-------------------------------------------------------------------------------
   Compute the temperature of an antenna on the ground. 
   Rain acts as an attenuator for the sky.

   Type TAntennaGround for a demo. See also TSky and LossPrecipitation.
-------------------------------------------------------------------------------
   Form:
   tA = TAntenna( tSky, aRain, tGround )
-------------------------------------------------------------------------------

   ------
   Inputs
   ------
   tSky          (1,1)  Ambient temperature of the sky
   aRain         (1,1)  Rain Loss (dB)
   tGround       (1,1)  Ambient temperature of the ground
                        
   -------
   Outputs
   -------
   tA            (1,1)  Antenna noise temperature
                        
-------------------------------------------------------------------------------
  	References:	Maral, G. and M. Bousquet. (1998.) Satellite Communications
               Systems. Wiley. p. 37.
-------------------------------------------------------------------------------