? Model the Coaxial Feed
The last modeling step is the construction of the coaxial feed as the excitation source for the patch antenna. This action introduces the working coordinate system (WCS). Because the feeding point is located asymmetrical to the circular patch it is advisable to activate the local coordinate system (WCS
To define the new center point for the coaxial feed the local coordinate system is moved along the positive v-direction (WCS Move Local Coordinates, 9.2 mm in the following dialog box:
). Therefore, please enter a value of
Local Coordinate System,
).
Now it is possible to design the coaxial feed by constructing two cylindrical shapes, similar to the previously defined circular patch.
Please activate the cylinder creation mode again (Objects Cylinder,
Basic Shapes
). First, enter the values for the coaxial substrate cylinder using the Tab key, again
skipping the input of the inner radius. The cylinder has an outer radius of 4 mm and an extension in the negative w-direction of 2.1+0.7=2.8 mm. Please check your settings against the following dialog box:
Select the previously defined Substrate material from the Material dropdown list and create the cylinder with the OK button.
As a result, the cylinder shape component1:solid1 intersects with two already existing shapes, the solid component1:substrate and the ground plane component1:ground. Here it is necessary to determine the type of intersection for the shapes. It is more convenient to combine the two substrate materials into a single shape, so please mark the radio button Add both shapes in the Shape Intersection dialog box as presented below and confirm with OK:
In the second case, the substrate cylinder must be inserted into the PEC material of the ground plane. Please mark the radio button Insert highlighted shape from the Shape Intersection dialog window as presented below and confirm again with OK:
The following screenshot allows you to double-check your model (please use Ctrl+w or toggle the wireframe visualization mode on and off):
to
The inner conductor is constructed by defining another cylinder made of PEC material. Please define the cylinder with an outer radius of 1.12 mm and again an extension of 2.8 mm in the negative w-direction. The cylinder creation dialog should appear as follows:
This time, select PEC from the Material dropdown list and define again a suitable name (e.g. feed) for the cylinder shape. Create the cylinder by pressing the OK button.
Please note: In this case no Shape intersection dialog window will appear, because the PEC shape is defined after the normal material shape (here: Substrate). This implies that the PEC shape is automatically inserted into the intersected shape. Refer to the Getting Started manual for more details.
After applying the OK button the final model will look like the below figure (again use Ctrl+w or
to toggle the wireframe visualization mode on and off):
Common Solver Settings
To this point, only the structure itself has been modeled. Now it is necessary to define some solver-specific elements. For an S-parameter calculation you must define input and output ports. Furthermore, the simulation needs to know how the calculation domain should be terminated at its bounds.
? Define the Waveguide Port
The next step is to add the excitation port to the patch antenna device, for which the reflection parameter will later be calculated. The port simulates an infinitely long coaxial waveguide structure that is connected to the structure at the ports plane.
A waveguide port extends the structure to infinity. Its transversal extension must be large enough to sufficiently cover the corresponding modes. In contrast to open port structures, the port range in this case is clearly defined by the outer shielding conductor of the coaxial waveguide.
Consequently, the easiest way to define the port range is to pick the face (Objects
Pick
Pick Face, ) of the coaxial feed (Substrate material) as demonstrated below (the model is rotated again to the bottom side first):