2.2      Circuit Settings

The Circuit button  in Model tab and Model->Circuit Settings... command from main menu invoke Circuit Settings dialogue. The options available in this dialogue are arranged in three tabs, Basic, Circuit Type, and Advanced.

In the Basic tab the user specifies the frequency band of interest. If the defined range is the same as the excitation frequency range and should be also used for postprocessings calculations the user can assign it automatically by pressing Set for Ports and Set for Postprocessings buttons respectively. The user further have a choice of the Default medium. This type of medium will be assigned to any volume in the project, which has not been explicitly defined as made of some other medium. There is a choice of two types of default media: metal (convenient for shielded waveguide structures) or air (which would be convenient for radiation problems).

Note the following:

The choice of the default medium is important and accidental change of it may lead to wrong simulation results. That is why the current default medium is constantly signalled in the caption of the QW-Modeller application. On the entry to a new project the default medium is metal. Thus if the user wants to model a free space propagation (like for example in antenna applications) the default medium must change it to air. It has been noted that a wrong default medium setting is a common user-generated error. Thus the user should be careful with it.

Regardless of the choice of the default medium the default external boundaries of the FDTD mesh are assumed to be made of metal, thus those are electric boundary conditions. To assign to them different properties see Borders chapter for more information.

Units frame allows specifying the geometry units in which the project will be created and also the frequency units. These can be specified also in the Units settings.

Circuit Type tab allows determining the type of the circuit that will be analysed. In the current version of QW-Modeller, the user can choose either it will be typical three-dimensional (3D) or 3D periodic (3DP) scenario. In case of 3DP projects it is necessary to set the Periodicity direction (determine at which boundaries the periodic boundary conditions will be imposed), by checking appropriate axes and defining the Phase shifts. There are two ways of doing that. Firstly, it can be done explicitly by defining the Floquet Phase shifts per period in radians. This option is set as default and the Floquet phase shifts can be easily calculated using the following formulae:

                                                                                     (1)

                                                                                      (2)

                                                                                                (3)

where φ and θ are the spherical coordinates with Z reference axis, L_i is a spatial period of the structure along i axis and c stands for the light velocity. In the second option the user can define the incidence angles of the illuminating wave (Angles of incidence), directly by setting the values of φ and θ in degrees. For more information regarding periodic boundary conditions implemented in QuickWave refer to Periodic Boundary Conditions.

In the future versions of QW-Modeller the following circuit types will be enabled:

• 2Dvcoa (BOR) circuits, denoting axisymetrical structures - two dimensional in cylindrical coordinates (QW-V2D), also called Bodies of Revolution or BOR. In case of this type of circuits it will be necessary to define proper angular variation.

• 2DV circuits, usable for guided problems with a known phase constant (drawn as a two-dimensional structure in XY plane).

In the Advanced tab we can find Metal Losses Bandwidth choices that enables the choice regard the bandwidth for rigorous consideration of frequency-dependent skin effect in lossy metals. The details concerning the lossy metals model are given in the description of Metallic type of medium. In general, to reproduce the frequency dependence, we attach to each of the tangential magnetic field components an RL ladder composed of a finite number (K) of cells. With the number K increasing we can model accurately the skin effect in a wider band, but at the price of increasing computer time and memory. That is why we allow the user to make the choice of the bandwidth to be used. The three available options: Narrow, Decade and Two-Decades correspond to the number K varying from 2 to 12, with appropriate change in wide band properties of the model. The central frequency for the band is taken as: in the case of sinusoidal excitation - frequency of the source; in the case of pulse excitation - central frequency of the band of postprocessing; in the case of pulse excitation and no postprocessing - 10 GHz.

There are also five suppress options, for suppressing dielectric, metal or magnetic losses, singularity corrections, and SAR analysis. Suppressing the losses saves memory and computing time. Thus it is very convenient when we want to obtain faster preliminary simulation results without laborious modification of the entire project. Suppressing singularity corrections is only used in specific software operation, evaluating the influence of field singularities on the accuracy of FDTD results.

Python code

The python code, which can be useful when creating project scripts, generated by Circuit Settings dialogue for default parameters:

App.ActiveDocument.QW_MediaLibrary.BackgroundMedium = "air"

App.ActiveDocument.QW_Circuit.FreqencyFrom = 5.00000        

App.ActiveDocument.QW_Circuit.FreqencyTo = 15.00000

App.ActiveDocument.QW_Circuit.FreqencyStep = 0.10000

App.ActiveDocument.QW_Circuit.Units = "mm"

App.ActiveDocument.QW_Circuit.FrequencyUnits = "GHz"

App.ActiveDocument.QW_Circuit.Description = "No description"

App.ActiveDocument.QW_Circuit.CircuitType = "3D"

App.ActiveDocument.QW_Circuit.PeriodicityX = False

App.ActiveDocument.QW_Circuit.PeriodicityY = False

App.ActiveDocument.QW_Circuit.PeriodicityZ = True

App.ActiveDocument.QW_Circuit.PhaseShiftType = "Phase shift/period"

App.ActiveDocument.QW_Circuit.PhaseShiftX = 0.00000

App.ActiveDocument.QW_Circuit.PhaseShiftY = 0.00000

App.ActiveDocument.QW_Circuit.PhaseShiftZ = 0.00000

App.ActiveDocument.QW_Circuit.Phi = 0.00000

App.ActiveDocument.QW_Circuit.Theta = 0.00000

App.ActiveDocument.QW_Circuit.PhaseConstant = 0.00000

App.ActiveDocument.QW_Circuit.AngularVariation = 1

App.ActiveDocument.QW_Circuit.MetalLossesBandwidth = "Decade"

App.ActiveDocument.QW_Circuit.SuppressLossesDielectric = False

App.ActiveDocument.QW_Circuit.SuppressLossesMetal = False

App.ActiveDocument.QW_Circuit.SuppressLossesMagnetic = False

App.ActiveDocument.QW_Circuit.SuppressSingularityCorrections = False

App.ActiveDocument.QW_Circuit.SuppressDensity_SAR = False