Millimeter-Wave technology offers many advantages for communications and missile systems of the future. These benefits are presented with a discussion of their impact on millimeter-wave systems under development, including smart munitions, minimissiles, communications, fire control, and radiometry. Millimeter-wave solid-state power sources, in particular IMPATT diode, have made light-weight integrated high-frequency systems a reality. The development of these power sources, including IMPATT power combining, is crucial to future millimeter-wave systems.

High power sources of coherent radiation in the millimeter and submillimeter wavelength range are useful in a number of applications, including plasma heating, plasma diagnostics, radar and communications. Two of the most important sources in this wavelength range are the optically pumped laser and the gyrotron. Major recent advances in both laser and gyrotron research are described. Possible techniques for improving the efficiency and operating characteristics of these devices are also reviewed.

Amplifiers and oscillators, using one or more gallium arsenide (GaAs) double-drift IMPATT diodes have become one of the leading solid state contenders to replace electron tubes as power sources in millimeter wave systems. In this paper, we describe the state-of-the-art performance obtained on devices developed in our laboratory. Our approaches to diode modeling and circuit optimization are outlined.

The development of InP Gunn devices has progressed to manufacturing status for several basic products. Designs and processes have been established for InP Gunn oscillator diodes operating at 56 GHz, 80 GHz, and 94 GHz. This work has concentrated on designs especially for high cw efficiency at medium power levels suitable for short and medium range trans-mitters. At 56 GHz, cw efficiencies between 5% and 10% are readily obtainable, at 80 GHz efficiencies are 3.5% to 6.0% and at 94 GHz cw efficiencies range from 2.5% to 5%. Typical power levels are 250 mw at 56 GHz, 75 mw at 80 GHz, and 60 mw at 94 GHz. These performance characteristics are obtainable over standard temperature ranges (e.g., -40°C to +60°C HST). These InP Gunn devices are now being used in a variety of oscillator circuits and modified device designs are being used as well in stable, medium power, high efficiency amplifiers.

As the use of the millimeter wave (MMW) bands increases, the need for better spectral control of sources also increases because of widening application of this spectrum to Doppler radar, communication, and measurement systems. As the millimeter bands become more crowded, better frequency control will become necessary to avoid interference. There is also a real advantage to be gained in source power stability by phase-locking; locked sources typically exhibit output power stabilities of a few tenths of one percent. Phase-locking of MMW sources to a frequency standard also provides the basis for frequency measurements which are perhaps the most accurate measurements of any physical quantity ever made, with accuracies of 1 X 10-12 being attainable. Phase-Lock circuits using both linear and digital techniques are available to the MMW system designer, and both types are discussed in this paper along with some typical results obtained.

A wide variety of antennas has been designed or is currently under study for the millimeter wave region. An overview over these antennas is presented. Two classes of antennas are distinguished, i.e., antennas of conventional configuration and antennas based on new design approaches. The former class consists of radiating structures, such as reflector, lens and horn antennas, whose characteristics are well established. The latter class is comprised of antennas with significant features that are peculiar to the mm-wave band and includes radiating structures such as microstrip mm-wave antennas, dielectric antennas and integrated antennas.

A description is given of the use of the Fresnel zone plate as a focusing or a frequency-filtering device at millimeter wavelengths. Sample design data are given, as well as references to prior results. A newer type of zone plate is discussed which employs two dielectrics of equal thickness to produce a flat zone plate.

Traveling wave antennas for the millimeter wave range face two main problems: increased metal loss, and fabrication difficulties due to the smaller wavelengths. To overcome these two problems, a new class of uniform leaky wave antennas have been introduced. The antennas are longitudinally continuous to minimize the fabrication problems, and they are based on low-loss waveguides, such as groove guide and nonradiative dielectric (NRD) guide, to reduce the effects of higher loss. New techniques for obtaining controlled leakage have also been investigated. Four different leaky wave antenna structures are discussed here, two based on groove guide and two on NRD guide.

