In the period since the mid-70's there have been rapid technology advances for the millimeter-wave field, and these have led to investigations of phenomenology (target and background signatures, and propagation effects in smoke, dust, or inclement weather). Extensive use of this information is now being made in applications such as communications, radar, guidance, imaging, electronic warfare and radio astronomy.l Sources are available which can in some cases provide an order of magnitude more power, significantly longer life-times, or complex waveforms such as pulse compression or coherent MTI for radar applications, and in addition usable power has become available at higher frequencies. Furthermore, over a period of years the sensitivities of receivers have improved dramatically, with noise temperatures for uncooled mixers decreasing by nearly an order of magnitude, and cooled mixers reaching noise temperatures below 75°K near 100 GHz. The use of such structures as beam-lead detectors has improved the mechanical performance and reliability, too. Progress has been made in component development, also, with particular activity in quasioptical components, specialized transmission lines (such as suspended substrate micro-strip, fin-line, dielectric image line, and insular guide), and integrated and monolithic circuits. The following discussion reviews much of the recent technical progress in the field, and then gives a summary of several major application areas, such as missile guidance.
The development of InP materials and devices for oscillators and amplifiers has led to a number of products which are now being used in prototype millimeter-wave systems. The InP Gunn device is being developed specifically for low noise amplifiers from 26 GHz through 100 GHz and for medium power low noise oscillators from 40 GHz through 140 GHz. The use of the InP Gunn diode as a low noise amplifier has led to new developments which use the InP Gunn diode in medium power amplifier applications. The InP IMPATT also appears attractive as a millimeter-wave power device, especially in the 30 GHz to 100 GHz region, and it is now being developed at Ka-band frequencies. This paper summarizes the state of the art of the InP Gunn device, both for low noise and medium power amplification and for oscillators at 60 and 94 GHz. Also, results on the InP IMPATT development are presented.
This paper summarizes recent progress in CW and pulsed silicon IMPATT sources for the millimeter-wave frequency range from 30 to 300 GHz. The contrast in device structure and fabrication technology between the diodes designed for below and above 100 GHz operations is described. Current performance of IMPATT oscillators, amplifiers, and power combiners are reported. Recent activities in GaAs and InP IMPATT development are briefly discussed. Finally, system applications of millimeter-wave IMPATT sources are discussed.
Wideband mechanically tunable oscillators, having greater than 20 percent bandwidth, have been routinely constructed. The second or third harmonic output from an inductive radial mode resonant disc, or from a high Q cavity, tunable at both fundamental and harmonic frequencies, results in substantial power levels suitable for most local oscillator applications in the millimeter range extending up to approximately 100 GHz. When low noise performance is required the active device is a Gunn diode. In most applications packaged GaAs Gunn elements are employed. The use of InP Gunn devices promises to extend the fundamental operating range well beyond the upper limit of the W-Band (75-110 GHz) region. Correspondingly useful harmonic power output into the 300 GHz region is predicted from circuits utilizing this more recently developed device. On the other hand, electronic tuning of these sources has been limited to, at best, a few percent. Several configurations of series arranged varactor and Gunn diodes, along with novel applications of radial mode disc capacitors in full and reduced height rectangular waveguides, have led to greater than 10 percent electronic tuning range through the upper end of the V-Band (50-75 GHz) region. Another arrangement of series connected varactor and Gunn devices having quarter wave cylindrical resonators attached to the diodes, and constructed in coaxial cavities, have similarly produced wideband electronic tuning characteristics. Theoretical calculations have been carried out, for circuits using cascoded varactor and Gunn elements in conjunction with a non-linear radial mode disc capacitive transmission line, and compare favorably with measured results up through V-Band frequencies. Similar performance is predicted, for sources arranged in series geometries, well into the millimeter region.
Ion implantation has been attempted for the fabrication of double-drift silicon IMPATT diodes at millimeter wave frequencies in the range of 30 GHz to 220 GHz. The results, however, have been disappointing. This paper describes some of the reasons behind this apparent inadequacy of ion-implantation as revealed by spreading resistance probe. It also demonstrates an approach for successfully implementing ion implantation for double-drift silicon IMPATT structures, especially for frequencies above 100 GHz where the conventional double-epitaxy technique of double-drift structure realization has not yet been practical.
We present results for ambient temperature and cryogenic operation of mixer receivers for use in the 80-350 GHz range. These systems employ GaAs Schottky barrier diodes doped for optimum performance at 15 K, and make use of a combination of waveguide and quasioptical circuits for LO injection and sideband filtering. Cooled receiver temperatures (DSB) are ~ 65 K at 100 GHz, ~ 250 K at 225 GHz, and -- 530 K at 350 GHz. Local oscillator requirements are < 100 uW in the 3 mm range and 100-300 uW in the 1.5-1 mm range making it feasible to pump these mixers with frequency multiplied sources. The mixer receivers described are tunable over ~ 30-40% of their center frequency. The performance of the frequency multipliers is also discussed. The low noise performance has been achieved in part by use of specially designed FET amplifiers which are cooled to 15 K. For the receivers described, amplifiers centered near 1.5 GHz with ~ 400 MHz bandwidth have been employed.
