Design of miniaturized multi band microstrip antennas with helical slot patterns on patches

In this paper, a novel method is proposed for the miniaturization of a multi-band microstrip antennas by cutting a helical slot pattern on the patches. In this way, the current paths are cut by the slots and become quite long, which eventually lead to the drastic miniaturization of antenna, by up to 50 times. The proposed antenna radiates at five resonance frequencies in the band 0.3-2.5 GHz, which are all lower than those of a solid patch without any slots. The radiation patterns of the antennas at these frequencies are stable. A multilayer antenna structure with a feed in the form of a probe and L-shaped metallic strips are proposed to counter the effect of inductive loadings of the slots and thus achieve a wideband input impedance matching.