This is not a homebrew by me. It is a mesurement of NVAK feeders for 5.6 GHz. We mesure two and we see simalar results. From 4.9 - 6.1 they have less than -15 dB SWR.
The scaling is 5 dB per square and the mesurement range is from 4 GHz to 7 GHz. The markers are to 4.9 and 6.1 GHz. You can see a deep to about 5.4 to 5.5 at -25dB.