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Mobile Phone Patent Abstract
A mobile phone has an upper antenna at the top of a casing constituting
a body and a lower antenna at the bottom of the casing. The mobile
phone includes an influence-on-antenna evaluation unit for evaluating
the influence of the ambient environment on each of the antennas
by determining an input impedance (Z) of each antenna at predetermined
time intervals during connection and by comparing the determined
input impedance with a predetermined input-impedance reference value
(Z0). Transmission power corresponding to the amount of radio waves
radiated is supplied to the antenna that is less affected by the
ambient environment and transmission power is not supplied to the
antenna that is more affected by the ambient environment.
Mobile Phone Patent Claims
What is claimed is:
1. A mobile phone comprising: a casing that constitutes a body;
an upper antenna at the top of the casing; a lower antenna at the
bottom of the casing; and an influence-on-antenna evaluation unit
for evaluating the influence of the ambient environment on each
of the antennas by determining an input impedance (Z) of each antenna
at predetermined time intervals during connection and by comparing
the determined input impedance with a predetermined input-impedance
reference value (Z0), wherein transmission power corresponding to
the amount of radio waves radiated is supplied to the antenna that
is less affected by the ambient environment and transmission power
is not supplied to the antenna that is more affected by the ambient
environment, and wherein; the variation is given by adding the square
differences (|Z(.omega..sub.i)-Z0(.omega..sub.i)|.sup.2) between
input impedances (Z(.omega..sub.i)) and input-impedance reference
values (Z0(.omega..sub.i)) at a plurality of frequency points .omega..sub.i
(i=1, 2, . . . N (an integer)) within a predetermined frequency
band.
2. An analysis device included in the mobile phones, the mobile
phone comprising: a casing that constitutes a body; an upper antenna
at the top of the casing; a lower antenna at the bottom of the casing;
and an influence-on-antenna evaluation unit for evaluating the influence
of the ambient environment on each of the antennas by determining
an input impedance (Z) of each antenna at predetermined time intervals
during connection and by comparing the determined input impedance
with a predetermined input-impedance reference value (Z0), wherein
transmission power corresponding to the amount of radio waves radiated
is supplied to the antenna that is less affected by the ambient
environment and transmission power is not supplied to the antenna
that is more affected by the ambient environment, wherein the input-impedance
reference value (Z0) is the impedance of an antenna located in free
space, wherein the analysis comprises: a free-space-impedance storage
unit for storing in advance the input-impedance reference value
(Z0) of an antenna in free space; an upper-impedance calculation
unit for calculating the input impedance of the upper antenna during
connection; a lower-impedance calculation unit for calculating the
input impedance of the lower antenna during connection; an upper-impedance-variation
calculation unit for calculating the square difference between the
input impedance of the upper antenna and the input-impedance reference
value in free space; a lower-impedance-variation calculation unit
for calculating the square difference between the input impedance
of the lower antenna and the input-impedance reference value in
free space; a comparison unit for comparing an upper-impedance variation
calculated by the upper-impedance-variation calculation unit with
a lower-impedance variation calculated by the lower-impedance-variation
calculation unit; and a switch unit for switching on or off the
upper antenna and the lower antenna, wherein the switch unit supplies
power only to the lower antenna by transferring no power from a
power amplifying unit to a feed unit in the upper antenna when the
upper-impedance variation is greater than the lower-impedance variation
based on the comparison result given by the comparison unit, and
wherein the switch unit supplies power only to the upper antenna
by transferring no power from the power amplifying unit to the lower
antenna when the lower-impedance variation is greater than the upper-impedance
variation.
3. An analysis device according to claim 2, wherein: the upper
antenna and the lower antenna are inverted L antennas.
4. An analysis device according to claim 2, wherein: the upper
antenna and the lower antenna are helical antennas.
5. An analysis device according to claim 2, wherein: the upper
antenna and the lower antenna are monopole antennas.
