Design of broadband antennas in UHF (ultra-high frequency) band for gpr (ground penetrating radar) applications

Ground Penetrating Radar (GPR) is an important remote sensing method. This method is used to detect underground and hidden objects inside concrete blocks and asphalt floors. Ground Penetrating Radars are based on the principle of electromagnetic reflection from different medium. The electromagnetic signal transmitted to the ground reflected back from some layers or objects are collected and processed to get underground images. This information can be used to determine the depth, size, shape, and water density of the target. A basic GPR system consists of a transmitting antenna, a receiving antenna, processing and imaging units. The system performance depends on the basic antenna and radar parameters such as frequency band, transmitter power, antenna gain, dynamic range. These parameters are calculated by keeping the electrical loss of environment (earth, asphalt, concrete etc.) and scattering characteristics of buried object into consideration. Therefore, first antenna parameters are calculated and analyzed according to GPR system requirements and then the design is simulated and optimized on the basis of these parametric analysis. In this thesis, Vivaldi antenna which is an antenna type that can be used for GPR systems is presented and various methods for improving system performance are explained. The optimized antenna is fabricated. The proposed Vivaldi antenna can operate in between 0.5 GHz to 3 GHz frequency band. An antenna array is designed to reduce the side lobes of the designed antenna. This linear antenna array consists of eight Vivaldi antenna elements which are arranged at intervals of approximately a half wavelength (65 mm) of the highest operating frequency. As a result of this study, the gain of the system has increased whereas side lobe levels of the antenna has reduced significantly for 0.5 GHz, 1 GHz, 1.5 GHz, 2 GHz, 2.5 GHz and 3 GHz frequencies of the operating band. A reflector plate is inserted to reduce the back lobe of the antenna array. This reflector plate has reduced the backward radiation level and the front to back ratio has reached 4-14 dB.