The state-of-the-art has now matured to the point where millimeter wave systems are often a viable replacement and improvement over older microwave (or infrared) systems. However, the decline in defense spending, the sluggish global economy, and increased competition dictate that to be successful a combination of hard and soft system analysis approaches must be applied to the system engineering methodology. This paper surveys recent developments in millimeter wave technology, system engineering methodology, and an overview of recent applications.

The concept of imaging spectrometry is finding broad application in scientific instrumentation for Earth-based, airborne, and space applications. An imaging spectrometer is characterized by the combination of imaging with complete sampling in the spectral domain. In so doing, material identification can be accomplished and displayed in conjunction with the conventional recognizable image. An imaging spectrometer incorporates a wide variety of technologies, including focal plane arrays, imaging and spectrometer optics, and spectral dispersing devices. The design of a successful system involves a complex set of trade-offs incorporating the properties and limitations of the various technologies. For applications in the infrared, additional technologies such as focal plane cooling are required, and the other technologies present more limitations and constraints. This paper describes the system design process for a typical application, and discusses the system performance parameters and trade-offs, including choice of system architecture, signal to noise ratio, system resolution, spectral performance, calibration, and the effect of artifacts such as detector non-uniformity.

Thin film resistor technology represents one of the more promising approaches to the problem of providing infrared projection capabilities, particularly when the requirement is for small arrays that operate at high speed at temperatures above 200 degree(s)C. In this paper, the fabrication and characterization of an infrared projector device based on a 2 X 36 thin film resistor array is described. Finite element heat analysis was used during the design phase in order to determine the steady state and transient temperature response of the array. The arrays were fabricated on a polyimide layer on a silicon wafer substrate by using conventional techniques for photolithography, etching, and vacuum deposition. Each resistor element in the array is thermally isolated from its neighboring element by a trench in the polyimide. Characterization of the individual resistors has demonstrated a surface temperature of at least 230 degree(s)C. A transient response of 150 microsecond(s) has been observed for the 10 - 90% rise and fall times.

In this research, a principal unmodeled error contributor in radome analysis is identified as the local plane approximation at the ray intercept point. An improved approach to modeling and computing the effects of the radome wall was developed which improves the radome wall transmission wall analysis in three respects: use of surface integration, utilization of a divergence factor (DF) to account for wall curvature, and incorporation of the effects of multiple refraction (MR). Modeling an incident plane wave on an external reference plane as an ensemble of Huygen's sources, geometric optics is used to trace the fields from the reference plane through the radome wall to a receiving monopulse antenna, where the wall transmissions on each ray are collected. The fact that the integration of a bundle of rays through the radome wall, as opposed to a single ray, more densely samples the curvature variation results in a more robust model. A DF derived from Snell's law for spherical shells accounts for the local wall curvature at the ray intercept point. To validate the approach, a microwave measurement setup was assembled around a network analyzer. Swept frequency data were obtained for similar monolithic wall dielectric panels but with different wall curvatures. Comparisons were then with measured data and the predictions of the model herein.

We describe the modeling of the backscattering of extended radar targets and discuss an experimental based method of determining the model parameters. These target models can be used in simulation and evaluation problems where we give some examples for a high resolution radar. In a large number of applications of these radars (frequency 94 GHz and higher), the resolution of the cell is smaller than the complete target. For MMW the backscattering of the illuminated section of that target is characterized by the interference of a `large amount' of scatterers. For the radar-cross-section (RCS) of the illuminated target section (so called `local' RCS), this results in such an extreme variation with respect to angle and frequency, that a deterministic description doesn't seem to be adequate. In these circumstances, our MMW-target-model provides spatial and aspect angle depending statistical data. As an example, the complete procedure is demonstrated with a 94 GHz FMCW-Radar with a 3-dB-beam of approx. 2 degree(s).

