Plane antenna system for mobile communication equipment

A flat antenna unit for a mobile communication equipment which is pasted on the mobile communication equipment so that it is touched by a human hand when in use, comprising a flexible insulated base; a receiving circuit which is formed on the flexible insulated base and which comprises three conductive layers of a pair of U-shaped conductive layers which are isolated and symmetrically disposed each other, a pair of conductive layers which have bent sections at the ends thereof and which are isolated and symmetrically disposed on the both sides of the U-shaped conductive layers, and a conductive layer which is isolated from the above-mentioned conductive layers as well as from the U-shaped conductive layers and which is located above the U-shaped conductive layer; and an insulator which is formed by potting insulating ink for example and which is coated on the receiving circuit. The flat antenna unit is characterized in that when the insulator is touched by the hand, a tuning capacitor is formed between the hand and the receiving circuit via the insulator. Thereby, the inventive antenna unit can eliminate troubles during speech like noise and interruption even when the radio efficiency is bad in using the mobile communication equipment such as a portable phone at places where the strength of electric field is weak.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a flat antenna unit for a mobile 
communication equipment and more particularly to a technology which can 
enhance a communication sensitivity of a portable telephone by pasting the 
antenna unit on the back thereof. 
2. Description of Related Art 
When a mobile radio communication equipment such as a portable phone is 
used at places where the strength of electric field is low like a valley 
between tall buildings, within a building and within a vehicle, its radio 
efficiency drops, thus causing troubles in communication such as noise and 
speech interruption. 
Then, in order to eliminate such troubles, there have been provided various 
antenna units including a so-called seal type flat antenna which is pasted 
on the back of a portable phone. 
For instance, Japanese Utility Model Publication No. 3015919 has disclosed 
a flat antenna unit in which two antenna sect ions having symmetrical 
shapes and in which tuning capacitors are formed at both ends thereof are 
connected via a coupling circuit and both ends of the coupling circuit are 
connected by a feeder line. Further, Japanese Patent Laid-Open No. Hei. 
5-259724 has disclosed a printed antenna similarly provided with feeding 
points and grounding sections. 
Japanese Patent Laid-Open No. Hei. 6-140822 has disclosed a flat antenna 
unit in which a layer of a conductive material is provided on a supporting 
member and a receiving circuit is provided thereon as a receiving element 
of the flat antenna unit. 
Still more, Japanese Patent Laid-open No. Hei. 4-14304 has disclosed a 
bi-directional loop antenna in which a conductor of a reactance element is 
added to each loop conductor so as to bring antenna impedance closer to 
terminal resistance. 
By the way, the flat antenna unit must be miniaturized, lightened and 
thinned in order to paste on the back of the portable phone and is 
required that an occupied area of its antenna pattern is small, the rate 
of dielectric loss is low, the radio efficiency is high, the sensitivity 
is high, and the like. 
From these points of view, the flat antenna unit disclosed in Japanese 
Utility Model Publication No. 3015919 has had a problem that the two 
symmetrical antenna sections in which the tuning capacitors are formed at 
the both ends must be connected by the coupling circuit and the impedance 
of the coupling circuit must be adjusted with the impedance of the antenna 
sections so that they are equalized. Similarly to that, the flat antenna 
unit disclosed in Japanese Patent Laid-Open No. Hei. 5-259724 has had a 
problem that it requires the feeding points and the grounding points, thus 
increasing the occupied area of the antenna pattern. The flat antenna unit 
disclosed in Japanese Patent Laid-Open No. Hei. 6-140822 has had problems 
that not only the layer of the conductive material must be provided on the 
supporting member but also the receiving circuit must be provided thereon 
in the receiving element of the flat antenna unit and that the process for 
forming the receiving circuit is complicated because it is formed by means 
of hot resist technology. The bi-directional loop antenna disclosed in 
Japanese Patent Laid-Open No. Hei. 4-14304 has had a similar problem that 
the process for forming the circuit is complicated because the occupied 
area of the relatively simplified antenna pattern is reduced by bringing 
the antenna impedance closer to the terminal resistance. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a 
technology which can eliminate the drawbacks of those prior art 
technologies. 
According to the present invention, there is provided a flat antenna unit 
for a mobile communication equipment which is pasted on the mobile 
communication equipment so that it is touched by a human hand when in use, 
comprising a flexible insulated base; a receiving circuit which is formed 
on the surface of the flexible insulated base and which comprises three 
conductive layers of a pair of U-shaped conductive layers which are 
isolated and symmetrically disposed each other, a pair of conductive 
layers which have bent sections at the ends thereof and which are isolated 
and symmetrically disposed on the both sides of the U-shaped conductive 
layers, and a conductive layer which is isolated from the conductive 
layers as well as from the U-shaped conductive layers and which is located 
above the U-shaped conductive layer; and an insulator which is coated on 
the receiving circuit. It is characterized in that when the insulator is 
touched by the hand, a tuning capacitor is formed between the hand and the 
receiving circuit via the insulator.

DESCRIPTION OF PREFERRED EMBODIMENTS 
As shown in FIGS. 1A and 1B, a flat antenna unit 1 for a mobile 
communication equipment comprises, on the surface of a flexible insulated 
base 2, a receiving circuit 7 comprising three conductive layers of a pair 
of U-shaped conductive layers 3 which are isolated and symmetrically 
disposed each other, a pair of conductive layers (hereinafter referred to 
as bent conductive layers) 5 which have bent sections 4 at the ends 
thereof and which are isolated and symmetrically disposed on the both 
sides of the U-shaped conductive layers 3, and a conductive layer 
(hereinafter referred to as an upper conductive layer) 6 which is isolated 
from the bent conductive layers 5 as well as from the U-shaped conductive 
layers 3 and which is located above the U-shaped conductive layer 3. The 
receiving circuit 7 is coated by an insulator 8. 
