  An exact series expansion for the field radiated by a monopole ring source
with angular variation in source strength is derived from a previously
developed expression for the field from a finite disk. The derived series can
be used throughout the field, via the use of a reciprocity relation, and can be
readily integrated to find the field radiated by arbitrary circular sources of
finite extent, and differentiated to find the field due to higher order sources
such as dipoles and quadrupoles.
