# Patent

## Title
Antenna device having enhanced reception sensitivity in wide bands

## Abstract

An antenna device includes a rectangular parallelepiped base member made of a dielectric or magnetic material, a band-shaped first radiation conductor, including a plurality of divided first radiation conductor portions, spirally wound around the base member, a plurality of variable capacitance elements connected between pairs of adjacent portions and disposed on a upper surface of the base member, and a feeding conductor for supplying a tuning voltage to the variable capacitance elements. The first radiation conductor has first radiation conductor parts respectively formed on upper, lower, and rear side surfaces of the base member and first connecting through-holes passing through the upper and lower surfaces are provided in the base member, and the first radiation conductor part on the upper surface and the first radiation conductor part on the lower surface are connected to each another by the first through-holes, and the feeding conductor is disposed on the front surface of the base member.

## Background
BACKGROUND OF THE INVENTION 
1. Field of the Invention
The present invention relates to an antenna device that can be tuned to wideband frequencies.
2. Description of the Related Art
A known antenna device 10 is described with reference to FIGS. 4 and 5. A conductor 12 made of a fine metal wire is spirally wound around a ferrite magnetic core 14. Ends of the conductor 12 form connection terminals 16 and 18. The conductor 12 includes a plurality of divided conductor portions 12′, and the conductor portions 12′ are connected to one another by a plurality of capacitance elements 20. As shown in FIGS. 4 and 5, the antenna device 10 is such that the capacitance elements 20 are physically distributed in the conductor 12 to have a closed loop form. The antenna device 10 responds to a particular frequency (see, for example, Japanese Unexamined Patent Application Publication No. 51-83755 (FIGS. 1 and 3) and its corresponding U.S. Pat. No. 3,946,397).
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.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an antenna device by which enhanced 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 rectangular parallelepiped base member made of a dielectric or magnetic material, a band-shaped first radiation conductor, including a plurality of divided first radiation conductor portions, spirally wound around the base member, a plurality of variable capacitance elements connected between pairs of adjacent portions among the divided first radiation conductor portions and disposed on an upper surface of the base member, and a feeding conductor for supplying a tuning voltage to the variable capacitance elements. The first radiation conductor has first radiation conductor parts respectively formed on upper, lower, and rear side surfaces of the base member and first connecting through-holes passing through the upper and lower surfaces are provided in the base member, and the first radiation conductor part on the upper surface and the first radiation conductor part on the lower surface are connected to each another by the first through-holes, and the feeding conductor is disposed on a front surface of the base member.
Preferably, the variable capacitance elements include varactor diodes, the adjacent divided first radiation conductor portions are alternately connected between pairs of anodes of the varactor diodes and between pairs of cathodes of the varactor diodes, and a ground conductor formed at least on the lower and front surfaces is provided at one end of the base member. Second through-holes passing through the upper and lower surfaces may be provided and connected to the ground conductor on the lower surface, and may be connected to the divided first radiation conductor portions, which are connected between the varactor diodes on the upper surface through a first resistor. The first radiation conductor portions, which are connected between the pairs of cathodes of the varactor diodes, may be connected to the feeding conductor by a second resistor, and the first and second resistors may be disposed on the upper surface of the base member.
An antenna feeding conductor coupled with the first radiation conductor is disposed on the front surface.
The antenna device may further include a second radiation conductor wound around the base member. The second radiation conductor may be connected to the first radiation conductor by switching elements, with the switching elements disposed on the upper surface of the base member, and a switching voltage feeding conductor for applying a switching voltage for controlling the switching elements to be opened and closed may be disposed on the front surface of the base member.
According to the present invention, an antenna device includes a rectangular parallelepiped base member made of a dielectric or magnetic material, a band-shaped first radiation conductor, including a plurality of divided first radiation conductor portions, spirally wound around the base member, a plurality of variable capacitance elements connected between pairs of adjacent portions among the divided first radiation conductor portions and disposed on an upper surface of the base member, and a feeding conductor for supplying a tuning voltage to the variable capacitance elements. The first radiation conductor has first radiation conductor parts respectively formed on upper, lower, and rear side surfaces of the base member and first connecting through-holes passing through the upper and lower surfaces are provided in the base member, and the first radiation conductor part on the upper surface and the first radiation conductor part on the lower surface are connected to each another by the first through-holes, and the feeding conductor is disposed on a front surface of the base member. Thus, in addition to obtaining good reception sensitivity, a bias feeding conductor for feeding a variable capacitance element tuning voltage can be disposed on a front surface of a base member, which is effective in reducing antenna device size.
In addition, according to the present invention, the variable capacitance elements include varactor diodes, the adjacent divided first radiation conductor portions are alternately connected between pairs of anodes of the varactor diodes and between pairs of cathodes of the varactor diodes, and a ground conductor formed at least on the lower and front surfaces is provided at one end of the base member. Second through-holes passing through the upper and lower surfaces are provided and connected to the ground conductor on the lower surface, and are connected to the divided first radiation conductor portions, which are connected between the varactor diodes on the upper surface through a first resistor. The first radiation conductor portions, which are connected between the pairs of cathodes of the varactor diodes, are connected to the feeding conductor by a second resistor, and the first and second resistors are disposed on the upper surface of the base member. Thus, antenna device size can further be reduced.
According to the present invention, an antenna feeding conductor coupled with the first radiation conductor is disposed on the front surface. Thus, establishing connection to a receiver circuit is facilitated.
