Communications: radio wave antennas – Antennas – With housing or protective covering
Reexamination Certificate
1997-08-21
2001-12-11
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
With housing or protective covering
C343S7000MS, C343S702000, C343S895000, C343S718000
Reexamination Certificate
active
06329961
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to antennas and resonant-frequency-adjustment methods therefor, and in particular, to an antenna and a resonant-frequency-adjustment method therefor which are for use in a portable radio.
2. Description of the Related Art
Whip antennas are conventionally used for portable radio devices such as liquid-crystal televisions (90 to 800 MHz) and FM radios (75 to 90 MHz) (88 to 108 MHz in the U.S.) (hereinafter referred to generally as “portable radios”). Loop antennas are used for pagers.
A conventional whip antenna must be extended for use. In a frequency band equal to or less than 1 GHz, the length of the whip antenna needs to be 7.5 cm or longer, which makes it unstable when setting up a portable radio, and presents a problem when the radio falls.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a small-sized antenna which can be built into the casing of a portable radio.
To this end, according to an aspect of the present invention, the foregoing object may be achieved through provision of an antenna in which the whole or part of a coiled conductor composed of a metallic wire is covered with a covering material comprising a resin, or a mixture of such a resin and a filler, having a dielectric constant e where 1<&egr;≦10.
According to another aspect of the present invention, the foregoing object may be achieved through provision of an antenna in which the whole or part of a base member composed of a dielectric material, having a conductor wound on the surface thereof, is covered with a covering material composed of a resin or a mixture of the resin and a filler having a dielectric constant &egr; where 1<&egr;≦10.
Preferably, the antennas satisfy the following numerical expression: 1.3≦l/a ·n≦4 where l represents the coil length of the conductor; a: the diameter of the conductor; and n: the number of turns of the conductor.
In each antenna one end of the conductor may be connected to an input/output terminal formed on the surface of the covering material.
According to a further aspect of the present invention, the foregoing object may be achieved through provision of a method for adjusting the resonant frequency of the antenna, in which the method comprises either the step of changing a winding interval for a part of the conductor which is not covered with the covering material, or the step of covering with a mixture of a resin and a filler a part of the conductor which is not covered with the covering material.
According to the foregoing aspects of the present invention, a coiled conductor is covered with a covering material composed of a resin or a mixture of the resin and a filler, the covering material having a dielectric constant &egr; expressed as 1<&egr;≦10. The covering material has a wavelength shortening effect which can electrically shorten the coil length of the conductor. Accordingly, the desired characteristics of an antenna are satisfied, and compared with a conventional monopole antenna, the antenna can be reduced in size to 1/9 or less of the volume of the conventional whip antenna in a frequency band at or below 1 GHz, and can be built into the casing of a portable radio.
By satisfying the relation 1.3≦l/a ·n≦4, the characteristics of an antenna can be improved without enlarging the size of the antenna.
Since a coiled conductor is wound on the surface of a base member, changes in the cross-sectional shape of the winding, taken perpendicular to the winding axis, and changes in its winding pitch, can be avoided. Therewith, undesirable changes in the antenna characteristics can be reduced.
If the surface of a covering material is provided with an input/output terminal, the antenna can be easily surface-mounted.
The resonant frequency of the antenna can be adjusted by either the step of changing a winding interval of the conductor which is not covered with the covering material, or the step of covering with a resin, or a mixture of a resin and filler, a part of the conductor which is not covered with the covering material. Thus, the antenna can be adjusted with the antenna mounted on a mounting board.
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Mandai Harufumi
Tsuru Teruhisa
Clinger James
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Wong Don
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