Antenna apparatus capable of producing desirable antenna radiation patterns without modifying antenna structure

A portable communication system includes a first metal housing for containing a high frequency circuit unit such as a transmitting circuit and a receiving circuit, a second metal housing for containing a low frequency circuit unit such as a control circuit, and also an antenna mounted on the first metal housing. An antenna apparatus for this portable communication system is arranged by the above-explained antenna, first and second metal housings, and also a control element for controlling distribution of high frequency currents flowing through the first and second metal housings. An antenna radiation pattern of this antenna apparatus can be optimized by controlling an impedance of the control element.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to an antenna apparatus used in a 
portable communication apparatus. More specifically, the present invention 
is directed to a structure of an antenna apparatus capable of producing 
desirable antenna radiation patterns without modifying the antenna 
structure. 
2. Description of Prior Art 
As is well known in the field, an electromagnetic radiation pattern of an 
antenna would be varied when a conductive article would be located 
adjacent to this antenna, since a high-frequency current may flow through 
the antenna during transmission/reception of electromagnetic waves. 
Therefore, to obtain a desirable radiation pattern of the antenna, effect 
of the conductive member in the vicinity of the antenna should be taken 
into consideration. For example, in the portable communication apparatus, 
since a circuit board is provided with a grounding conductive layer of a 
comparatively large surface area, the effect of such grounding conductive 
layer should be taken into consideration. In recent, to protect the 
circuit boards from external electromagnetic effect, portable 
communication apparatus are provided with an electromagnetic shield plate 
or such circuit boards are installed within a metal housing. But, in the 
portable communication apparatus, attention should be paid to effects of 
the electromagnetic shield plate and the metal housing. 
FIG. 1 is a view illustrating a structure of antenna apparatus which has 
been proposed recently. The antenna apparatus draws much attention in the 
art, since the antenna apparatus is effective to obtain a desirable 
radiation pattern, and is often used for a communication apparatus of a 
type in which the circuit board is electromagnetically shielded with a 
metal housing. 
As shown in FIG. 1, the antenna apparatus is composed of an antenna 1 (a so 
called .lambda./4 monopole antenna) having a length of one fourth of a 
wave length and a metal housing 2 formed with a notch 3 in the side wall 
thereof. The notch 3 is formed with an opening end 3a in the side wall 
thereof. The notch 3 is formed in the side wall of the metal housing at a 
position apart by a length of .lambda./4, i.e., a length of 0.25.lambda. 
from the upper surface on which an electric supplying point 1a is 
provided. The notch 3 has a depth of 0.25.lambda., and the ceiling and 
bottom composing the notch 3 are connected by an end wall (the leftend 
wall as viewed in FIG. 1). Therefore, the notch 3 has a stub function. 
Then, the portion defined from the uppermost portion of the right side 
surface of the metal housing to the opening end 3a of the notch 3, namely 
the portion having the length of 0.25.lambda. will be cooperated with the 
.lambda./4 monopole antenna 1, which are therefore operated like a 
.lambda./2 dipole antenna. 
The above-described conventional antenna apparatus requires the notch 3 
having the depth of 0.25.lambda. (wavelengths). As a result, the 
horizontal (transverse) width 1 of the metal housing 2 necessarily becomes 
longer than 0.25.lambda., which may impede compactness of the metal 
housing 2. 
As to the manufacturing stages of the conventional antenna apparatus, when 
another antenna apparatus is manufactured which is operable in another 
frequency different from that of the above-described conventional antenna 
apparatus by changing the length of the above-described .lambda./4 
monopole antenna 1, a length from an upper surface of a metal housing to 
an opening end should be varied in order to be fitted to this new 
frequency. As a consequence, there are drawbacks in the conventional 
antenna apparatuses that various metal housings whose notch forming 
positions are different from each other should be manufactured, depending 
upon the frequencies of the electromagnetic waves used in the 
communications. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a compact antenna 
apparatus capable of producing a better radiation pattern. 
Another object of the present invention is to provide an antenna apparatus 
capable of controlling a radiation pattern without modifying an antenna 
structure. 
A further object of the present invention is to provide an antenna 
apparatus with less limitations in a constructive matter and a mounting 
way, while producing a better radiation pattern. 
To achieve the above-described objects, an antenna apparatus, according to 
one aspect of the present invention, comprises: 
a first conductor; 
an antenna mounted on said first conductor; 
a second conductor separately provided with said first conductor; and 
a control element electrically connected between said first conductor and 
said second conductor, for controlling distribution of high frequency 
currents flowing through said first and second conductors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to the drawings, antenna apparatuses according to presently 
preferred embodiments of the present invention will now be described. 
FIGS. 2A and 2B schematically show a structure of an antenna apparatus 
according to a first embodiment of the present invention. The antenna 
apparatus according to this first embodiment is arranged by, as 
represented in FIG. 2A, a monopole antenna 11, a main conductive housing 
12 (for example a main metal housing), on which upper surface a feeding 
point 11a for this monopole antenna 11 is formed, a sub-conductive housing 
(for instance, a sub-metal housing) 13 independently provided with this 
main conductive housing 12, and a control element 14. The control element 
14 is connected between the main metal housing 12 and the sub-metal 
housing 13, and controls a current distribution of a high frequency 
current flowing through the main metal housing 12 and the sub-metal 
housing 13. 