Certain high power microwave (HPM) applications require output power in the range of only a few hundred megawatts effective radiated power (ERP) in a portable configuration. This paper describes a portable HPM device prototype that was developed, demonstrated, and evaluated.

The electrical test of aircraft radomes are usually made on an outdoor far field test range, and are both extensive and expensive, often requiring days of effort per radome. A new method of testing is posed where point-by-point microwave reflectometer (amplitude and phase) data are used, in conjunction with a predictive algorithm, to extrapolate equivalent wall layer parameters at the measurement point. These data are then incorporated in a ray trace computer code to predict full radome BSE and loss contours without the need for a full outdoor test range; significant cost and schedule savings accrue. Millimeter wave reflectometer data are also shown to be potentially valuable in detecting and characterizing certain types of defects.

Wide use of computing engineering and radiolocation and communication systems has promoted development of new methods and means of receiving and processing signals based on discrete transformations in orthogonal function classes. A technical realization of the devices which use basic function systems to describe two-dimensional signals in quasi-optics becomes a simpler one when using orthogonality properties of Gaussian wave beams. A multimode two-mirror open resonator (OR) (of Fabry-Perot type) with an input partially transparent reflector is an ideal tool for orthogonal transformation of fields in the millimeter- wave region. The paper reveals the concept, gives assessments to the spectral methods of recording and analyzing an electromagnetic SHF-field amplitude-phase structure and describes possible application methods.

Here we try to summarize modern views on physical essence and technical opportunities of different laser technologies for MOC fabrication. This paper based previously on our own investigations made at the Laser Technologies Chair of IFMO, St. Petersburg and sometimes on the experience of other authors.

The operation principle of the optical transistor is based on the optical bistability phenomenon and inversionless (differential) amplification in the passive Fabry-Perot resonator (OR), filled with a substance having non-linear adsorption or refraction. In the millimeter wave range such resonator with a paramagnetic saturated by the UHF field under the ESR conditions is used to reach the similar purposes. In the paper the results of experimental and theoretical investigations of the non-linear OR (quasi-optical ESR-cell) with the ruby layer in 4-millimeter wave range at the temperatures T

The results of the analysis of the stability of stationary solutions of wave equations describing a behavior of the nonlinear Fabry-Perot interferometer with a saturated paramagnetic filling are presented in this paper. The cases when paramagnetic medium is characterized by a homogeneously and non-homogeneously broadened line of the magnetic resonance have been considered. The analysis of the stability has been conducted using the two-layer Newton- Kantorovich method. Some characteristics of the electrodynamic structure under consideration have been calculated under conditions of high and low quality of the resonance structure and the absence of frequency deviation and magnetic field. These are transmission and absorption coefficients. Areas of unstable behavior of these characteristics of the resonance structure have been found.

Neutron scattering on dynamic polarized proton targets is a rather efficient method for obtaining a high polarizing neutron beam. Here we study an optimization problem of proton targets using knowledge of behavior of electrodynamical parameters in the millimeter wave band. We have considered such problems as: (1) a high level of working material nuclear polarization of the target at low SHF-pumping power; (2) transparence of the target for neutrons; (3) optimal dimensions of the target and concentration of paramagnetic admixture in the target body. In this paper analysis and characteristic calculations of multilayer resonance electrodynamical structures have been carried out. They may be used for creation of polarized targets in millimeter wave bands. Thus, the main purpose of the investigation is the studying of fundamental properties of spin systems interfering with electromagnetic field in polarized targets with an inhomogeneous structure.

