Recently finished designing and testing a pair of UHF band compact inverted-F antennas (IFA). The room available for this design was very limited and required the radiating element to be meandered in order to achieve the required frequencies.
The challenges of the design included the compact size and the complexity of the surrounding environment. This included other PCBs in close proximity, LAN connectors, batteries, header pins, etc. Fortunately, CAD files were available for all of these features, making it possible to simply import the files directly into FEKO and start working.
The design procedure for this project was as follows:
- Import the CAD files of the other PCBs and the enclosure.
- Select a solution technique. In this case the Finite Element Method (FEM) was a perfect fit.
- Lay out the basic IFA geometry parametrically, including the meander.
- Manually run the model to zero in on the required frequency and bandwidth.
- Perform a series of mesh convergence runs to find the best compromise between run speed and solution accuracy.
- Select the optimizer and determine what parameters and ranges to use, etc.
- Run the optimizer once or possibly several times zeroing in on a final solution.
- Run several more manual runs to get the final geometry and performance desired, if necessary.
- Built and test it.
It is always a good idea run the model manually in the beginning to get a handle on how the antenna performs in relation to the various parameters (length, width, meander length, etc.). Completing this step helps provide a better understanding of how the antenna works and the insight needed to address problem issues that may pop up later.
In this case FEKO was almost dead on with the final measured values. This does not always happen – actually, the measured values are rarely this good — but the quality of the CAD models and the material properties was very close in the frequency range designed.
ARSI 