Ultrawideband Horizontally Polarized Omnidirectional Array Antenna

An ultrawideband horizontally polarized (HP) omnidirectional array antenna, characterized by superior out-of-roundness, is proposed in this letter. The array antenna comprises 16 radiating elements with a hybrid wide-angle impedance matching layer, a feed network, and a paraboloidal metal reflector. Specifically, three-order dipoles (TODs) are embraced as the radiating elements to obtain ultrawideband characteristics by adjusting the arm-length ratio of each order appropriately. Meanwhile, a compact feed network is designed in the center of the ring formed by radiating elements, ensuring uniform feeding for each element. Despite maintaining equal amplitude and phase in the feed, the array manifests out-of-roundness deterioration in the reference horizontal plane. To address this concern, a double-layer metal plate is introduced to form a paraboloidal reflector with the reference ground. This structure eliminates the ripples of the radiation pattern, thereby effectively enhancing the out-of-roundness. A prototype is fabricated and measured. The proposed antenna achieves a 4.0:1 operating bandwidth and exhibits excellent omnidirectional pattern characteristics, with out-of-roundness in the horizontal plane less than 1 dB throughout the full operating bandwidth.