1. Field of the Invention
The present invention relates to an antenna device that can be tuned to wide band frequencies.
2. Description of the Related Art
A known antenna device 10 is described with reference to
The known antenna device resonates with a particular frequency. Thus, when the known antenna device receives over wide bands, its reception sensitivity in frequencies other than the particular frequency decreases.
It is an object of the present invention to provide an antenna device by which good reception sensitivity can automatically be obtained in wide bands.
According to an aspect of the present invention, an antenna device is provided which includes a prism-shaped or plate-shaped base member made of a dielectric or magnetic material, band-shaped first and second radiation conductors wound around the base member and connected to each other, and a band-shaped third radiation conductor wound around the base member and connected to the second radiation conductor. The first and second radiation conductors are respectively formed by a plurality of divided first radiation conductor portions and a plurality of divided second radiation portions, and the divided first radiation conductor portions are connected in series by first variable capacitance elements. The divided second radiation conductor portions are connected in series by second variable capacitance elements, and a node between the first and second radiation conductors is used as a feeding end.
Preferably, the first radiation conductor resonates with a high range of the UHF band within a variable capacitance range of the first variable capacitance elements, and a series radiation conductor comprising the second and third radiation conductors resonates with a low range of the UHF band within a variable capacitance range of the second variable capacitance elements.
The variable capacitance elements may include varactor diodes, and a tuning voltage may be applied to each varactor diode through each radiation conductor.
According to the present invention, an antenna device includes a prism-shaped or plate-shaped base member made of a dielectric or magnetic material, band-shaped first and second radiation conductors wound around the base member and connected to each other, and a band-shaped third radiation conductor wound around the base member and connected to the second radiation conductor. The first and second radiation conductors are respectively formed by a plurality of divided first radiation conductor portions and a plurality of divided second radiation conductor portions are connected in series by first variable capacitance elements. The divided second radiation conductor portions are connected in series by second variable capacitance elements, and a node between the first and second radiation conductors is used as a feeding end. Thus, resonations with two frequencies can be established and each resonant frequency can be changed.
In addition, according to the present invention, the first radiation conductor resonates with a high range of the UHF band within a variable capacitance range of the first variable capacitance elements, and a series radiation conductor comprising the second and third radiation conductors resonates with a low range of the UHF band within a variable capacitance range of the second variable capacitance elements. Television signals in two ranges of the UHF band can be received.
In addition, according to the present invention, the variable capacitance elements may include varactor diodes, and a tuning voltage may be applied to each varactor diode through each radiation conductor. Thus, television signals in two ranges can simultaneously be received.
An antenna device 1 of the present invention is described below with reference to FIGS. 1 to 3.
In
Similarly, the second radiation conductor 23 is also formed by a plurality of divided portions. Among divided second radiation conductor portions 23a, 23b, and 23c, two adjacent conductors are connected to each other by each of second variable capacitance elements (varactor diodes) 26 (26a to 26c). The third radiation conductor 24 is connected to the second radiation conductor 23c by the variable capacitance element 26c. The first variable capacitance element 25 and the second variable capacitance element 26 are provided on an upper surface of the base member 21.
The first radiation conductor portion 22d and the second radiation conductor portion 23a are connected to each other by a connection conductor 27 formed on the upper surface of the base member 21. In the vicinity of the connection conductor 27, a ground conductor 28 and a feeding conductor 29 are formed. The ground conductor 28 and the feeding conductor 29 extend to side surfaces of the base member 21. The connection conductor 27 is connected to the ground conductor 28 by an impedance-matching capacitor 30 and is connected to the feeding conductor 29 by a coupling capacitor 31.
The antenna device 1 having the above-described configuration is used in, for example, a portable device (e.g., a cellular phone) assumed to receive analog television broadcasting or digital terrestrial broadcasting, and is mounted on a motherboard (not shown) of the portable device. The feeding conductor 29 is connected to a tuner circuit (RF) formed on the motherboard. A tuning voltage Vt is supplied from the motherboard to the first radiation conductor portion 22b, and the second radiation conductor portions 23a and 23c through resistors. The first radiation conductor portions 22a and 22c, the second radiation conductor portion 23b, and the third radiation conductor 24 are grounded for DC on the motherboard by resistors. This applies the tuning voltage Vt between two ends of the first variable capacitance elements 25 and between two ends of the second variable capacitance elements 26.
The connection conductor 27 serves as a feeding end P, an end of the first radiation conductor portion 22a serves as a first open end Q1, and an end of the third radiation conductor 24 serves as a second open end Q2.
An electrical length of the first radiation conductor 22 is set so that a resonance occurs with a high range (for example, 620 MHz to 770 MHz) of the UHF band within a variable capacitance range of each first variable capacitance element 25. An electrical length of the entirety of the second radiation conductor 23 and the third radiation conductor 24 is set so that a resonance occurs with a low range (for example, 470 MHz to 620 MHz) of the UHF band within a variable capacitance range of the first variable capacitance element 26.
Part A of
When establishing a resonance with a minimum frequency of 620 MHz in the high band by using the first radiation conductor 22, as shown in part D of
Since the same tuning voltage is applied to the first variable capacitance elements 25 and the second variable capacitance elements 26, television signals on two channels corresponding to the high band and the low band are input to the tuner circuit. Therefore, a television signal in either band can arbitrarily be selected in the tuner circuit without switching the bands.
Number | Date | Country | Kind |
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2004-325463 | Nov 2004 | JP | national |