Radio propagation prediction in aeronautical services, where both mobile and base terminals can be anywhere from ground level to 50000 m, must be handled differently from instances where terminals are on the surface of the earth. The aeronautical propagation model is specifically designed for this environment.
The RadioObjx Aeronautical Propagation model allows the planning and coordination of aeronautical mobile systems but can be applied where there is need for prediction of ground-to-air, air-to-ground and air-to-air paths. For more information about ATDI software components for use with ATDI planning tools or embedded in other third party systems, please contact us.
Core Transmission Model
The model is a hybrid, based on a core transmission model and an optional obstacle diffraction algorithm. The core model reproduces the published set of reference curves in the ITU-R recommendation entitled Propagation Curves for Aeronautical Mobile and Radio Navigation Services using the VHF, UHF and SHF bands. The obstacle model is based on the recommendation ITU-R P. 526-7 Propagation by Diffraction, and if selected, the diffraction losses calculated will be added to the loss of the core transmission loss. The model manifests itself as a DLL that may be used in conjunction with ATDI planning tools or as a COM object or EXE to be embedded in other software systems.
The core transmission loss model is based on an implementation of the IF-77 propagation algorithm, from which the original curves of ITU-R P. 528-2 were derived. This means that heights and frequencies that do not exist in the published curves are computed rather than interpolated. The model is constrained to give basic transmission loss for 5%, 50% and 95% of the time for antenna heights in the range 0.5 to at least 50,000metres. The frequency range of the implementation is limited to the range from 100MHz to 20GHz and is applicable to paths of up to 1800km.
Obstacle Diffraction Model
The core model diffraction computations are limited to smooth earth calculations and no account is made of irregular terrain obstacles. While IF-77 has an obstacle model, this is not applied because it suffers from a limitation that the highest antenna height must be greater than the highest obstacle and would be invalid for low altitude aeronautical platforms. A separate algorithm is used to correct the core model based upon the double isolated edge method specified in the section Diffraction over obstacles and irregular terrain from § 4.4 of ITU-R P.526-7. This model is applied only to obstacles in the region near the radio horizon limited to 15km from the transmitter and receiver and is not applied to obstacles in the mid path. This approach gives a conservative correction to the core model without overestimating obstacle diffraction loss.