Ultrawideband composite cavity-backed rounded triangular bowtie antenna with stable patterns

A composite cavity-backed rounded triangular bowtie antenna (TBA) is investigated and differentially fed by a parallel strip line with a transition from a microstrip line. The cylindrical and the cup-shaped cavities are two special cases of the composite cavity. By optimizing dimensions of the cavity and the TBA, large impedance bandwidth and stable radiation patterns can be achieved simultaneously. The measured results of the prototype are as follows: An SWR ≤ 2 bandwidth of over 120% (2.47-over 10 GHz), a broadside gain of 8.5-15.9 dBi, stable radiation patterns across the whole operating band, and its total electrical dimensions are 0.23λ_m in height and 0.99λ_m in diameter (λ_m is the free-space wavelength at the lower edge of the SWR ≤ 2 frequency band). Identical TBAs backed by a cylindrical cavity and by a planar disk are also studied, and comparisons among three antennas are performed to illuminate the improvements of impedance matching and radiation performances brought by the composite cavity.