Ozone is one of the most important minor gas constituents of the atmosphere. Global depletion of the protective ozone layer in the last decades accompanied with such anomalous events as ozone holes in Antarctic and Arctic [1, 2] requires reliable long-term monitoring of ozone and ozone-related minor atmospheric gases from both satellites and ground level. Ground-based millimeter-wave (MMW) monitoring of atmospheric ozone is low-dependent on weather conditions, covers broad altitude region from the lower stratosphere to mesosphere, and is possible in day and night time [3,4]. These features of MMW measurements provide their advantages over traditional optical methods (UV spectrometers and lidars) and ozone sondes.A new transportable MMW spectrometer for ground-based monitoring of vertical distribution of atmospheric ozone (ozonometer) was designed and built at the LPI in cooperation with a number of leading scientific institutes of Russia. The instrument measures broadened spectral line of the atmospheric ozone thermal emission centered at 142.175 GHz (wavelength of 2.1 mm). Vertical ozone distribution in the stratosphere and mesosphere over point of observations (altitudes 12-75 km, up to 95 km at night) may be retrieved from the spectral line contour using special mathematical methods [4].The ozonometer consists of low-noise receiver, acousto-optical and filter-bank spectrum analyzers and PC with special software. The instrument may be operated in both automatic and manual mode. General view of the ozonometer is shown at Fig. 1. At present the instrument is placed at the LPI in Moscow before window closed with thin radio transparent polyethylene film. Elevation angle of antenna is selected at observations depending on weather conditions. Antenna pattern width is of 1.5° at -3 dB level [5].Room temperature heterodyne receiver [5] of the ozonometer is based on planar Schottky diode mixer [6, 7] and consists of optical and high-frequency blocks (Fig. 1, left). Optical block includes input Gaussian quasioptics [8], the mixer and local oscillator, corrugated horns to launch Gaussian beams, preamplifier of the first intermediate frequency (IF1) 3.5…4.0 GHz, and control interfaces. Quasioptical units are flat antenna mirror, chopper wheel of 200 mm diameter, room-temperature (hot) calibration load periodically placed across the signal beam, liquid nitrogen cooled reference load with brightness temperature varying from 85 K to 295 K by rotating wire grid, single sideband (SSB) filter, path length modulator to avoid distortions from standing waves, diplexer to combine signal and local oscillator beams and filtering local oscillator noise, and off-axis elliptic and parabolic mirrors for focusing Gaussian beams. Diameters of all apertures were selected to be no less than 4.5 w , where w is parameter of field distribution across main Gaussian mode [8]. The chopper wheel switches the receiver input between sky and the reference load with frequency of 30 Hz. The SSB filter and diplexer are Martin-Puplett interferometers. Meas...