Printed circuit antennas are attractive radiation sources both at microwave and millimeter wave frequencies. However, for millimeter wave applications where the substrate is likely to be electrically thick, it is important to understand the basic effects of a thick substrate on radiation characteristics. In particular, it is concluded here that dipole radiation properties become sensitive to loss as the substrate becomes thick. Furthermore, the efficiency of dipoles on thick substrates tends to be low, especially as the dielectric constant of the substrate increases. A method of improving both the efficiency and gain can be used for thick substrates however, which uses a superstrate layer on top of the antenna.

This paper describes an infrared detection technique used to observe localized heating in resistive and lossy dielectric materials irradiated by an incident electromagnetic wave. Radiation patterns from horn antennas operating at 94 GHz are detected through the heating in screen material placed in the region of interest.

A number of waveguiding structures for millimeter-wave use are compared from the characteristic and application points of view.

A systematical analysis of nonuniform dielectric waveguides by the method of staircase approximation is presented. Extensive numerical data are obtained to develop guidelines for the design of transition dielectric waveguides for millimeter-wave applications

To resolve the controversy regarding hooking of the whisker tip without damage as a reliable method for stabilizing the MOM point contact diode without significant degradation of diode performance, a systematic study is implemented to control the fabrication of such tips, the contacting process and monitoring of diode performance in the microwave and mm wave region. The fabrication and contacting processes are monitored by microscopes, and the tip with and without hooking is scrutinized with the SEM. Results so far have indicated the reproducibility of the etching process, and the tolerance range of tip dimensions that will make contacting process and surface less critical. Improvement in stability is also significant with controlled hooking of the tip with no noticeable loss of diode sensitivity. The stability is long term and is quite immune to moderate vibrations and laser heating. Diode performance is monitored at 10 and 50 GHz in direct detection and mixing both before and after hooking.

Affordable Packaging Techniques usable at Millimeter wave frequencies, for application in radios, munitions, and missiles are discussed. Specific examples of several techniques are presented, and the interaction of these techniques with the emerging technology of monolithic millimeter wave integrated circuits is discussed.

Notable advances in printed circuit and solid state devices are now allowing a high degree of subsystem integration at millimeter wave frequencies. These developments provide the basis for more complex and sophisticated radar, receiver and communication sub-systems for millimeter wave applications.

The renewed interest in millimeter-wave systems in recent years has stimulated development effort of various solid-state devices. As a result, millimeter-wave IMPATT and Gunn device technologies are now well established for systems applications and the GaAs FET technology has been progressing rapidly extending its upper frequency range to beyond 70 GHz. This paper presents an overview of the current status of millimeter-wave active solid-state devices. The design, material, and fabrication of each device are briefly described and current performances of these devices are reported.

The development of millimeter-wave integrated circuits has been progressing at a very rapid pace at TRW. Recent developments concentrated on microstrip and wideband stripline components. State-of-the-art performance has been achieved for most of these components. This paper presents these recent advances in Gunn VCOs, stripline mixers, microstrip mixers, multipliers, and filters.

A 90/180 GHz multichannel radiometer is currently under development for NASA's 1985 Hurricane Mission onboard the Convair 990 research aircraft. The radiometer will be a fixed beam instrument with dual corrugated horns and a common lens antenna designed to operate simultaneously at 90 and 180 GHz. The all solid state front-end will contain three double side band data channels at 90 ± 3 GHz, 180 + 3 GHz, and 180 ± 7 GHz. These frequencies are chosen to coincide with those proposed for the Advanced Moisture Sounding Unit (AMSU) radiometer which is scheduled for future orbital deployment onboard a Tiros-N satellite. The airborne radiometer will mount in a window port on the CV-990 and will maintain a fixed beam view approximately 14 degrees off zenith. Primary scientific interests for this instrument are the gathering of atmospheric humidity data near the water vapor absorption line of 183.35 GHz and the collection of atmospheric precipitation signatures at 90 GHz. The radiometer design is a Dicke chopper arrangement selected to achieve maximum absolute temperature accuracy and minimum brightness temperature sensitivity. In addition, the instrument will be self-calibrating with built-in temperature controlled calibration loads. Analog outputs of the three data channels will be calibrated DC voltages representing the observed radiometric brightness temperatures over the selected integration time.