6. An analysis method of the mobile phone, the mobile phone comprising
a casing that constitutes a body; an upper antenna at the top of
the casing; a lower antenna at the bottom of the casing: and an
influence-on-antenna evaluation unit for evaluating the influence
of the ambient environment on each of the antennas by determining
an input impedance (Z) of each antenna at predetermined time intervals
during connection and by comparing the determined input impedance
with a predetermined input-impedance reference value (Z0), wherein
transmission power corresponding to the amount of radio waves radiated
is supplied to the antenna that is less affected by the ambient
environment and transmission power is not supplied to the antenna
that is more affected by the ambient environment, wherein the input-impedance
reference value (Z0) is the impedance of an antenna located in free
space, the method comprising: a free-space-impedance storage step
for storing the input-impedance reference value (Z0) of an antenna
in free space; an upper-impedance calculation step for calculating
the input impedance of the upper antenna during connection; a lower-impedance
calculation step for calculating the input impedance of the lower
antenna during connection; an upper-impedance-variation calculation
step for calculating the square difference between the input impedance
of the upper antenna and the input-impedance reference value in
free space; a lower-impedance-variation calculation step for calculating
the square difference between the input impedance of the lower antenna
and the input-impedance reference value in free space; a comparison
step for comparing an upper-impedance variation calculated by the
upper-impedance-variation calculation step with a lower-impedance
variation calculated by the lower-impedance-variation calculation
step; and a switching step for switching on or off the upper antenna
and the lower antenna, and wherein in the switching step, power
is supplied only to the lower antenna by transferring no power from
a power amplifying unit to a feed unit in the upper antenna when
the upper-impedance variation is greater than the lower-impedance
variation based on the comparison result given by the comparison
step, and wherein in the switching step, power is supplied only
to the upper antenna by transferring no power from the power amplifying
unit to the lower antenna when the lower-impedance variation is
greater than the upper-impedance variation.
7. An analysis method of the mobile phone, according to claim 6,
wherein: the upper antenna and the lower antenna are inverted L
antennas.
8. An analysis method of the mobile phone, according to claim 6,
wherein: the upper antenna and the lower antenna are helical antennas.
9. An analysis method of the mobile phone, according to claim 6,
wherein: the upper antenna and the lower antenna are monopole antennas.
Mobile Phone Patent Description
BACKGROUND OF THE INVENTION
The present invention relates to mobile wireless equipment typified
by, for example, mobile phones. More particularly, the present invention
relates to a mobile phone having higher antenna performance, an
analysis device included in the mobile phone, and an analysis method
used in the device.
The development of compact embedded antennas has become increasingly
desired in recent years as mobile phones have become smaller. Well-known
antennas that are in common use include linear antennas, such as
monopole antennas, helical antennas, and inverted L antennas. The
monopole antenna and the helical antenna are attached to the top
of the casing of a mobile phone and protrude from the casing; whereas
the inverted L antenna is attached along the casing of a mobile
phone, thus being suitable as an embedded antenna.
Foldable mobile phones whose operation panel and display are protected
from damage in transit are known. Each foldable mobile phone has
two casings that are connected by a hinge part for folding. The
antenna is attached to one of the casings.
FIG. 1A is a front view of a known foldable mobile phone and FIG.
1B is a cross-sectional view thereof. Referring to FIGS. 1A and
1B, the foldable mobile phone has an upper casing 103 including
a display 107 and a speaker 106, a lower casing 104 including a
keyboard 109 and a microphone 108, and a hinge part 105 that connects
the upper casing 103 and the lower casing 104 for allowing them
to be closed. An antenna 110 is usually attached to the top of the
upper casing 103.
A printed circuit board (not shown) is provided in the upper casing
103 or the lower casing 104. The printed circuit board has a transmission
unit for supplying transmission power, a power transfer unit for
transferring the power to the antenna 110, and a power amplifying
unit for amplifying the power. The transmission power is usually
supplied to the antenna through an output terminal of the power
amplifying unit. A matching circuit (now shown) is provided between
the power amplifying unit and the antenna. The matching circuit
is designed such that the input impedance of the antenna matches
the impedance at the output terminal of the power amplifying unit.
As described above, a common mobile phone is designed such that
the input impedance of the antenna is in a matching condition.
Generally, a user making a call by using a mobile phone (during
connection) holds the body of the mobile phone with his/her hand
to hold the speaker over his/her ear. Since the mobile phone including
the antenna is close to the user, the input impedance of the antenna
during connection varies depending on the influence of the human
body.
For example, with a mobile phone having the antenna at the top
of the upper casing, the input impedance of the antenna mainly varies
in accordance with the influence of the head of the user. In contrast,
with a mobile phone having the antenna at the bottom of the lower
casing, the input impedance of the antenna mainly varies in accordance
with the influence of the hand of the user.
