This paper proposes an ultra-low-profile ultrawideband antenna comprising a mode-compressed dipole and U-shaped reflector. The radiating element of the antenna is a wide-width mode-compressed dipole structure loaded with short stubs and slots, and it is positioned on top of the dielectric substrate. The wide-width dipole compresses the third-order mode of the dipole, while the added short stubs generate a resonant mode at lower frequencies and compress the fifth-order mode of the dipole. The slots added to each wide-width dipole arm generate a resonant mode for the antenna and improve its radiation pattern characteristics. For the impedance matching of the antenna, indirect feeding was applied using a driving element located at the bottom of the dielectric substrate. The proposed antenna has a –10 dB impedance bandwidth range of 0.99–5.15 GHz (135.5%), and its gain varies from 3.5 to 6.4 dBi within the operating bandwidth. The electrical size of the proposed antenna is only 0.257 λL × 0.132 λL × 0.0528 λL
