The propagation of radio waves through the Earth's atmosphere at millimetre wavelengths (i.e. at frequencies ranging from 30 to 300 GHz) can be affected by the absorption, dispersion and scattering caused by tropospheric constituents (e.g. atmospheric oxygen and water vapour, cloud, rain, and other atmospheric molecules such as CFCs, sand and dust particles), as well as by atmospheric turbulence and the stratification of atmospheric layers.

QinetiQ developed the global prediction model MAPEL, in collaboration with the Universities of York and Bath, to aid the design and deployment of millimetre wave systems at 10-50 GHz for terrestrial, satellite, and airborne platforms.

Given transmitter and receiver location (latitude, longitude, altitude), frequency, and month of year, the model first characterises the tropospheric environment through which the millimetre wave signals will propagate (e.g. water vapour density, rainfall rate and height, cloud coverage, etc.), then determines the path legnth through the various tropospheric features, and finally predicts the attenuation and its associated probability. Model outputs are of the form of contour coverage maps showing either the signal availability at specific attenuation threshold, or the signal attenuation and range to be overcome to meet the desired system requirements.

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The figure shows contours of signal availability as a function of the required link margin (i.e. the predicted excess attenuation) and range (due north and south of a transmitter at 51°N), at a frequency of 38 GHz for the month of June.

Model Features

• Global monthly model predictions
  - signal attenuation
  - availability
• Variable rainfall height
• Geographical location specified
• All attenuation mechanisms considered
  - rain types, clouds, melting layer
• Oxygen and water vapour attenuations

Predictions Usage

• Scenario modelling
• Link budget analysis
• Generation of coverage maps
• Optimising system deployments

Model Applications

• Long range airborne communications
• Covert airborne communications
• Airborne reconnaissance
• UAV applications