In this embodiment, both the main metal housing 12 and the sub-metal 
housing 13 are made by mechanically processing metal plates. 
Alternatively, either an outer surface, or an inner surface of a resin 
housing may be metal-plated to fabricate these conductive housings 12 and 
13. Within the main metal housing 12, a high frequency circuit portion 
such as a transmitter circuit and a receiver circuit is stored. Within the 
sub-metal housing 13, other circuits, typically a low frequency circuit 
portion such as a control circuit and a power supply circuit are stored. 
The high frequency circuit unit stored within the main metal housing 12 is 
connected to the other circuit unit stored in the sub-metal housing 13 by 
way of a circuit connecting line 15 penetrating through a through hole 12a 
formed in the metal housing 12 and a through hole 13a formed in the metal 
housing 13. The connection structure will be described more in detail with 
reference to FIG. 3 to FIG. 7, and is so designed that the main metal 
housing 12 is not shortcircuited with the sub-metal housing 13 via the 
circuit connecting line 15 in view of high frequency signals. 
The control element 14 is stored in a circular tube 16 made of a resin, one 
end of which is connected to the lower surface of the main metal housing 
12 and the other end of which is connected to the upper surface of the 
sub-metal housing 13. It should be noted that when both the main metal 
housing 12 and the sub-metal housing 13 are manufactured by metal-plated 
resin housings, the control element 14 is connected to the respective 
metal-plated portions of these resin housings. 
As previously explained, the control element 14 has such a function to 
control the current distributions of the high frequency currents flowing 
through the main metal housing 12 and the sub-metal housing 13 while 
electromagnetic waves are transmitted and received. Therefore, passive 
elements such as a resistor, a capacitor and a coil, and also a 
negative-resistance element, such as an ESAKI tunnel diode may be employed 
as this control element 14. When an attention is paid to the 
characteristics and also the cost of the control element 14, a capacitor 
and a coil are preferable as this control element 14. 
In case of this first embodiment, the control element 14 and the connection 
line thereof are stored in the circular tube 16 made of a resin, whereas 
since the main metal housing 12 and the sub-metal housing 13 are fixed to 
a predetermined positional relationship (will be discussed later), they 
may be provided without any sheath. 
In general, when a monopole antenna is employed as this antenna, the 
connecting position of the control element 14 with regard to the main 
metal housing 12 and the sub-metal housing 13 is preferably the farmost 
position apart from the antenna setting position on the main metal housing 
13. That is, as illustrated in FIG. 2A, when the monopole antenna 11 is 
positioned to the right end of the upper surface of the main metal housing 
12, it is desirable that the control element 14 is connected to the left 
end of the lower surface of the main metal housing 12. However, the 
connection position of the control element 14 is not limited to the 
above-explained position. For instance, a connection position between the 
control element 14 and the main metal housing 12 is set to a distance "d1" 
measured from the left end of the main metal housing 12, whereas another 
connection position between the control element 14 and the sub-metal 
housing 13 is set to another distance "d2" measured from the left end of 
this sub-metal housing 13, wherein the first distance "d1" is not equal to 
the second distance "d2". It should also be noted that the shapes of these 
main metal housing 12 and sub-metal housing 13, and also the arranging 
relationships thereof may be different from those of FIG. 2A. For 
instance, as illustrated in FIG. 2B, the main metal housing 12 is 
positionally shifted from the sub-metal housing 13 by a distance "S" along 
the horizontal direction. 
Actually, the antenna apparatus according to the first embodiment is stored 
within a resin case of a portable communication apparatus. 
As is known in the communication field, shapes and positional relationships 
of the main metal housing 12 and the sub-metal housing 13, as well as 
connection positions of the control element 14 with respect to both of 
these metal housings 13 and 14 may give influences to the current 
distributions of the high frequency currents flowing through the main 
metal housing 12 and the sub-metal housing 13, in other words, to the 
electromagnetic-wave radiation patterns of the antenna which are the same 
as the impedance value of the control element 14. As a consequence, the 
shapes and positional relationship of these metal housings 12 and 13, the 
connection positions of the control element 14 to these metal housings, 
and also the impedance value of the control element 14 should be 
determined in such a manner that the optimum antenna characteristics can 
be achieved under conditions where the antenna apparatus of the present 
invention is actually mounted on a case of a portable communication 
apparatus. In this case, the impedance value of the control element 14 may 
be varied without giving any influences to the shape of the antenna 
apparatus. In other words, the change of the impedance value of the 
control element 14 may be achieved by substituting the control element 14 
having one impedance value by the control element 14 having another 
different impedance value. As a consequence, even when such an optimum 
positional relationship or the like between the main metal housing 12 and 
the sub-metal housing 13 could not be achieved due to restrictions in 
designing of the main body made of resin for storing the antenna 
apparatus, the antenna characteristics may be selected, or approximated to 
the optimum values thereof by properly selecting the impedance value of 
the control element 14. 
When the main metal housing 12 is positionally shifted from the sub-metal 
housing 13 along the front/rear direction (namely, horizontal direction as 
viewed in FIG. 2B), since the front-to-rear ratio (i.e., the ratio of the 
antenna gain for the antenna apparatus on the front side thereof to the 
antenna gain thereto on the rear side thereof) of the antenna radiation 
gain is varied, the further preferable antenna characteristic may be 
achieved if the front-to-rear shift direction between the main metal 
housing 12 and the sub-metal housing 13 would be set in order that the 
antenna gain on the side opposite to an operator will be increased, while 
this antenna apparatus is actually mounted on the communication case. 
