Communications: radio wave antennas – Antennas – High frequency type loops
Reexamination Certificate
2001-12-27
2003-05-13
Nguyen, Hoang (Department: 2821)
Communications: radio wave antennas
Antennas
High frequency type loops
C343S7000MS, C343S857000, C343S895000
Reexamination Certificate
active
06563469
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a digital radio receiver for receiving an electric wave from an artificial satellite (that may be called a “satellite wave”) or an electric wave on the ground (that may be called a “ground wave”) to listen in a digital radio broadcasting and, in particular, to a loop antenna for use in the digital radio receiver.
In recent years, a digital radio receiver, which receives the satellite wave or the ground wave to listen in the digital radio broadcasting, has been developed and is put to practical use in the United States of America. The digital radio receiver is mounted on a mobile station such as an automobile and can receive an electric wave having a frequency of about 2.338 gigahelts (GHz) to listen in a radio broadcasting. That is, the digital radio receiver is a radio receiver which can listen in a mobile broadcasting. In addition, the ground wave is an electric wave in which a signal where the satellite wave is received in an earth station is frequently shifted a little.
In order to receive such an electric wave having the frequency of about 2.338 GHz, it is necessary to set up an antenna outside the automobile. Although a variety of antennas having various structures have been proposed, the antennas of cylindrical-type are generally used rather than those of planer-type (plane-type). This is because a wider directivity is achieved by forming the antenna into a cylindrical shape.
A loop antenna is known in the art as one of the antennas of the cylindrical-type. The loop antenna has structure where one antenna lead member is wound around a peripheral surface of a hollow or solid cylindrical (which is collectively called “cylindrical”) member in a loop fashion, namely, is an antenna having the form of a loop. The cylindrical member may be merely called a “bobbin” or a “dielectric core” in the art. In addition, the antenna lead member may be merely called a “lead.” It is known in the art that the loop antenna acts as an antenna having a directivity in a longitudinal direction thereof if the antenna lead member has an all around length which is selected to about one wavelength. This is because the antenna lead member has a sinusoidal distribution of a current.
Although it is necessary for the loop antenna to feed to it, a four-point feeding is generally adopted to the loop antenna. In order to receive circular polarization, feeding is carried out at four points having a phase difference of 90 degrees from one another. The loop antenna with the four-point feeding is called in the art a four-point feeding loop antenna. In a conventional four-point feeding loop antenna, a feeding is directly carried out to a loop portion.
More specifically, the conventional four-point loop antenna comprises a cylindrical body formed by rounding a flexible insulation film around a central axis in a cylindrical fashion, a loop portion made of conductor that is formed on the cylindrical body along a peripheral surface thereof around the central axis in a loop fashion, and four feeders formed on the peripheral surface of the cylindrical body to feed the loop portion at four points. In addition, each of the four feeders consists of a vertical feeding portion and the loop portion is directly connected with each of the four feeders.
After the electric wave is received by the loop portion as a received wave, the received wave is divided through the four feeders into four partial received waves which are phase shifted and combined by a phase shifter so as to match phases of the four partial received waves to obtain a combined wave, and then the combined wave is amplified by a low-noise amplifier (LNA) to obtain an amplified wave which is delivered to a receiver body. A combination of the four-point feeding loop antenna, the phase shifter, and the low-noise amplifier is called an antenna unit.
In the manner which is described above, inasmuch as the conventional four-point feeding loop antenna comprises the four feeders each consisting of the vertical feeding portion and directly feeds to the loop portion from the four feeders, the conventional four-point feeding loop antenna is disadvantageous in that it has a too high feeding impedance. Thus, the conventional four-point feeding loop antenna is disadvantageous in that a special matching circuit for obtaining an impedance match is required aside from the four-point loop antenna.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a four-point feeding loop antenna into which a matching circuit is integrated.
Other objects of this invention will become clear as the description proceeds.
According to an aspect of this invention, a four-point feeding loop antenna comprises a cylindrical body formed by rounding a flexible insulator film member around a central axis in a cylindrical fashion. The cylindrical body has a peripheral surface. Made of conductor, a loop portion is formed on the cylindrical body along the peripheral surface around the central axis in a loop fashion. In order to feed to the loop portion at four points, four feeders are formed on the peripheral surface of the cylindrical body. Each of the four feeders comprises a vertical feeding portion having one end grounded and another end extending toward the loop portion, a zigzag line disposed between the other end of the vertical feeding portion and the loop portion, a tap for feeding from a feeding terminal to the vertical feeding portion.
In the above-mentioned four-point feeding loop antenna, the flexible insulator film member may substantially have a rectangular shape having an upper side, a lower side, a first lateral side, and a second lateral side. In this event, the cylindrical body is formed by connecting the first lateral side with the second lateral side. The loop portion may be formed on one surface of the flexible insulator film member in the vicinity of the upper side. The one end of the vertical feeding portion may lie on the lower side.
REFERENCES:
patent: 5134422 (1992-07-01), Auriol
patent: 5986616 (1999-11-01), Edvardsson
patent: 6075501 (2000-06-01), Kuramoto et al.
Miyata Masaaki
Miyoshi Akira
Frishauf Holtz Goodman & Chick P.C.
Mitsumi Electric Co. Ltd.
Nguyen Hoang
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