Concentric, closing rings on radar display in rain

[Toccata]

Can you help diagnose the issue, if any, in my DRS12A radar (6 foot open array) depicted on the attached photo? This was taken on a rainy day but only occurred sporadically during the day (maybe twice during a 10-hour run). The red target ring starts at the outside of the range but then spirals in until the entire screen is filled. Thanks.

 

[Johnny Electron]

My best guess is you have water in your antenna. You should inspect the array for cracks and proper sealant where the array meets the gear box. You can open the scanner (on a nice day) and inspect for signs of water around the upper waveguide area and then move the array back and forth with the gear box open to see if you hear any water inside the array.