Performance of spiral-mode microstrip (SMM) antenna and its mystery and remedy of gain loss at low end of operating band

Since the first publication on the spiral-mode microstrip (SMM) antenna in 1991, there has been considerable interest in this antenna because of its multioctave bandwidth and its low-profile and conformability similar to the microstrip patch antennas. There has been considerable misunderstanding, as well as disbelief and a sense of mystique, about this antenna, which we would like to clarify in this paper. The authors address here only its mode-1 performance, which has been the focus of discussions in the literature.