4.3 define_antenna

• description: Allows generating time-varying fields using a modulated sine-wave current source.
• example:
  &define_antenna  
      start = 0.01, end = 0.02, position = 0.03,  
      direction = "z",  
      current = 1,  
      frequency = 2856e6,  
      waveform = "spline.wf"  
  &end

  This defines a current source in the longitudinal direction extending from z of 1cm to 2cm at a radius of 3cm. The amplitude of the current is 1A with a frequency of 2856MHz, modulated by the envelope in SDDS file spline.wf.

• synopsis and defaults:
  &define_antenna  
      double start = 0;  
      double end = 0;  
      double position = 0;  
      STRING direction = "z";  
      double current = 0;  
      double frequency = 0;  
      double phase = 0;  
      STRING waveform = NULL;  
      double time_offset = 0;  
  &end

• details:
  • direction: may take values ”z” and ”r”, indicating an antenna extending in the longitudinal or radial direction, respectively.
  • start, end: starting and ending limits of the antenna in the direction direction.
  • position: position of the antenna in the ”other” direction. I.e., it is the r position if direction is ”z”, and the z position if direction is ”r”.
  • current, frequency, phase: basic parameters of the antenna waveform.
  • waveform, time_offset: specifies an envelope function for the antenna drive. The SDDS file waveform must contain at least two columns, named t (for the time in seconds) and W, specifying the envelope W(t). The antenna is driven by the function I * W(t - t_o) * sin(2 * π * f + ϕ), where I is the current in Amperes, t is the time in seconds, t_o is time_offset in seconds, f is frequency in Hertz, and ϕ is phase in radians.