Improvement of bow-tie antennas for pulse radiation

In some applications, such as impulse ground penetrating radar (GPR), one frequently needs a transmit waveform with minimal late-time ringing caused by multiple reflections at the antenna open ends. We propose a novel method in which late-time ringing can be significantly reduced while keeping radiation efficiency high. End reflections are reduced by extending the length of the antenna using an array of conducting strips so as to form an array of narrow slots in front of the open ends. The energy reflected at the open ends is therefore reduced and partly induced on the strips. The method has been implemented on a circular-end bow-tie antenna and experimentally verified using a monocycle with duration of 0.8 ns as input pulse. It has been observed that the transmit waveform has the shape of the time derivative of the input pulse with a very flat tail. The slots/strips profile can be optimized to obtain minimal late-time ringing, and the feed point to first slot distance can be optimized to obtain maximal pulse amplitude which can be as high as nearly twice the amplitude of a conventional bow-tie antenna.