Dual band CP antenna by adding sleeves to the monopole

Methods of adding sleeves to a printed monopole to generate dual-band circularly polarized waves are reported. The monopole usually contains a narrow strip (extended from the feed line) or a wide strip (also called the rectangular patch). Normally, it radiates a single-band linearly polarized wave. In the narrow strip case, we found that dual-band CP waves can be generated by adding an L-sleeve to an L-narrow strip. In the wide-strip case, the configuration of a truncated patch along with two sleeves is studied to generate a dual-band circularly polarized antenna with high boresight gains at 2.45 GHz and 5.7 GHz.