A number of applications of millimeter waves can benefit from development of low-cost, planar antenna elements, which can be combined into either phased arrays or arrays with imaging properties. Such applications range from communication, navigation and battle-field passive and active systems to remote sensing and space science instrumentation. This paper discusses the general requirements on such planar antenna elements, with specific data for three examples: (i) the Vivaldi (tapered slot) antenna, (ii) printed dipole arrays, and (iii) planar slot arrays. It is shown that such elements can be used for both prime-focus paraboloids and Cassegrain systems, with excellent aperture efficiency and beam efficiency, with the potential number of elements in the hundreds. In order to be optimally useful, planar antennas should be suitable for integration with receiver elements, i.e. mixer diodes and IF-amplifiers. It seems feasible to construct monolithic versions of these arrays in the future.
This paper introduces a proposed imaging system suitable for millimeter and submillimeter wavelengths, based on heterodyne mixing at the focal plane of an optical system. We have designed a prototype planar antenna array and quasi-optical system and present measurements at 9 GHz and at 140 GHz of beam patterns and sensitivity for a single two-element, full-wave, printed dipole array incorporating a GaAs beamlead diode. Scale model studies were carried out in the 8-10 GHz range, where the design was optimized. Subsequent measurements were made with a tunable carcinotron at 128-140 GHz on an appropriately scaled array.
Many optical components in the visible or near infrared make use of thin film evaporation technology to produce coatings for narrowband filters, high-frequency and low-frequency pass filters, beamsplitter and antireflector coatings. The extension of these techniques to wavelengths beyond 50 um is virtually impossible due to absorption and the difficulty of adhesion of thick films. Many devices however can be fabricated using metallic mesh or its complementary structure as the reflecting elements in interference filters. This paper will discuss the performance of such filters, of either bandpass or blocking characteristics, and the application of these structures to high-resolution spectroscopy. Beamsplitters using the polarization properties of metallic mesh will also be discussed.
Radiative transfer in the earth's atmosphere is modeled by a computer code called RADTRAN. RADTRAN may be used to model atmospheric transmission and emission in the frequency range of 30-300 GHz. Two versions of this computer code exist: the first is RADTRAN which incorporates six model clear atmospheres, six cloud models, six rain models and eight humidity models to model worldwide atmospheric conditions; the second is MWTRAN which is approximately one-sixth of the physical size of RADTRAN. Both RADTRAN and MWTRAN allow the researcher to read in any model data in any format.
A general treatment is given to electromagnetic wave propagation through a non-particle containing, randomly dispersing and absorbing atmosphere. The model, based on weak fluctuation theory, is capable of describing the propagation of five different wave types. Fundamental statistical quantities such as log-amplitude and phase correlation functions, structure functions and the mutual coherence function of a general beam wave are derived. The atmospheric fluctuations are introduced into the model via the von Karman spectrum. Due to its qualifications, the model finds particular application to millimeter and near-millimeter wave propagation.
An experiment to study the effect of a meterologically well-characterized atmosphere on near-millimeter wave propagation has been designed and is being implemented. The primary emphasis of this experiment is on measurement of atmospheric mutual coherence function (MCF) simultaneously with measurement of temperature/humidity structure parameters C2T C2Q, and CTQ. Quasi-optical techniques, which make use of the Fourier transforming properties of focussing reflective optics, will be applied to measure real and imaginary parts of the MCF, while fast temperature and humidity sensors will provide derived structure parameters. This paper will discuss experimental concepts and range instrumentation.
The effects of atmospheric turbulence on millimeter wave propagation are not as well understood as the corresponding effects on optical propagation, generally because of the strong dependence of turbulence effects on the absolute humidity structure parameter CQ2 (as opposed to just the temperature structure parameter CT2 and the cross-correlation CTQ) in this frequency range. Scattered results at 35, 94, 140, and 220 GHz are available, but in almost all cases, available atmospheric data are inadequate, generally because turbulence measurements were obtained incidental to other propagation experiments. This paper attempts to compare available results to theory, and shows that agreement in most cases is plausible. An experiment designed to characterize millimeter wave turbulence at several frequencies of interest, while at the same time determining values of appropriate atmospheric parameters, will be discussed. Included in the planned investigation are measurements of the mutual coherence function showing angle-of-arrival effects and intensity fluctuations.
Systems for making automatic noise figure measurements of millimeter wave mixers have been developed using both analog and digital techniques. The effect of IF mismatch on the measured noise figures is also determined with these methods. The measurement systems are versatile enough to be used to measure the noise figure of receivers anywhere from 30 to 300 GHz.
Noise measurements on the self-oscillating mixer at 60 GHz have been made in both GaAs and InP Gnn devices. These devices were fabricated using an image guide design as the transmission media. The double side-band noise figure and conversion characteristics were measured and it is shown that the noise performance of these devices make them attractive for application where low cost, simplicity in circuitry, and small physical size are important factors.
