This letter presents a dual-band circularly polarized (DBCP) microstrip antenna with an ultra-thin substrate made of liquid crystal polymer (LCP). The proposed antenna consists of a gridded patch and a round of via fence for dual-band radiation and size miniaturization. Compared with previous designs, the proposed antenna has two improvements in structures with merits: first, a parasitic patch is added below the gridded patch to tune the ratio of dual-band frequencies; second, a stacked feeding network with dual orthogonal L-shaped probes is designed for profile reduction, also providing the feasibility of differential feed and dual-linear polarization. Based on the co-design of the gridded patch, the parasitic patch, and the stacked feeding network, all layers of the antenna are clamped into a flexible board with an ultra-thin thickness of 0.6 mm (0.013 λ ₀ , λ ₀ is the free-space wavelength at 6.5 GHz), and taped out with the flexible LCP process. The measured results show the bandwidths of total efficiency over 25% are 6.25-6.74 GHz and 7.92-8.17 GHz with circular polarization, proving to be a feasible solution for flexible antennas in space-limited mobile handsets.

We demonstrated a nonvolatile grating using an azobenzene polymer film with polarized two color beams. The reorientation of azobenzene molecules can be optimized when the two color light beams are polarized perpendicularly. The stored information can be read repeatedly without volatility with the same wavelength as the writing beam.

Vortex beams with orbital angular momentum (OAM) significantly enhance system capacity, and high-precision recognition of OAM mode through atmospheric turbulence (AT) channels can markedly improve the information transmission capability of free-space optical communication systems. In this paper, with a cylindrical lens-assisted distinguish between positive and negative OAM, a reliable neural network combining multi-scale dilated convolution (MSDC) unit and multi-level feature fusion (MLFF) module is proposed to detect high order AT-distorted OAM modes. The network fully exploits the features in light-intensity images to achieve a highest recognition accuracy of 99.4% for mode-orders from -20 to +20 in a hybrid ATs dataset (C _n ² = 5×10⁻¹⁶, 5×10⁻¹⁴, 5×10⁻¹²m^-2/3), and almost 96% even in strong turbulence. Experimental results on accuracy, efficiency, reliability, and robustness demonstrate that the proposed method excels and provides a trustworthy solution for complex AT-distorted OAM mode recognition.

This paper proposes a comprehensive analysis on the efficiency performance of an ultrathin circularly polarized (CP) microstrip antenna. For ultrathin antennas with intrinsic narrow bandwidth, traditional parasitic-loading methods for bandwidth enhancement encounter significant in-band efficiency reduction, which is named as "efficiency dip", due to the strong differential coupling between main and parasitic resonators. To address this issue, we propose a feasible structure of parasitic resonator pair. In this case, the common and differential modes of the resonator pair are excited simultaneously, with the parasitic common mode to eliminate the efficiency dip. Inevitably, another efficiency dip appears due to the parasitic differential mode, but is located out of band without bandwidth deterioration. A prototype is fabricated and tested, showing a CP bandwidth of 3.5% with an extremely low profile of 0.012 λ0 (λ0 is the free-space wavelength at the center frequency). The final efficiency is over 68% across the band. This paper provides a guideline for designing wideband CP antennas with ultrathin profile and small area, e.g., for mobile terminals.

As a common technique to broaden the bandwidth of ultrathin microstrip antennas, adding the parasitic elements often encounters the problem of efficiency dip. This phenomenon is due to the radiation cancellation caused by the out-of-phase currents between the parasitic element and the main radiator. This paper proposes a solution by introducing another parasitic element near the initial one and enabling them to resonate in differential mode, the radiation cancellation at the efficiency dip can be significantly mitigated without attenuating bandwidth expansion. To illustrate this method, an ultrathin dual-polarized microstrip antenna is presented as an example. By designing a pair of L-shaped parasitic strips and converting the parasitic mode from common mode to differential mode, the in-band gain variation is reduced from 5.8 dB to 1.9 dB. The measured results show that the antenna operates with an impedance bandwidth of 2.3% in an extremely low profile of 0.008 λL (λL is free-space wavelength at 7.9 GHz). The proposed method mitigates efficiency dips caused by the parasitic elements, exhibiting a feasible solution for bandwidth expansion of ultrathin microstrip antennas while holding the high efficiency.

The accuracy of line-of-sight (LOS)-based indoor visible light positioning (VLP) depends directly on the accuracy of the received LOS power. In an actual indoor visible light communication (VLC) system, the total received power contains the LOS power and diffuse power, and the proportion of diffuse component varies significantly with the receiving orientation of the user equipment (UE). In the trilateration positioning process, this is bound to bring a very high level of inaccuracy for at least one or two of them when determining the distance between the positioned LED and UE. To solve this problem, we employed channel estimation and Parseval’s theorem to remove the diffuse component from the total received power. The simulation results show that the higher the channel estimation accuracy, the smaller the discrepancy between the estimated and actual LOS power, and the greater the localization accuracy. At the same channel estimation accuracy, the comparison results demonstrate that the localization performance of the proposed method is higher than LLS-1, in which the total received power is directly adopted to estimate the distance. The localization performance of LLS-2 deteriorates significantly compared to the proposed method. This result indicates that the receiving orientation cannot be neglected during the distance estimation process even though the estimated accuracy of LOS power is high. Deriving the Cramér–Rao low bound (CRLB) for LOS-based indoor VLP with receiving orientation, we compared the localization performance for the proposed method with LLS-1, LLS-2, and the CRLB at various signal-to-noise ratios (SNRs). The results show that the localization error of all the received positions in the room can reach the CRLB at approximately 25 dB. However, localization errors based on LLS-1 and LLS-2 cannot achieve the theoretical CRLB even at a high SNR.