As the method for fixing the main metal housing 12 and the sub-metal 
housing 13 in the preset optimum arranging relationship, there are 
available a method for integrally molding the metal housings 12 and 13, 
and a method for separately fixing the metal housings 12 and 13 to the 
communication unit case by a screw. 
In the antenna apparatus constructed in the above-described manner, when 
the monopole antenna 11 is energized from the feeding point 11a, a current 
is distributed on monople antenna 11, so that electromagnetic waves are 
radiated from this monopole antenna 11. In response to this radiation of 
the electromagnetic waves, the main metal housing 12 and the sub-metal 
housing 13 are energized, so that currents are also distributed on these 
metal housings and thus electromagnetic waves are radiated therefrom. The 
current distributions occurred in this time respond to the impedance of 
the control element 14 used to electrically couple the main metal housing 
12 with the sub-metal housing 13. Similarly, the antenna radiation pattern 
will respond to this impedance. 
In case that the above-described control element 14 would be designed to 
essentially have only a reactance component (namely, inductance and 
capacitance components only), i.e., not to essentially have a resistance 
component, a loss in the portion of the control element 14 is negligible. 
Next, referring to FIG. 3 to FIG. 7, a description will be made of a 
structure for electrically opening a circuit connecting line 15 from both 
of the main metal housing 12 and the sub-metal housing 13. The circuit 
connecting line 15 is to connect the circuit unit stored within the main 
metal housing 12 to the circuit unit stored within the sub-metal housing 
13. 
FIG. 3 schematically shows a first structural example. FIG. 3A is a front 
view of one metal housing, for example, the main metal housing 12 whose 
one surface has been taken out. FIG. 3B is a sectional view of this metal 
housing, taken along a line 3B--3B of FIG. 3A. As illustrated in FIG. 3, 
the circuit connecting line 15 has one end connected to a connection 
terminal of a circuit board 17 employed in the main metal housing 12, and 
also the other end which passes through a through hole 12a formed in this 
main metal housing 12 and is extracted outside this main metal housing 12. 
Then, 1/4.lambda. open stub 18 having a portion located near the 
above-described though hole 12a, as an opening end, is arranged to be 
connected to the circuit connecting line 15 at a base portion 18a. It 
should be noted that although not shown in the drawing, the 
above-described other end of the circuit connecting line 15 extracted from 
the main metal housing 12, is penetrated through another through hole 
formed in the sub-metal housing 13, and then is conducted into this 
sub-metal housing 13, thereby being connected to a connection terminal of 
a circuit board provided within the sub-metal housing 13. Also, within 
this sub-metal housing 13, another 1/4.lambda. open stub similar to the 
above-mentioned 1/4.lambda. open stub 18 is provided in a similar 
positional relationship. 
In accordance with the above-explained structure, a radio frequency current 
(namely, current with frequency under use) flowing over an outer surface 
of the metal housing 12, does not flow into the circuit connecting line 
15, because the 1/4.lambda. open stub 18 is present. As a result, no radio 
frequency (RF) current flows from the main metal housing 12 via the 
circuit connecting line 15 to the sub-metal housing 13. It should be 
understood that since, normally, a plurality of circuit connecting lines 
are employed to connect these two metal housings 12 and 13 with each other 
in the portable communication apparatus, each of these circuit connecting 
lines is connected by way of the above-described arrangement. 
FIG. 4 schematically shows a second structural example. FIG. 4A is a front 
view of the main metal housing 12 whose one surface has been taken out, 
and FIG. 4B is a sectional view thereof, taken along a line 4B--4B of FIG. 
4A. This second structural example shows such a structure of 1/4.lambda. 
open stub 18 being arranged when a plurality of circuit connecting lines 
are employed. As illustrated in FIG. 4, a plurality of circuit connecting 
lines 15a to 15c are extracted from the circuit board 17 outside the main 
metal housing 12. The 1/4.lambda. open stub 18 of this structure has a 
base portion 18a whose width is wide. Then, 1/4.lambda. open stub 18 is 
connected via a dielectric substance 19 to the plural circuit connecting 
lines 15a to 15c at this base portion 18a. It should be noted that since 
this 1/4.lambda. open stub 18 is not directly and electrically connected 
to the circuit connecting line 15 at this time similar to the 1/4.lambda. 
open stub 18 of FIG. 3, the first-mentioned 1/4.lambda. open stub 18 is 
shortcircuited via a conductive line 20 to the main metal housing 12. As a 
result, no RF current flows through the circuit connecting lines 15a to 
15c in a similar condition to that of the first structural example. 
