4.1     Units

The  button in Model tab and Parameters->Units... command from main menu invoke Units dialogue, which allows specifying the geometry units in which the project will be created and also the frequency units.

The following choices are available for geometrical units:

·       metres [m]

·       millimetres [mm]

·       microns [um]

·       nanometres [nm]

·       inches [inch]

·       mils [mils]

The following choices are available for frequency units:

·       petahertz [PHz]

·       terahertz [THz]

·       gigahertz [GHz]

·       megahertz [MHz]

·       kilohertz [kHz]

·       hertz [Hz]

The geometry and frequency units can be changed at any stage of project preparation. Please note that the unit change does not force automatic recalculation of previously entered data.

It should be noted that as an exception, the data introduced in Project Media dialogue must be always expressed in GHz.

QW-Simulator operates internally in millimetres. Thus, as field normalisation defines, QW-Simulator will display the values of electric and magnetic field in [V/mm] or [A/mm], respectively. Conversion from the user-selected units into millimetres is performed by QW-Editor at Export of shape files.

In principle, the choice of units is arbitrary, but in certain specific applications a limited dynamic range of QW-Editor’s operations should be taken into account:

·       You can write very long numbers into the QW-Editor’s dialogues. However, all resultant coordinates (describing all created or modified elements, lines, points, ports etc.) will be instantaneously snapped by QW-Editor to 5 digits after decimal point (i.e., 10^-5 in current units).

·       In project files (*.pro) saved by QW-Editor upon the Save operation, all coordinates are written with the accuracy as above.

·       In shape files (*.sh3) saved by QW-Editor upon the Export operation, all coordinates are written with the accuracy of 15 significant digits in millimetres always (in exponential form if necessary).

The above limitations should not restrict flexibility of applying the software or its overall accuracy, as long as you proceed in a reasonable way, and do not try to define a circuit that is really one micron thick at the level of one thousand inches. As a safe guideline, we recommend such choice of the units that the project does not exceed below -20000 units or above +20000 units in any dimension. Note that the above snapping of coordinates has been introduced in purpose, to avoid hazards with declaration of shapes. In other words we are trying to limit the risk of introduction of unintentional slots or overlapping appearing in the considered structure due to limited accuracy of computer floating point operations on geometrical dimensions.

The geometry and frequency units can be also changed in the Circuit dialogue.