Although the influence of the human body is described above, the
impedance characteristics of the antenna generally vary during connection
in accordance with the influence of the ambient environment, such
as scattering material (including dielectric material, metallic
bodies, and so on) around the mobile phone. The amount of variation
in impedance of the antenna generally increases as the influence
of the ambient environment increases, so that a predetermined matching
condition tends to vary. In a mismatched condition, the power transferred
from the power amplifying unit to the antenna returns. From the
view point of the antenna, the returning power is return loss, which
causes the power supplied to the antenna to decrease. As a result,
the communication characteristics, such as antenna gain, of the
mobile phone are reduced.
In this manner, a large variation in the impedance of the antenna
and a large return loss cause the antenna gain to decrease. Accordingly,
the influence of the return loss on the mobile phone should normally
be reduced as much as possible in order to maintain the antenna
gain, by optimizing the matching circuit and so on in view of an
estimated variation in impedance of the antenna during connection.
However, since the variation in impedance of the antenna strongly
depends on the way the mobile phone is held by the user, which differs
from person to person, the actual variation in impedance may exceed
the pre-estimated variation in impedance. In particular, a known
mobile phone generally has a single transmission antenna, so that
the user has no choice other than to use a reduced-gain antenna.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide
a mobile phone having larger antenna gain, an analysis device included
in the mobile phone for acquiring larger antenna gain, and an analysis
method used in the device. This is achieved by sequentially selecting
an antenna having the least influence of the ambient environment
and by utilizing the selected antenna as a transmission antenna
during connection.
The present invention provides, in its first aspect, a mobile phone
having an upper antenna at the top of a casing constituting a body
and having a lower antenna at the bottom of the casing. The mobile
phone includes an influence-on-antenna evaluation unit for evaluating
the influence of the ambient environment on each of the antennas
by determining an input impedance (Z) of each antenna at predetermined
time intervals during connection and by comparing the determined
input impedance with a predetermined input-impedance reference value
(Z0). Transmission power corresponding to the amount of radio waves
radiated is supplied to the antenna that is less affected by the
ambient environment and transmission power is not supplied to the
antenna that is more affected by the ambient environment.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a front view showing the structure of a known mobile
phone;
FIG. 1B is a cross-sectional view of the known mobile phone in
FIG. 1A;
FIG. 2A is a front view showing the structure of a mobile phone
according to an embodiment of the present invention;
FIG. 2B is a cross-sectional view of the mobile phone in FIG. 2A;
FIG. 3 is a block diagram showing the functional structure of the
analysis device included in the mobile phone according to the embodiment
of the present invention;
FIG. 4 is a diagram showing the hardware configuration of the mobile
phone according to the embodiment of the present invention;
FIG. 5 is a diagram showing the relationship between the mobile
phone and a caller;
FIGS. 6A and 6B are diagrams showing the relationship between the
mobile phone and the caller;
FIG. 7 is a flowchart showing the analysis process of the analysis
device included in the mobile phone according to the embodiment
of the present invention;
FIG. 8A is a front view of a mobile phone, according to an embodiment
of the present invention, having L antennas at the upper half and
the lower half;
FIG. 8B is a cross-sectional view of the mobile phone in FIG. 8A;
FIG. 8C is a front view of the mobile phone in FIG. 8A when the
casing is closed; and
FIG. 8D is a cross-sectional view of the mobile phone in FIG. 8C.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will now be described with
reference to the attached drawings. FIG. 2A is a front view and
FIG. 2B is a cross-sectional view of a mobile phone according to
an embodiment of the present invention. Referring to FIGS. 2A and
2B, the mobile phone has an upper antenna 101 at the top edge of
an upper casing 103 and has a lower antenna 102 at the bottom edge
of a lower casing 104. The mobile phone of the present invention
is characterized by this antenna structure, compared with known
mobile phones. Although the two antennas protrude from the upper
casing 103 and the lower casing 104, respectively, in this embodiment,
the upper antenna 101 and the lower antenna 102 may be embedded
in the upper casing 103 and the lower casing 104, respectively.
The functional structure of the mobile phone according to this
embodiment will now be described. FIG. 3 is a block diagram showing
the functional structure of the mobile phone according to this embodiment.
A free-space-impedance storage unit 201 stores impedance reference
values. The free-space-impedance storage unit 201 stores, for example,
input impedances Z.sub.free(.omega..sub.i) (the symbol will be described
below) of antennas located in free space. The input impedances Z.sub.free(.omega..sub.i)
are calculated experimentally or by electromagnetic analysis at
a plurality of points within a predetermined frequency band by using
the casing structure of the mobile phone according to this embodiment.