Millimeter waves have the advantage of greater resolution over longer wavelength microwaves, for a given antenna size, while still penetrating clouds and fog to provide near all-weather operation compared to high resolution infrared and optical sensors which are blinded except in clear weather. Millimeter-wave imaging, from aircraft and spacecraft, has been used to provide information on soil moisture, type and porosity; to locate field and vegetation boundaries and snow cover; to define intense fire areas through smoke; to infer the thickness and water content of clouds; to map the location and distribution of weather fronts, convection zones, severe storms, and precipitation; to detect and quantify marine oil spills; to map ocean thermal fronts and measure marine wind speed; to delineate the ice-ocean edge; to locate icebergs, polynas, and leads; to enable optimum transport through the ice pack; to identify and map sea ice type, age, and concentration; and to detect ships, aircraft, and man-made features through adverse weather for various surveillance and targeting applications. The emission, absorption, and transmission of atmospheric constituents and their effects on the choice of observational frequency, along with the general radiative properties of terrain and ocean surfaces, are briefly discussed. Major emphasis is placed on the application of millimeter-wave imaging to the all-weather location and measurement of sea ice properties.

Recent interest in millimeter-wave imaging systems has focused attention on some of the problems associated with the forward-looking mode of operation. In this article, brightness temperatures of various material surfaces have been computed to illustrate the problem of contrast reversal at low grazing angles. When detection conditions are known, contrast reversal angles can be predicted using surface and weather modeling.

In recent years detection of stationary ground targets such as tanks and trucks by airborne MMW radars mounted on helicopters have received significant technical attention [1, 2, 3]. This detection should take place in the presence of ground clutter return and under adverse weather conditions such as fog and rain. Since the detection ranges are not very long (in the order 5 kilometers) MMW radars are well suited for this application. The primary reason is the fact that these radars, because of their higher frequencies (i.e., smaller beamwidths), subtend smaller ground clutter areas in which the target is located. This gives a better target to clutter signal ratio. Similarly, again because of their smaller beamwidths, they subtend smaller rain volumes, reducing the effect of increased noise due to rain backscattering. In this paper, basic radar search equations are given for detection of targets in the clear (non clutter environment). The increased noise level due to ground clutter and atmospheric disturbances such as rain is also calculated. Additionally, methods of calculating atmospheric attenuation are outlined and applied to example problems. Two MMW (35 and 95 GHz) radar parameters are used in the detection of ground targets. It has been shown that for a given an-tenna size, the higher frequencies (i.e., 95 GHz) result in better detection ranges of stationary ground targets than the lower frequency (35 GHz). The reason is the smaller beamwidth and thereby the smaller clutter area coverage.

Millimeter wave sensor research over the past years has been directed toward the development of a feature space for targets and background that is disjoint over a broad range of parameters. The results have been mixed at best. The BRL program is directed toward the investigation of the polarization and frequency characteristics of various types of background. The data would be collected so as to provide both systems engineers and systems analysts a useful and general set of millimeter wave background maps for development of performance estimates of current and proposed weapon systems. This paper highlights some of the key features of the instrumentation and measurement parameters which the authors believe to be important in establishing the polarization and frequency characteristics of both benign and hostile terrain backgrounds.

This paper discusses the design to be used in the development of a high power, wide bandwidth, coherent 95 GHz instrumentation radar. The system design provids for operation of the radar in two separate transmitter modes; a moderate power, 100 Watt peak power mode using a state-of-the-art wideband TWTA with greater than 2 GHz of bandwidth and a high power, 1 kWatt peak power mode using a state-of-the-art EIKA. The radar will be polarzation agile and coherent frequency agile, making it possible to measure the complete polarization scattering matrix as a function of frequency and resolution.

