A Dual Band Circularly Polarized Antenna based on a Microstrip Patch Filled with Left-Handed Structures

Microstrip patches filled with left-handed structures are proposed to obtain dual band circularly polarized antennas. The proposed antennas have two modes at different frequencies with similar characteristics to the fundamental mode of a conventional patch. These modes are excited in two orthogonal directions with a 90deg phase shift to obtain dual band circularly polarized antennas. The most important feature of the proposed antennas is that the frequency ratio between the working frequencies can be set within a large range: from values smaller than 1.2 to values larger than 2.2. Finally, a dual band circularly polarized antenna for GSM 1800 and WCDMA is designed, manufactured and measured. The working ratio is only 1.17, which cannot be obtained with other approaches.