Moreover, according to the present invention, an antenna device further includes a second radiation conductor wound around the base member. The second radiation conductor is connected to the first radiation conductor by switching elements, with the switching elements disposed on the upper surface of the base member, and a switching voltage feeding conductor for applying a switching voltage for controlling the switching elements to be opened and closed is disposed on the front surface of the base member. Thus, an antenna device that performs reception while switching two bands can be reduced in size.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an antenna device of the present invention;
FIG. 2 is a lower view of the antenna device of the present invention;
FIG. 3 is an equivalent circuit diagram of the antenna device of the present invention;
FIG. 4 is a perspective view of a known antenna device; and
FIG. 5 is an equivalent circuit diagram of the known antenna device.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
An antenna device 1 of the present invention is described below with reference to FIGS. 1 to 3. FIG. 1 is a perspective view, FIG. 2 is a lower view of the antenna device 1, and FIG. 3 shows an equivalent circuit.
Referring to FIGS. 1 and 2, on upper, rear side, and lower surfaces of a rectangular parallelepiped base member 21 made of a dielectric or magnetic material, a band-shaped first radiation conductor 23 in which radiation conductor portions are formed is spirally wound is formed through a plurality of first through-holes (two-sided conduction holes) 22 (22a to 22h) penetrating the upper and lower surfaces of the base member 21. The first radiation conductor 23 includes a plurality of divided radiation conductor portions 23a to 23e, and the divided radiation conductor portions 23a to 23e are connected in series by varactor diodes (variable capacitance elements) 24 (24a to 24d). As shown in FIG. 3, among the varactor diodes 24, pairs of adjacent varactor diodes each have opposing anodes and opposing cathodes.
In other words, the cathode of the leftmost varactor diode 24a is connected to the radiation conductor portion 23a, and the anode of the varactor diode 24a is connected to the radiation conductor portion 23b. The anode of the following varactor diode 24b is connected to the radiation conductor portion 23b, and the cathode of the varactor diode 24b is connected to the radiation conductor portion 23c. The cathode of the following varactor diode 24c is connected to the radiation conductor portion 23c, and the anode of the varactor diode 24c is connected to the radiation conductor portion 23d. The anode of the following varactor diode 24d is connected to the radiation conductor portion 23d, and the cathode of the varactor diode 24d is connected to the radiation conductor portion 23e. 
At one end of the base member 21, a ground conductor 25 is formed on four surfaces, that is, upper, lower, rear side, and front surfaces of the base member 21. On the upper surface of the base member 21, an impedance-matching capacitor 26 is disposed which connects, to the ground conductor 25, the radiation conductor portion 23a at a position closest to the ground conductor 25. The radiation conductor portion 23a is coupled with an antenna feeding conductor 28 by a first coupling capacitor 27. The antenna feeding conductor 28 extends from the upper surface to the front surface. 
A first resistor 29a is connected to the radiation conductor portion 23a by the first through-hole 22a, and the first resistor 29a is connected to a bias feeding conductor 30. The bias feeding conductor 30 extends from the upper surface to the front surface. A second resistor 31a is connected to the following radiation conductor portion 23b by the first through-hole 22b, and the second resistor 31a is connected to a second through-hole 32a. A first resistor 29b is connected to the following radiation conductor portion 23c by the first through-hole 22d, and the first resistor 29b is connected to the bias feeding conductor 30. A second resistor 31b is connected to the following radiation conductor portion 23d by the first through-hole 22f, and the second resistor 31b is connected to the second through-hole 32b. A first resistor 29c is connected to the following radiation conductor portion 23e by the first through-hole 22h, and the first resistor 29c is connected to the bias feeding conductor 30. The first and second resistors 29 and 31 are also disposed on the upper surface of the base member 21.
The second through-holes 32a and 32b are two-sided conduction holes, and they establish connection to the ground conductor 25 on the back side. In the above-described connections, each varactor diode 24 has an anode connected to the ground conductor 25 and a cathode connected to the bias feeding conductor 30.
An end of the last divided first radiation conductor portion 23e serves as a first open end, and is connected to a diode (switching element) 34 by a second coupling capacitor 33 disposed on the upper surface of the base member 21. A node between the second coupling capacitor 33 and the diode 34 is connected to a switching voltage feeding conductor 36a by a third resistor 35a. The second coupling capacitor 33 and the diode 34 are disposed on the upper surface of the base member 21, and the switching voltage feeding conductor 36a extends from the upper surface to the front surface. A second radiation conductor 37 is connected to the diode 34. The second radiation conductor 37 is also wound around the base member 21, and is partly wound through a third through-hole 38. A third resistor 35b is connected to the second radiation conductor 37 through the third through-hole 38, and is connected to a switching voltage feeding conductor 36b. The switching voltage feeding conductors 36a and 36b are arranged in parallel on the front surface.
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 television broadcasting, and is mounted on a motherboard of the portable device. The antenna feeding conductor 28 is connected to a tuner circuit (RF) formed on the motherboard. In addition, a tuning voltage Vt is supplied from the motherboard to the bias feeding conductor 30, and the ground conductor 25 is grounded on the motherboard. This applies the tuning voltage Vt between ends of the varactor diodes 24. Also, the switching voltage feeding conductors 36a and 36b are supplied with a switching voltage from the motherboard.
An electrical length of the first radiation conductors 23 is set to resonate with, for example, the UHF band (470 MHz to 770 MHz) within a variable capacitance range of the varactor diodes 24. Therefore, when the diode 34 is off (opened), the antenna device 1 can receive a television signal having an arbitrary frequency in the UHF band since an end of the radiation conductor portion 23e serves as an open end.
In addition, the electrical length of the entirety of the first radiation conductors 23 and the second radiation conductor 37 so as to resonate with the VHF band within a variable capacitance range of the varactor diode 24, when the switching element 34 is turned on (short-circuited), the end of the second radiation conductor 37 serves as an open end, whereby the antenna device 1 can receive a television signal.
In the present invention, the first radiation conductor 23 is wound around the base member 21 through the first through-holes 22. Thus, the bias feeding conductor 30 for feeding the tuning voltage to the varactor diode 24 can be disposed on the front surface, which is effective in reducing the size of the antenna device 1.

