Background
Recently, my ham radio friend Stan Wood invited me to help him tune an order of these satellite antennas that he designs, makes, and sells. He came up with this design over 15 years ago and has sold hundreds. Stan is an extraordinary engineer, and his knowledge of antenna design is immense. I am incredibly thankful for this opportunity to have learned from him.
These antennas are circularly polarized S-Band antennas used for telemetry uplink and downlink by different satellites worldwide. The tuning process consists of shortening (and hopefully not needing to lengthen) the 4 elements sticking out, modifying the length of the Teflon dielectric in the center, and the length of a copper impedance matching sleeve around the feed pin.
Tuning Process
The antenna was then put on a test bench to determine its S11 parameters for return loss, and S21 parameters from a horizontally polarized antenna that could be rotated to determine the circular polarization of the antenna. The antenna was repeatedly modified and then tested until a perfect match was found.
Issues and Results
As we began to try to tune them, we were having a lot of difficulty getting the match and circular polarization right. We found that the elements needed to be much longer than they ever needed to be before. After more investigation, we realized that the angles of the elements from the center feed were all over the place, ranging from 30-60 degrees instead of the designed 45 degrees. Because of this manufacturing defect of the center feed from an external machine shop, we couldn’t finish tuning all the antennas and only were able to complete a few during the period which I was helping him.
Overall, I learned a lot about how antenna theory and design work in practice and especially how circularly polarized antennas are designed.