Specifically, the free-space-impedance storage unit 201 stores values
given by the following mathematical expression (1): Z.sub.free(.omega..sub.i),
.omega..sub.min<.omega..sub.i<.omega..sub.Max, i=1, . . .
, N (1)
In this mathematical expression (1), .omega..sub.i denotes a predetermined
angular frequency, .omega..sub.min denotes a minimum angular frequency
within the frequency band, .omega..sub.max denotes a maximum angular
frequency within the frequency band, and N denotes an integer.
An upper-impedance calculation unit 202 calculates upper-antenna
impedances at a plurality of points within a predetermined frequency
band. Specifically, the upper-impedance calculation unit 202 measures
a voltage V.sub.up and a current I.sub.up of an upper-antenna feed
unit at regular time intervals during connection to calculate the
ratio of the voltage and the current. More specifically, the upper-impedance
calculation unit 202 calculates input impedances Z.sub.up(.omega..sub.i)
of the upper antenna using the following mathematical expression
(2):
.function..PI..function..PI..function..PI..times. ##EQU00001##
An upper-impedance-variation calculation unit 203 calculates square
differences (corresponding to the variations) between the input
impedances Z.sub.free(.omega..sub.i) in free space and the input
impedances Z.sub.up(.omega..sub.i) of the upper antenna within a
predetermined frequency band based on the upper-antenna impedances
calculated by the upper-impedance calculation unit 202. Specifically,
the upper-impedance-variation calculation unit 203 calculates an
upper-impedance variation .DELTA.Z.sub.up using the following mathematical
expression (3):
.DELTA..times..times..times..function..PI..function..PI. ##EQU00002##
This variation is used as an index indicating the degree of influence
of the ambient environment on the upper antenna. A small variation
means a low degree of influence of the ambient environment.
A lower-impedance calculation unit 204 calculates lower-antenna
impedances at a plurality of points within a predetermined frequency
band. Specifically, the lower-impedance calculation unit 204 measures
a voltage V.sub.udr and a current I.sub.udr of a lower-antenna feed
unit at regular time intervals during connection to calculate the
ratio of the voltage and the current. More specifically, the lower-impedance
calculation unit 202 calculates input impedances Z.sub.udr(.omega..sub.i)
of the lower antenna using the following mathematical expression
(4):
.function..PI..function..PI..function..PI..times. ##EQU00003##
A lower-impedance-variation calculation unit 205 calculates square
differences (corresponding to the variations) between the input
impedances Z.sub.free(.omega..sub.i) in free space and the input
impedances Z.sub.udr(.omega..sub.i) of the lower antenna within
a predetermined frequency band based on the lower-antenna impedances
calculated by the lower-impedance calculation unit 204. Specifically,
the lower-impedance-variation calculation unit 205 calculates a
lower-impedance variation .DELTA.Z.sub.udr using the following mathematical
expression (5):
.DELTA..times..times..times..function..PI..function..PI. ##EQU00004##
A comparison unit 206 compares the upper-impedance variation .DELTA.Z.sub.up
calculated by the upper-impedance-variation calculation unit 203
with the lower-impedance variation .DELTA.Z.sub.udr calculated by
the lower-impedance-variation calculation unit 205 to determine
the degree of influence of the ambient environment on the antennas.
Specifically, the comparison unit 206 calculates Max (maximum) and
Min (minimum), which are factors for selecting either of the antennas,
using the following mathematical expression (6): if .DELTA.Z.sub.up>.DELTA.Z.sub.udr
then Max=1, Min=0, else Max=0, Min=1 (6)
A switch unit 207 switches on or off the upper antenna and the
lower antenna based on Max and Min calculated by the comparison
unit 206. At the start of talking, both the upper antenna and the
lower antenna are switched on and power is supplied from a power
amplifying unit to both antennas. The switch unit 207 performs switching
based on the result given by the following mathematical expression
(7) during an observation period .DELTA.t. For example, when Max
is equal to one (Max=1), the upper antenna is switched off, while
the lower antenna is switched on (this state is hereinafter expressed
as switch.sub.up=off). When Max is equal to zero (Max=0), the lower
antenna is switched off, while the upper antenna is switched on
(this state is hereinafter expressed as switch.sub.udr=off). Power
is supplied only to the antenna that is switched on. If Max=1 then
switch.sub.up=off, else switch.sub.udr=off (7)
The hardware configuration of the mobile phone according to the
embodiment will now be described. FIG. 4 is a diagram showing the
hardware configuration of the mobile phone according to the embodiment
of the present invention. Referring to FIG. 4, the mobile phone
has a storage medium 301 that stores necessary data, a measuring
device 302 for measuring required physical values, and a processing
unit. The processing unit includes an I/O device 303 for inputting
and outputting data and measured values, a memory 304 for storing
the data and the measured values read from the I/O device, and an
arithmetic unit 305 for controlling the overall processing unit
and performing calculations. A connecting path 306 connects the
above components.