FIG. 5 schematically indicates a third structural example. FIG. 5A is a 
front view of the main metal housing 12 whose one surface has been taken 
out, and FIG. 5B is a sectional view thereof, taken along a line 5B--5B 
shown in FIG. 5A. This third structural example is very similar to the 
first structural example except that the 1/4.lambda. open stub 18 shown in 
FIG. 3 and a portion of the circuit connecting line 15 are formed on a 
printed circuit board 21, so that a similar effect to that of the first 
structural example can be obtained. In addition thereto, since a portion 
of the circuit connecting line 15 and the 1/4.lambda. open stub 18 are 
formed on the printed board 21, there is another merit that as the 
structural feature, this portion becomes strong in view of the structural 
aspect. It should be noted that when a plurality of circuit connecting 
lines 15 are formed on the print board 21, 1/4.lambda. open stub 18 is 
formed similar to the second structural example shown in FIG. 4 in such a 
manner that the base portion thereof is made from a plate-shaped member 
with a wide width, and a plurality of circuit connecting lines are 
connected via the dielectric substance at this base portion. 
FIG. 6 schematically illustrates a fourth structural example. FIG. 6A is a 
front view of the main metal housing 12 whose one surface has been taken 
out, and FIG. 6B is a sectional view thereof, taken along a line 6B--6B of 
FIG. 6A. In this fourth structural example, a coaxial cable 22 is employed 
as the circuit connecting line 15. As shown in FIGS 6A and 6B, an opening 
portion 23c of a sleeve 23a, which has a length of 1/4.lambda. (hereafter 
referred to as a 1/4.lambda. sleeve), is electrically connected to the 
through hole 12a of the main metal housing 12. Then, one end portion of an 
internal conductor 22a of the coaxial cable 22 functioning as the circuit 
connecting line 15 is connected to the connecting terminal of the circuit 
board 17 provided within the main metal housing 12. An outer conductor 22c 
of the coaxial cable 22 which is electrically insulated via an insulating 
layer 22b from an inner conductor 22a thereof, is electrically connected 
to a shortcircuiting lid portion 23b of the sleeve 23a. 
In accordance with this fourth structure, as previously explained, since 
the 1/4.lambda. sleeve is employed and the coaxial cable 22 is penetrated 
through this 1/4.lambda. and then extracted outside the main metal housing 
12, it is achieved that the RF current flowing through the outer surface 
of this metal housing 12 does not flow via the outer conductor 22c of the 
coaxial cable 22 through the other sub-metal housing 13. Additionally, 
since the 1/4.lambda. sleeve is utilized, the inside of the main metal 
housing 12 is completely shielded from the outer space, so that the 
shielding effect could be considerably improved. It should be noted that 
when a plurality of circuit connecting lines are employed, such a coaxial 
cable having a plurality of inner conductors may be utilized. 
FIG. 7 schematically indicates a fifth structural example, namely a front 
view of the main metal housing 12 whose one surface is taken out. In this 
fifth structural example, an optical fiber 24 is used as the circuit 
connecting line 15. As illustrated in FIG. 7, an electric signal derived 
from the circuit board 17 employed within the metal housing 12 is supplied 
via a connecting line 26 to an optical/electric converter 25. Then, this 
electric signal is converted into an optical signal by the 
optical/electric converter 25. Accordingly, the resultant optical signal 
is transferred via the optical fiber 24 to the other sub-metal housing 13. 
This optical fiber 24 is penetrated through the through hole 12a formed in 
the metal housing 12 and then extracted outside this metal housing 12. An 
optical signal sent from the sub-metal housing 13 via the optical fiber 24 
is converted by way of the optical/electric converter 25 into the electric 
signal, and this electric signal is transferred via the connecting line 26 
to the circuit board 17. 
With such a fifth structure, since the optical fiber 24 is the insulating 
material, no RF current may flow from the outer surface of the main metal 
housing 12 via the optical fiber 24 to the sub-metal housing 13. When the 
optical/electric converter 25 has the multiplexing function, only one 
optical fiber may be required even when signals are transmitted/received 
at the same time. 
FIG. 8 schematically shows a construction of an antenna apparatus according 
to a second embodiment of the present invention. FIG. 8A shows a front 
surface and a left side surface of this antenna apparatus. FIG. 8B 
represents in detail a connection portion of a control element 14 with 
regard to the main metal housing 12 and the sub-metal housing 13. It 
should be noted that the same reference numerals shown in FIG. 2 will be 
employed as those for denoting the same or similar constructive elements. 
In this second embodiment, since the monopole antenna 11 is provided on the 
upper left end portion of the main metal housing 12, the control element 
14 is provided in such a manner that a lower right portion of the main 
metal housing 12 is connected with an upper right portion of the sub-metal 
housing 13. It should also be noted that the circuit connecting line 15 
for connecting the circuit employed in the main metal housing 12 with the 
circuit employed in the sub-metal housing 13, owns such an extracting 
structure that the metal housings 12 and 13 are not shortcircuited with 
each other in view of the high frequency aspect. 
As illustrated in FIG. 8B, the control element 14 according to this second 
embodiment is constructed by a capacitor. This capacitor is formed in such 
a manner that a dielectric plate 27 is interposed between an upper right 
end portion of a front surface of the sub-metal housing 13, and a lower 
end portion of a metal plate 28 whose upper end portion is directly and 
electrically connected to a lower right portion of a front surface of the 
main metal housing 12. Then, an impedance value of this capacitor is 
selected to be a value at which an optimum antenna radiation pattern 
within the horizontal plane can be obtained. It is, of course, possible to 
employ a chip capacitor, instead of this dielectric plate 27. An adhesive 
connection between the dielectric plate 27 and the sub-metal housing 13, 
and another adhesive connection between the dielectric plate 27 and the 
metal plate 28 may be performed by way of a conductive adhesive agent or 
adhesive resin agent. Another connection between the metal plate 28 and 
the main metal housing 12 may be performed by means of soldering and 
welding. 
