A metasurface-based Direction of Arrival (DoA) estimation method is presented. The method exploits the properties of space-time modulated reflective metasurfaces to estimate in real-time the impinging angle of an illuminating monochromatic plane wave. The approach makes use of the amplitude unbalance of the received fields at broadside at the frequencies of the two first-order harmonics generated by the interaction between the incident plane wave and the modulated metasurface. Here, we first describe analytically how to generate the desired higher-order harmonics in the reflected spectrum and how to realize the breaking of the spatial symmetry of each order harmonic scattering pattern. Then, the one dimensional (1D) omnidirectional incident angle can be analytically computed using +1st and -1st order harmonics. The approach is also extended to 2D DoA estimation by using two orthogonally arranged 1D DoA modulation arrays. The accuracy of 1D DoA estimation is verified through full-wave numerical simulations. Compared to conventional DoA estimation methods, the proposed approach simplifies the computation and hardware complexity, ensuring at the same time estimation accuracy. The proposed method may have potential applications in wireless communications, target recognition, and identification.

This paper proposes a low-profile metasurface antenna capable of beam direction manipulation that operates within the millimeter-wave frequency spectrum. The design encompasses a non-offset substrate-integrated waveguide (SIW) slot array antenna and a near-field Huygens metasurface. The SIW slot array antenna functions as a source, providing spherical wave excitation, whereas the near-field Huygens metasurface enable precise tailoring of the phase distribution above the SIW slot array antenna. The Huygens response of the meta-atom and the suppression of the open stopband (OSB) in the non-offset SIW slot array antenna are comprehensively illustrated. A simulation model that integrates the functionalities of both wave port and Floquet port is introduced to achieve more accurate electromagnetic responses from the near-field Huygens meta-atom; thereby facilitating enhanced control over electromagnetic wave propagation. To validate the aforementioned benefits, three prototype antennas with varying pointing angles were meticulously designed, fabricated, and experimentally evaluated. The results exhibit good concordance between the simulations and measurements across several key parameters, including the reflection coefficient and radiation pattern.

An in-line type X-band phase detector is presented in this letter. It is constructed by a power combiner and a capacitive power sensor with clamped-clamped beam to obtain large dynamic range with respect to RF power. The fabrication process is based on MEMS technology. Experiments show that the return loss is smaller than -12.3dB over X-band, the isolation is better than -9.1dB and the insertion loss is around -3.5dB. Conversion between phase, power and capacitance is accomplished inside the detector for phase detection from 0 to 180 deg. The varying capacitance of the beam can sustain a dynamic range of 0.25~2W with satisfactory detection sensitivity, 163.8aF/deg at 2W. Third-order intermodulation distortion (IM3) of the detector is rather small and the IIP3 is about 37.4dBm for 10kHz frequency interval.