NASA's Mission to Planet Earth attempts to address issues related to environmental change through extensive scientific investigation and global monitoring. As part of this effort, the Earth Observing System Microwave Limb Sounder (EOS-MLS), Joe W. Waters principal investigator, was proposed and is currently in development. The Submillimeter-Wave Radiometer Development group at JPL along with collaborators at the Rutherford Appleton Laboratory in the United Kingdom and a small number of US laboratories are developing space-borne radiometer components to satisfy the detection requirements for EOS-MLS from 200 to 650 GHz with possible extension up to 2.5 THz (119 micrometers ). This conference paper summarizes the development that has been ongoing, with emphasis on the millimeter- and submillimeter-wave mixers. Detailed design and performance data for a subharmonically pumped antiparallel-pair planar-diode mixer are presented including computational simulations and measured mixer noise and conversion loss at 215 and 640 GHz. Results from a modest test program comparing the performance at 215 GHz of planar GaAs antiparallel-pair mixer diodes, planar In₅₃Ga₄₇As devices, GaAs planar-doped-barrier diodes and a GaAs millimeter-wave integrated circuit (MMIC) mixer are also presented. Finally, current and future development efforts in the areas of submillimeter-wave local oscillators, integrated planar-diode mixers, IF amplifiers, and THz radiometers are outlined.

In this paper experimental results of cryogenic tankage mass measurements and descriptions of level sensors using optical and millimeter wave signal beams are presented. The discussed results are based on a 100 GHz frequency modulated radar mass sensor. Test results are compared with a similar system which makes use of a laser beam and a frequency modulated microwave subcarrier. In addition the performance of a laser triangulation level sensor is presented which is suitable for normal gravity applications. Performance prediction in terms of the resolution and measurement accuracy are discussed with emphasis on the measurement difficulties encountered while using liquid hydrogen under normal gravity conditions. For a mass sensor the small 11% refractive index change between an empty and a filled tank of hydrogen causes a loss of measurement accuracy by a factor of ten, as compared to a level sensor. This loss is common to all mass propellant sensing systems, including the conventional capacitance probe sensor. Special processing techniques are indicated. Extensions of the presented millimeter wave mass sensor concept for micro and zero gravity cryogenic systems and for other special space related propellant conditions such as slush hydrogen are discussed.

A miniature millimeter-wave tracking sensor has been developed that can provide small- diameter hypervelocity missiles with the ability to acquire and track ground mobile and airborne military threats. It has adequate power to acquire small targets at beyond one kilometer range, sufficiently low sidelobes to suppress clutter and countermeasures, and a sufficiently deep tracking null for high angular accuracy. A five-port monopulse unit, the sensor is 1.7 inches (43 mm) in diameter and weighs only 120 grams. It consists of a 94 GHz hybrid-integrated frequency-modulated continuous wave (FMCW) transceiver and a dielectric lens antenna. The transceiver, which consists of Gunn Transmitter, circulator, three mixers, three couplers, and two comparators (azimuth and elevation), is built on three thin quartz substrates. Integral with it is a cluster of five dielectric monopulse feeds. The transmitter generates more than 60 milliwatts of average power which is linearly modulated over a period of one millisecond. The modulation is sufficiently linear to permit range resolutions as high as 30 centimeters. When the sensor was tested, its beamwidth was measured at 4 degrees. Also, its sum channel sidelobes are 39 dB below the level of the main beam, and its difference null depth is 44 dB.

A theoretical model of the microwave radiative temperature rate information for the moving target both in the time-domain and the frequency-domain is presented here, especially the circumstances of the rotative target and straight-line moving target on the background are discussed. It shows that the moving target can be detected by this characteristic information in mm-wave radiative remote sensing.

A novel design for a compact, light weight, imaging spectrometer has been proposed for an orbiting Lunar mapping mission. Simple in design, its dual arm optical system employs a transmission grating and a dichroic mirror to provide continuous two-octave spectral response. The grating's first order wavelengths are reflected into the SWIR arm, while the second order wavelengths are transmitted to the VNIR arm. The instrument design is that of a push broom camera. It uses one of the detector(s) dimensions for spectral selection, the other detector(s) dimension for cross-track spatial selection, and the forward motion of the platform (in this case, a spacecraft) for down-track spatial coverage.

