Octave Bandwidth Transmitarrays With a Flat Gain

A wideband linearly polarized transmitarray antenna operating in 7–16 GHz is presented in this paper. First, a wideband element with three metallic layers is proposed, which is composed of a split circular ring connected by a narrow strip in the middle layer, and two polarizers in the upper and bottom layers. This element features a low transmission loss and approximately linear phase curves in a wide frequency band over one octave. Then, an optimization method is introduced to design the transmitarray that follows the bandwidth definition of 1 dB gain drop. The first key point of this method is determining the transmitarray element distribution with the weighted reference phases. The second is realizing wideband performances by controlling the calculated directivities and radiation patterns of the modified wideband transmitarray model at all operating frequencies. In the experiment, a $25\times 25$ -element horn-fed transmitarray with a $240 \times 240$ mm² aperture area is designed and fabricated. The simulated results show that its bandwidths of 0.5, 1.5, and 3 dB gain drop are 41%, 56%, and 71%, respectively. Moreover, a peak aperture efficiency of 40.7% is achieved. Measured results agree reasonably well with the simulated ones. These results validate the proposed wideband element and the optimization method.