Communications: radio wave antennas – Antennas – With radio cabinet
Reexamination Certificate
2003-02-21
2004-10-19
Wimer, Michael C. (Department: 2821)
Communications: radio wave antennas
Antennas
With radio cabinet
C343S745000, C343S895000
Reexamination Certificate
active
06806836
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a helical antenna apparatus provided with two helical antenna elements, and to a radio communication apparatus provided with the same helical antenna apparatus. In particular, the present invention relates to a helical antenna apparatus for use in a mobile radio system, such as, mainly in a portable telephone, a radio transceiver for business use or the like, and a radio communication apparatus provided with the same antenna apparatus.
2. Description of the Prior Art
FIG. 22
is a perspective view showing one example of a situation in which a prior art portable radio transceiver
101
for business use is used. The VHF band of 150 MHz to 450 MHz is assigned as a radio frequency to the portable radio transceiver
101
for business use. Therefore, a normal-mode helical antenna apparatus
102
attached to the portable radio transceiver
101
is often employed as an antenna as shown in FIG.
22
.
FIG. 23
is a circuit diagram showing an equivalent circuit of the helical antenna apparatus
102
for use in the portable radio transceiver
101
for business use of
FIG. 22
, and
FIG. 23
includes an image of the helical antenna apparatus
102
of
FIG. 22
inside of a radio transceiver housing.
Referring to
FIG. 23
, a helical antenna element
1
and a helical antenna element
2
are constituted so as to be symmetrical with respect to a feeding point, and have the same size parameters (winding diameter, number of turns, winding pitch) as those of each other. In this case, a capacitance element
3
a
having a predetermined fixed electrostatic capacity is connected between the helical antenna element
1
and the helical antenna element
2
. By the capacitance element
3
a
and a balanced to unbalanced transformer
6
, impedance matching is achieved between an input impedance Za of the helical antenna apparatus
102
and a coaxial cable
7
of a transmission line, and an impedance of the helical antenna apparatus
102
seen from an input connector
8
is set so as to become 50&OHgr; (See, for example, a prior art document of “Koichi Ogawa et al., “An Analysis of the Effective Radiation Efficiency of the Normal Mode Helical Antenna Close to the Human Abdomen at 150 MHz and Consideration of Efficiency Improvement”, The Transactions of the Institute of Electronics, Information and Communication Engineers in Japan, (B), Vol. J84-B, No.5, pp.902-911, May, 2001).
FIG. 24
is a graph showing a frequency characteristic of a voltage standing wave ratio (VSWR) in the helical antenna apparatus
102
of
FIG. 23
, and
FIG. 24
illustrates the impedance characteristic of the helical antenna apparatus
102
designed for the 150 MHz band portable radio transceiver for business use. In this graph, the helical antenna elements
1
and
2
have a length of about 10 cm, and have an average shape as a portable radio transceiver on the market. As shown in
FIG. 24
, there is achieved an extremely good impedance matching state in which the VSWR is almost one at 150 MHz. However, the bandwidth in which the VSWR is equal to or smaller than two is within a range of 2 MHz, and this represents an extremely narrow band characteristic.
In general, the frequency assigned to the portable radio transceiver for business use has a range of 10 MHz and higher. Therefore, according to the impedance characteristic shown in
FIG. 24
, there arise such a problem that the actual gain of the helical antenna apparatus
102
is significantly reduced due to an impedance mismatching loss when the antenna apparatus is used at a frequency other than the frequency at which matching is achieved. In order to cope with this problem, the current measures are to prepare a plurality of helical antenna elements that have different center frequencies and obtain satisfactory impedance with respect to all the frequencies by replacing the antenna according to the operation frequency. As described above, the first problem of the helical antenna for business radio use is that that the impedance characteristic has a narrow range.
The feature in use of the portable radio transceiver for business use is that the radio transceiver is mounted on a human body so as not to hinder the business in a manner different from that of the portable telephone and the like. Upon having a telephone conversation using the radio transceiver, the user utilizes a microphone and an earphone as shown in FIG.
22
. At this time, as is apparent from
FIG. 22
, the helical antenna apparatus
102
is brought into contact with the abdomen of the user
103
. The antenna characteristics in this situation are described in detail in, for example, the above-mentioned prior art document, which was written by the present inventor and the others. The outline thereof will be described below.
FIG. 25A
is a perspective view showing a positional relation between the helical antenna apparatus
102
and a human body model
201
of
FIG. 23
, and
FIG. 25B
is a Smith chart showing a range dependence characteristic of the input impedance Za of the helical antenna apparatus
102
of FIG.
23
.
As shown in
FIG. 25A
, the helical antenna apparatus
102
is located so as to be close to the human body model
201
of an elliptic columnar configuration but be separated at a distance D.
FIG. 25B
shows calculated values of the input impedance Za when the distance D between the helical antenna apparatus
102
and the human body is changed, and the frequency is 150 MHz. As shown in
FIG. 25B
, the input impedance Za has its inductive reactance increasing as the helical antenna apparatus
102
approaches the human body. This is attributed to that the mutual inductance has equivalently increased as the results of an electromagnetic interaction between the helical antenna apparatus
102
and the human body.
FIG. 26
is a graph showing a loss power ratio with respect to the distance D between the human body and the antenna of the helical antenna apparatus
102
of
FIG. 23
, and
FIG. 26
shows calculation results of various power losses of the helical antenna apparatus
102
appearing as the result of the impedance change shown in
FIGS. 25A and 25B
.
Referring to
FIG. 26
, Pt represents the summation of power losses, Pm represents a power loss due to impedance mismatching, Pa represents a power loss due to the metal resistance of the antenna, and Ph represents a power loss due to the electromagnetic absorption of the human body. The horizontal axis of
FIG. 26
represents the distance D between the antenna and the human body, and the vertical axis represents the rate of each power loss (loss power ratio) with respect to the summation Pt of the power losses.
As is apparent from
FIG. 26
, if the helical antenna apparatus
102
approaches the human body, then the impedance mismatching loss Pm comes to share the greater part of the whole loss power in comparison with the metal conductor loss Pa of the antenna and the absorption power loss Ph of the human body. This is caused due to that the input impedance Za of the helical antenna apparatus
102
becomes remarkably large inductive as the distance D decreases, as shown in FIG.
25
B. As the result of
FIG. 26
, the prior art document analytically describes that the radiation efficiency at a distance of D=2 cm has an extremely low value of equal to or smaller than −20 dB.
As is comprehensible from the above-mentioned analytical results, the other problem of the helical antenna apparatus
102
of
FIG. 22
is an increase in power loss due to impedance mismatching in a situation in which a human body is located so as to be close to the apparatus.
As described above, the helical antenna apparatus
102
for business radio use has the following two problems. The first problem is the narrow range of the impedance characteristic, and the second problem is the increase in power loss due to impedance mismatching when a human body is located so as to be close to the apparatus. These two problems are each attributed to the impedance mismatching between the input i
Iwai Hiroshi
Koyanagi Yoshio
Ogawa Koichi
Wenderoth , Lind & Ponack, L.L.P.
Wimer Michael C.
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