Since the height of sea detection radar antenna and ship targets is relatively low, it is generally believed that its over-the-horizon detection is mainly caused by the evaporation duct at sea. To fully understand the influence of atmospheric ducts on radar over-the-horizon detection, a shore-based navigation radar was used to carry out over-the-horizon detection experiments; radiosondes were used to measure the atmospheric profile and evaporation duct monitoring equipment was used to measure the evaporation duct. Based on experimental data and model simulation, a comparative analysis of a navigation radar’s over-the-horizon detection, the evaporation duct, and the lower atmospheric duct is presented in this study. The results show that the atmospheric duct can affect the signal propagation of the navigation radar, thus resulting in over-the-horizon detection. The long-range over-the-horizon detection of the navigation radar is caused by the strong lower atmospheric duct, while the evaporation duct can generally only form weak over-the-horizon detection, which is different from the general cognition.

The design and implementation of the filters for the fifth-generation (5G) mobile communication systems are challengeable due to the demands of high integration, low-cost, and high-speed data transmission. In this paper, a dual-wideband bandpass filter (BPF) and a tri-wideband BPF for 5G mobile communications are proposed. The dual-wideband BPF consists of two folded open-loop stepped-impedance resonators (FOLSIRs), and the tri-wideband BPF is designed by placing a pair of folded uniform impedance resonator inside the dual-wideband BPF with little increase in the physical size of the filter. By employing a novel structural deformation of a stepped-impedance resonator, the FOLSIR is achieved with a more compact structure, a controllable transmission zero, and an adjustable resonant frequency. The measurement results show that the working bands of the two filters are 1.98–2.28/3.27–3.66 GHz and 2.035–2.305/3.31–3.71/4.54–5.18 GHz, respectively, which are consistent with the full-wave EM simulation results. The implemented filters have a compact size and the results show low loss, good out-of-band rejection, and wide passbands covering sub-6 GHz bands of 5G mobile communications and a commonly used spectrum.

We propose a flexible anti-metal radio frequency identification (RFID) tag antenna based on a high-conductivity graphene assembly film (HCGAF). The HCGAF has a conductivity of 1.82 × 10⁶ S m⁻¹, a sheet resistance of 25 mΩ and a thickness of 22 μm. The HCGAF is endowed with high conductivity comparable to metal materials and superb flexibility, which is suitable for making antennas for microwave frequencies. Through proper structural design, parameter optimization, semiautomatic manufacturing and experimental measurements, an HCGAF antenna could realize a realized gain of –7.3 dBi and a radiation efficiency of 80%, and the tag could achieve a 6.4 m read range at 915 MHz on a 20 × 20 cm² flat copper plate. In the meantime, by utilizing flexible polyethylene (PE) foam, good conformality was obtained. The read ranges of the tags attached to curved copper plates with different bending radii were measured, as well as those of those attached to several daily objects. All the results demonstrate the excellent performance of the design, which is highly favorable for practical RFID anti-metal applications.

We demonstrate a flexible radiofrequency filter based on graphene assembly films with a high conductivity up to 10⁶ S/m and a thickness of 10 μm. The flexible high-conductivity graphene film (HCGF) used in the filter has a fifth-order low-pass Chebyshev frequency response, and it operates at 3.6 GHz with a 0.82 dB in-band maximum insertion loss and 26.21 dB insertion loss at 5 GHz. Such performance observed in the HCGF-based flexible filters is comparable to that of commercial copper-based filters in passband and roll-off. The HCGF exhibits good mechanical flexibility even after 200 cycles of bending. Nearly no mechanical failure or performance degradation occurs during 20 cycles of 0°–50° bending for the flexible HCGF filter. Our results suggest that the flexible HCGF filter has good repetitive bending stability. This makes this type of filter suitable for future applications in flexible wireless communication.

Using intelligent optimization algorithms to retrieve atmospheric duct parameters by monitoring automatic identification system (AIS) signals at sea is a new passive remote sensing technology for atmospheric ducts. To thoroughly compare and analyze the inversion results of different intelligent optimization algorithms and optimize the parameters of the algorithms, this study considered a simulated atmospheric duct environment for atmospheric duct inversion using the genetic, simulated annealing, and particle swarm optimization (PSO) algorithms. The results indicated that the PSO algorithm exhibited the best inversion performance. The inversion results of the simulated annealing particle swarm optimization (SAPSO) and PSO algorithms under different inversion parameters were further statistically analyzed, and the atmospheric duct parameters were obtained from measured AIS signals based on the SAPSO algorithm. The inversion results verified the effectiveness of the proposed algorithm, and they continuously improved with additional calculations in the inversion algorithm. However, the changing trend gradually slowed. Therefore, in practical applications, the inversion time consumption should be balanced with the inversion effect to optimize the inversion parameters.

The resonance performance analysis of graphene antennas is a challenging problem for full-wave electromagnetic simulators due to the trade-off between the computer resource and the accuracy of results. In this paper, an equivalent circuit model is presented to provide a concise and fast way to analyze the graphene-based THz bowtie antenna. Based on the simulated results of the frequency responses of the antenna, a suitable equivalent circuit of Resistor-Inductor-Capacitor (RLC) series is proposed to describe the antenna. Then the RLC parameters are extracted by considering the graphene bowtie antenna as a one-port resonator. Parametric analyses, including chemical potential, arm length, relaxation time, and substrate thickness, are presented based on the proposed equivalent circuit model. Antenna input resistance R is a significant parameter in this model. Validation is performed by comparing the calculated R values with the ones from full-wave simulation. By applying different parameters to the graphene bowtie antenna, a set of R, L, and C values are obtained and analyzed comprehensively. A very good agreement is observed between the equivalent model and the numerical simulation. This work sheds light on the graphene-based bowtie antenna’s initial design and paves the way for future research and applications.