A Novel Dual-Layer 2-bit MMW Transmitarray Based on Two Pairs of Orthogonal Modes

This communication proposes a dual-layer 2-bit phase quantization transmitarray antenna (TA) based on two pairs of orthogonal modes (TPOMs) for 77-GHz applications. In comparison to the typical multilayer configurations, the proposed element can be constructed by using only two metal layers without metallic vias. It is found that the two orthogonally placed strips of each element can construct a cavity-like structure, where TPOMs are formed. Two L-shaped slots are etched on the two strips to improve the mode coupling coefficient and each pair of orthogonal modes can achieve mutual conversion, which allows to perform the rotation of polarization in two bands. The high-frequency modes and the low-frequency modes can be adjusted to resonate at the same frequency of 77 GHz, forming a 90° phase difference. By placing the position of the L-shaped structure symmetrically, the path of the mode coupling is then reversely rotated, thus forming a 180° phase difference. Using these three approaches, the 2-bit elements are realized with good performance of wideband and low loss. To realize the beam scanning in a certain range, the phase coding of the array is optimized by the main beam control method (MBCM). Finally, a circular array with 1224 elements is fabricated. The measured results show that the designed array can maintain a relatively stable gain and beamwidth within the scanning range of ±30°.