to detect the presence and thickness of dielectric materials, such as explosives, by measuring the frequency response of the return signal. Interference between the reflected signals from the front and back surfaces of the dielectric provides a characteristic frequency variation in the return signal, which may be processed to yield its optical depth [Bowring et al, Meas. Sci. Technol. 19, 024004 (2008)]. The depth resolution depends on the sweep bandwidth, which is typically 10 to 30 GHz. By using super-heterodyne detection the range of the object can also be determined, which enables a signal from a target, such as a suicide bomber to be extracted from background clutter. Using millimetre wave optics only a small area of the target is illuminated at a time, thus reducing interference from different parts of a human target. Results are presented for simulated explosive materials with water or human backing at stand-off distances. A method of data analysis that involves pattern recognition enables effective differentiation of target types.

Guns and knives have become a significant threat to public safety. Recently, a variety of techniques based on Electromagnetics (EM) have been used for their detection. For example, walk-through metal detection has been used in airports; X-ray and THz detection systems have been used for luggage screening. Different EM frequencies for metallic object detection have demonstrated different merits. This paper reports on a 1-14 GHz swept-frequency radar system for metallic object detection using reflection configuration. The swept frequency response and resonant frequency behaviour of a number of metallic objects, in terms of position, object shape, rotation and multiple objects have been tested and analysed. The system working from 1 to 14 GHz has been set up to implement sensing of metal items at a standoff distance of more than 1 meter. Through a series of experimental investigations, it can be found that the optical depths derived from the Fourier Transform of the power spectrum profile is in close relation with the relative location of the metallic object. The cross correlation between coherence-polarisation and cross-polarisation RF returns can be used to distinguish different objects. Therefore the optical depth and the cross correlation can be used as useful features for metallic object detection and characterisation in this portion of the microwave frequency spectrum.

This paper describes the research efforts made at the Swedish Defence Research Agency (FOI) concerning through-the-wall imaging radar, as well as fundamental characterization of various wall materials. These activities are a part of two FOI-projects concerning security sensors in the aspects of Military Operations in Urban Terrain (MOUT) and Homeland Defence. Through-the-wall high resolution imaging of a human between 28-40 GHz has been performed at FOI. The UWB radar that was used is normally a member of the instrumentation of the FOI outdoor RCS test range Lilla Gåra. The armed test person was standing behind different kinds of walls. The radar images were generated by stepping the turntable in azimuth and elevation. The angular resolution in the near-field was improved by refocusing the parabolic antennas, which in combination with the large bandwidth (12 GHz) gave extremely high resolution radar images. A 3D visualization of the person even exposed the handgun tucked into one hip pocket. A qualitative comparison between the experimental results and simulation results (physical optics-based method) will also be presented. The second part of this paper describes results from activities at FOI concerning material characterization in the 2-110 GHz region. The transmission of building, packing and clothing materials has been experimentally determined. The wide-band measurements in free space were carried out with a scalar network analyzer. In this paper results from these characterizations will be presented. Furthermore, an experimental investigation will be reported of how the transmission properties for some moisted materials change as a function of water content and frequency. We will also show experimental results of how the transmission properties of a pine panel are affected when the surface is coated with a thin surface layer of water.

Radar simulation involves the computation of a radar response based on the terrain's normalized radar cross section (RCS). In the past different models have been proposed for modeling the normalized RCS. While being accurate in most cases they lack intuitive handling. We present a novel approach for computing the mean normalized radar cross section for use in millimeter wave radar simulations based on Phong lighting. This allows us to model radar power return in an intuitive way using categories of diffuse and specular reflections. The model is computational more efficient than previous approaches while using only few parameters. Furthermore, we give example setups for different types of terrain. We show that our technique can accurately model data output from other approaches as well as real world data.

Most parts of the electromagnetic spectrum are well understood and exploited, but the terahertz region between the microwave and infrared is still relatively under developed. Potential receiver applications are wide-ranging and cross-disciplinary, spanning the physical, biological, and medical sciences. In this spectral region, Schottky diode technology is uniquely important. InP MMIC amplifiers are generally limited to frequencies less than ~200 GHz, above which their noise performance rapidly deteriorates. Superconducting circuits, which require cooling, may not always be practical. Either as varistor diodes (heterodyne mixing), or varactor diodes (sub-millimetre power generation), Schottky technology underpins terahertz receiver development.

We report on MMIC-based analog frontend components for imaging radar and radiometry at high millimeter-wave frequencies. The MMICs are realized in our metamorphic HEMT technology. In W-band, the focus is on analog frontends with multi-pixel capability. A compact four-channel receiver module based on four single-chip heterodyne receiver MMICs achieves a noise figure of 4.2 dB and a conversion gain of 7 dB. A W-band five-to-one switch MMIC with less than 3.5 dB insertion loss addresses four antenna ports and uses an integrated reference termination for pixel normalization. Both components operate in a frequency range from 75 to 100 GHz, making them suitable for broadband imaging systems with high geometrical resolution. After an overview of MMIC amplifier performance over the entire millimeter-wave frequency range, we present a chip set for imaging radar at 210 GHz, comprising linear and frequency-translating circuits.