The principle of the mobile phone according to the embodiment of
the present invention will now be described. The input impedances
of the antenna of a mobile phone are usually performance indices
dependent on an antenna element and a casing attached to the antenna
element. The input impedance is specifically given by the following
mathematical expression (8) by using a voltage V.sub.free and a
current I.sub.free of the connecting part of the antenna element,
serving as a feed unit, and the casing, where .omega. denotes the
angular frequency.
.function..PI..function..PI..function..PI. ##EQU00005##
The input impedances of the antenna of a mobile phone in free space
are measured or calculated experimentally or by electromagnetic
analysis. An output impedance Z.sub.out(.omega.) at the power amplifying
unit usually matches the input impedance Z.sub.free(.omega.) of
the antenna at a predetermined frequency within a frequency band
so that power supplied from the power amplifying unit to the antenna
does not return. When an impedance matching circuit is used, an
impedance Z.sub.matick(.omega.) of the antenna viewed from the power
amplifying unit is approximately given by the following mathematical
expression (9). Z.sub.matick(.omega.)=Z.sub.out(.omega.) (9)
Since a human body near the antenna has an influence for the input
impedance of the antenna during actual talking, as described above,
the input impedance of the antenna varies to a greater degree than
the input impedance in free space. The input impedance of the antenna
during connection is given by the following mathematical expression
(10) by using a voltage V.sub.com and a current I.sub.com of the
antenna feed unit during connection:
.function..PI..function..PI..function..PI. ##EQU00006##
In this case, an impedance Z(.omega.), where the impedance matching
circuit in free space is used, is different from the output impedance
Z.sub.out(.omega.) at the power amplifying unit. Hence, part of
the power supplied to the antenna returns to the power amplifying
unit. The return ratio .rho. is given by the following mathematical
expression (11):
.rho..function..PI..function..PI..function..PI..function..PI. ##EQU00007##
The mathematical expression (11) shows that the return loss decreases
as the impedance Z(.omega.) during connection becomes close to the
impedance in free space, thus reducing the influence owing to the
impedance variation.
Accordingly, the determination of the square difference between
the input impedance during connection and the input impedance in
free space permits the impedance variation owing to the electromagnetic
coupling between the mobile phone and a caller to be determined.
The index in this case is given by the following mathematical expression
(12) where .DELTA.Z denotes an impedance variation:
.DELTA..times..times..times..function..PI..function..PI..times.
##EQU00008##
In this mathematical expression (12), .omega..sub.i(i=1, . . .
N(integer)) is given by sampling the angular frequency of the frequency
band in question a finite number of times given by N. The relationship
shown in the following mathematical expression (13) is established,
where .omega..sub.min denotes the lower limit of the frequency band
and .omega..sub.max is the upper limit of the frequency band. .omega..sub.min<.omega..sub.i<.omega..sub.Max,
i=1, . . . , N (13)
The impedance variation .DELTA.Z can be used as an evaluation index
for selecting an appropriate antenna. As shown in FIG. 5, for example,
an upper-antenna attachment position 401 in the upper half of the
casing of the mobile phone is close to the head 402 of the caller.
In the situation where a lower-antenna attachment position 404 is
not covered with the hand 403 of the caller, the attachment of the
antenna to the upper-antenna attachment position 401 increases the
impedance variation and also increases the return loss of the power
supplied to the antenna, compared with the case where the antenna
is attached to the lower-antenna attachment position 404.
As shown in FIGS. 6A and 6B, when the lower-antenna attachment
position 404 in the lower half of the casing of the mobile phone
is close to the head of the caller (refer to FIG. 6A) or when the
lower-antenna attachment position 404 is covered with the hand 403
of the caller (refer to FIG. 6B), the attachment of the antenna
to the lower-antenna attachment position 404 increases the impedance
variation and also increases the return loss of the power supplied
to the antenna.