## Claims

1. An antenna device comprising:
a rectangular parallelepiped base member made of a dielectric or magnetic material;
a band-shaped first radiation conductor, including a plurality of divided first radiation conductor portions, spirally wound around the base member;
variable capacitance elements connected in series between adjacent pairs of the divided first radiation conductor portions and disposed on an upper surface of the base member; and
a feeding conductor for supplying a timing voltage to the variable capacitance elements, wherein
the first radiation conductor has first radiation conductor parts respectively formed on upper, lower, and rear side surfaces of the base member and first connecting through-holes passing through the upper and lower surfaces are provided in the base member;
the first radiation conductor part on the upper surface and the first radiation conductor part on the lower surface are connected to each another by the first through-holes, and the feeding conductor is disposed on a front surface of the base member;
the variable capacitance elements includes varactor diodes, the adjacent divided first radiation conductor portions are alternately connected between pairs of anodes of the varactor diodes and between pairs of cathodes of the varactor diodes, and a ground conductor formed at least on the lower and front surfaces is provided at one end of the base member;
second through-holes passing through the upper and lower surfaces are provided and connected to the ground conductor on the lower surface, and are connected between the varactor diodes on the upper surface by a first resistor; and
the first radiation conductor portions, which are connected between the pairs of cathodes of the varactor diodes, are connected to the feeding conductor by a second resistor, and the first and second resistors are disposed on the upper surface of the base member.

2. The antenna device according to claim 1, wherein an antenna feeding conductor coupled with the first radiation conductor is disposed on the front surface.

3. The antenna device according to claim 1, further comprising a second radiation conductor wound around the base member,
wherein the second radiation conductor is connected to the first radiation conductor by switching elements, with the switching elements disposed on the upper surface of the base member, and a switching voltage feeding conductor for applying a switching voltage for controlling the switching elements to be opened and closed is disposed on the front surface of the base member.