We recently completed a project where the goal was to maximize the bandwidth of a rectangular stacked patch antenna. Here are the steps we took:
Step 1: Create the Geometry
First we came up with a starting point for the geometry, given the material selection constraints dictated by the design. In this case, the maximum thickness of the driven patch was limited to 60 mils. To keep it simple, we started with the same thickness for the other elements.
The initial patch sizes were determined by selecting patch sizes that were geometrically spaced in the band of interest.
Step 2: Go for VSWR
Next, we adjusted the length and width of the stack’s driven patch to get the best VSWR possible without the other two patches.
Step 3: Optimizing
Using the previous analysis as a starting point, we added the first parasitic patch and allowed the optimizer to find the best VSWR possible across the band.
The optimizer was given the freedom to adjust:
- The length and width of the driven element.
- The length, the width, and the height of the parasitic element above the driven element.
- The position of the feed pin.
FEKO has many different optimizations available. We used the Global Response Surface Method (GRSM) in this case since it converges on a reasonable answer very quickly.
We ended up with close to 20% VSWR bandwidth. This approach, though not giving us the final answer we were looking for, gives us the starting point for the next round of optimization.
Step 4: Add a Second Parasitic Patch
We repeated the optimization process, adding the length, width, and height of the second parasitic patch as degrees of freedom for the optimizer to work with. The height of the first parasitic patch was fixed at the nearest commercially available height for this particular substrate.
Again, using the GRSM the optimizer converged on a good answer fairly quickly.
Step 5: Manual Runs
At this point, we tried to move the Smith chart response a little closer to 50 ohms. We followed up by using a local optimizer to maximize the available 10dB return loss bandwidth.
Results
We ended up with just short of 30% bandwidth using one driven element and two parasitic elements while having constraints on the maximum thickness and type of substrate utilized in the design.
Though this process flow may not work for all cases, it did work well in this design considering all of the interdependencies and constraints.
ARSI 