Ultrawideband Low-Profile Transmitarray With Vivaldi Array Feed

A transmitarray antenna (TAA) with a small-scale phased array antenna (PAA) feed is proposed in this communication. After modeling the PAA-fed TAAs and constructing the cost functions, a threestep optimization process is introduced to determine the TAA element arrangement as well as the PAA feed excitation coefficients. Then, a novel ultrawideband TAA element is proposed, which has a pair of connected sheep-horn metallic patterns in the middle layer sandwiched by two metallic orthogonal grid polarizers on the upper and bottom layers. Furthermore, traditional Vivaldi antenna element is identified as the element of a 4x8-element PAA feed array (central 4x4 active elements), which is employed to illuminate a 25 x 25-element circular TAA with a focus-to-diameter (F/ D) ratio of mere 0.43. The simulated results show that stable radiation patterns with good main beam shapes and reasonable sidelobe levels are obtained in the interested frequency band. The measured results agree reasonably well with the simulated ones, validating the feasibility of our method to design an ultrawideband lowprofile PAA-fed TAA.