Double-Layer Transmitarray Antenna Using Specially Designed Substrate

In this letter, a novel double-layer transmitarray element is proposed. Different from the traditional transmitarray element design, the proposed double-layer element uses a specially designed substrate. The combined substrate is composed of two horizontally arranged different dielectric materials. By etching metal double square loops on this combined substrate, the phase shift range of the transmitarray element can be enlarged remarkably. Then, the 360° transmission phase range can be realized with a maximum transmission amplitude loss of less than 3.8 dB, when the loop length D of the element varies from 8.75 to 9.65 mm. To experimentally validate this novel design, a prototype of 121-element transmitarray is fabricated and tested. The measured gain of the transmitarray at 12 GHz is 22.6 dBi with 44% aperture efficiency. Moreover, this novel design can view as a new kind of high-performance two-layer transmitarrays.