Increasing interest in and greater usage of the millimeter-wave frequency bands has resulted in a need for better characterization of atmospheric effects at these frequencies. While attenuation is recognized as the most significant effect, recent measurements of fluctuations in intensity and phase caused by atmospheric turbulence have shown that these phenomena will also degrade system performance at both millimeter-wave and microwave frequencies. This paper describes the millimeter-wave and meteorological instrumentation used to make these measurements and gives selected results. It is determined that phase fluctuations as great as 1.5 radians and intensity fluctuations as large as 2.8 dB are observed over a 1370 m path in hot, humid weather. The effects of these fluctuations on the performance of practical, existing microwave phased array and monopulse systems are assessed. It is determined that phase fluctuations in particular will degrade the performance of microwave adaptive nulling arrays and monopulse trackers.

An experimental coherent pulsed radar operating at 225 GHz is described. This system uses a pulsed, phase-locked extended interaction oscillator transmitter and an f/4 (frequency divided by 4) subharmonic mixer pumped by a phase-locked Gunn oscillator as the receiver. A quasi-optical circular polarization duplexer combines transmitter and receiver signals into the same antenna. Results obtained with this system include the detection of targets out to ranges of 3.5 km and observation of Doppler spectra of trucks and tracked vehicles, including contributions from both body and tracks.

• Development of an integrated path layout, fleet sizing and evaluation, and simulation tool, known as the AGVS Engineering Design Workstation, or AGVS EWS [1,2]. This tool is intended to be used by industrial engineers planning AGVS applications.

An extensive set of millimeter wave propagation measurements was made during 1983 to 1985 by a team of scientists from NOAA's Wave Propagation Laboratory and Georgia Institute of Technology. Millimeter wave fre quencies from 116 to 230 GHz were propagated over a 1.4 km horizontal path in Flatville, Illinois. Simultaneous, extensive measurements of the meteorology allowed a detailed comparison of the propagation characteristics with the current state of the atmosphere. We report on the observations of millimeter wave propagation characteristics in clear air. Amplitude and phase spectra for propagation in clear air are compared with theory derived using the weak refractive turbulence approximation. Excellent agreement is found when refraction fluctuations dominate over absorption fluctuations. Further, probability density functions appear to be, respectively, lognormal (amplitude) and Gaussian (phase difference).

: From 1983 to 1985 a team of scientists from NOAA's Wave Propagation Laboratory and Georgia Institute of Technology conducted an extensive set of millimeter wave propagation measurements. In five, thirty-day sessions, chosen for the widest variety of weather conditions, we propagated millimeter wave frequencies from 116 to 230 GHz over a 1.4 km horizontal path in Flatville, Illinois. Simultaneous, extensive measurements of the meteorological allowed a detailed comparison of the propagation characteristics during clear air and severe weather. Amplitude and phase spectra for propagation in clear air are compared with theory derived using the weak refractive turbulence approximation. Excellent agreement is found. Further, probability density functions appear to be; respectively, lognormal (amplitude) and Gaussian (phase difference), as expected from application of the central limit theorem. Interesting meteorological observations and their millimeter wave signatures will also be presented. (Author)

: A system has been developed to measure relative atmospheric transmission for the near-millimeter wave range of frequencies, 60-100 GHz. A 400 m long propagation range has been established. A transmitter/receiver system at one end of a link incorporates a rapid-scanning Fourier transform spectrometer. It involves a novel mirror drive which moves both interferometer mirrors simultaneously. The interferometric section is a polarizing Martin-Puplett type. The grid polarizers are made photolithographically. The source is a hot mercury lamp in a cavity, and the detector, an InSb photoconductive element. Scans of 7.5 GHz resolution require about 0.2 sec. A dihedral retroreflector 200 m from the transmitter/receiver reflects the signal back and completes the link. Calibration spectra are obtained from a short path to a second retroreflector. System tests are described.

Scintillations of intensity and phase difference were measured at millimeter wavelengths in a horizontally homogeneous atmospheric surface layer. Simultaneous micrometeorological and optical propagation measurements characterized the clear-air turbulence. Predicted and measured propagation statistics are in good agreement. It is shown that the phase structure function showed a rolloff at large spa...

