This article is a practical guide on how to feed a microstrip annular-ring slot antenna on a finite ground using an edge feed.
As an example, we will have a look at a microstrip annular-ring slot antenna with a feed line that is connected by an SMA connector to a coaxial cable.
The front and side (section) view of the physical microstrip antenna for illustration purposes. Dimensions not to scale.
The annular-ring slot antenna is modelled using a finite ground plane. Since we are using a finite ground plane, we cannot use a microstrip port. Microstrip ports are only supported with planar multilayer substrates A good approximation of a microstrip annular ring antenna is to use an edge port. A voltage source is then added to the edge port to excite the patch antenna.
An annular-ring slot antenna on a finite substrate with a feedline at the bottom of the substrate. Left: 100% opacity; Right: 20% opacity.
Note: A port cannot be placed on the boundary of a finite dielectric substrate when using the method of moments (MoM).
Since there is the restriction that a port cannot be placed on the edge of a finite substrate when using MoM, the model is adjusted to have a separation gap. The edge port is to be placed on the face perpendicular to the feedline.
To adjust the model to allow placing an edge port:
- Subtract a volume from the finite substrate where the edge port will be placed.
Subtract a volume from the finite substrate.
- Create two polygons to connect the top PEC face and the feedline at the bottom. To keep the port edge smaller than lamba/30, taper the face to the centre where the port will be located. The faces will be in the shape of a “bow tie”.
Two faces are created that taper to an edge length smaller than λ/30. The edge port will be placed on the faces on either side of the edge.
- Union the model to ensure mesh connectivity.
- Set the faces of the “bow tie” to PEC.
The “bowtie” faces are set to PEC.
To excite the patch antenna:
- Add an edge port on the edge smaller than lambda/30.
Add an edge port to the faces.
The Create Edge Port dialog.
- Add a voltage source to the edge port.
A voltage source is added to the edge port.
Tip: An alternative method to feed the model is to add the physical connector and excite the face of the connector, see How to feed a microstrip patch antenna with an SMA connector on a finite ground.
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