While searching for resources explaining complex signals, I came across a discussion (https://www.dsprelated.com/showthread/comp.dsp/223558-2.php) mentioning the fact that respondents were unable to locate the 4-article series on Complex Signals, published in RF Design, December 1989, Jan 1990, March 1990, and May 1990.

I had saved the article at the time it was published, and it was instrumental in helping me drop the scales from my eyes of not only the subject of complex signals, but also helping to graphically understand what's going on with a DFT -- correlating a complex (spiral) signal with the signal being analyzed.

It has been archived as a print of a microfilm and is accessible at the url:
RF Design, 1989-1990 results
The first article in the series:

Complex Signals, Part 1

You must log in to "borrow" the magazine for 1 hour at a time.

Fun fact!:  Noel Boutin was one of my teachers, back in the days, at Sherbrooke University in Quebec.  Noel was voted the most appreciated teacher of the EE program on most years I was there.

The best profs are the ones that make new concepts relate to something you already know and who don't hide behind writing out equations in one hand and eraser in the other (showing my age again).

I like the way Prof. Boutin throws shade on every other Signals textbook author, who "with one exception (1), the exponential shown in Figure 3 [spiral with projections of the real & imaginary planes] is never pictured in modern textbooks on signals, circuits and systems." 

Richly deserved IMHO. And the exceptional textbook is his own. Mike drop.