Results are presented from measurements of the effects of inclement weather on the fluctuations in amplitude and phase of millimeter-wave (MMW) signals propagated through the atmosphere. These measurements were made at frequencies near 116, 140, 173, and 230 GHz at a site near Champaign-Urbana, Illinois, in a community chosen for its exceptional flatness and lack of terrain features that might per...

Atmospheric turbulence, which is a readily observed phenomenon at visible wavelengths, also causes fluctuations in intensity and phase at millimeter wavelengths. This paper describes a series of experiments conducted at a site near Flatville, IL which measured these effects at a broad range of MMW frequencies in clear air, rain, fog, and snow. It was found that the maximum rms intensity fluctuations observed were 14% of the mean, while the largest rms angle-of-arrival fluctuations were 36 microradians. Discussions of the experimental arrangement, as well as results obtained in measuring the probability distribution functions of fluctuations, the mutual coherence function, spectral densities, and pertinent atmospheric parameters will be presented.

: This report describes work done on Contract DAAG29-81-K-0173, An Investigation of Millimeter Wave Propagation in the Atmosphere: Measurement Program, conducted by the Georgia Tech Research Institute during the period September 1981 through May 1987. The objective of this program was to measure the effects of atmospheric turbulence on the propagation of millimeter wave radiation, with emphasis on inclement weather effects. Five separate measurement sessions were conducted at a site near Urbana, Illinois, and these measurements were made jointly with personnel from the National Oceanic and Atmospheric Administration, who furnished meteorological instrumentation and information on experiment design. Personnel from the Atmospheric Sciences Laboratory at White Sands Missile Range also contributed to this program. Measurements were made at frequencies near 118, 142, 173, and 230 GHz to cover all of the major atmospheric features in the millimeter wave spectral range, and were made during clear air, rain, fog, and snow. The equipment comprised a small step-van transmitter truck and an array of four receivers, pumped by a common local oscillator, mounted in a semi-trailer.

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.

Utilization of the near-millimeter-wave band is limited by atmospheric effects on propagation. Although this paper is restricted to clear-air effects, it is pointed out that these phenomena, which are molecular in origin, are also present to a significant degree in adverse weather. The paper surveys theoretical and observational knowledge concerning absorption, emission, refraction, and turbulence effects in clear air and in the spectral range 90 to 1000 GHz. Modeling practices are also reviewed.

Observations were conducted over uniform, exceptionally flat farm land in Illinois during clear weather in July, 1983. Scintillation data were obtained at 116.30 and 172.91 GHz for a path 1.4 km long. Rigorous micrometeorological measurements, some of them path averaging, were made along the path. The results of these tests will be described.

Increasing emphasis is being placed on the study of the effects of atmospheric turbulence on the propagation of millimeter and submillimeter waves because of the potential usefulness of these frequency bands in both military and civilian applications. The characterization of millimeter wave turbulence effects is more complicated than that of the optical propagation case because of a strong dependence on the humidity structure parameter CO2, as well as on the temperature structure parameter Gr2. In addition, there is a dependence on the cross-correlation of these two parameters, denoted by CI-0. Measured results on the effects of atmospheric turbulence on millimeter wave propagation, which include both amplitude and phase fluctuations, are very limited and have generally been obtained incidental to other propagation measurements. However, comparison of these limited experimental results with theory has shown good agreement. This paper compares scattered results measured at 35, 94,140, and 220 GHz to theory, and shows that agreement in most cases is plausible. A future experiment specifically designed to characterize millimeter wave turbulence, with special emphasis on measurement of the pertinent atmospheric parameters, is also described.

This system, used to measure the effects of atmospheric turbulence at frequencies between 116 and 173 GHz, comprises a front-fed, off-axis parabola transmitting antenna located 1.4 km from a receiver array. The five antennas in the latter receive local oscillator power from a phase-locked klystron source via a low-loss lens beam waveguide distribution system.