Theory and Experiment on Annular Ring Tapered Slot Antenna

In this paper, a novel annular ring tapered slot antenna is proposed for the first time, accompanied by an initial physical explanation of its multi-modal operation. The antenna operates across a wide bandwidth in multiple modes, with the lower frequency band functioning in the TEmnmode, and the lowest frequency in the TE11mode, while the higher frequencies operate in a mixed TEM-TM mode. In contrast to conventional tapered slot antennas, which operate exclusively in the TEM mode, the proposed design utilizes an annular structure, allowing it to operate in the TEmnmode at lower frequencies. This unique feature decouples the resonant frequency at lower frequencies from the slot size, allowing the extension of the lower frequency range without enlarging the tapered slot. This design enables wide beamwidth performance at higher frequencies. The combination of the small slot aperture and the annular ring structure allows the antenna to maintain wide beamwidth across a broad frequency range. Beamwidths exceeding 60 degrees in both the E-plane and H-plane are achieved over a 10:1 frequency range. The antenna can be used as a probe antenna for near-field measurements in anechoic chambers of large test objects, such as vehicles, and as a source antenna for reflective and transmissive metasurfaces.