Dual plate antenna

Portable radio equipment which is thin enough to enhance portability and, yet, has a sufficiently high antenna gain. The equipment has an antenna which is made up of a pair of metal plates located face-to-face, and a short-circuiting member for short-circuiting the metal plates. A circuit board loaded with radio circuitry is interposed between two metal plates with the radio circuitry being connected to the antenna. A capacitor is connected between the metal plates to lower the resonance frequency of the antenna, as needed. A circular cell for powering the equipment is located in a cell receiving portion near the short-circuiting member.

BACKGROUND OF THE INVENTION 
The present invention relates to thin card-like portable radio equipment in 
which an antenna having a high gain is incorporated. 
A predominant type of antenna built in portable radio equipment is a loop 
antenna which is capable of feeding electromagnetic energy around the 
equipment efficiently to circuitry. A loop antenna has one or more turns 
forming loops and transforms magnetic fluxes intersecting the loops into 
electric energy so as to feed it to the circuitry. Generally, a problem 
with a loop antenna is that as the aperture of the loop or loops 
decreases, the number of magnetic fluxes intersecting the aperature and, 
therefore, the antenna gain decreases. Nevertheless, in parallel with the 
current trend toward miniature portable radio equipment, there is an 
increasing demand for a miniature built-in loop antenna. In this 
situation, the antenna gain attainable with miniature radio equipment and, 
therefore, the communicatable range is limited. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide portable 
radio equipment which is thin enough to enhance portability and, yet, 
provided with a built-in antenna having a high antenna gain. 
It is another object of the present invention to provide generally improved 
portable radio equipment. 
Thin portable radio equipment of the present invention comprises an antenna 
comprising a first and a second flat antenna element located to face each 
other, and a short-circuiting member for short-circuiting the first and 
second antenna elements, and a circuit board located between the first and 
second antenna elements and loaded with radio circuitry which is connected 
to the antenna.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1 of the drawings, portable radio equipment embodying the 
present invention is shown and generally designated by the reference 
numeral 10. As shown, the equipment 10 has a first antenna assembly 12 and 
a second antenna assembly 14 which are implemented by a first antenna 
element 16 and a second antenna element 18, respectively. The antenna 
elements 16 and 18 are constituted by a flat metal plate each. A case 20 
made of a plastic or similar insulative material is adhered to the edges 
of the first antenna element 16. Nuts 22, 24, 26, 28 and 30 are buried in 
the case 20. The second antenna element 18 is provided with holes 32, 34, 
36, 38 and 40 which are associated with the nuts 22, 24, 26, 28 and 30, 
respectively. As shown in FIGS. 2A and 2B, the first and second antenna 
elements 16 and 18, i.e., the first and second antenna assemblies 12 and 
14 are positioned face-to-face and then screws 42, 44, 46, 48 and 50 are 
driven into the aligned holes 32, 34, 36, 38, and 40 and nuts 22, 24, 26, 
28 and 30 whereby the two assemblies 12 and 14 are firmly connected to 
each other. 
As shown in FIG. 3 in an enlarged scale, none of the nuts 22, 24, 26, 28 
and 30 extends throughout the case 20. This prevents the first and second 
antenna elements 16 and 18 from being short-circuited via the nuts 22 to 
30. In FIG. 3, the reference numeral 52 designates a layer of adhesive 
adapted to fix the case 20 to the first antenna element 16. 
As shown in FIGS. 1, 2A and 2B, a circuit board 54 carrying radio circuitry 
(not shown) thereon is mounted on the inner surface of the second antenna 
element 18 with the intermediary of an insulating film 56 (FIG. 2B). The 
insulating film 56 may be implemented as a sheet of polyester or similar 
insulating material. Connectors 58, 60 and 62 are rigidly mounted on the 
first antenna element 16 by spot welding or similar technology. Threaded 
holes 58a, 60a and 62a are respectively formed in the connectors 58, 60 
and 62, while a hole 63 is formed through the second antenna element 18 
and holes 64 and 66 are formed through the circuit board 54. Screws 68, 70 
and 72 are driven into the threaded holes 58a, 60a and 62a through the 
aligned holes 63, 64 and 66, whereby the first antenna element 16 is 
electrically connected to the second antenna element 18 or the circuit 
board 54. More specifically, the first and second antenna elements 16 and 
18 are electrically interconnected by the connector 58, while the first 
antenna element 16 and predetermined portions of the circuit board 54 are 
electrically interconnected by the connectors 60 and 62. In this manner, 
the antenna elements 16 and 18 and circuit board 54 can be assembled, 
disassembled and maintained with ease as needed, because their 
interconnection is implemented by screws 68, 70 and 72. 
