W4ZCB emailed me about this, but my attempts to reply have failed. Anyway,
W4ZCB suggested his paper, which has a nice physical (non mathematical)
explanation of the far field.

http://www.setileague.org/articles/hps_ham.htm
http://www.setileague.org/articles/ham/farfield.pdf

Unfortunately, it does not solve my particular problem.

--
Dave (from the UK)

Hmmmmmmmmmmm. Sorry about the one way skip, my ISP apparently doesn't like
your ISP. Happens occasionally. Glad you found Pauls article, was going to
be a bear for me to scan it for about the 10th time.

So, I give up, what IS your particular problem? As stated, the far field
depends on the antenna gain.

W4ZCB