Frequency characteristics of the ESPAR antenna

Simulation results showing the frequency characteristics and radiation patterns of the electronically steerable passive array radiator (ESPAR) antenna are presented. Three software packages (NEC2, HFSS and XFDTD) were used to obtain the results. Five different loading cases optimised at 2.4 GHz provided main lobe direction ranging between 0° and 360° azimuth. All five cases had minimum S ₁₁ values between 2.35 GHz and 2.4 GHz resulting in a resonant frequency variation of 2.2%. S ₁₁ response was found to be better than -9 dB in all cases, with 4 cases exhibiting results better than -11.90 dB. -10 dB S ₁₁ bandwidths in these cases were greater than 200 MHz. Highest gain variations in the H field between the cases was 1.5 dB, with maximum gain values ranging from 4.46 dBi to 5.99 dBi. Gain variation 100 MHz either side of resonance was smaller than 0.44 dB. Radiation patterns taken over the 200 MHz (8.4%) bandwidth were only slightly different from the resonant patterns.