JPH04213907A - Antenna system - Google Patents

Abstract

PURPOSE:To attain miniaturization and high efficiency while covering a broad band of transmission reception by varying a resonance frequency of the antenna system electrically so as to select the resonance frequency in response to the frequency of each time slot. CONSTITUTION:A varactor diode is employed for a capacitance change circuit 2. Then a voltage varying with a time slot of transmission reception is impressed connecting point between an antenna 1 and the varactor diode 2 via a choke coil. When the voltage is impressed, the capacitance of the varactor diode 2 is reduced and the resonance frequency gets higher, then the resonance frequency is switched by adjusting the impressed voltage.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an antenna device.
In particular, the present invention relates to an antenna device used in a TDMA system that performs simultaneous transmission and reception communications using different frequencies for transmission and reception.

[0002] In recent years, the number of car phone subscribers has increased rapidly, and new systems have been urgently developed to accommodate this increase. The next system aims to increase subscriber capacity, improve confidentiality, and diversify services through digitalization.

[0003] Particularly in the case of mobile phones, the goal is to reduce the device size to 150 cc or less with the same functions as car phones, and for this reason, it is necessary to make each element used smaller, more efficient, and lower in power consumption. This is the most important issue. Antennas are indispensable for mobile phone terminals, and these antennas are also required to be more compact and highly efficient than ever before.

0004

[Prior art and issues] Figure 7 shows the next generation digital mobile phone.
The frequency bands used in the car telephone system are shown, in this example the transmitting frequency fT and the receiving frequency fR
are placed 130 MHz apart, and the antenna device needs to cover a 150 MHz band from 810 to 960 MHz. This has a specific bandwidth of 17% (with a center frequency of 885MHz).
= 150/885), but a small antenna with a wide band exceeding 10% of the fractional band cannot be easily realized.

In other words, when the antenna is made smaller by lowering the resonant frequency by some means such as loading an inductance, the band characteristics of the antenna due to natural resonance (λ/2 for a dipole antenna, λ/2 for a monopole antenna)
4) is known to be narrower than that of 4 (resonance at 4). In this way, miniaturization of antennas and broadbandization have contradictory characteristics.

Furthermore, when matching is performed using a matching circuit, the band becomes narrower and the matching circuit causes loss, which tends to lower efficiency. In this way, when the transmitting and receiving frequency bands are separated as shown in FIG. 7, it is difficult to realize a small and highly efficient antenna that covers a wide transmitting and receiving frequency band with one antenna.

[0007]Also, a dual-frequency resonant antenna with resonance points in each band has been devised, but the structure is complicated and
There was a problem in that the adjustment was critical and easily influenced by nearby human bodies.

[0008] Therefore, it is an object of the present invention to realize a compact and highly efficient antenna device for use in a TDMA system to be adopted in the next generation digital mobile/car phone system while covering a wide band for transmission and reception. .

[0009]

[Means for solving the problem] In the TDMA system to be adopted in the next generation digital mobile/car phone system, time division is used to prevent transmission and reception time slots from overlapping on the time axis, as shown in Figure 8. Transmission is performed using three channels/carrier through multiplexing, and the antenna device is never used on both frequencies at the same time.

The present invention focuses on this point and solves the above problem by switching the resonant frequency according to the frequency of each time slot using means for electrically varying the resonant frequency of the antenna device. It is something to do.

In the antenna device of the present invention shown in FIG. 1(a), a capacitance change circuit 2 is connected in parallel with the antenna 1, and a voltage V that changes in accordance with the transmission/reception time slot is applied to the capacitance change circuit 2. It is configured as follows.

In addition, in the antenna device of the present invention shown in FIG. 1(b), an inductance changing circuit 3 is connected in series with the antenna 1, and a voltage V that changes in accordance with the transmission/reception time slot is applied to the inductance changing circuit 3. The configuration is such that the voltage is applied.

Furthermore, in the antenna apparatus of the present invention shown in FIG. The configuration is such that the voltage is applied to the switching circuit 6 to short-circuit the stub portion 5.

[0014]

[Operation] In the present invention shown in FIG. 1(a), a voltage V as shown in FIG. 2, which changes in accordance with the transmission/reception time slot, is applied to the capacitance changing circuit (2) to change its capacitance.

The equivalent circuit in this case is shown in FIG. 3(a), and when the capacitance decreases due to the above voltage application, the antenna 1 and the capacitance 2 constituting the distributed constant circuit as shown in FIG. The resonant frequency of the series resonant circuit will increase, and if the capacitance increases, the resonant frequency will decrease.

In the present invention shown in FIG. 1(b), the voltage V as shown in FIG.
is applied to the inductance changing circuit (3) to change its inductance.

The equivalent circuit in this case is shown in FIG. 3(b), and when the inductance 3 decreases due to the above voltage application, the distributed constant circuit of the antenna 1 and the inductance 3 are changed as shown in FIG. The resonant frequency of the series resonant circuit between the antenna 1 and the ground capacitance C (shown by the dotted line) will increase, and if the inductance increases, the resonant frequency will decrease.

In the present invention shown in FIG. 1(c), the voltage V as shown in FIG. 2 changes according to the transmission and reception time slots.
is applied to the switching circuit (3) to change its inductance.

