"J.B. Wood" wrote in
:

The small loop is assumed to lie in the x-y plane of an x-y-z orthogonal
Cartesian coordinate system where theta and phi are the angles measured
from the z-axis and x-axis, respectively.


Just two axes? I've been asking on and off for advice on something... I was
shown a nice design for a loop a few weeks ago, it was a helix, so in 3 axes.
What advantage if any does that give over a loop in only two axes? As a guess
I'll suggest it offers finer directional selectivity, but I'm hoping someone
who really knows about this can tell me.