I’ve been struggling to get radar plots working nicely with Gnuplot. I finally realised that loads of options were missing from the creaky version installed in Ubuntu 10.04 (there’s some custom software to which we’ve lost the source + so I don’t dare upgrade currently!). After a bit of Google searching, I found this PPA of backports:
https://launchpad.net/~gladky-anton/+archive/gnuplot