Changes

=== Changing the FDTD Mesh Settings ===

[[EM.Cube]]'s [[FDTD Module|FDTD module]] discretizes objects using what is often referred to as the “staircase approximation”. In this mesh generation scheme, the structure is recreated using a large number of cubic cells carefully assembled in a way that approximates the shape of the original structure. By default, a carefully calculated, "<u>'''Adaptive'''</u>" mesh of your physical structure is generated in order to satisfy the following criteria:

When an FDTD simulation starts, your project's source starts pumping energy into the FDTD 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. 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.

[[Image:FDTD42.png|thumb|250px|[[FDTD Module]]'s Ideal Source dialog]]

* In the '''Source Properties''' section, you can specify the '''Source Amplitude''' in Volts and the '''Phase''' in Degrees.

[[Image:FDTD43.png|thumb|200px|[[FDTD Module]]’s Lumped Source dialog]]

* In the '''Source Properties''' section, you can specify the source '''Amplitude''' in Volts, '''Phase''' in Degrees and internal '''Resistance''' in Ohms.

Waveguide structures have many applications at microwave and millimeter wave frequencies. For example, a rectangular waveguide is used to feed a pyramidal horn antenna. A waveguide structure is usually excited using some type of strategically located probe mechanism. This can be modeled using a lumped source placed on a wire structure made up of line objects. Alternatively, use can use [[EM.Cube]]'s '''Waveguide Sources''', a special type of source that excites a prescribed modal field distribution in a rectangular waveguide structure. The scattering [[parameters]] are calculated from knowledge of incident and reflected fields at designated waveguide ports. Waveguide sources typically provide more accurate results for scattering [[parameters]] compared to lumped ports as they represent the actual dominant propagating modes at the transmission line ports.

* In the '''Source Properties''' section, you can specify the source '''Amplitude''' in Volts, and the '''Phase''' in Degrees.

[[Image:FDTD45.png|thumb|300px|[[FDTD Module]]'s Distributed Source dialog]]

{{isoimg|FDTD52.png|A coaxial line port using four symmetric lumped sources.}}

In [[EM.Cube]]'s [[FDTD Module]] you can define simple lumped elements such as resistors, inductors, capacitors as well as nonlinear diodes. Although lumped loads are not sources and do not excite a structure, their properties are similar to lumped sources. Lumped Loads are incorporated into the FDTD grid across two adjacent nodes in a similar manner to lumped sources. Likewise, lumped loads are defined on Line objects. In order to create a lumped load, you must have at least one line object in your project.

If the project workspace contains an array of hollow box objects to model a rectangular waveguide array, you can also define an array of '''Waveguide Sources''' to be placed across those waveguides. If you insert a new waveguide source, all hollow box array objects, if any, will be listed as eligible objects for waveguide source placement. A waveguide source will be placed on each element of the array. All the waveguide sources will have identical direction and offset. However, you can prescribe certain amplitude and/or phase distributions. The available '''Weight Functions''' include '''Uniform''', '''Binomial''', '''Chebyshev''' and '''Data File'''. In the last case, you need to set a value for maximum side lobe level ('''SLL''') in dB. You can also define a '''Phase Progression''' in degrees along each of the three principal axes.

[[Image:FDTD46.png|thumb|300px|[[FDTD Module]]'s Plane Wave dialog]]

A plane wave box placed around a PEC sphere object. The trident at the corner of the box shows the propagation vector as well as the E-field and H-field polarization vectors.

[[Image:FDTD47.png|thumb|250px|[[FDTD Module]]'s Gaussian Beam dialog]]

A Gaussian beam box placed around a horizontal PEC plate. The trident at the corner of the box shows the propagation vector as well as the E-field and H-field polarization vectors. The titled transparent green circle shows the footprint of Gaussian beam at its focal (waist) point.

==Running FDTD Simulations==