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 diameter R of a quadrupole antenna.

Aim. To analyse the impact of the diameter 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 diameter of the ground plane was determined at low f_н and upper f_в 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 R=12λ₀  is preferable for a quadrupole antenna at low GNSS frequencies. A further increase in the ground plane size will insignificantly improve its characteristics.

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