The equivalent circuit in this case, as shown in FIG. 3(C), is composed of the resistance R0 of the conductor of the inverted F antenna 4, the radiation resistance Rr, the combined inductance L of the stub portion 5 and the antenna 4, and the resistance of the conductor of the inverted F antenna 4. A parallel resonant circuit is formed with the composite capacitance C of the ground capacitance, and the above voltage V is applied to the switching circuit 6 due to the above voltage application, thereby shorting the stub portion 5, and the above composite inductance L decreases. As a result, the resonant frequency of this parallel resonant circuit increases as shown in FIG.

[0020] In this way, by switching the resonant frequency according to the frequency used in each time slot, the antenna device can cover both transmitting and receiving bands as long as it satisfies the predetermined frequency band. This eliminates the need for broadband characteristics that have made it difficult to miniaturize the antenna device, making it possible to realize a compact and highly efficient antenna.

[0021]

Embodiments Hereinafter, embodiments of the antenna device according to the present invention will be described. In the drawings, the same reference numerals indicate the same or corresponding parts.

FIGS. 4(a) and 4(b) are similar to FIG. 1(a).
4(a) shows an embodiment of the antenna device according to the present invention shown in FIG. 4(a). In the embodiment shown in FIG. A voltage (see FIG. 2) that changes depending on the transmission/reception time slot is applied to the point via the choke coil 11. Note that the choke coil 11 is for preventing high frequency waves from leaking into the applied voltage V, and 10 indicates a power feeding section of the antenna 1.

In operation, when a voltage that changes in accordance with the transmission/reception time slot is applied to the varactor diode 2, the capacitance of the varactor diode 2 decreases and the resonant frequency increases as shown in FIG. Therefore, by adjusting this applied voltage V, the resonance frequency can be switched.

Furthermore, in the embodiment shown in FIG. 4(b), the capacitance changing circuit 2 is constituted by a series circuit of a capacitance 22 and a PIN diode 23, and the above applied voltage V is applied to the connection point through the choke coil 11. It is configured to give.

Therefore, in this case, since the PIN diode 23 is turned on by the applied voltage V, the capacitance 22 is
It will be switched between when it is separated from the In the latter case, the capacitance of the space connected in series with the antenna 1 is small, and in the former case, the resonant frequency is lowered by the capacitance 22 connected in series with the antenna 1.

FIG. 5 shows an embodiment of the antenna device according to the present invention shown in FIG. 1(b). In this embodiment, the inductance changing circuit 3
1 and a PIN diode 32 in parallel, and the applied voltage V is applied to both ends of this parallel circuit via choke coils 12 and 13.

In this embodiment, when the applied voltage V as shown in FIG. is in a state where the inductance 31 is not connected in series, and when the applied voltage V is not applied, the PIN diode 32 is off, so the inductance 31 is connected in series to the antenna 1, and resonance occurs as shown in FIG. The frequency will drop.

Although the monopole antenna has been described above, band switching can be performed in the same way for other types of antennas.

That is, FIG. 6 shows an embodiment of the antenna device using the inverted F antenna according to the present invention shown in FIG. 1(c). In this embodiment, the switching circuit 6
A PIN diode is used as the PIN diode.

Therefore, the applied voltage V is
When applied to the PIN diode 6 through
The side of the stub portion 5 of the antenna that is not on the feeder 10 side is short-circuited, and as explained in FIG. 3(c), the combined inductance L of the antenna 1 and the stub portion 5 decreases, causing resonance as shown in FIG. The frequency will increase. In this way, the resonant frequency can be switched by changing the position of the short stub using the PIN diode.

[0031]

As explained above, according to the antenna device according to the present invention, the resonant frequency can be switched according to the frequency of each time slot using means for electrically varying the resonant frequency of the antenna device. With this configuration, the broadband characteristics required of the antenna device can be relaxed, and the antenna can be of single resonance. Therefore, the antenna can be made smaller and more efficient.

[0032]

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the principle of an antenna device according to the present invention.

FIG. 2 is a time chart diagram showing changes in applied voltage V and resonant frequency of the antenna device according to the present invention.

FIG. 3 is an equivalent circuit diagram of the antenna device according to the present invention.

FIG. 4 is a circuit diagram showing an embodiment of the antenna device of the present invention.

FIG. 5 is a circuit diagram showing an embodiment of the antenna device of the present invention.

FIG. 6 is a circuit diagram showing an embodiment of the antenna device of the present invention.

FIG. 7 is a diagram showing frequency bands used in the next generation car telephone system.

FIG. 8 is a diagram showing transmission and reception timing by time division multiplexing of the next generation car telephone system.

[Explanation of symbols]

1 Antenna 2 Capacitance change circuit 3 Inductance change circuit 4 Inverted F antenna 5　Stub part 6 Switching circuit

Claims (3)

[Claims] [Claim 1] An antenna device characterized in that a capacitance change circuit (2) is connected in parallel with an antenna (1), and a voltage that changes according to a transmission/reception time slot is applied to the capacitance change circuit (2). . [Claim 2] An antenna device characterized in that an inductance changing circuit (3) is connected in series with the antenna (1), and a voltage that changes in accordance with the transmission/reception time slot is applied to the inductance changing circuit (3). . [Claim 3] A switching circuit (6) is connected to the matching short stub portion (5) of the inverted F antenna (4), and a voltage that changes according to the transmission/reception time slot is applied to the switching circuit (6). and the stub part (
5) An antenna device characterized by short-circuiting.