Communications: radio wave antennas – Antennas – Spiral or helical type
Reexamination Certificate
2001-05-17
2002-08-06
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Spiral or helical type
C455S276100
Reexamination Certificate
active
06429830
ABSTRACT:
BACKGROUND OF THE INVENTION:
This invention relates to a digital radio receiver for receiving an electric wave from an artificial satellite (which may be called a “satellite wave”) or an electric wave on the ground (which may be called a “ground wave”) to listen in a digital radio broadcasting and, in particular, to an 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 2.3 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 2.3 GHz, it is necessary to set up an antenna outside the automobile. Although such antennas have been proposed those having various structures, the antennas of stick-type are generally used rather than those of planer-type (plane-type). In addition, in the manner which is well known in the art, an electromagnetic wave radiated in a free space is a transverse wave having electric and magnetic fields which vibrate at right angles to each other in a plane perpendicular to the direction of motion and the electric field and the magnetic field have variable strength in the plane. A polarized wave is an electromagnetic radiation in which the direction of the electric field vector is not random. The satellite wave is a circular polarization while the ground wave is a linear polarization. Accordingly, exclusive antennas are required to receive both of the satellite wave and the ground wave.
Now, the description will be mainly made as regards the antennas for receiving the satellite wave. A helical or helix antenna is known in the art as one of the antennas of the stick-type. The helical antenna has structure where at least one antenna lead member is wound around an outer peripheral surface of a hollow or solid cylindrical (which is collectively called “cylindrical”) member in a helix fashion (spiral fashion), namely, is an antenna having the form of a helix. 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.” The helical antenna can effectively receive the above-mentioned circular polarization. The cylindrical member or the bobbin is made of an insulation material such as plastics. In addition, the antenna lead members are equal, for example, in number to four. On the other hand, it is remarkably difficult to really wind the plurality of antenna lead members around the outer peripheral surface of the cylindrical member or the bobbin in the helix fashion. Accordingly, alternatively, another helical antenna is proposed in which an antenna pattern film where a plurality of conductive patterns are printed or formed on an insulation sheet or a flexible film is wound around the outer peripheral surface of the cylindrical member or the bobbin.
In general, the hollow cylindrical member is used rather than the solid cylindrical member. This is because the solid cylindrical member has a heavy weight and requires a large amount of material on manufacturing. However, a conventional helical antenna comprising the hollow cylindrical member is advantageous in that it has a weak structure in strength.
In addition, such as a helical antenna has a resonance frequency which is determined due to a height (length), a diameter, a relative dielectric constant (relative permittivity), and so on of the cylindrical member. Accordingly, in order to receive the satellite wave (circular polarization) having the frequency of about 2.3 GHz using the helical antenna, it is necessary to make a resonance point (or the resonance frequency of the helical antenna) equal to a desired resonance frequency of 2.3 GHz. However, inasmuch as variations in size are not avoided on a process of manufacturing the helical antenna, it is necessary to adjust the resonance frequency of the helical antenna to match the desired resonance frequency.
In prior art, a conventional adjustment method is a cutting method comprising the step of cutting a tip portion of the helical antenna to adjust the length of the helical antenna. However, the cutting method is disadvantageous in that it takes a lot of time in the manner which will later be described in detail.
In addition, a conventional helical antenna is manufactured by winding the antenna film pattern around the outer peripheral surface of the bobbin and by fixing the antenna film pattern on the bobbin by means of an adhesive tape, an adhesive agent, or the like. With this structure, the conventional helical antenna is advantageous in that the antenna film pattern may be peeled off the bobbin due to a long service and it is difficult to stably fix the antenna film pattern on the outer peripheral surface of the bobbin. In addition, when the helical antenna is mounted on the automobile, vibrations and shocks are given to the helical antenna. Under the circumstances, sufficient antivibration and anti-shockness are not obtained in the above-mentioned conventional helical antenna in which the antenna pattern film is fixed on the outer peripheral surface of the bobbin by means of the adhesive tape, the adhesive agent, or the like.
Attention will be directed to a four-phase feel helical antenna which has four antenna lead members wound around the outer peripheral surface of the bobbin. After the satellite wave is received by the four antenna lead members as four received waves, the four received waves are phase shifted and combined by a phase shifter so as to match phases of the four received waves to obtain a combined wave, and then the combined wave is amplified by a low-noise amplifier to obtain an amplified wave which is delivered to a receiver body. A combination of the four-phase feed helical antenna, the phase shifter, and the low-noise amplifier is called an antenna unit.
In addition, the helical antenna may have only one antenna lead member. In this event, the phase shifter is removed from the antenna unit. In other words, the antenna unit consists of the helical antenna and the low-noise amplifier.
A conventional antenna unit is provided with a bottom case which is Adisposed at a lower end of the helical antenna and in which the low-noise amplifier is received. Inasmuch as the bottom case is required in the conventional antenna unit, the bottom case hinders miniaturization of the antenna unit and restricts design of the antenna unit. In the conventional antenna unit, the phase shifter and the low-noise amplifier are constructed as separated parts and provided with connectors for connecting therebetween.
With this structure, assembling of the antenna unit is complicated and it is difficult to precisely evaluate performances at an output of the phase shifter and an input of the low-noise amplifier after assembling of the antenna unit.
In addition, a conventional antenna unit is provided with a ground plate having a plane shape on which the helical antenna is perpendicularly set up in the manner which will later be described in conjunction with
FIGS. 39 and 40
. Inasmuch as the ground plate has the plane shape, the conventional antenna unit is disadvantageous in that it is difficult to decrease ground noises and to improve an antenna sensitivity.
In order to receive both of the satellite wave and the ground wave, a special antenna unit comprising a helical antenna and a rod antenna is known in the art in the manner which will later be described in conjunction with FIG.
44
. Such a special antenna unit is called a composite antenna unit. In the composite antenna unit, the helical antenna is fo
Awa Hirokazu
Miyata Masaaki
Noro Junichi
Dinh Trinh Vo
Frishauf Holtz Goodman & Chick P.C.
Mitsumi Electric Co. Ltd.
Wong Don
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