On the Use of U-Slots in the Design of Dual-and Triple-Band Patch Antennas

The general method of using U-slots to design dual- and triple-band patch antennas is described. In this approach, one starts with a broadband patch antenna, which can consist of one or more patches. When a U-slot is cut in one of the patches, a notch is introduced into the matching band, and the antenna becomes a dual-band antenna. If another U-slot is cut in the same patch or in another patch, a triple-band antenna results. This method is applied to the L-probe-fed patch, the M-probe-fed patch, as well as the coaxially fed and aperture-coupled stacked patches. It is found that the patterns and gains of the dual-and triple-band antennas are similar to those of the original broadband antenna. Because the band notches introduced by the U-slots occur within the bandwidth of the antenna without slots, this method is suitable when the frequency ratios of the adjacent bands are small, usually less than 1.5.