![]() ![]() Then, the reflected wave is received and recorded by the receiving antenna. Active remote sensing refers to a remote sensing system in which a certain form of electromagnetic wave is emitted to the target from an artificial radiation source on a remote sensing platform. When a GPR is used for deep exploration, increased numbers of errors and greater signal attenuation during data reception and processing often occur. In some cases, such a design can cause problems, such as the multi-path effect and polarization mismatching. In most bi-static antenna GPRs, a dipole antenna is used as the transmitting antenna, and another antenna device is used as a receiving antenna, with both being horizontally linearly polarized (LP) antennas. However, in high-depth GPR remote sensing, conventional methods do not easily meet the requirements. Different channels correspond to different detection depths and resolutions. In 2019, the Chinese Academy of Sciences successfully loaded the Chang’e-4 lunar lander with dual-channel antennas (60 MHz and 500 MHz), making it possible to obtain a large amount of precious lunar geological data. The corresponding main-frequency antenna was used for different detection depth requirements, and the maximum detection depth reached 80 m in coal mine detection, with weak attenuation and positioning accuracy that reached 3 m. It was shown that the high-depth GPR system proposed by Xu Xianlei in 2018 could work at 12.5 MHz–50 MHz, and the corresponding antenna lengths were 8.25 m–2.25 m. In 2015, several scholars combined multiple-input multiple-output (MIMO) antenna technology with multi-polarization technology to overcome the interference caused by changes in the antenna radiation direction and target scattering cross-sectional area in the measurement process, and the detection accuracy for underground targets was significantly improved. More importantly, by reducing the exploration frequency to 10 KHz, the exploration depth could also be greatly increased by about tenfold.Īs important aspects of bi-static antenna GPR systems, transmitting and receiving antennas play key roles in sounding. The analysis and simulation results demonstrated that, comparing circular polarization and linear polarization with the premise of the same transmitting power, the SRE CP multiple-dipole antenna array radiation source achieved a significant enhancement (about 7 dB) in the signal-to-noise ratio (SNR) as the radiant energy was collected at the receiving antenna. A large-aperture CP multiple-dipole array is used instead of a small-size LP dipole antenna. A novel sequential rotationally excited (SRE) circularly polarized (CP) multiple-dipole array for a bi-static antenna GPR for deep exploration is proposed in this paper. In the receiving antenna, the issues caused by the multi-path effect and polarization mismatching can be addressed, even if LP antennas are used. ![]() In contrast, at the radiation source, with the use of large-aperture multiple-dipole antennas and multi-channel sequential rotational excitation, the electromagnetic wave can radiate in the form of circular polarization at a low frequency. For most bi-static antenna GPRs, a dipole antenna is used as the transmitting antenna and another antenna device is used as a receiving antenna, with both being horizontally linearly polarized (LP) antennas. In order to penetrate the deeper Earth, it is necessary to increase the size of the antenna in accordance with the wavelength ratio and, thus, reduce the radiation frequency. Due to the frequency (1 MHz–3 GHz) of GPRs, the depth of geological exploration is shallow (0.1–30 m). As an effective active remote sensing technology for the exploration of shallow underground targets, ground-penetrating radar (GPR) is a detection method that can be used to obtain information about the characteristics of underground targets by transmitting an electromagnetic wave from an antenna and analyzing the propagation of the electromagnetic wave underground. ![]()
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