As shown in FIGS. 1, 2A and 2B, terminals 74 and 76 are affixed to the 
second antenna element 18 by spot welding, for example. Tips 74a and 76a 
of the terminals 74 and 76, respectively, are soldered or otherwise 
connected to predetermined portions P1 and P2 of the circuit board 54. The 
terminals 74 and 76, therefore, set up electrical connection between the 
second antenna element 18 and the circuit board 54. The circuit board 54 
has two connecting portions 78 and 80. 
Referring to FIGS. 4A to 4C, there are shown in an enlarged scale a portion 
where the antenna elements 16 and 18 and circuit board 54 are 
interconnected and the portion P1 of the circuit board 54. As shown, the 
connecting portion 78 is cut and raised in the form of a tongue from the 
circuit board 54 and is angularly movable about at least one side thereof. 
The connecting portion 78, therefore, is flexible enough to free the 
circuit board 54 from excessive stresses. Circuit patterns 82 and 84 
formed of copper foil, for example, are printed on the circuit board 54 
and connected to radio circuitry which is provided on the circuit board 
54. The connecting portion 80, like the connecting portion 78, is formed 
in a tongue configuration. 
As shown in FIG. 2A, a capacitor 86 is loaded between the portion P2 of the 
circuit board 54 and the connecting portion 80 (where the connected 62 is 
connected) as needed. The radio circuitry provided on the circuit board 54 
is connected to between the portion P1 and the connecting portion 78 
(where the connector 60 is connected). 
FIG. 5 shows the antenna arrangement of the illustrative embodiment 
schematically. As shown, the antenna built in the radio equipment 10 has a 
so-called inverted F antenna configuration which is thin and, yet, high in 
antenna gain. If the dimensions of radio equipment are small for a given 
wavelength .lambda. of an electromagnetic wave, the resonance frequency 
particular to an antenna of the equipment will increase. The capacitor 86 
is loaded to lower the resonance frequency, as needed. 
Referring to FIGS. 1 and 2A again, a nickel-cadmium cell, lithium cell or 
similar circular cell 88 is retained by a cell case 90 and a terminal 
plate 92. The terminal plate 92 has negative terminals or contacts in the 
form of tongues 94 which are individually engaged with positive electrodes 
of the cell 88. The outer periphery of the cell 88 serves as a positive 
electrode. Hence, when the cell 88 is inserted into the case 90 in a 
direction indicated by an arrow A, the periphery of the cell 88, i.e., the 
positive electrode and the terminal plate 92 which is connected to the 
negative terminal are respectively brought into connection with cell 
terminals 96 and 98 which are provided on the circuit board 54. The cell 
case 92 has a pair of stops 100a and 100b extending sideways from opposite 
edges thereof. The stops 100a and 100b mate respectively with recesses 
102a and 102b which are formed in the case 20, thereby firmly maintaining 
the cell 88 in the equipment 10. 
Since the first and second antenna elements 16 and 18 are short-circuited 
by the connector 58, and potential difference between the antenna elements 
16 and 18 is small in the vicinity of the connector 58. Therefore, by 
locating the cell 88 in close proximity to the connector 58, it is 
possible to safeguard the antenna characteristics against critical 
influence of various kinds of scattering such as the scattering in the 
dimensions of the cell 88 and cell case 90 and the scattering in the 
position of the cell 88 relative to the equipment 10. For this reason, the 
radio equipment 10 is so configured as to accommodate the cell 88 in a 
position X, FIG. 2A, close to the connector 58 which short-circuits the 
antenna elements 16 and 18. Such a configuration will be described more 
specifically hereinafter. 
Assume that the radio equipment 10 is designed for a 280 megahertz 
application, that as shown in FIGS. 2A and 2B it has a width W of 80 
millimeters, a depth D of 50 millimeters, and a height H of 4.5 
millimeters, and that the circular cell 88 has a diameter R of 23 
millimeters and a thickness t of 2.8 millimeters. Experiments were 
conducted to determine the influence of the cell 88 on the antenna 
characteristics with respect to two difference positions of the cell 88, 
i.e., the position X close to the connector 58 and a position Y, FIG. 2A 
remote from the connector 58. The experiments showed that the loss 
resistance R (X) of the antenna associated with the position X and the 
loss resistance R (Y) associated with the position Y are 1.4 ohms and 1.8 
ohms, respectively. Since antenna gain is inversely proportional to loss 
resistance, the results of experiments prove that the antenna gain is 
improved when the cell 88 is located in the position X than in the 
position Y by a degree I= 10 logR (Y)/R(X). Hence, I=10 logR (Y)/R(X) 
(Y)/R(X)=10 log 1.8/1.4.apprxeq.1 (dB), meaning an improvement in antenna 
gain by about 1 (dB). 
In summary, it will be seen that the present invention provides portable 
radio equipment which has a thin handy configuration and, yet, insures a 
sufficiently high antenna gain. 
Various modifications will become possible for those skilled in the art 
after receiving the teachings of the present disclosure without departing 
from the scope thereof.