The featured antenna construction of the second embodiment is one of the 
most simple constructions when a chip type element is utilized as the 
control element 14. Other chip type elements, namely a chip resistor and a 
chip coil may be similarly employed. 
Referring now to FIG. 9 to FIG. 13, a description will be made of 
simulation results of the antenna apparatuses according to the present 
invention. 
FIG. 9 schematically illustrates a structure of a simulation model. In this 
embodiment, two simulation models have been considered. The first 
simulation model is constructed in such a manner that two conductive 
members 30 and 31 are separated from each other by 0.05.lambda. 
(".lambda." being a waveform corresponding to a center frequency under use 
in the below-mentioned descriptions), the vertical length of which is 
selected to be 0.5.lambda., the horizontal length of which is selected to 
be 0.4.lambda., and the thickness of which is selected to be 0.3 mm. 
Furthermore, the monopole antenna 11 is provided on an upper left end 
portion of the first conductive member 30, and a lower right end portion 
of the first conductive member 30 is connected via a passive load (passive 
element) 32 with an upper right end portion of the second conductive 
member 31. In other words, the first simulation model corresponds to such 
a simulation model that the vertical length "L", the horizontal length 
"W", and the thickness "t" of the main and sub-metal housings 12 and 13 
employed in the antenna apparatus shown in FIG. 8 are selected to be 
0.5.lambda., 0.4.lambda., and 0.3 mm respectively, and a space "G" between 
these metal housings is selected to be 0.05.lambda.. 
The second simulation model is such a model that a box shape having a 
thickness of 10 mm is constructed of the first and second conductive 
members 30 and 31. That is, the second simulation model corresponds to 
such a model that the vertical length "L", the horizontal length "W", and 
the thickness "t" of the metal housings 12 and 13 employed in the antenna 
apparatus shown in FIG. 8 are selected to be 0.5.lambda., 0.4.lambda. and 
10 mm, respectively, and also a space "G" between both of these metal 
housings 12 and 13 is selected to be 0.05.lambda.. In this second 
simulation model, the communication circuit is not stored with the first 
and second conductive members 30 and 31, but also no circuit connecting 
lines are employed. However, since the antenna apparatus shown in FIG. 8 
has such a structure that the main metal housing 12 is not shortcircuited 
to the sub-metal housing 13 via the connecting line 15 with respect to the 
high frequency current, this second model perfectly corresponds to the 
antenna apparatus illustrated in FIG. 8. The monopole antenna 11 used in 
the first and second simulation models has the length of 0.22.lambda. and 
the diameter of 0.0025.lambda., and a cylinder shape. 
The simulation was carried out for the above-explained two models under 
such conditions that the experimental frequency was selected to be 1.9 
GHz, the real part of the impedance of the passive load 32 was selected to 
be 0 to 10 Kiloohms, and the imaginary part thereof was selected to be -10 
Kiloohms to +10 Kiloohms. As a result, it could be found that when the 
real part of this passive load's impedance was zero ohm, namely this 
impedance contained only reactance component, the optimum experimental 
results could be obtained. In the above-described simulation models, when 
the reactance component was -250 ohms, the actual measurement was carried 
out. 
FIG. 10 and FIG. 11 graphically illustrate calculation results and 
measurement results as to the antenna gains (radiation gains of 
electromagnetic waves) under such a condition that the real part of the 
impedance of the passive load 32 was selected to be zero ohm. 
FIG. 10 indicates calculation results of averaged radiation gains for the 
above-described two simulation models within the X- Y plane under such 
conditions that the real part of the impedance of the passive load 32 is 
selected to be zero ohm, whereas the imaginary part thereof is shifted 
within a range from -1 Kiloohms to +1 Kiloohms. It should be noted that as 
shown in FIG. 9, the X axis of this coordinate system indicates the 
thickness of the conductive member 30, the Y axis thereof shows the 
horizontal direction of this conductive member 30, and the Z axis thereof 
denotes the direction parallel to the axis of the antenna 11. It should be 
understood that generally speaking, since the antenna apparatus employing 
the monopole antenna 11 is used under such a condition that the axis of 
the monopole antenna 11 is essentially directed to the vertical direction, 
an X-Y plane essentially implies the horizontal plane. Also, the averaged 
gain implies the predicted gain value of the antenna under such an 
assumption that vertically polarized radio electromagnetic waves uniformly 
would reach in an omnidirection within the horizontal plane (X-Y plane). 
In FIG. 10, an abscissa of this coordinate system shows the value of the 
imaginary part (reactance Z.sub.L) of the passive load 32, whereas an 
ordinate thereof denotes the averaged radiation gain. Furthermore, a solid 
line of FIG. 10 shows calculated values of the first model (namely, the 
thickness of the conductive member is selected to be 0.3 mm), and a broken 
line indicated calculated values of the second model (namely, the 
thickness of the conductive member is selected to be 10 mm). Symbol "o" 
indicates the actually measured values in the first model. In FIG. 10, the 
following three measured values are indicated by such cases that the 
reactance Z.sub.L is -j250 ohms, the reactance Z.sub.L is zero ohm (i.e., 
both of the first and second conductive members are shortcircuited), and 
the reactance Z.sub.L is infinite (namely, the passive load 32 is not 
connected between the first and second conductive members). 
