A Note on the Difference Between Equiangular and Archimedes Spiral Antennas (Correspondence)

There seems to exist in the literature considerable confusion about the various types of spiral antennas, their characteristics, and their bandwidth capabilities. One evidence of this confusion appeared in a paper by Bower and Wolfe, in which they state that the Archimedes spiral antenna can be specified in terms of angles and hence belongs in the class of "frequency--independent antennas. "Frequency--independent antennas are relatively new; in fact, until 1955 there was no evidence that a "frequency-independent" antenna did, indeed, exist. Therefore, it would appear appropriate to delineate the characteristics and the terminology of the antennas involved. Perhaps this brief report of some recent work at the University of Illinois Antenna Laboratory will aid in pointing up the differences in operation of the logarithmic (i.e., equiangular) and Archimedean spiral antennas.