Communications: radio wave antennas – Antennas – Spiral or helical type
Patent
1996-05-23
1999-01-19
Le, Hoanganh
Communications: radio wave antennas
Antennas
Spiral or helical type
343702, 343900, H01Q 136
Patent
active
058618597
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an antenna assembly, and more particularly to an antenna assembly suitable for use in a compact portable radio apparatus.
BACKGROUND ART
In recent years, portable radio apparatuses have been reduced in size and weight. Accordingly, antenna assemblies used for such portable radio apparatuses are also required to be smaller. As an antenna assembly which satisfies the above requirements, many manufacturers are developing whip antennas which can be retracted into the housing body when it is used for communications. In earlier stage, portable radio apparatuses of relatively simple structure have utilized this type of whip antenna.
However, such a simple antenna has the following problem.
Specifically, the antenna, when extended from the housing body, is operative as a monopole antenna, whereas it cannot obtain a sufficient gain when retracted in the housing body. It can be considered that this is because the antenna retracted in the housing body is placed near the ground to cause an input impedance to increase, whereby impedance matching can not be established.
Thus, to improve the gain of the antenna when retracted in the housing body, a whip antenna of a so-called top loading type came into use instead of the simple whip antenna described above. The top loading type whip antenna refers to an antenna assembly which has a helical antenna electrically connected to the top end of a rod antenna.
When this type of whip antenna is extended from the housing body for use, radio waves can be radiated from both of the helical antenna and the rod antenna. When the antenna is retracted into the housing body, radio waves can be radiated from the helical antenna.
However, this type of whip antenna includes the rod antenna which does not contribute to the radiation of radio waves when it is retracted. The helical portion operates as an open stub.
The open stub may badly affect the input impedance of the antenna. Specifically, the open stub causes the impedance matching to be disrupted due to the distance between the rod antenna and a circuit board in the housing space and so on.
Thus, it cannot be said that this type of whip antenna is well designed. In addition, the whip antenna of top loading type, if not shielded completely, also has several problems, for example, that signals interfere from the retracted rod antenna and signals go into a shielded portion, and so on.
As a result of investigations for solving the above-mentioned problems, an antenna assembly has been developed, in which a rod antenna, when retracted into the housing body, is electrically isolated from a helical antenna. A prior art example of such an antenna assembly will be described with reference to FIGS. 1 to 6.
FIGS. 1 to 6 show two states of the antenna assembly equipped in a portable radio apparatus, that is, an extended state and a retracted state. It should be noted that in the drawings, illustration of the whole portable radio apparatus is omitted, and the antenna assembly and portions of the portable radio apparatus associated with the connection to the antenna assembly only are described. Also, corresponding parts in the various drawings are designated the same reference numerals.
First, the structure of an antenna assembly 1 shown in FIGS. 1 and 2 will be described. The antenna assembly 1 is composed of two antenna portions, that is, a rod antenna 1A and a helical antenna 1B. The rod antenna 1A is operative mainly when the antenna assembly 1 is extended from a housing body 2, while the helical antenna 1B is operative when the antenna assembly 1 is retracted into the housing body 2.
The antenna assembly 1 is attached to the housing body 2 by screwing an antenna connection fitting 1C on the antenna side into an antenna fixture 2A arranged in a non-metallic housing body 2.
The housing body 2 contains a circuit board 3 on which a variety of circuits as well as a power supply circuit 3A for the antenna assembly 1 are integrated. The power supply circuit 3A not only supplies the antenna assembly 1 with e
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patent: 4868576 (1989-09-01), Johnson
patent: 5343213 (1994-08-01), Kottke et al.
patent: 5438339 (1995-08-01), Itoh et al.
patent: 5479178 (1995-12-01), Ha
patent: 5548827 (1996-08-01), Hanawa et al.
patent: 5612704 (1997-03-01), Cole
Ito Hiroki
Kanayama Yoshiki
Kuroda Shin-ichi
Toriyama Ichiro
Tsuda Shinichiro
Le Hoang-anh
Maioli Jay H.
Phan Tho
Sony Corporation
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