I am attempting to contact the author of that paper, G. W. Horn (I4MK),
to see if he will permit me to publish his paper on the web for a few
months. If I am successful, I will post the web link on this list.

I have another paper which may be of interest: "A Broadband Quadrature
Coupler", Microwave Journal, May 1983, pp. 216-219. The authors employ
a pair of four-port directional couplers and a balun. Now all I have
to do is figure out how to construct a four-port directional coupler
for the 0.5-2.0 MHz band!

Vinton