Dual band circularly polarized patch antenna

The need for frequency reuse has stimulated interest in multi-frequency antennas. Although multi-frequency operations can be obtained by using wide band antennas and suitable electronic circuits, this solution has several drawbacks in terms of efficiency and noise performances. Most of all, wide bandwidths are difficult to be achieved with planar structures. An inherently multi-resonant planar antenna allows to benefit from the well known advantages in size/weight/cost reduction while retaining rather good noise temperature and efficiency. Typically, a dual frequency operating mode is attained by using multi-layer stacked patches. Single layer structures for linear polarization have been proposed in Maci et al. (1987) and Yazidi et al. (1993). Both structures are based on a rectangular patch loaded by two slots. As demonstrated in Maci et al., when these slots are etched close to the radiating edges, they do not change significantly the first resonant frequency and the radiation pattern of the patch. Furthermore they introduce another resonance with a radiation pattern similar to the former. This latter resonance is strongly dominated by the slot lengths. In the present paper the use of slot loaded patches is extended to circular polarization (CP). This is obtained by properly shaping the patch and by introducing two other loading slots. Experiments are shown and discussed.<>