As apparent from FIG. 10, the calculated values represent peaks in the 
range from -j300 ohms to -j600 ohms for both of the first and second 
simulation models irrelevant to the thicknesses of the first and second 
conductive members 30 and 31. Also, the actually measured values represent 
values substantially equal to these calculated values. 
In FIGS. 11A, 11B and 11C, there are indicated antenna gain patterns in the 
X-Y plane, the Y-Z plane, and the Z-X plane, respectively. In these 
drawings, a broken line, a solid line, and a dot/dash line represent 
patterns of antenna gains calculated in this first simulation model under 
such a condition that the reactance Z.sub.L is selected to be -j116 ohms, 
-j250 ohms, and -j517 ohms, respectively. Symbol o indicates values 
actually measured under such a condition that the reactance Z.sub.L is 
selected to be -j250 ohms in the first simulation model. 
As understood from these drawings FIGS. 11A to 11C, the gain of the antenna 
apparatus according to the present invention within the horizontal plane 
becomes very high. In particular, the gain on the Y axis is approximated 
to the ideal gain value of 0 [dBd]. Although not shown in these drawings, 
the calculation values and the actual measurement values with respect to 
the second simulation models were substantially identical to those of the 
first simulation model. 
For the sake of reference purpose, antenna gain patterns within the X-Y 
plane, the Y-Z plane, and the Z-X plane when the first conductive member 
30 is directly connected to the second conductive member 31 without the 
passive load 32, are represented in FIG. 13A to FIG. 13C. These antenna 
gain patterns are similar to those obtained under such a condition that 
the main metal housing 12 is shortcircuited to the sub-metal housing 13 
via the circuit connecting line 15 in view of the RF currents within the 
antenna apparatus shown in FIG. 8. As apparent from the comparisons of the 
antenna gain pattern shown in FIGS. 11A to 11C and FIGS. 13A to 13C, the 
antenna apparatus of the present invention could have considerably high 
gain, i.e., better antenna characteristics. 
The calculation results shown in FIG. 10 and FIG. 11 also represent that 
the antenna radiation patterns can be controlled by controlling the 
impedance of the passive load 32. In other words, these calculation 
results show that the averaged gain within the X-Y plane, and the gains on 
the respective axis can be varied by changing the impedance of the passive 
load 32. 
FIG. 12 represents an input admittance of the monopole antenna 11 when a 
frequency is varied. An abscissa of FIG. 12 indicates the frequency and an 
ordinate thereof shows the input admittance. 
In this drawing, a solid line and a broken line represent a real part and 
an imaginary part of the input admittance when the reactance Z.sub.L is 
selected to be -j250 ohms, and is actually measured in the first 
simulation model. Also, symbols "+", "o", and "*" show calculation results 
obtained when the reactance Z.sub.L is selected to be -j116 ohms, -j250 
ohms, and -j517 ohms, respectively, in this first simulation model. 
As apparent from FIG. 12, a resonant frequency (namely, a frequency at 
which an imaginary part of an input admittance becomes 0) for the 
calculated value and the actually measured value when the reactance 
Z.sub.L is selected to be -j250 ohms, and also the calculated value when 
the reactance Z.sub.L is selected to be -j517 ohms, is 1.79 GHz. As a 
result, the resonant frequency in these cases becomes low by approximately 
6% with respect to 1.9 GHz. This implies that the length of the monopole 
antenna 11 can be shortened by approximately 6%. Accordingly, the feature 
of the antenna apparatus according to the present invention may contribute 
that the length of the monopole antenna 11 is shortened. 
FIG. 14 and FIG. 15 schematically indicate antenna apparatuses according to 
a third embodiment and a fourth embodiment of the present invention. These 
third and fourth embodiments embody controls of antenna radiation patterns 
by adjusting the impedance of the passive load 32, which could be 
confirmed by the above-described simulation. 
First, the antenna apparatus shown in FIG. 14 is constructed in such a 
manner that the control element 14 is arranged by a capacitor 14a and a 
variable-capacitance diode 14b, and the impedance of the control element 
14 is controlled in accordance with operations of an external key 33 and 
conditions of received signals. An RF circuit 17a and the like are 
contained within the main metal housing 12, whereas a control circuit 17b 
and the like are included in the sub-metal housing 13. The control circuit 
17b supplies a controlling voltage via a resistor 17c to a junction 
between the capacitor 14a and the variable-capacitance diode 14b based 
upon levels of the received signal entered from the RF circuit 17a via the 
circuit connecting line 15. As a result, a capacitance of this 
variable-capacitance diode 14b, namely the impedance of the control 
element 14 is varied, so that the antenna radiation pattern is varied. 
When the antenna radiation pattern is controlled by way of the external 
operation key 33, as shown in FIG. 14, the external operation key 33 is 
connected to the control circuit 17b. When the external operation key 33 
is operated, the control circuit 17b furnishes a controlling voltage via 
the resistor 17c to the junction between the capacitor 14a and the 
variable-capacitance diode 14b based upon, for example, operation times of 
this operation key 33, thereby changing the impedance of the control 
element 14. 
