AMC surface based on spiral strips and its applications for low‐profile broadband planar antennas

Abstract

A novel artificial magnetic conductor (AMC) surface based on spiral strips is proposed, which consists of 9 × 9 AMC cells. Each AMC cell includes a spiral strip to increase its inductance, thus featuring a wide bandwidth of 42% for ±90° reflection phase. The AMC surface is applied to three planar dipole antennas for lowering the antenna heights, including a linearly polarised (LP) antenna, a dual-polarised (DP) antenna, and a circularly polarised (CP) antenna. It is shown by simulation and experiment that the LP antenna achieves an impedance bandwidth of 40% (0.68-1.02 GHz) for | S 11 | <; -15 dB and a gain of 8 dBi, the DP antenna realises an impedance bandwidth of 33% (0.69-0.96 GHz) for | S 11 | <; -15 dB, an isolation of 30 dB, and a gain of 8 dBi, and the CP antenna has an overlapped bandwidth of 33% (0.75-1.05 GHz) for | S 11 | <; -15 dB and axial ratio <;3 dB. The heights of all the three planar antennas are lowered from 0.265-0.3 λ 0 to 0.083 λ 0 .