Circularly polarized traveling-wave microstrip antenna

In the proposed antenna, a high-order mode is used in a double-layer structure to facilitate the radiation process while matching the input impedance. The high-order modes become leaky when the propagation constant is less than that of the free-space wave number. The major technical difficulties for the leaky-wave excitation are the input impedance matching and the suppression of the surface modes. A double-layer structure has been proposed by the authors to vary the field strength at the feed location, thus property matching the input impedance. Once the input impedance is chosen for a particular leaky-wave propagation, the surface modes will be automatically suppressed due to the difference between the impedances of the surface and leaky waves. In order to produce a circularly polarized (CP) radiation, the double-layer microstrip structure is made to a circular shape. As the leaky wave propagates along the circular microstrips of a properly designed double-layer antenna, a good CP radiation results over a wide frequency range.