In the antenna apparatus of the fourth embodiment indicated in FIG. 15, an 
electric-field strength (intensity) detecting circuit 17d is provided 
within the main-metal housing 12, an electric-field strength of an 
electromagnetic wave received by the RF circuit 17a is detected by the 
electric-field strength detecting circuit 17d, a controlling voltage 
determined in response to this detected electric-field strength is applied 
via the resistor 17e to the junction point between the capacitor 14a and 
the variable-capacitance diode 14b, whereby the impedance of the control 
element 14 may be varied. 
In FIGS. 16 to 19, there are illustrated such examples that the antenna 
apparatuses according to the present invention are actually mounted within 
main body cases of portable communication units. 
FIG. 16 shows a first actually mounted example. FIG. 16A is a perspective 
view of this first example where the internally provided antenna apparatus 
may be observed from outside of the main body case of the portable 
communication unit. FIG. 16B schematically shows an arranging condition of 
the major components employed within the main body case. The main metal 
housing 12 and the sub-metal housing 13 of the antenna apparatus are fixed 
to the arrangements as shown in the main body case 40 made of a resin. 
Within the main body case 40, there are provided a speaker 41 for 
producing sounds, a display device 42 such as an LCD (liquid crystal 
display) for displaying various data, a keyboard 43 for entering the 
various data, and a microphone 44 for acoustically receiving a sound 
signal of a speaker. Since the mounting positions of the speaker 41 and 
the display device 42 are located in an upper half portion of the main 
body case 40 corresponding to the storage position of the main metal 
housing 12 for including the RF circuit and the like, a signal line 41a of 
the speaker 41 and a signal line 42a of the display device 42 are once 
drawn, or extracted into the main metal housing 12. Then, these signal 
lines 41a and 42a are connected to the control circuit employed in the 
sub-metal housing 13 as one of the circuit connecting lines 15. On the 
other hand, since the mounting positions of the keyboard 43 and the 
microphone 44 are located in a lower half portion of the main body case 40 
corresponding to the storage position of the sub-metal housing 13, a 
signal line 43a of the keyboard 43 and a signal line 44a of the microphone 
44 are directly drawn into the sub-metal housing 13 and then are connected 
to the control circuit employed within this sub-metal housing 13. It 
should be noted that since the signal line 42a of the display device 42 is 
practically constructed of a large number of signal lines, for instance, a 
display drive circuit and the like may be provided within the main metal 
housing 12 so as to reduce the total number of circuit connecting liens 
15. Reference numeral 45 shows a cell for supplying power to the 
respective circuits. 
FIG. 17 schematically indicates a second actually mounted example. There is 
only such a difference between the second actually mounted example and the 
first actually mounted example as follows: That is, the main metal housing 
12 of the antenna apparatus is positionally shifted toward the side of the 
speaker 41, namely toward the front side of the main body case 40. This 
second actually mounted structure becomes effective in such a case that 
the front-to-rear ratio of the antenna radiation pattern is varied. This 
front-to-rear ratio implies a ratio of an antenna gain on the front side 
of the main body case 40 to an antenna gain on the rear side thereof. In 
other words, it is a useful actually mounted structure in case that the 
antenna gain on the rear side of the main body case 40 located opposite to 
the operator side during the communication operation. 
When the main metal housing 12 is installed in the vicinity of the speaker 
41 and display device 42, the main metal housing 12 may be formed to 
directly receive the speaker 41 and display device 42. As well, the 
sub-metal housing 13 may be formed to directly receive the keyboard 43 and 
the microphone 44. As a result, the assembling operation of parts into the 
main body case 40 can be simplified. 
FIG. 18 schematically indicates another actually mounted example of the 
antenna apparatus having no sub-metal housing 13. In FIG. 18, reference 
numeral 46 denotes a circuit board on which a control circuit and the like 
are mounted. This circuit board 46 is constructed of a laminated board 46a 
whose conductive layers are multilayer. The grounding conducive layer may 
be formed by arbitrary layers. In this example, the conductive layer 46b 
at the rear surface is utilized as the grounding conductive layer. Then, 
the main metal housing 12 including the RF circuit unit is connected via 
the control element 14 and the grounding conductive layer 46b formed on 
the rear surface of the circuit board 46. Also, the signal line 41a of the 
speaker 41 and the signal line 42a of the display device 42 are connected 
to relevant terminals formed on the circuit board 46 as one of the circuit 
connecting lines 15, whereas the signal line 43a of the keyboard 43 and 
the signal line 44a of the microphone 44 are directly connected to the 
corresponding terminals formed on the circuit board 46. As one 
modification, in case that the RF circuit unit is similarly not stored 
within the main metal housing 12, a grounding conductive layer of the 
circuit board on which this RF circuit unit is mounted is connected via 
the control element 14 with the grounding conductive layer 46b of the 
circuit board 46, and the circuit connecting line 15 for connecting both 
of these circuit units is arranged by an optical fiber. That is, these 
circuit units may be connected with each other by way of the connecting 
structure as illustrated in FIG. 7. 