There is a strong need for wideband and sensitive THz receivers for radio astronomy and remote sensing applications, for which superconducting Hot Electron Bolometer (HEB) mixers are very competitive. Besides, new THz applications have arisen because of interesting interaction with various media, for which room temperature detectors are highly attractive. We have used YBa2Cu3O7-d (YBCO) oxides to fabricate bolometers, either of high-Tc superconducting HEB type (high oxygen content, &dgr; < 0.3) or semiconducting type (low oxygen content, &dgr; > 0.5). Firstly, we fabricated HEBs made from superconducting YBCO ultrathin films (15 to 40 nm thick) etched to form submicrometer constrictions. In order to investigate the feasibility of highly sensitive HEB linear arrays for passive THz imaging applications, extensive technological runs were performed to prevent ageing effects on both the pixel electrical and optical characteristics. Secondly, we designed YBCO semiconducting bolometric pixels for room temperature operation. Due to the reduced sensitivity and bandwidth with respect to superconducting HEBs, we considered the feasibility of 2D arrays for active THz imaging. As a first experimental step, pixel responsivity and thermal crosstalk between pixels were studied in the 1 Hz to 100 kHz modulation frequency range, so to evaluate the adequate frame refreshing rate.

There is a strong need for wideband and sensitive THz receivers for radio astronomy and remote sensing applications, for which superconducting Hot Electron Bolometer (HEB) mixers are very competitive. Besides, many new THz applications have arisen because of interesting interaction with various media. For practical and economical issues, room temperature detectors are highly attractive for these latter. We have used YBaCuO oxides to fabricate bolometric pixels, either of high-Tc superconducting HEB type (high oxygen content) or semiconducting type (low oxygen content). In the THz range, such materials without any antenna would be totally reflective to the electromagnetic radiation. Moreover, integrated planar antenna structures are recommended for optimal coupling to the small detection area. The aim of this work was to investigate broadband THz antennas coupled to YBaCuO pixels, and address the specific problems arising for each family. For HEBs, self-complementary log-periodic wideband antennas, exhibiting quasi-constant impedance, were chosen. After designing / simulating the THz antenna, we scaled it down to the microwave region for experimental validation purposes. A key issue arose because a thick (10 cm) and MgO electrically equivalent substrate (epsr = 10) was needed to fabricate the large-scale model. For room temperature semiconducting pixels, the main objective was to maintain a large bandwidth despite the difficult matching of the antenna impedance to the large bolometer resistance, namely in the kΩ range. Starting from a high-impedance single dipole-like structure, multi-dipole solutions were investigated to increase the bandwidth. Radiation pattern and polarization issues have also been considered.

A novel imaging system for mm wavelength and THz radiation is presented in this paper. The imaging system is based upon an inexpensive neon indicator lamp or glow discharge detector (GDD) that serves as a pixel in a focal plane array (FPA). It was shown in previous investigations that inexpensive neon indicator lamp GDDs are quite sensitive to mm wavelength and THz radiation. The diameter of the GDD lamp is 6 mm and thus the FPA can be diffraction limited. Using such neon lamps we realize a 4X4 FPA. We used a Polyethylene lens to focus the radiation on the FPA. First imaging results of the novel mm-wave and THz imaging system are presented here. They images are of decent quality. Increasing the resolution of the FPA to 8X8 or 16X16 will improve significantly the quality of the photos in the mm-wave and THz radiation. Our goal is to construct a 128X128 imaging system using the GDD technology.

We report on simulations of arrays of free standing THz sources for high brightness applications in THz active imaging and sensing. THz-photomixing sources for wide tunable, room-temperature, narrow linewidth, and CW operation are considered. All the source elements are coherently driven to allow for controlled interference of the beam pattern. The center peak not only gains more power but also becomes much narrower due to interference, compared to a single emitter. The peak intensity increases with the square of the number of sources. This can improve both the resolution and the dynamic range for stand-off active imaging and sensing applications. We discuss the effect of different source layouts with respect to the illumination pattern on the target.

Millimeter wave (mmW) imaging is continually being researched for its applicability in all weather imaging. While previous accounts of our imaging system utilized Q-band frequencies (33-50 GHz), we have implemented a system that now achieves far-field imaging at W-band frequencies (75-110 GHz). Our mmW imaging approach is unique due to the fact that optical upconversion is used as the method of detection. Optical modulators are not commercially available at W-band frequencies; therefore, we have designed our own optical modulator that functions at this frequency range. Imaging at higher frequencies increases our overall resolution two to three times over what was achieved at Q-band frequencies with our system. Herein, we present imaging results obtained using this novel detector setup, as well as key imager metrics that have been experimentally validated.

The object of this paper is to study the fundamental characteristic of the 2 dimensional triangular lattice photonic crystals. The structure we studied consisted of a periodic array of dielectric rods in a dielectric slab. This structure has a certain forbidden gap which can be found by solving the Maxwell Equation. In this paper, we studied the frequency independent material for finding the dispersion curves using the plane wave expansion method. For the application in microwave and photonic devices, the scattering parameters of the structure must be studied. We used CST Microwave Studio to analyze the scattering parameters and the result is discussed. We also investigated the effect of different background material.