# '''Gaussian Beam Source''': A distributed source with a complex-valued focused Gaussian beam profile defined using a virtual box object enclosing the entire physical structure.
# '''Huygens Source''': A distributed source defined based on know tangential electric and magnetic field components on the surface of a virtual box object.
Â
When an FDTD simulation starts, your project's source starts pumping energy into the computational domain at t > 0. Maxwell's equations are solved in all cells at every time step until the solution converges, or the maximum number of time steps is reached. A physical source has a zero value at t = 0, but it rises from zero at t > 0 according to a specified waveform. [[EM.Tempo]] currently offers four types of temporal waveform:
Â
# Sinusoidal
# Gaussian Pulse
# Modulated Gaussian Pulse
# Arbitrary User-Defined Function
Â
A sinusoidal waveform is single-tone and periodic. Its spectrum is concentrated around a single frequency, which is equal to your project's center frequency. A Gaussian pulse decays exponentially as t → ∞, but it has a lowpass frequency spectrum which is concentrated around f = 0. A modulated Gaussian pulse decays exponentially as t → ∞, and it has a bandpass frequency spectrum concentrated around your project's center frequency. For most practical problems, a modulated Gaussian pulse waveform with EM.Tempo's default [[parameters]] provides an adequate performance.
Â
If you use a Gaussian pulse or a modulated Gaussian pulse waveform to drive your FDTD source, after a certain number of time steps, the total energy of the computational domain drops to very negligible levels. At the point, you can consider your solution to have converged. If you drive your FDTD source by a sinusoidal waveform, the total energy of the computational domain will oscillate indefinitely, and you have to force the time loop to terminate after a certain number of time steps assuming a steady state have been reached.
===Defining a New Source===
* To change the amplitude and/or phase of a source, click the button labeled '''Excitation Waveform''' to open the Waveform Dialog.
* From the waveform dialog, you can also change the waveform type, if necessary.
Â
Once you define a source, you can always changes its [[parameters]] later from its property dialog, which can be accessed from its right-click contextual menu. You can also delete sources.
===Ideal Source===
===Waveforms & Discrete Fourier Transforms===
{{mainpage|When an FDTD simulation starts, your project's source starts pumping energy into the computational domain at t > 0. Maxwell's equations are solved in all cells at every time step until the solution converges, or the maximum number of time steps is reached. A physical source has a zero value at t = 0, but it rises from zero at t > 0 according to a specified waveform. [[Waveforms EM.Tempo]] currently offers four types of temporal waveform: # Sinusoidal# Gaussian Pulse# Modulated Gaussian Pulse# Arbitrary User-Defined Function A sinusoidal waveform is single-tone and Discrete Fourier Transformsperiodic. Its spectrum is concentrated around a single frequency, which is equal to your project's center frequency. A Gaussian pulse decays exponentially as t → ∞, but it has a lowpass frequency spectrum which is concentrated around f = 0. A modulated Gaussian pulse decays exponentially as t → ∞, and it has a bandpass frequency spectrum concentrated around your project's center frequency. For most practical problems, a modulated Gaussian pulse waveform with EM.Tempo's default [[parameters]]}}provides an adequate performance.  If you use a Gaussian pulse or a modulated Gaussian pulse waveform to drive your FDTD source, after a certain number of time steps, the total energy of the computational domain drops to very negligible levels. At the point, you can consider your solution to have converged. If you drive your FDTD source by a sinusoidal waveform, the total energy of the computational domain will oscillate indefinitely, and you have to force the time loop to terminate after a certain number of time steps assuming a steady state have been reached.
The accuracy of the FDTD simulation results depends on the right choice of temporal waveform. [[EM.Cube]]'s default waveform choice is a modulated Gaussian pulse. At the end of an FDTD simulation, the time domain field data are transformed into the frequency domain at your specified frequency or bandwidth to produce the desired observables.
In addition to the default waveforms, [[EM.Cube|EM.CUBE]] allows the ability to define custom waveforms by either time or frequency specifications on a per source basis.
Of [[FDTD Module]]Click here to learn more about EM.Tempo's observables, the near fields, far fields and all of their associated [[parametersWaveforms and Discrete Fourier Transforms]] like directivity, RCS, etc., are calculated at a certain frequency that is specified as part of the definition of the observable. On the other hand, port characteristics like S/Y/Z [[parameters]], VSWR and periodic characteristics like reflection and transmission coefficients, are calculated over the entire specified bandwidth of your project.
* '''Domain Energy''' for calculating the total electric and magnetic energy in the computational domain.
* '''Periodic Characteristics''' for calculating the reflection and transmission coefficients when your periodic structure is excited by a plane wave source.
Â
Of [[EM.Tempo]]'s frequency domain observables, the near fields, far fields and all of their associated [[parameters]] like directivity, RCS, etc., are calculated at a certain single frequency that is specified as part of the definition of the observable. On the other hand, port characteristics like S/Y/Z [[parameters]], VSWR and periodic characteristics like reflection and transmission coefficients, are calculated over the entire specified bandwidth of your project.
Â
===Defining a New Observable===
Â
To create a new observable, follow these steps:
Â
* Right click on the name of the observable type in the '''Observables''' section of the navigation tree and select '''Insert New Observable...''' from the contextual menu. This opens up the respective Observable Dialog.
* You can change the default name of the observable as well as its color.
* Change the location of the observable, if necessary, by the changing the values of the supplied coordinate fields.
* Change the orientation of the observable, if necessary.
* In the case of frequency domain observables, change the observed frequency or frequency range, if necessary.
Â
Once you define an observable, you can always changes its [[parameters]] later from its property dialog, which can be accessed from its right-click contextual menu. You can also delete observables.
===Probing Fields in Time and Frequency Domains===