New termination for ultrawide-band slot spirals

Slot-spiral antennas utilizing very shallow reflecting cavities have previously been demonstrated by the authors for extremely broadband-conformal applications. We have previously demonstrated the importance of an integrated planar balun and feed for realizing the slot spiral\´s bandwidth potential. Of equal importance, is the development of a termination that is applicable to the slot radiator. In this paper, we demonstrate a new slot spiral arm termination which, in conjunction with the reflecting cavity and planar infinite balun, allows for very thin yet extremely broadband spirals. The included measurements show that a slot spiral with a diameter of 5.75" and a thickness of merely 0.5" delivers a typical gain of 5 dB_ic from 750 MHz to 4 GHz with good axial ratio performance. Additional loading (both inductive and dielectric) applied to the same spiral can extend its operational bandwidth down to 200 MHz for the same size aperture