They would be rock solid if nothing is moving in the nearfield of the antenna.  
However your particular antenna will have lobes in slightly different positions 
and magnitudes.  The plot you get is the antenna that was hand tweaked and 
tested on the range.  Production models vary a bit from antenna to antenna.  

This is kind of like the pattern your headlights cast on your garage door.  You 
will see bands and irregularities on the edges of the light pattern.  They 
really don’t move but are a function of how the light was sealed together.  

From: Adam Moffett 
Sent: Tuesday, September 20, 2016 10:57 AM
To: Animal Farm 
Subject: [AFMUG] Antenna side lobes...do they move much?

My question is about the polar plot for a sector antenna where you see tiny 
lobes coming off it.  Such as in between the rear lobe and the main lobe there 
might be several tiny lobes.  I've always thought RSSI was unstable when you 
hit the sector from a weird direction like that.

If I could see the radiation pattern in realtime would those lobes be 
stationary or would they dance around a little?  

I'm just looking for an underlying reason for things I've seen in the field, 
and maybe a real justification to use when I tell people not to do that.

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