The Space Infrared Telescope Facility -- SIRTF -- will be a cryogenically cooled observatory for infrared astronomy from space and is planned for launch early in the next decade. SIRTF will build on the scientific and technical results obtained by IRAS, COBE and ISO, but it will go beyond these cryogenic space missions by making extensive use -- for both imaging and spectroscopy -- of large-format detector arrays. This paper discusses a newly modified baseline SIRTF mission and its scientific capabilities.

Conventional approaches to spectroscopy at thermal infrared (IR) wavelengths have involved either cooling of the spectrometer to reduce background radiation in the waveband of interest, or the provision for a cold optical chopper, or both. These methods always required rigorous baffling, and often, relay optics to preclude the viewing of warm surrounds by the detectors, leading to increased cost, complexity, mass and power. A technique has been devised wherein energy at only the wavelength to be measured is imaged onto a detector column. This can provide radiance signal-to-(background) noise ratios > 300 when viewing the Earth in emitted thermal infrared while allowing the optics and the spectrometer to remain at local ambient temperature. Shuttering or chopping of the optical signal is not required with this scheme. A newly developed variable spectral filter is placed in proximity to the detector array to accomplish the necessary background radiation rejection. The theory leading to the development of this filter is described, and a discussion of the application to real optics/detector combinations is provided. A `proof-of-concept' instrument, the Thermal InfraRed Imaging Spectrometer has been built to demonstrate the practibility of the concepts described above. This unit and plans for developmental testing along with proposed areas of improvement are discussed.

Two types of Fourier transform infrared (FTIR) remote sensing systems are designed to do long term monitoring of the earth atmosphere temporally and spatially at Taiwan ground station. One of them is the FTIR coupled with one km long path White cell. It is capable of measuring the trace gases at the surface level with a sensitivity of 1 ppbv. The concentrations of CO, N₂O, and CO₂ are measured using this surface long path White cell FTIR. The other FTIR system is the FTIR coupled with a telescope tracked to the sun or moon. A sandwich detector of combining InSb and MCT photoconductors is used as the InSb mode, MCT mode. The concentrations of CO and O₃ in the upper atmosphere are measured. The concentration of CO is therefore compared between the ground surface level and the troposphere level.

An IR solar spectrometer (ISS), which basically consists of three components: coelstat, spectrometer and data acquiring unit, was developed. With ISS we measured the solar spectra in the wavelength range of 2915 - 2920 cm^-1 on the ground to derive the abundance of atmospheric CH₄. In this spectrum range, CH₄ is the main absorption gas and other gases' absorption can be omitted. The measurement results in the winter of 1991 show that the mixing ratio of CH₄ is around 1.6 ppm, with the mean measurement error about 10%.

Initial analyses of ambient carbon monoxide measurements based on infrared diode laser spectroscopy are presented. Correlation of CO concentration with anthropogenic sources, wind direction, and solar activity have been found.

In the past year, there has been substantial impetus for NASA to consider missions that are of relatively low cost as a trade off for a higher new mission launch rate. To maintain low mission cost, these missions will be of short duration and will use smaller launch vehicles (e.g., Pegasus). Consequently, very low volume, very low mass instrument (a.k.a. miniature instrument) payloads will be required. Furthermore, it is anticipated that the number of instruments flown on a particular mission will also be highly constrained; consequently increased instrument capability will also be desired. In the case of infrared instruments, focal planes typically require cooling to ensure high performance of the detectors, especially in the case of spectrometers where high D^* is necessary. Since a major portion of an instrument's mass and power budget is consumed by the focal plane cooler, detector technologies that require only modest or no cooling can contribute significantly to the realization of a miniature infrared instrument. InGaAs detectors feature high D^*, low dark current, and response not only in the 1 - 3 micrometers SWIR regime, but also in the visible regime as well. The latter feature can extend the versatility of a given spectrometer by enabling greater spectral band response while maintaining focal plane simplicity. In this paper, we discuss the InGaAs detector technology and its potential application in miniature infrared instruments.

