We apply the ESPRIT algorithm to decompose the currents on a helical antenna into different traveling wave modes. The strengths, phase velocities and decay constants of the various modes are extracted across frequencies. Their contributions to the antenna performance including gain, polarization and time-domain radiated pulse shape are investigated. Our results show that the T0+ mode is a dominant contributor to the helix gain at the low end of the frequency band while the T1+ mode contributes significantly to the gain at higher frequencies. It is also found that the reflected current modes from the open end reduce the circular polarization purity of the helix. Lastly, it is observed that the T1+ and T0+ modes contribute constructively to a low-dispersion pulse from the antenna.
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