US Patent 8102330 Dual band circularly polarized feed

Dual band antenna systems and methods providing isolation between bands are provided. The system includes a pair of superimposed antenna radiating elements, each of which is connected to an associated feed network. The feed networks may comprise a quadrature hybrid networks. Coupling paths between the first and second feed networks are arranged such that a first component of a first signal coupled from a first feed network to a second feed network will be 180° out of phase with a second signal component of the first signal coupled from the first feed network to the second feed network at the input/output of the second feed network. The resulting destructive interference results in isolation between the bands.