Study of the Backscatter Radiation Pattern of a Quadrupole Antenna with a High-Impedance Ground Plane of Large Electrical Sizes

Introduction. The multipath resistance of GNSS antennas is largely determined by the gain slope of the amplitude radiation pattern at sliding angles (angles close to the horizon). The gain slope of the antenna radiation pattern is determined by the size of its ground plane. This article investigates the dependence between the gain slope and ground plane radius R of a quadrupole antenna.Aim. To analyse the impact of the radius of conventional and high-impedance ground planes on the backscatter radiation pattern of a quadrupole antenna at sliding angles.Materials and methods. Computer simulations were carried out in CAD CST Studio Suite using the methods of finite element analysis (FEM), finite difference time domain (FDTD) and template based post-processing.Results. Quadrupole antennas with a capacitive high-impedance ground plane and a conventional flat ground plane were simulated. The dependence of the average gain slope at sliding angles on the radius of the ground plane was determined at low fн and upper fв GNSS frequencies. The analysis of the down/up ratio, the rolloff gain and the multipath ratio for R= 1…20 of the wavelength of capacitive high-impedance and ground planes conventional flat was performed. It was established that higher gain slopes can be obtained using different types of ground planes; however, lower backscatter radiation values are achievable only using high-impedance structures. It was observed that the same slope of the radiation pattern (about 1 dB/°) for GNSS lower frequencies can be obtained at different R=12λ0, and, presumably, at 20λ0.Conclusion. A high-impedance ground plane with a diameter of 2R=12λ0 is preferable for a quadrupole antenna at low GNSS frequencies. A further increase in the ground plane size will insignificantly improve its characteristics.

Absorbing Aerosol Sensor on Gao-Fen 5B satellite

The Absorbing Aerosol Sensor (AAS) will be launched aboard the GaoFen-5B satellite in China. The main purpose of AAS is to monitor absorbing aerosols by measuring the solar backscatter radiation. AAS is an ultraviolet-visible imaging spectrometer that uses a single charge coupled device to capture both the spectrum and the cross-track direction with a 114° wide swath. The large field of view enables daily global coverage with 4-km spatial resolution. The spectral range of the instrument extends from 340 to 550 nm with spectral resolution (full width at half maximum) of 2 nm. This paper provides details of the instrument design, including system design, optical design, and mechanical design, as well as detector and calibration unit on orbit. The numerous simulations show that all design results satisfy the specification and vibration requirements of the instrument.

A study on a dental device for the prevention of mucosal dose enhancement caused by backscatter radiation from dental alloy during external beam radiotherapy

The changes in dose distribution caused by backscatter radiation from a common commercial dental alloy (Au–Ag–Pd dental alloy; DA) were investigated to identify the optimal material and thicknesses of a dental device (DD) for effective prevention of mucositis. To this end, 1 cm3 of DA was irradiated with a 6-MV X-ray beam (100 MU) in a field size of 10 × 10 cm2 using a Novalis TX linear accelerator. Ethylene vinyl acetate copolymer, polyolefin elastomer, and polyethylene terephthalate (PET) were selected as DD materials. The depth dose along the central axis was determined with respect to the presence/absence of DA and DDs at thicknesses of 1–10 mm using a parallel-plate ionization chamber. The dose in the absence of DDs showed the lowest value at a distance of 5 mm from the DA surface and gradually increased with distance between the measurement point and the DA surface for distances of ≥5 mm. Except for PET, no significant difference between the DA dose curves for the presence and absence of DDs was observed. In the dose curve, PET showed a slightly higher dose for DA with DD than for DA without DD for thicknesses of ≥4 mm. The findings herein suggest that the optimal DD material for preventing local dose enhancement of the mucosa caused by DA backscatter radiation should have a relatively low atomic number and physical density and that optimal DD thickness should be chosen considering backscatter radiation and percentage depth dose.