JP2003298341A - Tuning antenna - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To obtain an ultra-small and high-gain tunable antenna. SOLUTION: A conductive film constituting a microstrip is formed on the front and back surfaces having a dielectric constant of about 8, and an open end thereof is connected via a series circuit of a bias source, two sets of variable capacitance diodes and a resistor. The variable capacitance diode and the ground are connected by a variable capacitance diode in the opposite direction to provide a tuning capacitance. The capacitance of the variable capacitance diode changes according to the bias voltage, and the tuning frequency as an antenna can be changed. The other variable capacitance diode is used for matching adjustment. An antenna tunable to the UHF band of television broadcasts can be obtained in a size that can be mounted on the shield case of the TV tuner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small tunable antenna, and more particularly to a tunable antenna using a dielectric capable of receiving in the UHF band.

[0002]

2. Description of the Related Art UHF band terrestrial digital television broadcasting is scheduled to start from 2003, and a small size television screen can be received even on a liquid crystal screen of a personal digital assistant (PDA). A small tunable antenna that can be built into an adapter card such as a PDA or mobile phone is required.

Conventional terrestrial television broadcasting is analog broadcasting, and VHF-L band, VHF-H band and UHF band are used. However, in the main VHF band, the TV antenna becomes large and the portable TV is in a practical range. Has not reached. In addition, V
90-180MHz for HF-L band, 170-222MHz for VHF-H band
And the UHF band is 470-770 MHz.

Since the terrestrial digital television broadcasting uses the UHF band, a smaller antenna than the VHF band can be used. However, even at 500 MHz, the 1/2 wavelength becomes 300 mm, and the standard antenna size requires 300 mm. Conventionally, a half-wavelength broadband non-tuning type metal conductor antenna (dipole type, Yagi type, rod type, etc.) or a one-wavelength metal conductor loop type, which is designed under the condition that the antenna is not close to earth, is used.
Since the basic size of the standard antenna is 1/2 wavelength, the size of the UHF antenna in the 500MHz band is 300mm as described above, and it is attached to a typical PDA body size of 60mm x 150mm or a smaller mobile phone. Too big to be.

In order to mount a memory card-sized TV receiving adapter such as a compact flash (registered trademark) for insertion into a PDA or a mobile phone, etc., a TV antenna is simultaneously mounted on the memory card in addition to a micro TV tuner. There is a need. Considering that the UHF band TV tuner is expected to have a size of 35 mm × 18 mm × 5 mm, it should be 30 mm × 18 mm × 5 mm or less.

Conventional television antennas are generally metallic conductors 1
It is a dipole type with two wavelengths or a one wavelength loop type and is a non-tuning type. There is a telescopic rod antenna, but it is not a tuned type because it adjusts the gain by mechanical expansion and contraction. The problem with the 1/2 wavelength type is that the width is narrow, but the size length is almost twice as long as the 1/4 wavelength type. Also, the problem of the one-wavelength loop type is one
That is, the area increases with a square cross-sectional area of a quarter wavelength.

[0007]

The compact flash (registered trademark) of a typical PDA with a size of 74 mm × 138 mm and an option card of a mobile phone has a size of about 40 mm × 30 mm, and the antenna is on the compact flash (registered trademark). It is necessary to install it together with the UHF band TV tuner section. Further, it is required to have a planar ultra-miniaturized structure having no movable portion and no protrusion. In order to obtain high gain with a very small size, it is necessary to have a tuning type structure that adjusts matching with respect to frequency changes. The present invention provides a tunable antenna that meets such requirements.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems by shortening the conductor using a dielectric material and connecting a variable capacitance diode to make the frequency variable.

That is, in a tunable antenna in which a variable capacitance diode is connected to the antenna element to change the frequency, the antenna element has conductor films forming microstrips on the front and back surfaces of a rectangular parallelepiped dielectric, It is characterized in that the open end of the conductor film is connected to a bias source via two sets of variable capacitance diodes.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The components of the antenna of the present invention are:
(1) An antenna element in which a conductor has a quarter-wave structure microstrip structure with a short-circuit on one side and an open on one side in the dielectric, and (2) two sets of variable capacitance diodes, which are to be mounted on a printed wiring board. Completed by. Further, they may be integrated with the tuner unit.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. (A) is a bottom view of a dielectric, (B-1) is a plan view, and (B-
2) is a front view, (B-3) is a side view of the open end, and (B-
4) is a side view of the short-circuited end. A rectangular parallelepiped dielectric 15 having a printed conductor 14 formed thereon is mounted on the surface of a printed circuit board 12 having a conductor pattern 11 formed on one surface. Further, the inner conductor of a coaxial line (not shown) is connected to the RF terminal of the conductor pattern 11 and is connected to the RF section of the tuner.

The printed conductor 14 formed on the dielectric 15 constitutes a conductor portion of the antenna and acts as a microstrip formed on the front and back surfaces of the dielectric 15. Therefore, the surface in contact with the printed board 12 is connected to the conductor pattern which is grounded. On the open end side of the printed conductor 14, the printed conductor is formed so as to wrap around from the side surface of the dielectric to the bottom surface,
It is connected to a floating conductor pattern formed on the surface of the printed circuit board. As shown in FIG. 1 (B-1), this conductor pattern is connected to a bias source via two series resistors R and a variable capacitance diode VCD.

