A new low-profile wideband linear-to-circular polarization conversion microstrip slot antenna based on a metasurface for C-band satellite communication applications is proposed in this paper. The metasurface basically consists of four unit cells with parasitic square cross gaps arranged in a 2 × 2 layout. By loading the metasurface on the microstrip slot antenna, linearly polarized (LP) waves from the source antenna are converted into circularly polarized (CP) waves. Then, by etching three more parasitic square cross gaps in the middle of the metasurface, enhanced impedance bandwidth and axial ratio bandwidth (ARBW) are achieved. Furthermore, an equivalent circuit and a phase analysis are presented to explain how a wide ARBW is realized by the metasurface. A final model with an overall size of 36 × 36 × 3.5 mm³ (approximately 0.65λ₀ × 0.65λ₀ × 0.06λ₀ at 5.5 GHz) was designed and fabricated. The measured S₁₁ bandwidth and 3 dB ARBW were 39.25% from 4.28 GHz to 6.37 GHz and 17.77% from 5.18 GHz to 6.19 GHz, respectively. As a result, the proposed antenna shows great potential for satellite communication applications due to its low profile and compact structure, wide impedance bandwidth, and wide axial ratio bandwidth.

This paper presents a miniaturized frequency selective surface (FSS) based on the convoluted and interdigitated stripe with multiple narrow passbands/wide stopbands in the L-/S-/C-/X-/Ku-/K-band. By using the convoluted and interdigitated stripe, the coupling inside is well controlled, so that the spatial efficiency is maximized to provide a high miniaturization. An equivalent circuit model is presented to reveal the working mechanism of the proposed FSS. The proposed structure forms four transmission band rejections of 3 dB in 1–6.65 GHz, 8.35–16.9 GHz, 18.0–24 GHz, and 24.50–27.84 GHz. The size of the unit cell is 0.09λ₀ × 0.09λ₀, where λ₀ is the wavelength of the first resonance frequency. The proposed FSS has a good angle stability and polarization stability in a scanning range up to 60°. For verification, an FSS prototype has been fabricated and measured. The measured results were in agreement with the simulated results. The proposed FSS can be used in practical applications such as radomes, antenna reflectors, and spatial filters.

The knowledge of heart and respiratory rates (HRs and RRs) is essential in assessing human body static. This has been associated with many applications, such as survivor rescue in ruins, lie detection, and human emotion detection. Thus, the vital signal extraction from radar echoes after pre-treatments, which have been applied using various methods by many researchers, has exceedingly become a necessary part of its further usage. In this review, we describe the variety of techniques used for vital signal extraction and verify their accuracy and efficiency. Emerging approaches such as wavelet analysis and mode decomposition offer great opportunities to measure vital signals. These developments would promote advancements in industries such as medical and social security by replacing the current electrocardiograms (ECGs), emotion detection for survivor status assessment, polygraphs, etc.

A new broadband circularly polarized (CP) metasurface (MS) antenna based on characteristic mode analysis (CMA) is proposed. The antenna consists of 4×4 truncated Γ-shaped unit cells and is fed by an improved slot coupling structure. The characteristic modes required to achieve CP are analyzed by CMA, and the CP performance is improved by changing the characteristic currents distribution. By introducing a stepped slot structure on the slot floor, the bandwidth of the antenna has been further broadened. By loading the microstrip line to feed the MS, left-handed circular polarization (LHCP) can be realized. In addition, the equivalent circuit method is used to explain how the designed MS antenna achieves CP. The overall size of the designed and fabricated MS antenna is 0.72 ${\lambda }_0$×0.72 ${\lambda }_0$×0.08 ${\lambda }_0$ at 6.2 GHz. The measured −10 dB impedance bandwidth of the antenna is 25.17% (5.21 GHz-6.71 GHz) and the measured 3 dB axial ratio bandwidth is 17.42% (5.87 GHz-6.99 GHz). Moreover, the highest gain in the working frequency band is 7.52 dBic. The proposed CP MS antenna has good application prospects in C-band satellite communications.

This paper proposes a phase angle-modulated bat algorithm (P-AMBA) for high-dimensional binary optimization. The idea was to reduce the optimization time by introducing angle modulation technology to reduce the optimization dimensions. Different from the original angle-modulated bat algorithm (AMBA), the control of the trigonometric generating function cosine wave is by introducing new parameters, thereby improving the perturbation ability of the function curve near the x-axis. P-AMBA can explore more 0/1 solutions, and it has advantages in optimizing convergence speed and global search capabilities. The numerical results of the 0–1 knapsack problem tests show that P-AMBA is superior to the contrast algorithms on optimization ability and optimization time. Finally, the experimental result of a compact dual-band planar monopole antenna design showed the effectiveness of P-AMBA in engineering applications.

Detecting multiple human targets in indoor scenarios using ultra-wideband (UWB) radar usually involves false detection results caused by the secondary reflections, which might reduce the target detection accuracy and cause a more severe deterioration when the number of targets increases. This article proposed a two-step accuracy improvement method for multitarget detection in environments with multiple human targets of more than three and strong secondary reflections by the surroundings, especially the walls. Based on the rough detection results acquired by the modified CA-CFAR (MCA-CFAR) processing, the first step achieves the primary false alarm suppression using a short-window accumulation in the time domain. Then, the second step applies the decision confidence on the detection results from the first step to assess the reliability of results for improved accuracy. The two-step accuracy improvement could thus have a higher accuracy through cascading false alarm suppression. The effectiveness and accuracy of the proposed algorithm are verified based on the experimental results.