Georgia Tech has developed a new state-of-the-art 95 GHz instrumentation radar designated HIRES-95. It is designed specifically for full polarization scattering matrix measurements and characterization applications. The transmission waveform, the system polarization, and the range and angular resolutions are selectable from a variety of operational modes. For example, the system can operate with CW, FM-CW or pulsed waveforms including coherent pulse-to-pulse frequency agility; it can operate in either a coherent or a noncoherent mode; the system is dual polarized and has pulse-to-pulse (or transmission to transmission) polarization agility; it can operate with either linear polarization or circular polarization; both the angular and range resolutions are continuously selectable to a maximum resolution of approximately one foot in each dimension.

The use of integrated circuit techniques for millimeter wave transducers has now moved from a research curiosity to an engineering discipline. Microstrip is the preferred transmission media to demonstrate a wide variety of RF component functions. For applications involving precision weapon systems, a soft substrate is preferred since it provides lower cost, improved survivability, and functional versatility when compared with the traditional hard candidates such as quartz. The MESFET is rapidly emerging as a key building block for monolithic supercomponents up to a frequency of approximately 40 GHz. Both planar and conformal antennas are being developed again based on a soft substrate with photolithographic processing. The marriage of planar integrated circuit transceivers with thin, planar antennas is providing a new generation of low cost, producible and miniature millimeter wave transducers for demanding systems requirements.

This paper reviews the current status of automated multipart network analyzer (ANA) systems as used in the measurement of microwave parameters such as reflection coefficient, generalized scattering (S) parameters, and power. Multipart (typically at least a six-port) network analyzers have particular advantages at millimeter-wave frequencies because they do not require complex detection circuitry at the reflectometer sidearms. This also eliminates the need for the frequency down conversion usually required in most commercially available analyzers based on the four-port reflectometer.

Since the summer of 1983, Georgia Tech and NOAA have been engaged in a program whose purpose is to measure, the effects of atmospheric turbulence on the propagation of millimeter waves (MMW). Five different measurement sessions have been conducted, and observations have been made in clear air, rain, fog, and snow at frequencies of 116, 118, 142, 173, and 230 GHz, so that results have been obtained on or near all atmospheric features of interest in this range, including to 118 GHz oxygen line, the 140 GHz window, the 183 GHz water line, and the 230 GHz window'. These measurements have been made over a 1.4 km path at a site near Urbana, Illinois, chosen for its exceptional flatness. Figure 1 is a diagram of the layout of the experiment site and Figure 2 is a photograph of the propagation path looking from transmitter toward receiver. In making measurements of this type, it is important that the path and surrounding terrain be flat, homogeneous, and free of trees or other obstructions, to avoid perturbation of the atmospheric fields. The following sections discuss the equipment used to make these measurements and give some preliminary results.

In this paper we describe a new method for measuring the dielectric and absorption constants of materials at millimeter frequencies. This new method is called digital spectrometry and rests on a little known property of Fresnel's equations for reflection at 45° and the recent appearance of highly accurate digital voltmeters. The fundamental equations for digital spectrometry are presented and in the final section of the paper the experimental configuration is described.

Instrumentation for studying the propagation of near-millimeter waves has been designed and is currently being implemented at a one mile long test site in Sandusky, Ohio. An optically pumped near-millimeter wave (NMM) laser, used as a source of radiation for frequencies near 300GHz, is located at one end of this site. The beamwidth of the laser, at the other end of the propagation path, is controlled by a two-lens optical system placed at the laser's output. The receiver, which is controlled by a 68000 microprocessor,consists of a parabolic reflector, focal plane scanner, and a fast liquid helium cooled InSb detector. Measurement of the characteristics of the received beam is based upon a quasi-optical method. Simultaneously with the propagation measurements, the temperature/humidity atmospheric stru-cture parameters and characteristics of hydrometeors in the path are obtained. These two measurements will then be correlated to provide a meteorologically well-verified propagation model for near-millimeter wavelengths.

The design of a broad-band open resonator for millimeter wave frequency dependent characterization of material complex permittivity and permeability is described and measured results for common dielectrics are presented.