Based on the proposed miniaturized polarization conversion metasurface (PCM), a checkerboard metasurface is designed, which can realize radar cross section (RCS) reduction in the ultra-wide range of 4.3~13.5 GHz (103%) by using the principle of reflection phase cancellation. The characteristic mode analysis (CMA) method is introduced to establish the checkerboard PCM as the radiation patch, and a wideband low-profile antenna for the C-band is achieved, with a bandwidth of 4.8~6 GHz (22.2%). The highlight and advantages are that the size of the checkerboard PCM is significantly reduced, and its side length is close to the radiation wavelength of the antenna. The antenna element based on this checkerboard PCM has the characteristics of small size and wide frequency range of RCS reduction, and the low-RCS antenna array can be realized by paving them seamlessly. Moreover, the checkerboard PCM not only suppresses scattering but also improves antenna performance, plays an important role in achieving wideband and enhancing radiation directivity.

A compact planar multiple-input multiple-output (MIMO) antenna array for 5G band is proposed in this paper. To improve the isolation of compact microstrip antenna array, this paper mainly presents an electromagnetic resonant ring method for MIMO antenna array. The proposed antenna can cover both the 3.3-3.6 GHz and 4.8-5 GHz bands proposed for the 5G band. The antenna proposed in this paper consists of two symmetrical meandered monopole radiators, grid structures, and a Y-shape element. Two different sizes of split-ring resonators (SRRs) are used to suppress the interference of the coupled signal to the antenna system; thereby it can reduce the mutual coupling effect. The experimental results show that the mutual coupling between the two elements is below -25 dB in both of the bands after adding the SRRs. And this antenna is only 23×19 mm². Its compact size and structure can be used as a mobile terminal antenna.

This letter proposes an ultra-wideband and high-gain antipodal tapered slot antenna (ATSA) with gradient refractive index (GRIN) lens. The GRIN lens consisting six metamaterial lenses is placed in the maximum radiation direction of the ATSA to greatly enhance its radiation capability. We found that the proposed GRIN lens antenna has a wide impedance bandwidth of 175.7% (0.84 - 13 GHz) and -3 dB gain bandwidth of 65.8% (5.86 - 11.6 GHz). Its gain is averagely increased by 4.81 dB in the whole operating band, and the maximum gain reaches 20.55 dBi at 9.5 GHz. The simulation and measured results demonstrate that the designed GRIN lens antenna has excellent performance and is suitable for short-pulse ground penetrating radar systems. It also provides reference for other occasions that require high-gain and wideband antennas.

Road safety is important for the rapid development of the economy and society. Thus, it is of great significance to monitor the dynamic changing processes of road diseases, such as cavities, to provide a basis for the daily maintenance of roads and prevent any possible car accidents. The ground penetrating radar (GPR) technology is widely used in road disease detection due to its advantages of nondestructiveness, rapidness, and high resolution. Traditionally, one-time 2D GPR detection cannot obtain the 3D spatial changes of subgrades. Thus, we developed a road subgrade monitoring method based on the time-lapse full-coverage (TLFC) 3D GPR technique by focusing on solving the key problems of time and spatial position mismatches in experimental data. Moreover, we used the time zero consistency correction, 3D data combination, and spatial position matching methods, as they greatly improve the 3D imaging quality of underground spaces. Finally, the time-lapse attribute analysis method was used in the TLFC 3D GPR data to obtain detailed characteristics and an overall rule of the dynamic subgrade change. Overall, this research proves that TLFC 3D GPR is an optimal choice for road subgrade monitoring.

A novel compact antipodal tapered slot antenna (ATSA) for short-pulse ground penetrating radar (GPR) systems is presented. In order to improve the GPR antenna’s radiation capability, we load the artificial material (AM) lens and reflector in the blank area of the antenna’s substrate. Benefiting from the planar and compact structure of AM lens and reflector, original ATSA’s directivity and radiation gain can be enhanced without decreasing its bandwidth or increasing any additional burden. To validate the proposed ATSA’s performance, two prototypes (with and without AMs) are simulated, fabricated, measured, and compared. The simulation and experimental results indicate that the proposed ATSA has a −10 dB impedance bandwidth of 176.9% (0.43–7.0 GHz) and a −3 dB gain bandwidth of 111.1% (2.0–7.0 GHz). Besides, the radiation gain has been improved by about 2 dB while keeping the stable and endfire patterns over the frequency band. In addition, the transmission response in time domain indicates that it has a small ringing. The proposed ATSA is suitable for short-pulse GPR systems due to its excellent radiation performance. The introduced AM lens and reflector provide an effective way to improve antenna performance, which can be used in many other wireless systems.

A metamaterial slab covered antipodal Vivaldi antenna (MSAVA) is proposed to improve the radiation properties of the antipodal Vivaldi antenna (AVA). The metamaterial covers (MCs) consist of two types of metal rectangular ring arrays that have a higher effective permittivity than the substrate. The MCs can achieve a guiding effect and direct electromagnetic waves radiated from the side of AVA to the end‐fire direction. The original AVA and the proposed MSAVA are simulated, fabricated and measured. The results show that of the two antennas is less than −10 dB in the frequency band of 0.95–11 GHz. Due to the introduction of MCs, MSAVA obtains a much narrower H ‐plane's half‐power beamwidth, and the E ‐plane's is narrowed as well. The radiation gain is also improved in the frequency band. Moreover, the maximum gain of the proposed MSAVA is 17.67 dBi. Compared with the original AVA, the maximum gain is enhanced by 6.86 dB for the proposed MSAVA. The presented MSAVA featuring broad bandwidth, high gain and narrow beam has a high potential in ground penetrating radar, microwave imaging application and other broadband wireless systems.