1. Field of the Invention
The present invention generally relates to an antenna for wireless data communications. More particularly, the present invention relates to an antenna for providing omni-directional radiation pattern and circular polarization.
2. Description of the Related Art
Typically, desktop computers, notebook computers, palm-top computers, or personal digital assistants communicate with a host computer system for data communications via wiring hardware, such as coaxial cables or twisted-pair cables. However, for avoiding drawbacks of hardware cabling, wireless communications have been gradually applied to the computer system for transmitting or receiving data.
With respect to wireless data communications, antennas play an important role for transmitting and receiving electromagnetic waves in any direction. Usually, the antennas utilized thereby should be provided with omni-directional radiation pattern in the azimuth direction, but null in the top direction. Therefore, a rod-like antenna, such as a dipole antenna, is considered to be suitable for transmitting and receiving vertically polarized waves and thus widely applied to the communication devices nowadays.
In a wireless communication system, data signals may be reflected from many surrounding objects so that the reflected waves may combine with the data signals in a constructive or destructive manner. However, though the dipole antenna can be employed to receive and transmit the vertically polarized waves, multi-path interference, diffraction or reflection occurring in surroundings may change the vertically polarized waves in phase for long-distance communications. Even worse, data signals may be altered from the vertically polarized waves to horizontally polarized waves that can not be received by the dipole antenna thereby causing data loss. Thus, there is a need to provide an antenna that can process the vertically polarized waves and the horizontally polarized waves as well.
Therefore, it is an object of the present invention to provide a circular polarization antenna for wireless data communications. The circular polarization antenna is provided with a horizontal polarization loop antenna and a vertical polarization monopole antenna resonating together to form omni-directional radiation patterns in the azimuth direction but null pattern in the top direction for receiving or transmitting circularly polarized electromagnetic waves.
For achieving the aforementioned object, the present invention provides an apparatus for wireless data communications, which comprises a substrate, a microstrip line of a quarter-wavelength, a contact pad, an impedance transformer of the quarter-wavelength, a ground plane, a loop antenna of the quarter-wavelength and a monopole antenna of the quarter-wavelength. The substrate has a first surface and a second surface opposite to the first surface. The microstrip line, the contact pad, the impedance transformer are formed on the first surface of the substrate. Both the ground plane and the loop antenna are formed on the second surface. The loop antenna is configured with one end connected to the ground plane, and another end overlapped with the microstrip line and spaced from the ground plane. The monopole antenna is attached to the contact pad.
Moreover, the present invention provides an apparatus for wireless data communications, which comprises a substrate, a first conductive layer and a second conductive formed on opposite surfaces of the substrate, and a monopole antenna. The first conductive layer has a microstrip line, a contact pad and an impedance transformer connected in series, and the second conductive layer has a ground plane and a loop antenna. The loop antenna has one end connected to the ground plane, and another end overlapped with the microstrip line and spaced from the ground plane. The monopole antenna is attached to the contact pad.
Furthermore, an apparatus is provided for processing an electromagnetic signals having horizontally polarized waves and vertically polarized waves, which comprises a loop antenna of a quarter-wavelength formed on a substrate to receive the horizontally polarized waves, and a monopole antenna of the quarter-wavelength secured to the substrate to receive the vertically polarized waves.