Two Types of Bandwidth Evaluation of Crossed Spherical Helix Antennas Using Numerical Simulation

Comparing the bandwidths of a crossed spherical helix antenna (XSHA) and conventional antennas is challenging owing to significant change in the radiation efficiency with respect to frequency even at low voltage standing wave ratio (VSWR). Thus, two types of evaluation were performed in this work to demonstrate the wideband property of XSHA. First, the antennas were assumed to be made of a perfect conductor and were compared regarding only the VSWR bandwidth. Next, we compared the bandwidth at radiation efficiency of lossy antennas based on the generalized effective fractional bandwidth $(B_{e}).\ B_{e}$ is the product of the bandwidth and the radiation efficiency varying with frequency. Numerical simulations were conducted to compare the bandwidths for $VSWR \leq 3$ . The bandwidth of the XSHA is 2.19 and 2.11 times wider than those of single resonance antenna in lossless and lossy cases, respectively. Compared with a dual resonance antenna, the bandwidth of the XSHA is 1.36 times greater at acceptable radiation efficiencies of 50%.