ABSTRACT
This work presents a strategy for independent control of the amplitude and phase of transmissive circular-polarization (CP) waves. The designed meta-atom consists of an elliptical-polarization receiver and a CP transmitter. By changing the axial ratio (AR) and polarization of the receiver, amplitude modulation can be realized based on polarization mismatching theory, with negligible cumbrous components. While by rotating the element, a full phase coverage enabled by the geometric phase is achieved. Subsequently, a CP transmitarray antenna (TA) with high gain and low side-lobe level (SLL) is implemented to experimentally validate our strategy, and the tested results match well with the simulated ones. During the operating band from 9.6 to 10.4 GHz, the proposed TA obtains an average SLL of -24.5 dB, a lowest SLL of -27.7 dB at 9.9 GHz, and a maximum gain of 19 dBi at 10.3 GHz, with the measured AR lower than 1 dB, which mainly benefits from high polarization purity (HPP) of the proposed elements. The proposed strategy for full amplitude-phase manipulation of CP waves together with HPP paves a way for complicated field manipulations and indicates a promising candidate in antenna applications, such as anti-jamming systems and wireless communications.
ABSTRACT
Catalytic asymmetric [2 + 4] cycloadditions of 3-vinylindoles with ortho-quinone methides and their precursors were carried out in the presence of chiral phosphoric acid to afford a series of indole-containing chroman derivatives with structural diversity in overall high yields (up to 98%), good diastereoselectivities (up to 93:7 dr) and moderate to excellent enantioselectivities (up to 98% ee). This approach not only enriches the chemistry of catalytic asymmetric cycloadditions involving 3-vinylindoles but is also useful for synthesizing chiral chroman derivatives.