I had a 100cm prime focus dish laying around and I thought of making a circularly polarized feed for it, since it seemed pretty straightforward from what I've been reading. Helical feeds are supposed to be very wide and forgiving. So I built this feed: The problem I have is, even though the feed and signal are circularly polarized, if I rotate the feed or the antenna 90 degrees, the signal completely disappears. I was told I'm losing a lot of signal due to the fact that this antenna is for a linear feed and so it's turning my CP signal into LP, and then the feed is losing signal again due to the fact that it's CP again. What I tried was to cover my antenna with fine aluminium wire mesh (the kind you would use on a screen door), so the antenna ended up looking like this:
But again I have the problem that rotating either the antenna or feed make it lose signal. I don't have a VNA to analyze the feed (frequency of interest is 1.7GHz). So the best I can do is point it at a known satellite (in my case, GOES-16. I have a working system for it to which I can compare results, but it's a slightly larger antenna with a linear feed. GOES LRIT is linear).
- Does the wire mesh I added help with preventing the antenna from linearizing my circular polarized signal?
- What can be causing the problem of losing signal as I rotate the feed or antenna?
- If the signal is linear and my antenna and feed are circular, I'm supposed to get the same signal level regardless of rotation, right? I'll be losing 3dB due to polarization mismatch but it should be the same regardless.