The design of rectangular dielectric resonator antennas (DRA) with ultrawide bandwidths, in the range of 60-110%, is described. The DRA exploits multiple low-Q modes with overlapping bandwidths to achieve a wide contiguous bandwidth. This is achieved using a full-length, low-permittivity inset between a higher permittivity dielectric volume and a ground plane. With the proposed dielectric arrangement and a feed inside DR, it is possible to efficiently couple a sufficient number of such overlapping modes to a 50 Ω feedline. The volume of such DRAs is also reduced by means of a finite planar conducting wall. These advantages led to an example design with a bandwidth that is significantly wide and at the same time has a smaller DR volume than conventional DRAs. A prototype antenna designed to operate in the FCC UWB band from 3.1 to 10.6 GHz has a dielectric volume of 12 × 8 × 15.2 mm3 (or 1.7 × 10-3 λ03 at 3.1 GHz), and an average measured gain of 5 dB over the band.