A pressure sensitive adhesive double coated sheet 11 in which an adhesive 9 
is applied on the both sides of a sheet 10 is pasted on the back of the 
flexible insulated base 2 as shown in FIG. 1B. The adhesive double coated 
sheet 11 may be an adhesive tape as a matter of course. Further, a mount 
and the like on which the adhesive 9 is applied on the both sides thereof 
may be used instead of the adhesive double coated sheet 11. 
Further, an adhesive 12 may be applied on the back of the flexible 
insulated base 2 as shown in FIG. 1C. 
The flexible insulated base 2 is made of a flexible resin film such as a 
polyester film, a polyethylene terephthalate film or the like. 
The conductive layers 3, 5 and 6 composing the receiving circuit 7 may be 
formed by screen-printing conductive ink, paint or the like containing 
conductive fillers on the surface of the flexible insulated base 2. 
Preferably, the insulator 8 coating the receiving circuit 7 is formed by 
printing or potting insulating ink. It may be also preferable to make the 
insulator 8 to be clear so that the receiving circuit 7 therein can be 
seen from the outside as shown in FIG. 1A. 
In using such antenna unit 1, it is pasted on the back of the portable 
phone 13 via the adhesive double coated sheet 11 as shown in FIG. 1D in 
the mode having the adhesive double coated sheet 11 as shown in FIG. 1B. 
Or, the face of the adhesive 12 is pasted on the back of the portable 
phone 13 as shown in FIG. 1D in the mode having the adhesive 12 as shown 
in FIG. 1C. 
The antenna unit 1 is pasted at the location where a human hand touches in 
pasting on the back of the portable phone 13. That is, it is pasted there 
so that when the insulator 8 is touched by the hand, a tuning capacitor is 
formed between the hand and the receiving circuit 7 via the insulator 8. 
The receiving circuit 7 is composed of the patterns as described above and 
has a configuration convenient for forming the tuning capacitor between 
the receiving circuit 7 and the hand via the insulator 8. Further, the 
receiving circuit 7 receives radio waves caught by the human body, i.e. a 
good electrical conductor, as a large antenna and transmits it efficiently 
to the mobile communication equipment, thus enhancing the communication 
sensitivity of the mobile communication equipment in use. 
As described above, the receiving circuit configured in the specific manner 
is formed on the flexible insulated base 2 and is coated by the insulator 
in the inventive flat antenna unit. Further, the inventive flat antenna 
unit is used by pasting at the part of the portable phone where the human 
hand touches. When the insulator is touched by the hand, the tuning 
capacitor is formed between the hand, the insulator and the receiving 
circuit as described above. That is, the inventive antenna unit is 
arranged so as to be able to eliminate the troubles during speech like 
noise and interruption caused by the low radio efficiency in using the 
portable phone at places where field strength is weak by reducing the 
noise during the speech or by compensating the weak field strength by 
catching and condensing the radio waves by the human body which is a good 
electrical conductor as a large antenna and by forming the tuning 
capacitor as described above. 
The receiving circuit is composed of the circuit having the patterns of the 
specific configuration suited to such mode. That is, the three conductive 
layers in the receiving circuit have different occupied areas and shapes 
and form capacitors of specific capacitance, respectively, thus enhancing 
the efficiency of speech. Further, because the receiving circuit is formed 
on the flexible insulated base and is coated by the insulator or the 
insulator is formed by printing or potting the insulating ink as the other 
preferable embodiment of the inventive flat antenna unit, the flexible, 
small, light and thin flat antenna suitable for pasting on the back of the 
portable phone may be realized. Further, the inventive antenna unit 
requires no feeder line, coupling circuit or grounding circuit like the 
prior art units. It also requires to provide no receiving circuit on the 
layer of the conductive material nor to add a conductor of a reactance 
element to a loop conductor. Accordingly, the occupied area of the antenna 
pattern thereof is small, the rate of dielectric loss is low, the radio 
efficiency is high and the sensitivity is high, so that even when the 
radio efficiency drops in using the portable phone at places where the 
field strength is low like a valley between tall buildings, within a 
building and the like or in a state where fluctuation of intensity of the 
field strength is large like in a traveling vehicle and the like, the 
inventive antenna unit can prevent noise from entering or speech from 
being interrupted. 
Industrial Applicability: 
As described above, the inventive antenna unit can be applied usefully to a 
mobile communication equipment. That is, the present invention can achieve 
the flexibility, miniaturization, lightening and thinning which are 
required for the flat antenna to paste on the back of the portable phone. 
The inventive antenna unit also forms the tuning capacitor between the 
hand, the insulator and the receiving circuit when the insulator is 
touched by the hand, favorably receives the radio waves caught by the 
human body which is a good electrical conductor as a large antenna and 
transmits the radio waves to the mobile communication equipment 
efficiently, thus enhancing the communication sensitivity of the mobile 
communication equipment in use. Further, it requires no feeder line, 
coupling circuit or grounding circuit like the prior art units. It also 
requires to provide no receiving circuit on the layer of the conductive 
material nor to add a conductor of a reactance element to a loop 
conductor. Accordingly, the occupied area of the antenna pattern is small, 
the rate of dielectric loss is low, the radio efficiency is high and the 
sensitivity is high, so that even when the radio efficiency drops in using 
the portable phone at places where the field strength is low like a valley 
between tall buildings, within a building and the like or in a state where 
fluctuation of intensity of the field strength is large like in a 
traveling vehicle and the like, the inventive antenna unit can prevent 
noise from entering or speech from being interrupted. 
While the preferred embodiments have been described, variations thereto 
will occur to those skilled in the art within the scope of the present 
inventive concepts which are delineated by the following claims.