Communications: radio wave antennas – Antennas – With radio cabinet
Reexamination Certificate
2002-07-25
2003-12-09
Nguyen, Hoang V. (Department: 2821)
Communications: radio wave antennas
Antennas
With radio cabinet
C343S895000
Reexamination Certificate
active
06661383
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a helical antenna for a portable communication terminal such as a portable phone or personal digital assistant, etc., and also to a portable communication terminal with the helical antenna.
2. Description of the Related Art
A helical antenna is often used for a portable phone or personal digital assistant.
FIG. 11
shows an example of a conventional helical antenna.
As shown, the conventional helical antenna is formed by attaching a helical antenna element
22
to a metal element holder
21
, and covering the helical antenna element
22
with a cap
23
made of resin. The antenna is formed unitedly with a portable terminal casing
1
by an antenna holder
11
. The metal element holder
21
enables the transmission of a radio signal between the antenna element
22
and the radio circuit incorporated in the portable terminal casing
1
. Since a helical antenna can be easily downsized, the helical antenna is very suitable for portable communication terminals whose downsizing and thinning is a most important object.
Since, however, the helical antenna is used fixed to the portable terminal casing
1
, it is possible that the helical antenna will be brought into contact with an ear of a user during a call. Because of recent developments in downsizing and thinning of portable communication terminals, the helical antenna has come to be more liable to be brought into contact with an ear of a user. Where the helical antenna is in contact with an ear of a user, the characteristic of the helical antenna is degraded.
FIG.
12
A and
FIG. 12B
illustrate changes in the characteristic of the antenna due to a human body.
FIG. 12A
shows the characteristic of the antenna assumed that an ear of a user does not touch the helical antenna.
FIG. 12B
shows the characteristic of the antenna assumed that an ear of a user touches the helical antenna. As seen from
FIG. 12A
, where no ear touches the helical antenna, each voltage standing wave ratio (VSWR) is kept at respective desired values at frequencies A, B and C in the radio frequency band that is expected to be used. On the other hand, where an ear of a user touches the helical antenna, the central frequency of the antenna varies as shown
FIG. 12B
, and hence each of VSWRs corresponding to A, B and C assumes high values at the frequencies A, B and C. This means that the characteristic of the antenna is degraded.
Further, the characteristic of the helical antenna varies in accordance with the distance between a human body and the helical antenna.
FIG. 13
shows the result of a simulation concerning the degree of mismatch loss that occurs, in accordance with changes in the central frequency of a helical antenna, when a metal plate is made to be close to the element of the antenna. The metal plate is used because the electrical characteristic of the metal plate has a characteristic similar to that of a human body. As is evident from
FIG. 13
, the characteristic of the helical antenna is degraded as the distance between the helical antenna element and metal plate is reduced.
To reduce the influence of a human body upon the antenna, Jpn. Pat. Appln. KOKAI Publication No. 10-107526, for example, has proposed an antenna structure in which the antenna is located at a position displaced from the center of the antenna cover (i.e., cap of the antenna) so that the position of the antenna is away from a human body. If this structure is employed, the antenna element can be positioned from an ear of a user at a distance corresponding to the width of the antenna cover, thereby reducing the influence of the body of the user upon the antenna.
However, in general, the portable phone is used with the helical antenna attached to the top end of the rod antenna. Therefore, the helical antenna is rotatable about the rotational axis of the rod antenna on the casing of the phone. This means that while the helical antenna is being used, the antenna element is not always positioned farthest from the body of a user but may be positioned closest to the body. In this state that the antenna element is positioned closest to the body, the antenna element almost touches the ear of the user, and hence the antenna cannot exhibit a desired characteristic of the antenna element.
Jpn. Pat. Appln. KOKAI Publication No. 2001-127517 has proposed another antenna structure. In this structure, the helical element of the helical antenna has a linearly extended top end that reduces the influence of a human body upon the antenna orientation. This structure enables the top end of the antenna element to be always positioned away from an ear of a user by a distance corresponding to the radius of the radiation section (i.e., antenna cover). Thus, the influence of the body of a user can be reduced.
In this structure, however, the antenna element is not fixed in the radiation section, and hence the top end of the antenna element may be vibrated. Accordingly, during a call, the position of the antenna element may vary in the radiation section due to, for example, vibration of the phone, with the result that the distance to the body of a user becomes unstable and hence a good characteristic for the antenna element cannot be maintained. Furthermore, when the radiation section covers the antenna element, there is a possibility that the top end of the antenna element may be pressed against the inner wall of the radiation section and be deformed. Thus, the antenna element cannot always maintain a stable position.
BRIEF SUMMARY OF THE INVENTION
The present invention has been developed in light of the above and aims to provide a helical antenna including an antenna element that can be positioned at a constant distance from the body of a user, and hence can always exhibit a good characteristic for the antenna, and a portable communication terminal using the helical antenna.
To satisfy the aim, according to an aspect of the invention, there is provided a helical antenna for use in a portable communication terminal containing a radio unit which transmits and receives a radio signal, comprising:
an antenna element connectable to the radio unit and containing a bottom portion formed into a helical portion and a top portion formed into a linear portion, the linear portion being positioned along a screw axis of the helical portion;
a cap housing the antenna element if the cap covers the antenna element from a top end of the antenna element; and
a position portion provided in the cap, the position portion positioning the linear portion of the antenna element along the screw axis of the helical portion.
According to another aspect of the invention, there is provided a portable communication terminal comprising:
a portable communication terminal casing which houses a radio transmitting and receiving circuit; and
a helical antenna provided at an upper end of the portable communication terminal casing and connected to the radio transmitting and receiving circuit, the helical antenna comprising:
an antenna element containing a bottom portion formed into a helical portion and a top portion formed into a linear portion, the linear portion being positioned along a screw axis of the helical portion;
a cap housing the antenna element if the cap covers the antenna element from a top end of the antenna element; and
a position portion provided in the cap, the position portion positioning the linear portion of the antenna element along the screw axis of the helical portion.
According to yet another aspect of the invention, there is provided a helical antenna for use in a portable communication terminal containing a radio unit which transmits and receives a radio signal, comprising:
an antenna element connectable to the radio unit and containing a bottom portion formed into a helical portion and a top portion formed into a linear portion, the linear portion extending to a screw axis of the helical portion;
a cap housing the antenna element; and
a position portion provided in the cap, the position portion positioning the linear portion o
Sakurai Minoru
Shimanuki Masanobu
Chen Shih-Chao
Kabushiki Kaisha Toshiba
Nguyen Hoang V.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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