This paper discusses recent activities of the Jet Propulsion Laboratory (JPL) in the development of a new type of remote sensing multispectral imaging instrument using acousto- optic tunable filter (AOTF) as a programmable bandpass filter. This remote sensor filter provides real-time operation; observational flexibility; measurements of spectral, spatial, and polarization information using a single instrument; and compact, solid state structure without moving parts. An AOTF multispectral imaging prototype system for outdoor field experiments was designed and assembled. Some preliminary experimental results are reported. The field system is used to investigate spectral and polarization signatures of natural and man-made objects for evaluation of the technological feasibility for remote sensing applications. In addition, an airborne prototype instrument is currently under development.

The planned set of future NASA space astrophysics missions has been continually undergoing evaluation and analysis, to identify major technology needs and to suggest development programs capable of providing this necessary technology. At a recent workshop, a panel of users and technologists worked to assess the state-of-the-art of relevant approaches in the area of direct infrared (IR) detectors. The set of candidate mission concepts was grouped into the categories of low-background and moderate-background systems; development strategies were outlined for each. For low-background systems, detectors with the ultimate in sensitivity are required, and minimum read noise and dark current are critically important. For moderate- background systems, characteristics such as higher detector operating temperature, large charge storage capacity, and large (or very large) formats are important. Novel photon counting schemes could greatly enhance the capability of future systems. Since readouts often determine overall performance of IR focal plane systems, continued development was needed. Future development programs need to be well coupled to the expertise within the astronomical community.

A balloon-borne observatory (PRONAOS) including a two meter telescope associated with a submillimeter heterodyne spectrometer for radioastronomy is supported by the French space agency (CNES) to prepare the future space programs in astrophysics. This instrument will be used to simultaneously detect the 368 GHz O₂ and the 380 GHz H₂O lines in the interstellar medium. Observations in this part of the spectrum require low atmospheric water vapor and oxygen molecule emission, so that the telescope will fly under a 1,000,000 m³ balloon at an altitude of approximately equals 37 km. The receiver, under development at Meudon Observatory, includes a SIS mixer using Nb/AlOx/Nb tunnel junctions operating at 4 K, a 6 GHz IF low-noise cooled preamplifier, a LO quasi-optically injected with a phase locked Gunn oscillator and two cascaded frequency multipliers. Noise temperature as low as 300 K has been obtained; less than 200 K is expected. An 800 MHz Acousto-Optical Spectrometer (AOS) is used for the high resolution (800 kHz) spectral analysis. The optimization of the frequency resolution of the spectrometer was obtained in the design and building of a new kind of Bragg cell in LiNbO₃ centered at 2 GHz.

The progress of a program to develop Ge:Ga blocked-impurity-band (BIB) detector arrays for far-infrared space astronomy is reviewed. So far, the best devices, working in the 80 - 200 micrometers range, have responsive quantum efficiency better than 15%, detective quantum efficiency 10%, dark current 100 electrons s^-1, and response uniformity better than a few percent. Structures with both bulk absorbers and epitaxial absorbing layers have been studied, as well as a variety of surface passivation. Front-illuminated arrays as large as 6 X 6, with 0.5 mm pixels, have been fabricated. Present performance conforms very well to the standard model of BIB detector operation. Further improvements in quantum efficiency and dark current, and larger formats, are anticipated, and the devices may play an important role in several upcoming far-infrared astronomical experiments.

Germanium photoconductors are currently the most sensitive detectors for use in low background, far infrared applications. In particular, between the wavelengths of 40 micrometers and 200 micrometers , these detectors have been used in a number of existing or planned systems for space infrared astronomy. We describe briefly the physical mechanisms of photoconductivity, including a discussion of various non-ideal behaviors seen at low backgrounds. The requirements for specialized cryogenic electronics are discussed along with some current implementations. Examples of past focal plane array designs are given, and the extension of the technology to large format imaging arrays is described.