One of the above two sets of variable capacitance diodes VCD is connected via a capacitor C to a terminal RF which is connected to a coaxial line as a matching reactance. The other variable-capacitance diode VCD is connected singly or in series in opposite directions for improving linearity, and is connected to the ground GND as a variable tuning capacitor. The patterns are coaxial lines 19
And the inner conductor of is connected to the outer conductor.

FIG. 2 shows a state in which the antenna of FIG. 1 is incorporated in a memory card type television receiving adapter, which is directly mounted on the television tuner mounted on the receiving adapter board. By inserting this adapter into a PDA or a mobile phone, the received signal can be displayed on the screen.

FIG. 3 is an equivalent circuit diagram of the embodiment shown in FIG. The resonant frequency of the antenna is changed by the variable capacitance diode that changes the capacitance by the bias voltage from the bias source (Vt). At the same time, the coupling reactance is changed by another variable capacitance diode, and the reception signal of the antenna is matched and output from the coaxial line to the reception circuit in the entire frequency band.

FIG. 4 shows the relationship between the bias voltage and the tuning frequency of the tunable antenna according to the present invention. Bias voltage V
As t is increased, the tuning frequency also shifts to the higher direction,
It shows that V can be tuned in a wide band of about 800 MHz. This controls the frequency by changing the capacitance of the reactance (VCD) added between the open end of the 1/4 wavelength microstrip and GND, and inserts a variable capacitance diode in series between the receiving circuit terminal and the open end of the microstrip. The coupling capacitance is large on the low frequency side, and the coupling capacitance is small on the high frequency side to maintain matching in the entire frequency band. Figure 5 shows the SWR characteristics, where SWR <3
A bandwidth of 18 MHz with a good gain range is obtained.

The dielectric used as the antenna element has a permittivity of 8 and is 1 / V depending on the VCD connected in parallel.
It was possible to construct an antenna device that resonates four wavelengths with a size of 23 mm × 12 mm × 4 mm. This antenna has a thin structure with no moving parts, and the variable range of frequency is 470 to 770MHz.
The bandwidth of WR <3 is 18MHz, which is sufficiently wide compared to 6MHz of one TV channel.

Since the dielectric is mounted on the printed circuit board and the microstrip structure is adopted, the printed circuit board can be directly mounted on the shield case of the tuner.
The material of the dielectric can be arbitrarily selected, and a conductor film formed by another method can be used instead of the printed conductor. Also, the conductor pattern on the printed board can be changed as required.

[0019]

According to the present invention, a tunable antenna that can be integrated with a tuner in a television receiving adapter can be realized with a simple structure. Since it can cover the entire frequency band of UHF television broadcasting and has no moving parts, it can be made thin. Further, since the aperture is small with respect to the wavelength, it has a wide directivity, and the change in gain is small even if the mounted PDA or mobile phone tilts.

[Brief description of drawings]

FIG. 1 is a bottom view of (A) dielectric, (B-1) plan view, (B-2) front view, and (B-3) showing an embodiment of the present invention.
Side view, (B-4) Side view

FIG. 2A is a front view, FIG. 2B is a plan view, and FIG. 2C is a side view showing an embodiment of the present invention.

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

FIG. 4 is an explanatory diagram of characteristics of the tunable antenna according to the present invention.

FIG. 5 is an explanatory diagram of characteristics of the tunable antenna according to the present invention.

[Explanation of symbols]

11: Conductor pattern 12: Printed circuit board 14: Printed conductor 15: Dielectric VCD: Variable capacitance diode

Continued front page    (72) Inventor Yuri Gomachi             828 Hinohara, Tamagawa character, Tamagawa village, Hiki district, Saitama prefecture             Address Toko Co., Ltd. Tamagawa factory F term (reference) 5J045 AA02 AA05 DA09 EA07 HA06                       MA04 NA01                 5J046 AA01 AA02 AA04 AA07 AB13                       PA07                 5J047 AA01 AA02 AA04 AA07 AB13                       EF04 EF05

Claims (4)

[Claims] 1. A tunable antenna in which a variable capacitance diode is connected to an antenna element to change the frequency, and the antenna element is a conductor film forming a microstrip with one end short-circuited and the other end open on the front and back surfaces of a rectangular parallelepiped dielectric. A tunable antenna characterized in that the open end of its conductor film is connected to ground via a tuning variable capacitance diode and is connected to a bias source with a high impedance resistor. 2. A tunable antenna in which a variable capacitance diode is connected to an antenna element to change the frequency, wherein the antenna element is a conductor film forming a microstrip with one end short-circuited and the other end open on the front and back surfaces of a rectangular parallelepiped dielectric. The open end of the conductor film is connected to the bias source through two sets of parallel varactor diodes, and one of the varactor diodes serves as a tuning capacitance between the ground and the other is A tunable antenna characterized by being connected to a coaxial line as a reactance for matching adjustment. 3. An antenna element and a variable capacitance diode are 1
The tunable antenna according to claim 2, which is mounted on one printed wiring board. 4. The tunable antenna according to claim 3, wherein the tunable antenna is housed integrally with a tuner section in an adapter card of a portable device via an insulating layer.