A TEM horn antenna is usually in air-launched GPR system.Traditionally,the variation of characteristic impedance of a TEM horn antenna is designed to transform 50 Ω(characteristic impedance of a coaxial cable) to 376.7 Ω (free space wave impedance).However,difference exists between transmission-line wave characteristic impedance and free space wave impedance.In this paper,we discuss performance differences of antennas with different open end characteristic impedance.In addition,the simulated and experimental results show that a TEM horn antenna matched with impedance of 200 Ω has the best performance for air-coupled GPR applications.
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