1. Field of the Invention
The present invention relates to an antenna, and more particularly, to a dual-band circularly polarized antenna capable of implementing single-plane, dual-band circular polarization on a single dielectric substrate.
2. Description of the Prior Art
With advancement of wireless communication, various wireless applications have become one of the most important means of exchanging data (e.g. voice, text, video, etc.) in society. At the same time, in accordance with portability and functional requirements, light-weight, small form factor, and compactness have become the design criteria. Also, integration of multi-functionalities into a same mobile device has also become an inevitable trend. Therefore, a compact and multi-frequency band antenna has become a common goal for the industry.
For example, a common car satellite communication device usually integrates Global Positioning System (GPS) and Satellite Digital Audio Radio Service (SDARS) functionalities. Since GPS and SDARS have different operation frequency bands, and a GPS signal is a right-handed circularly polarized electromagnetic (EM) wave, a receiving antenna must have a right-handed circularly polarized radiation field pattern to receive the GPS signal. Similarly, a SDARS signal is a left-handed circularly polarized EM wave, and thus a receiving antenna must also have a left-handed circularly polarized radiation field pattern to receive the SDARS signal. In such a case, two separate antennas are usually needed for each signal. Please refer to FIG. 1, which is a schematic diagram of a microstrip antenna (Patch antenna) 10 of a conventional car satellite communication device. The microstrip antenna 10 includes an antenna A_GPS, an antenna A_SDARS, and a signal feed-in portion 106. The antenna A_GPS transmits and receives GPS signals, and the antenna A_SDARS transmits and receives SDARS signals. To obtain dual-band circular polarization, the microstrip antenna 10 is usually implemented via a multi-layer, stacked architecture. As shown in FIG. 1, the antenna A_GPS (formed by a dielectric substrate 102 and a microstrip radiation portion 108) and the antenna A_SDARS (formed by a dielectric substrate 104 and a microstrip radiation portion 110) are stacked together. However, despite small dimensions of the microstrip radiation portion, a dielectric substrate comparatively occupies considerable space, and is costly to manufacture. Therefore, reducing dimensions for a multi-band antenna while lowering costs has become an important issue for antenna design.