The three science instruments in the Space Infrared Telescope Facility (SIRTF) require infrared detectors and readouts that operate at cryogenic temperatures with very low dark current and read noise. Detectors are being developed for the spectral region between about 2 micrometers and 200 micrometers. This paper describes the performance requirements and updates the progress to date for several different development activities, encompassing indium antimonide detector arrays, arsenic doped silicon impurity band conduction (IBC) detector arrays, antimony doped silicon IBC detector arrays, and germanium photoconductor arrays. Progress is also reported for very low noise cryogenic silicon readout devices.

Sensitive heterodyne receivers are being built at ever higher frequencies with superconducting (SIS) junctions as the first mixer. These devices have extremely sharp non-linearities in their current-voltage characteristics as a result of quantum-mechanical tunneling of electrons across thin insulating barriers. The low energy scale set by the magnitude of the superconducting energy gap implies very low local oscillator power requirements for heterodyne operation. Some general system design considerations for astrophysical receivers are reviewed. These principles are illustrated by discussing two specific applications: a 230 GHz SIS receiver recently installed as a facility instrument at the Swedish-ESO submillimeter telescope in Chile, and the broader receiver requirements of the 6-antenna submillimeter array (SMA), an interferometer now being designed at the Harvard-Smithsonian Center for Astrophysics. The SMA will require receivers at frequencies as high as 820 GHz, and will place some unique demands on detector performance.

The submillimeter wavelength range (100 micrometers <EQ (lambda) <EQ 1 mm) is exceptionally rich in atomic and molecular transitions that provide direct measures of the chemical composition, temperature, density, and cooling of the interstellar medium. In part, this is due to the fact that the most abundant oxygen- and carbon-bearing species as well as the most common hydrides have their lowest lying transitions within this wavelength region. However, because of the great abundance of many of these same species in our own atmosphere (e.g., H₂O and O₂), terrestrial absorption at submillimeter wavelengths is strong, rendering much of the sky inaccessible to ground- and even airborne observing platforms. In recognition of the scientific importance of the submillimeter range to astronomy and the limitations placed on its pursuit by the atmosphere, both NASA and ESA have embarked on ambitious programs to explore these wavelengths from space. The Submillimeter Wave Astronomy Satellite (SWAS), part of NASA's Small Explorer Program, is the first of these endeavors. During its planned 3-year lifetime, SWAS will survey dense ((eta) _H(2) > 10³ cm^-3) molecular clouds and cloud cores within our galaxy in five astrophysically important transitions of H₂O, H₂ ¹⁸O, O₂, CI, and ¹³CO. SWAS is scheduled for launch in 1995.

The rf technology section of the Seeker Technology Branch is developing an in-house capability for modeling and measurement of target scattering and material characteristics at millimeter wave (mmW) frequencies. The goal of the modeling effort is to understand the basic mechanisms that contribute to the target scattering (coated and uncoated) at mmW frequencies. Surface variations can be a significant portion of a wavelength at mmW; therefore, surface roughness must be included in our derivations. We are developing theoretical target models for canonical shapes such as plates and spheroids. These models will be bistatic, fully polarimetric (to account for depolarization) and include surface roughness. In a parallel effort, we are developing models for the material parameters [(mu) ((omega) ) and (epsilon) ((omega) )] that are valid in the mmW region. Our measurement effort is two-fold: To verify theoretical models (target and materials), and to assess the effectiveness of actual countermeasures. This paper discusses our current hardware configuration, planned upgrades, outlines our modeling effort, and shows examples of the Millimeter-Wave Reflectivity Measurement System measurements.

Our goal is the determination of exploitable phenomena to improve terminal guidance systems for smart munitions. The analysis of actual data from sensors employed by smart munition is critical to develop models and better understand the basic physics of the sensor/target interaction. The research and seeker emulator radar (RASER) provides us with an unequaled research tool in these investigations. This paper discusses the capabilities and operation of the RASER as well as outlines some potential experiments.