The Boeing Aerospace Company is in the process of extending its existing passive Millimeter Wave Seeker Guidance Simulator into the active regime. This paper provides a brief review of the Boeing technology for terminally guided missile simulation and current passive millimeter wave seeker simulation techniques. With this background, the problems and experiences of including an active radar seeker in a non-anechoic, reflective test chamber are discussed. Finally, the theory to support actual active radar test data taken in our passive millimeter wave test chamber is presented.
Design development, and construction of a new millimetre-wave scattering facility for experimental RCS analysis is described. Operating at frequencies of 35, 64, and 90 GHz, it has a range length of 31.6 metres and employs a computerized string support system for target positioning and control.
A coherent instrumentation radar was designed and developed to support the collection of target and clutter backscatter data of 95 GHz. The radar is completely solid-state and uses a phase locked Gunn oscillator and injection locked IMPATT oscillators to achieve the frequency stability required for coherent signal processing. Data can be collected under a selectable set of pulsewidth, polarization and pulse repetition interval conditions. Since data integrity (coherence) is almost totally dependent on system spectral purity, major design effort was focused on signal generation and control. System tests have demonstrated that the required degree of stability and control has been achieved for operation with both stationary and moving targets.
A wideband, biphase coded, cw millimeter wave instrumentation radar has been constructed to obtain both unresolved and resolved radar cross section data of tactical vehicles and naval vessels. The radar operates at 95.6GHz with a selectable pseudo-noise code waveform which allows a variable range resolution and range ambiguity. The radar azimuth-elevation scanner is controlled by a microprocessor. Various scan patterns (e.g., raster) are stored in erasable programmable read only memory (EPROM). A "sliding code" signal correlation is used to obtain processing gain as well as bandwidth compression in order to simplify signal recording and digitizing. Radar performance is also described.
The Fire Control Division at ARRADCOM, Dover, NJ is developing the Lightweight Integrated MMW Sensor (LIMS) and the Advanced Fire Control Radar (AFCOR). The AFCOR is a dual-frequency (Ku and 94 GHz) coherent pulse doppler radar for improved track of low-angle airborne targets. The LIMS is a 94 GHz experimental sensor being developed to optimize ECCM and LPI characteristics while maximizing the range at which a target can be detected and tracked. The LIMS system consists of a programmable signal processor integrated with an experimental, coherent, solid-state, 94 GHz transceiver having a 1 GHz instantaneous bandwidth. The MMW sensor's waveform has good range resolution and utilizes a high duty cycle (low peak power, but high average power) for extended range detection compatible with the peak power limitations of MMW solid-state sources. The waveform modulation will be a combination of frequency hop (on a dwell-to-dwell basis), interrupted CW, and biphase code. The MMW sensor will, ultimately, incorporate PSP (Programmable Signal Processor) controlled RF power management for enhanced LPI. Polarization processing may be incorporated for stationary target discrimination and classification. A VHSIC radar processor is being procured from Westinghouse Corporation to provide: (1) Real-time processing in a comnact package for LIMS, and (2) Provide high throughput rate for simultaneous multiple target search and track for AFCOR.
Applications of MMW radiometers in the areas of covert ground based battlefield surveillance by space-borne sensors, storm research by high altitude airborne sensors, missile seeker terminal guidance, forward looking imaging for aircraft landing in low visibility conditions, and covert detection of low level aircraft are discussed in detail. Some representative parameters of state-of-the-art MMW receivers such as effective noise temperatures and RF bandwidths are given. Phenomenological factors such as MMW propagation loss and radiometric properties of the environment are listed and discussed.
New developments and applications for radiometric imaging systems are discussed. The basic operating principles of radiometry are reviewed and results are presented from two different Ka band (36 GHz) radiometric test beds. Passive weather detection is presented with actual results from an airborne imaging radiometer. Thunderstorm and cloud formations have been detected at ranges in excess of 20 NM. Tactical ground mapping and target detection is also presented with results from a ground based high resolution imaging radiometer. Enhanced target detection using a low power bistatic illuminator is demonstrated. An inverse filter algorithm has been developed to attain better than real beam resolution in high contrast images. Raw and enhanced images are presented for comparison.
This paper describes an airborne solid state, 95 GHz tracking radar being used to investigate techniques associated with a millimeter wave terminal homing technology development program. Particular emphasis is placed on the major technology aspects of the radar including the implementation of the four-horn monopulse tracking, the lens antenna, etc. The Georgia Institute of Technology, Engineering Experiment Station (GIT/EES) has designed and developed this state-of-the-art millimeter wave tracking radar system for use by Massachusetts Institute of Technology, Lincoln Laboratory (MIT/LL) under subcontract from the General Electric Company Aircraft Equipment Division. The system is being used in the Lincoln Laboratory Millimeter Terminal Homing Program as an instrument to help evaluate various millimeter wave system concepts.