-fdtd/-pexcitation: What port-mode should be excited

Here you specify what port-excitation shall be used. The excitation can be a switched on sine-signal, a gaussian pulse modulated with a sine, or a user specified signal.

 ##############################################################################
 # Flags: nomenu, noprompt, nomessage,                                        #
 ##############################################################################
 # section: -pexcitation                                                      #
 ##############################################################################
 # port  =  undefined                                                         #
 # mode  = 1                                                                  #
 # amplitude =        1.0                                                     #
 # phase     =        0.0                                                     #
 # frequency =  undefined                                                     #
 # bandwidth =  undefined                                                     #
 # risetime  =        0.0                                                     #
 # signalcommand= -none-                                                      #
 ##############################################################################
 # nextport, list, ?, return, help                                            #
 ##############################################################################

• port= NAME-OF-AN-ALREADY-DEFINED-PORT:
  The name of the port where the mode should be launched. This is a name that you have used in the section "-fdtd/-ports".
• mode:
  The number of the mode to launch. The modes are numbered sequentially, starting from 1. The modes are sorted by the negative real part of the square of their propagation constants.
• amplitude:
  The amplitude of the mode to launch. If the amplitude is zero, no mode is launched. If you specify a monochromatic excitation, ie if you specify a "risetime" /= 0, then the power of the excited wave in the steady state is "amplitude" watts. If you specify a broadband excitation, then the maximum power of the excited wave is approximately "amplitude" watts.
• phase:
  The phase of the excitation. Only useful when more than one mode is excited.
• frequency:
  If "risetime $\ne$ 0", ie when using a monochromatic excitation, the frequency of the excitiation. When "risetime = 0", ie when using a broadband excitation, the centerfrequency of the excitation.
• bandwidth:
  The frequency bandwidth of the time signal to use as excitation.
• risetime:
  If specified as nonzero, a monochromatic excitation is used. The risetime of the excitation is "risetime".
• list:
  Lists the names and planes of the ports as specified in section "-fdtd/-ports".
• signalcommand= NAME_OF_COMMAND:
  If specified as -none- the excitation will be computed from risetime, frequency, bandwidth and amplitude. If specified as any other string, every 100 timesteps the specified command is executed to compute the signal at the next 100 timesteps. The command is executed as:

         NAME_OF_COMMAND < ./gdfidl-actual-time-interval > ./gdfidl-actual-signal
  

  The file ./gdfidl-actual-time-interval contains the following data:
  • In the first line are iTime1, iTime2, TimeStep
    • iTime1: The number of the first timestep for which the signal shall be defined.
    • iTime2: The number of the last timestep for which the signal shall be defined.
    • TimeStep: The width of a timestep.
  • in the second line are Beta, Alpha, DeltaZ.
    • Beta: The real part of the propagation constant of the selected mode at the selected frequency frequency.
    • Alpha: The imaginary part of the propagation constant.
    • DeltaZ: The width of the mesh at the selected port.
  The signalcommand NAME_OF_COMMAND has to write to stdout simply the values of the signal at the timesteps iTime1 to iTime2, one line for each value.
• nextport:
  Switches to the next port-excitation. For the next ports, you may specify different parameters port, mode, amplitude and phase, but the parameters frequency, bandwidth and risetime are the same for all excited ports.

Example The following specifies that the fundamental mode of the port with name InputPort shall be excited. Its amplitude shall be '1', the centerfrequency of the excited pulse shall be 1.2 GHz, and the bandwidth of the excited pulse shall be 0.7 GHz.

 -fdtd,
    -pexcitation
        port= InputPort
        mode= 1
        amplitude= 1
        frequency= 1.2e+9
        bandwidth= 0.7e+9

Example The following specifies that the fundamental mode of the port with name InputPort1 shall be excited. Its amplitude shall be '1', the frequency of the excited signal shall be 1.2 GHz, and the risetime until steady state of the excitation shall be 10 HF-periods. In addition, the fundamental mode of the port with name InputPort2 shall be excited. Amplitude shall be '1'.

 -fdtd,
    -pexcitation
        port= InputPort1, mode= 1, amplitude= 1, phase= 0
        frequency= 1.2e9, risetime= 10 / 1.2e9
      nextport
        port= InputPort2, mode= 1, amplitude= 1, phase= 0

Example The following specifies that the fundamental mode of the port with name InputPort shall be excited. The portmode shall be computed for a frequency of 10 GHz, and the signal of the excitation shall be defined by an external signal command.

 -fdtd,
    -pexcitation
        port= InputPort
        mode= 1
        amplitude= 1
        frequency= 10 GHz
 #
 # compile the signalcommand
 #
 system(f90 signal-command.f -o signal-command)
        signalcommand= ./signal-command

This is the sourcefile signal-command.f:

      PROGRAM SignalCommand
      IMPLICIT DOUBLE PRECISION (a-h,o-z)

      Pi= 4*ATAN(1.0d0)
      Frequency= 10e9
      TRise= 10/Frequency
      TDecay= 20/Frequency
      THold= 50/Frequency
      READ (*,*) iTime1, iTime2, TimeStep
      READ (*,*) Beta, Alpha, DeltaZ
      DO iTime= iTime1, iTime2, 1
         ActualTime= iTime*TimeStep
         IF (ActualTime .LE. TRise) THEN
            Phi= ActualTime * Pi / TRise
            Factor= (1-COS(Phi))/2
         ELSE IF (ActualTime .LE. TRise+THold) THEN
            Factor= 1
         ELSE IF (ActualTime .LE. TRise+THold+TDecay) THEN
            Phi= (ActualTime - (TRise+THold)) * Pi / TDecay
            Factor= (1+COS(Phi))/2
         ELSE
            Factor= 0
         ENDIF
         Factor= Factor * TimeStep / DeltaZ
         WRITE (*,*) Factor*SIN(2*Pi*Frequency*ActualTime)
      ENDDO
      END PROGRAM SignalCommand