Using resistive loading to control the radiation efficiency of a spiral antenna

This work explores a method to manipulate the radiation efficiency of a spiral antenna, in a controlled manner, by the use of methodically placed resistive loading. Simulated and measured efficiency and reflection coefficient data are shown for various resistively loaded spiral antennas. The simulated efficiencies range from 1% to 90% within the frequency range of 0.1 to 2.5 GHz. Effective permittivity, specifically an effective substrate loss tangent, is related to the value of the resistive loading to explain the efficiency control mechanism. Efficiency decreases as the loaded resistance value decreases.