| The millimeter-wave (MMW) spectrum (30–300 GHz) offers a unique combination of features that are advantageous when retrieving information about the environment. Due to small wavelengths involved, physically small antennas may be used to obtain very high gains (>50 dB) and resulting high spatial resolutions. Moreover, some features have scattering and emission behaviors that are more sensitive at MMW wavelengths than at microwave wavelengths. Examples include, water vapor (H2O). fog, haze, clouds, ozone (O 3) molecules, and chlorine monoxide (ClO) have rotational spectra in this region.; The 75–110 GHz (W-band) atmospheric window is relatively quiet, and it can supply spectral information that can be useful in identifying and quantifying pollutants. Information such as the size and concentration of particulate pollutants can be obtained using radar techniques at W-band. Although there have been some activities at millimeter wave frequencies over very narrow bandwidths, there is a great need for wider bandwidth instruments for studying scattering and emission behaviors.; To address this need and provide a versatile system for laboratory studies of electromagnetic phenomena at millimeter-wave frequencies, a multifunctionmillimeter-wave sensor has been designed and developed. This instrument is an active/passive wide band sensor operating in the 75–110 GHz region of the millimeter wave spectrum in four primary modes: (1) As a spectrometer measuring absorption over the entire 75–110 GHz region. (2) As a radiometer measuring blackbody emissions over the entire 75–110 GHz region. (3) As a pulse radar over a 500 MHz bandwidth centered around 93.1 GHz with a peak power of 200 mW. (4) As a step frequency radar when used in combination with a network analyzer over selected 9 GHz bandwidth segments (75–84, 84–93, 93–102, and 102–110) of the 75–110 GHz region.; Measurements were performed on two volume fraction (15% and 20%) dense random media targets using this system. The results for backscattering and transmission measurements are presented for both targets for the frequencies from 95.1 to 110.1 GHz. |
