Communications: radio wave antennas – Antennas – Microstrip
Patent
1998-04-30
1999-12-21
Wong, Don
Communications: radio wave antennas
Antennas
Microstrip
343702, 343725, 343895, H01Q 138, H01Q 136
Patent
active
060055219
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a circularly polarized antenna which possesses directivity ranging from a low elevation angle to the zenith and is suitable for use in communications with a low or intermediate orbiting satellite, and to an antenna which has the advantage of becoming more compact and of being mounted on a portable telephone for use with a communications satellite or on a compact portable radio.
BACKGROUND OF THE INVENTION
The concept of a portable telephone which uses a low or intermediate orbiting satellite as a communications satellite, has recently been proposed by various corporations. As the frequency bands for use in such communications, a frequency band of 1.6 GHz is assigned to communications from a ground portable telephone to a communications satellite, and a frequency band of 2.4 GHz is assigned to communications from the communications satellite to the ground portable telephone. The frequency band of 1.6 GHz is also assigned to a frequency band for use in bidirectional communications between ground stations and the communications satellite. A circularly polarized wave is commonly used in the communications in order to ensure the quality of a communications circuit.
An antenna has already been proposed as means for improving the quality of the communications circuit (as disclosed in Unexamined Japanese Patent Application No. Hei-7-183719). Specifically, a base conductor extends from a plane antenna in the direction opposite to an antenna element in order to improve the directivity of the antenna at a low elevation angle. FIG. 10 illustrates an example of a conventional antenna. In order to improve the directivity of the antenna at a low elevation angle, a microstrip plane antenna (MSA) 1 is comprised of a dielectric substrate 1c, a patched radiating element 1b provided on the dielectric substrate 1c, a ground conductor 1d attached to the bottom of the radiating element 1b, and a cylindrical ground conductor 1e downwardly extending from the base conductor 1d.
In a case where the conventional antenna receives an incoming circularly polarized wave from a satellite or sends the circularly polarized wave from a ground station to the satellite at a low elevation angle, the gain of the antenna and the axial ratio of the circularly polarized wave become too large, which in turn affects the quality of the communications circuit that is liable to variations in the positional relationship between the antenna of portable communications equipment and the antenna of the satellite. Thus, it has been difficult to maintain the sensitivity of communication of the antenna in every direction of the sky.
The present invention has been conceived in view of the aforementioned drawback in the art, and the object of which is to particularly improve the directivity and axial ratio of an antenna having a circularly polarized wave mode at a low elevation angle.
According to the present invention, the above-described object is accomplished by the structure disclosed in appended claims of the specification. More specifically, the present invention provides a composite antenna comprising: wave mode and is made up of a conductive plate serving as a common base conductor, a dielectric layer provided on the conductor plate, and a patched radiating element provided parallel to the conductor plate with the dielectric layer between them; coaxial relationship with respect to the microstrip plane antenna and is provided below the conductor plate; and electrically connected to the conductor plate, thereby forming a helical antenna. The helical antenna may be connected to the conductor plate by DC or capacitive coupling.
The directivity of a radiation pattern at a high elevation angle greatly depends on a plane portion of the patched radiating element of the MSA. In contrast, the directivity of the radiation pattern at a low elevation angle greatly depends on the helical antenna and the electric field developed between the periphery of the patched radiating element of the MSA and the base cond
REFERENCES:
patent: 5313216 (1994-05-01), Wang et al.
patent: 5353035 (1994-10-01), Del Castillo Cuervo-Arango et al.
Ookita Hideto
Suguro Akihiro
Ho Tan
Kyocera Corporation
Wong Don
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