Miniaturized ultra-wideband self-complementary antennas using shunted spiral inductors

Miniaturized self-complementary wideband antennas using shunted spiral inductors are demonstrated. With Chu’s equivalent circuit, a shunt inductor is shown analytically to reduce the lower band-edge frequency. With practical shunt inductors consisting of lines and spiral inductors, line-length effect on bandwidth is clarified by simulation and measurement. With the optimized spiral inductors, miniaturized 50 Ω impedance-matched self-complementary antennas were designed and fabricated on a low permittivity (εr : 4.6) and low cost FR-4 substrate. Measured return loss less than −8.7 dB between 3.9 GHz and 11.2 GHz was obtained with the antenna of which radius is 10mm. Measured radiation patterns were omni-directional between 3 GHz and 9 GHz.