Communications: radio wave antennas – Antennas – With radio cabinet
Reexamination Certificate
1997-04-07
2001-05-29
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
With radio cabinet
C343S749000, C343S866000
Reexamination Certificate
active
06239753
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a transmitter-and-receiver device housing an antenna therein, and more particularly to an improved device applicable to a receiver of a battery-type keyless entry system mounted on a vehicle.
2. Discussion of the Related Art
There are conventionally employed a Yagi antenna or a helical antenna as a UHF beam antenna particularly in a band between 300 MHz and 400 MHz. Since the Yagi antenna is bulky and cannot be installed within a small transmitter-and-receiver device, the helical antenna is employed as an antenna internally installed in such a device.
FIG. 19
shows a schematic perspective view of a conventional transmitter-and-receiver device
201
housing a pair of helical antennas
202
, and
FIG. 20
shows a schematic front view of the device. An earthing conductor
204
is disposed below a lower wall of a print board
203
and a transmit-and-receive circuit section (not shown in drawings) is mounted on an upper wall of the board
203
. The pair of helical antennas
202
are connected in parallel and disposed in an orthogonal relationship wherein helical axes thereof are in parallel with the print board
203
. Each one end of the helical antennas
202
is connected with a feeder print pattern
205
connected with the transmit-and-receive circuit section.
The helical antenna
202
is of a dipole type to serve both as a loading coil function for increasing an electric length of an antenna (viz. for decreasing the antenna length) and an antenna function, but not satisfactory for miniaturizing and thinning the transmitter-and-receiver device
201
. In order to miniaturize and thin the transmitter-and-receiver device
201
housing the helical antenna
202
, it can be proposed to decrease a coil diameter D and a whole length L of the helical coil
202
and to lower a whole height H of the antenna.
Decreasing the coil diameter D and the whole length L of the helical antenna
202
decreases a volume (an effective volume of the antenna) for receiving and transmitting a radio wave, whereby unfavorably the receive sensitivity of the transmitter-and-receiver device
201
is lowered and the transmit power is decreased.
A radio wave is radiated from a slit space between the helical antenna
202
and the print board
203
. As the whole height H of the helical antenna
202
is lowered, the gap “d” is decreased and a transmit-and-receive resistance (radiation resistance) is increased so that a radio wave is hard to be radiated or injected.
The helical antenna
202
has the disadvantages that an input impedance viewed from the feeder print pattern or portion
205
is too small to make an impedance matching and its loss is large because the electrical length of the antenna has to be designed to be ¼ of a wavelength in use.
In
FIG. 22
there is shown a conventional transmitter-and-receiver device
207
provided with an antenna easy for impedance matching. In the device
207
, a rear end of an antenna body
209
disposed in parallel with a print board
208
is bent toward the board
208
, and an earth end
210
formed on the rear end is fixed to the print board
208
to be electrically connected to an earthing conductor
211
of the board. A front end of the antenna body
209
is an open end
212
. A feeder line
214
is extending from a middle of a portion of the antenna body
209
in parallel with the board
208
to connect the antenna
209
with a transmit-and-receive circuit
213
. A tip end of the feeder line
214
is fixed to the print board
208
to be connected with the transmit-and-receive circuit
213
disposed on the board.
Thus, F-shaped antenna
215
is formed by the antenna body
209
and the feeder line
214
, and provided with the earth end
210
at one end thereof across the feeder line
214
and the open end
212
at another end thereof. The input impedance can be easily adjusted by moving the feeder position on the antenna body
209
from the earth end
210
and the open end
212
. The transmitter-and-receiver device
207
provided with the antenna
215
is not proper for miniaturizing the antenna and the device because the whole length of the antenna must be designed to be &lgr;/4 of a desired frequency.
SUMMARY OF THE INVENTION
It is, therefore, a primary object of this invention to provide an improved compact transmitter-and-receiver device in which an antenna may be miniaturized and thinned without decreasing a receive sensitivity and increasing a transmit-and-receive resistance.
It is a further object of this invention to provide an improved transmitter-and-receiver device which is provided with an antenna disposed to be parallel with a print board to miniaturize the antenna or the device.
According to a first aspect of this invention there is provided a transmitter-and-receiver device including a circuit board having an earthing conductor and a transmit-and-receive circuit section which are disposed on the board, a loading coil disposed on the circuit board, and an antenna electrically connected with the transmit-and-receive circuit section through the loading coil. The transmitter-and-receiver device includes a transmitter, a receiver, and a transmitter-and-receiver. The loading coil is disposed to increase an electric length of the antenna and to reduce the antenna length, and also called as an extension coil. The antenna and the loading coil are separated and the loading coil is mounted on the circuit board, so that an antenna of a wire type or a belt type other than the coil type can be employed and thinned. In other words, the antenna is thinned by a coil diameter of a conventional helical antenna, and the transmitter-and-receiver device is miniaturized. By thinning the antenna the distance (a height of the antenna) between the antenna and the circuit board can have room, whereby the transmit-and-receive resistance is decreased and drop of an efficiency of the antenna is relatively reduced even if the transmitter-and-receiver device is miniaturized.
Since a phase of a signal necessary for resonance in the antenna of this invention is for the most part (viz. about &pgr;/2) served by a loading coil, the phase is almost arranged at an open end of the antenna and the drop of receive sensitivity and the transmit power is minimized in miniaturizing the transmitter-and-receiver device.
When the antenna is necessary to have a different frequency specification, the loading coil has only to be replaced without changing a main body of the antenna, and components can be in common use with reducing its manufacturing cost.
The loading coil of the transmitter-and-receiver device may employ a print coil, a chip coil or a small wound coil, or the like. Thus loading coil can be easily mounted on the circuit board. Accordingly, the productivity of the device is improved and its manufacturing cost is reduced.
The antenna of the transmitter-and-receiver device according to this invention may be horizontally bent from a vertical direction on a surface of the circuit board in an L-shape without vertically standing on the surface of the circuit board, so that the height of the device can be reduced and the device can be miniaturized and thinned.
A portion of the antenna in parallel with the surface (the right side) of the circuit board may be bent within a plane in parallel with the surface of the circuit board, or the antenna may be bent within the plane in parallel with the circuit board and along a peripheral edge of the board.
Thus, if the antenna is extended by bend within a plane parallel to the board, its whole length can be prolonged without bulking the antenna. Thus, the transmitter-and-receiver device can be made in a compact construction with improvement of the transmit-and-receive efficiency.
If necessary, an antenna support may be disposed between the antenna and the circuit board for supporting the antenna. By supporting the antenna with the antenna support, the antenna is prevented from being swung by external vibration with improving a vibration-resistant of the antenna. Accordingly,
Kado Seiji
Sato Kazuhiko
Foley & Lardner
Omron Corporation
Phan Tho
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