Increasing the probing depth of pulsed GPR by reducing the antenna impedance

Abstract

At the present time, dipole antennas with resistively loaded vibrators are widely used in pulsed georadar. The main property of such antennas is the emission of an electromagnetic wave into the subsurface medium with rapid attenuation of the ultra-wideband pulse to the end of the vibrators without reflection. When the total resistance of the vibrator decreases below 200 Ohms, parasitic self-oscillations appear in this antenna, limiting the increase in power supplied to the antenna. Development of a dipole antenna for subsurface ground penetrating radar with the ability to reduce the antenna impedance below 200 Ohms to increase the radiated power and increase the depth of ground penetrating radar. The design of a dipole antenna with several resistively loaded vibrators connected in parallel is proposed. The total resistance of a single vibrator is selected based on the stability requirements to prevent parasitic self-oscillations, but the impedance of the dipole antenna decreases in proportion to the number of connected vibrators. A dipole antenna with five dipoles connected and arranged parallel to each other has a gain 10 dB higher compared to a dipole with a single resistively loaded dipole. Compared to a plate antenna 3 meters long and 25 cm wide, a five-vibrator dipole antenna of the same length has a gain of 3.3 dB higher. Another advantage of the proposed antenna is its higher resolution. At the same time, insulated vibrators made of flexible conductors allow twisting to reduce the overall diameter of the dipole antenna, which allows its use in difficult engineering and geological conditions. Experiments with three-meter dipole antennas showed an increase in sounding depth in the Moscow region from 14 to 20 meters.