Accordingly, with the mobile phone having two antennas, one at
the upper half and one at the lower half of the mobile phone (refer
to FIG. 1), according to the present invention, the antenna less
affected by the return loss can be selected as desired by calculating
the impedance variation of the upper and lower antennas at regular
time intervals during connection and using the antenna having less
impedance variation for transmission. Hence, the antenna having
the higher antenna gain is utilized for transmission.
An analysis process of the mobile phone according to the embodiment
of the present invention will now be described. FIG. 7 is a flowchart
showing the analysis process of the analysis device included in
the mobile phone according to the embodiment of the present invention.
Referring to FIG. 7, in Step S501, a mobile phone is connected.
In Step S502, the upper and lower antennas are switched on and power
is supplied to both antennas. In Step S503, the process measures
the impedances of the upper and lower antennas. In Step S504, the
process calculates the square difference between the measured impedance
of the upper antenna and the impedance in free space and the square
difference between the measured impedance of the lower antenna and
the impedance in free space. In Step S505, the process compares
the square difference of the upper impedances with the square difference
of the lower impedances. When the square difference of the lower
impedances is greater than that of the upper impedances, the lower
antenna is switched off while the upper antenna is switched on.
When the square difference of the upper impedances is greater than
that of the lower impedances, the upper antenna is switched off
while the lower antenna is switched on. In Step S506, power is supplied
only to the antenna that is switched on. In Step S507, the process
repeats Steps S502 to S506 at regular time intervals until the mobile
phone is disconnected. In Step S508, the process terminates at disconnection
time.
As described above, the mobile phone according to the embodiment
of the present invention has two antennas and selects an antenna
having an input impedance during connection that is closer to the
input impedance in free space to use the selected antenna for transmission.
Accordingly, it is possible to provide a mobile phone having greater
antenna gain.
Although an example of the basic structure of the mobile phone
of the present invention has been described, the present invention
can be embodied in various improvements described below. Although
two antennas are attached to the mobile phone in the above example,
more than two antennas may be attached to the mobile phone. In such
a case, an antenna having the least variation of the input impedance
among the antennas is selected for transmission. Possible antennas
include linear antennas, such as monopole antennas, helical antennas,
and L antennas, and planar antennas, such as planar inverted F antennas,
microstrip antennas, and slot antennas.
A foldable mobile phone may be characterized by an antenna structure
when the casing is closed. FIG. 8A is a front view and FIG. 8B is
a cross-sectional view of a foldable mobile phone having L antennas
at the top and the bottom. FIG. 8C is a front view and FIG. 8D is
a cross-sectional view of the foldable mobile phone when the casing
is closed. As shown in FIGS. 8A and 8B where the casing is open,
an upper L antenna is attached to the mobile phone in the vicinity
of the center of one narrow side of the casing and a lower L antenna
is attached to the mobile phone in the vicinity of the center of
the other narrow side of the casing in a direction opposite to the
upper L antenna. With such an antenna structure, adjustment, for
example, of the positions where the antennas are attached to the
mobile phone and of the length of the antennas enables an equivalent
antenna having a different structure when the casing is closed to
be formed.
In other words, as shown in FIGS. 8C and 8D, the antenna elements
are aligned with each other when the casing is closed. For example,
when two L antennas having a long side of .lamda./4 (.lamda. denotes
wavelength) are used, the sum of the lengths of the aligned antennas
is .lamda./2. Hence, this antenna behaves like a .lamda./2 dipole
antenna. In consideration of the radiation from the antenna, the
antenna has a radiation directivity pattern like a figure-of-eight.
As described above, the antenna is used as a.lamda./4 L antenna
when the casing is open; whereas the antenna may be used like a
.lamda./2 dipole antenna when the casing is closed.
Although the mobile phone described above has the antennas at the
upper half and the lower half of the casing, the antennas may be
attached to any position other than the top and the bottom of the
mobile phone.
According to the mobile phone of the present invention, the determination
of the input impedance variation of each of a plurality of antennas
attached to the mobile phone during connection and the selection
of an antenna having the least input impedance variation during
connection among at least two antennas attached to the casing realizes
a transmission antenna that is influenced less by the return loss.
Such a transmission antenna provides greater antenna gain during
connection. |