The first documented traces of multiband Delta Loop antennas made of rigid structures go back to Frank Cooper‘s constructions (G2QT), in the la late 50s.
After gaining extensive experience as a builder of different kinds of antennas, Cooper managed to make a 6 element triband Delta Loop, which preferred to all the other ones because of its features: high gain and excellent front/back ratio. This model was published in the 1978 ARRL Antenna Anthology.
In Italy, in the early 70s, Giuseppe Molinaro (I1MOL) carried out a multiband Delta Loop project, which had a single matching system. This project became an article for QST, written along with Rick Tavan (N6XI), and then never published.
In November 1974, this time in USA, Allan A. Simpson (VE4AS) published on QST the description of his two-band Delta Loop in “Two-band delta loop array”
The single-matching-system Delta Loop by Molinari was later re-proposed by Silvano Contavalli (l4ZSQ) and Claudio Spada (l4USC) in “Costruiamo una Delta Loop per 20-15-10 m” on Radio Kit Elettronica 12/1981
In October 1986 the antenna project was published in the “Antenne progettazione e costruzione” book, edited by Nerio Neri (I4NE).
More elaborated versions, in terms of number of bands, electrical and mechanical complexity, were made since the 80s also by Koichi Nagai (JA3EY).
On the basis of an 8 element (4+4) Delta Loop for 21 and 28 MHz, the Japanese amateur radio operator also developed a four-band Delta Loop model by adding to the first design 6 more elements (3+3) for 18 and 24 MHz.
Later, 11 more loops for 144 MHz were added to the 14 el. four-band Delta Loop. The antenna, in its final version, had a total number of 25 elements for 5 bands, all placed on a unique boom.
In the meantime also examples of personal and commercial Delta Loops were made, with different electrical and mechanical systems, however worth to be considered.