FIG. 19 schematically shows another actually mounted example in which the 
antenna apparatus according to the present invention is installed into a 
folded type appliance case. As shown in FIG. 19, a main body case of this 
appliance is constructed of a first case portion 40a and a second case 
portion 40b, and these first and second case portions 40a and 40b are 
mechanically connected with each other by using a hinge portion 40c, 
whereby a folded type appliance case is formed. The main metal housing 12 
of the antenna apparatus is stored into the first case portion 40a, 
whereas the sub-metal housing 13 is stored into the second case portion 
40b. The antenna apparatus according to the present invention can be 
simply mounted even in the above-described folded type appliance case by 
merely employing flexible connecting lines as the circuit connecting line 
15 for connecting the main metal housing 12 to the sub-metal housing 13, 
and the connecting line for connecting the control element 1 to either the 
main metal housing 12, or the sub-metal housing 13. 
As apparent from the actually mounted examples shown in FIG. 16, FIG. 17 
and FIG. 19, the antenna apparatus according to the present invention 
could be mounted in the various modes without modifying the shapes of the 
main and sub-metal housings 12 and 13 for storing the circuit portions. 
Also, even if the circuit portions are not stored into these metal 
housings, as illustrated in FIG. 18, these circuit portions may be mounted 
in a similar manner to that of the two metal housings. 
It should be understood that although the antenna apparatuses of the 
above-described embodiments have been applied to the monopole antenna, the 
present invention is not limited to this monopole antenna, but may be 
applied to many other types of antenna such as a microstrip antenna and a 
reverse F type antenna. 
FIG. 20 schematically shows a structural example of a microstrip antenna. 
Reference numeral 50 indicates a plate-shaped microstrip antenna. The 
microstrip antenna 50 of this embodiment is formed in such a manner that 
one edge portion of a rectangular metal plate is folded to have a crank 
shaped section thereof. A major portion of this rectangular metal plate 
functions as a radiation element portion 50a, and the folded edge portion 
of this metal plate functions as a shortcircuit terminal portion 50c. The 
shortcircuit terminal portion 50c is fixed to the main metal housing 12. 
Power is supplied via a power feeding terminal 50b to a center of the 
radiation element unit 50a of this microstrip antenna 50. Not only the 
vertical length of the radiation element 50a of the microstrip antenna 50, 
but also the horizontal length thereof may be preferably made of 
1/2.lambda.. 
The setting position of the microstrip antenna 50 may be preferably set to 
such a position that the central position of the radiation element unit 
50a is located on the central line of the main metal housing 12. The 
optimum setting position of this microstrip antenna 50 is a substantially 
center portion of the major surface of the main metal housing 12, as 
illustrated in FIG. 20. A desirable position for connecting the main metal 
housing 12 with the sub-metal housing 13 via the control element 14, 
corresponds to a substantially central portion on a surface opposite to 
the surface where the microstrip antenna 50 is set. A setting position of 
the circuit connecting line 15 for connecting the circuit stored in the 
main metal housing 12 to the circuit employed in the sub-metal housing 13 
may be arbitrarily determined. 
When this antenna apparatus is stored into the main body of the portable 
communication unit, for example, the case 40 shown in FIG. 16, the surface 
on which the microstrip antenna 50 is mounted corresponds to the rear 
surface of the case 40 (namely, the surface where the speaker 41 and the 
display device 42 are not provided). 
FIG. 21 schematically illustrates a structural example of a reverse F type 
antenna. In this drawing, reference numeral 60 shows a plate-shaped 
reverse F type antenna. The plate-shaped reverse F type antenna 60 
according to this embodiment is so arranged that a radiation element 60a 
is formed on a dielectric plate 60d, and this dielectric plate 60d is 
adhersively connected to the surface of the main metal housing 12. The 
radiation element 60a is shortcircuited to the main metal housing 12 via a 
shortcircuit terminal 60c extending to the surface of the main metal 
housing 12 through the upper right end portion of the dielectric plate 60d 
from the upper right corner. Power is supplied to the radiation element 
60a via a power feeding terminal 60b provided on the right side surface of 
the dielectric plate 60d. Both the vertical length and the horizontal 
length of the radiation element 60a are selected to be 1/4.lambda., 
respectively. 
Preferably, the setting position of the reverse F type antenna is located 
at such a position on a line to connect the power supply terminal 60b with 
the shortcircuit terminal 60c, namely a position where the right side 
surface of the dielectric plate 60d is present on the central line of the 
main metal housing 12. The optimum setting position of this reverse F type 
antenna is such a position, as shown in FIG. 21, that the right side 
surface of the dielectric plate 60d is located substantially at the center 
of the major surface of the main metal housing 12. Both the position for 
connecting the main metal housing 12 via the control element 14 to the 
sub-metal housing 13, and also the setting position of the circuit 
connecting line 15 are similar to those of the above-described microstrip 
antenna 50. The direction of the antenna apparatus when this antenna 
apparatus is stored into the main body case of the portable communication 
unit, is set in a similar manner to that of the microstrip antenna 50. 
Although the number of conductive members such as the metal housings is 
selected to be two in the above-explained embodiments, the present 
invention is not limited to such a case where the quantity of conductive 
members is two. For example, as shown in FIG. 22, two sub-metal housings 
13 and 13 may be equipped with the main metal housing 12 on which an 
antenna 60 is mounted. In this case, there are provided the control 
element 14 for mutually connecting these metal housings, and also the 
circuit connecting line 15 for mutually connecting the circuits employed 
in these metal housings between the main metal housing 12 and the 
sub-metal housing 13, and also between the first sub-metal housing 13 and 
the second sub-metal housing 13, respectively.