Nya modeller för vågutbredning över mark. Jämförelse med GRWAVE

Authors:

  • Peter Holm
  • Börje Asp

Publish date: 2008-11-25

Report number: FOI-R--2564--SE

Pages: 30

Written in: Swedish

Keywords:

  • Radio wave propagation
  • ground wave model
  • GRWAVE.

Abstract

Within the project "Detvag FAS II", three new ground wave models have been developed. The models are intended to be used by applications using the Detvag90 calculation engine. The main reason for a further development of the Detvag90 program is a request of more computational efficient models for use in the applications WRAP and TCT. In Detvag90, the well known ground wave model GRWAVE is used for calculation of the transmission loss over smooth spherical earth. This model is accurate but computational intensive. Detvag90 includes also a fast model for smooth spherical earth. Unfortunately, this model is less accurate and limited to low antenna heights. Many quantities computed by the program GRWAVE only need to be calculated once when calculating many transmission loss values along a radius outwards from the transmitter. When calculating transmission losses for point-to-point, these quantities have to be recalculated for every point-to-point calculation. This fact makes the use of GRWAVE more computation intensive for point-to-point than for coverage calculations along several radii. Unfortunately, by different reasons, the applications WRAP and TCT are based on point-to-point calculations also for coverage calculations. Consequently, the purpose of this work has been to develop a new model doing the same kind of calculations as GRWAVE but in a more computation efficient way. The outcome of this effort resulted in three new models. The first one is a plane earth model, which is able to handle large antenna heights but is limited to short distances. The second model is a simplified spherical earth model, which is fast and able to handle distances larger than the new plane earth model. The third model is a spherical earth model, which, more or less, is valid for any set of input parameters; that is, no restrictions on antenna heights, propagation distance, etc.

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