Dragon's Teeth On Dish Strut?

Today Goonhilly Earth Station Ltd shared a tweet about how beautifully clean our Antenna 6 ("Merlin", "GHY-6") is getting, thanks to the team in the dish cleaning it out.

Within half an hour I got a text from a friend firstly complementing the social distancing, but then asking about the weird zigzags/curves on the inside of the strut. The strut is one of 3 that support the subreflector: this antenna is a Cassegrain type - with a hole in the centre that leads down into the beam waveguide. (If you want to know more about the geometry of the thing, check out the wikipedia page about Cassegrain optics.)

I've always called these things dragon's teeth, because actually they're pretty big, and they do the job of hiding the monster. What monster? And why are they there? And although we're near the seaside, aren't they the wrong way up to keep seagulls off?

I thought I'd explain what these are about, since someone once (in February 1996) explained them to me, and I've not seen anything about them since. So - the issue is that the struts themselves interfere with reflected signals - they manifest themselves in slightly weird ways in the signal space. (This is the primary motivation for offset feed antennas other than shadowing - reduced incident power - there's nothing in the way.)

The job of the dragon teeth is to randomly scatter reflected waves so that the field strength of the reflections from the highly regular geometrical structure is dispersed, can destructively interfere, and end up in the noise instead of 'loud' additional reflections. They greatly reduce artefacts (the monster that is scared off by the dragon) in the signal ultimately received, which in turn improves overall link performance. Hence the different sizes and distributions of the teeth. To make sure I close out the questions above - yes, they are the wrong way up for seagulls.

In fairness, I don't think these are quite as much use at the higher frequencies that we're upgrading this dish for, but its nice to have them, and they do no harm. Until you bang your head on them while cleaning the main reflector.

I'm very interested to have anyone throw anything more analytical and technical at me about this topic.