Communications: radio wave antennas – Antennas – Spiral or helical type
Reexamination Certificate
1999-08-03
2001-04-10
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Spiral or helical type
C343S702000
Reexamination Certificate
active
06215456
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an antenna unit using a helical antenna employed mainly in a radio paging receiver such as a pager and a radio receiver device using the same.
2. Description of the Related Art
In the radio paging receiver such as the pager in the prior art, normally the loop antenna is used as the antenna unit. A configuration of the antenna tuning control circuit in the loop antenna for the pager in the prior art will be explained with reference to
FIGS. 13 and 14
.
As shown in
FIG. 13
, the antenna tuning control circuit is constructed such that the impedance matching circuit
102
is connected to the antenna
101
, the central processing unit (CPU)
104
is connected to the control input terminal of the impedance matching circuit
102
via the low pass filter (LPF)
103
, and the high frequency amplifier
105
and the mixer
106
are connected to the output terminal of the impedance matching circuit
102
. The receiving frequency of the antenna
101
and the impedance matching circuit
102
can be set by inputting the control voltage from the CPU
104
after noise components are removed from the control voltage by the LPF
103
. The LPF
103
consists of the resistor R
1
and the capacitor C
1
. The received signal being set at the receiving frequency as above is amplified by the high frequency amplifier
105
and then set out to the receiver circuit including the mixer
106
at the succeeding stage.
The loop antenna employed as the antenna
101
is made up of antenna material such as metal, etc. which has a very short loop length (length about ⅕&lgr; to {fraction (1/10)}&lgr;, e.g., the loop length of about 15 cm to 10 cm when the receiving frequency band is set to 280 MHz) relative to the wavelength. Therefore, since the loop antenna has a very narrow frequency bandwidth, the frequency setting is needed every receiving frequency and thus the impedance matching is performed by the impedance matching circuit
102
each time.
FIG. 14
shows a concrete configuration of the antenna
101
and the impedance matching circuit
102
shown in FIG.
13
. The antenna
101
is composed of antennas L
1
, L
2
which are formed by a circuit pattern whose equivalent circuit is given by two series-connected coils, etc. The impedance matching circuit
102
is constructed such that a variable capacitor (trimmer capacitor) TVC and a variable capacitance diode (varactor diode) DVC are connected in series, and the variable capacitance diode DVC is grounded via a resistor R
2
and also grounded via a capacitor C
2
to pass a high frequency component. These antennas L
1
, L
2
are connected in parallel with the variable capacitor TVC and the variable capacitance diode DVC.
The variable capacitor TVC is provided to absorb variation of inductance of the antenna. The resonance frequency of the antennas L
1
, L
2
can be changed by varying the capacitance to be set to the receiving frequency f
0
. The variable capacitance diode DVC is provided to change the receiving frequency to another receiving frequency. The receiving frequency can be set by applying the control voltage from the CPU
104
every channel. It is possible to change the receiving frequency by adjusting the impedance in this manner.
The loop antenna has the problem that, if such loop antenna is located away from the human body, reduction in the antenna gain of about 5 dB is caused at the frequency of the 280 MHz band, for example, because of lost of the body effect. In recent, applications of the radio paging receiver are broadened other than the application as the so-called “calling terminal”. For example, there are applications as the information receiving terminal, the equipment controlling receiver terminal, etc. If the radio paging receiver is utilized as the information receiving terminal or the equipment controlling receiver terminal, it is often employed in a free space other than the neighborhood of the human body. In this case, improvement of the antenna gain due to the body effect cannot be expected. In addition, a null point is generated in the antenna radiation pattern since directivity of the loop antenna exhibits the 8-shaped characteristic, so that there is the case where the sufficient antenna characteristic cannot be guaranteed as the receiver.
According to a configuration of the above example in the prior art, in order to set the impedance at the receiving frequency f
0
, the impedance matching circuit which consists of variable capacitance elements such as the variable capacitor TVC, the variable capacitance diode DVC, etc. is needed to thus increase the configuration of the device in size. This is disadvantageous from the viewpoints of miniaturization and cost reduction by reducing the parts packaging area. In addition, in order to change the receiving frequency f
0
into another receiving frequency, the receiving frequency switching circuit which can set the channel by applying the control voltage from the CPU to the variable capacitance diode DVC every change of the channel is needed. Therefore, there is the problem that both the configuration of the device and its operation become complicated. In particular, if the antenna unit is separated from the receiver to use as an external antenna unit, a control line for applying an antenna control voltage from the CPU in addition to the receiving signal transmission line is also needed. Therefore, there is caused the problem that a cable wiring becomes complicated.
In the case that the whip antenna is employed as the external antenna unit, the large size antenna which has a vertical length of 25 cm, even if the ¼&lgr; antenna is employed, for example, is required at the 280 MHz band, and ideally the whip antenna is installed on the ground plate (referred to as a “GND plate” hereinafter) such as the iron plate, etc. as the installing location. Therefore, there are the problems that not only the size of the device is increased but also the installing location of the antenna unit is restricted.
SUMMARY OF THE INVENTION
The present invention has been made in light of the above problems and it is an object of the present invention to provide an antenna unit which can be employed in an information receiving terminal, an equipment controlling receiver terminal, etc. to be employed mainly in a free space, can eliminate a complicated impedance matching circuit, a frequency varying circuit, etc., can has non-directional without a null point in a directivity, can be constructed smaller in size and lower in production cost than a loop antenna, and can assure sufficient antenna characteristics in all directions and also achieve size reduction and simplification in configuration and reduction in cost, and a radio receiver device using the same.
In order to overcome the above problems, an antenna unit set forth in first aspect of the present invention, comprising a circuit substrate on which a receiver circuit is mounted; and a helical antenna connected to the circuit substrate and arranged substantially along one side of the circuit substrate; wherein impedance of the antenna unit can be adjusted at a desired frequency by changing an angle of the helical antenna relative to the circuit substrate.
An antenna unit set forth in second aspect of the present invention, comprising a circuit substrate on which a receiver circuit is mounted; and a helical antenna connected to the circuit substrate and arranged substantially along one side of the circuit substrate; wherein impedance of the antenna unit can be set at a desired frequency by arranging the helical antenna such that an angle of the helical antenna relative to the circuit substrate is set to a predetermined value.
According to the configuration in first aspect, the non-directional antenna unit which is small in size and low in cost and has no null point can be implemented by providing the antenna unit which has the helical antenna and the circuit substrate. Also, in first aspect, since the impedance of the antenna unit can be adjusted at a desire
Ho Tan
Matsushita Electric - Industrial Co., Ltd.
Pearne & Gordon LLP
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