HK1052084A - Two-resonance antenna - Google Patents

Description

Dual-resonance antenna

Technical Field

The present invention relates to a dual resonance antenna which can be used in mutually separated frequency bands for use in a mobile phone, a simple mobile phone (PHS mobile phone), and the like.

Background

The number of users of portable telephones and PHS increases year by year, and the frequency available is insufficient due to the increase in users. In this way, when the available frequency is insufficient due to the increase of users, the frequency band of the cellular phone may be roughly divided into two types of frequency bands that can be used in the entire area and those that can be used in the urban area. For example, while a GSM-type cellular phone in the european 900MHz band is used in the european community, a DCS-type cellular phone in the 1.8GHz band is used in the urban area to supplement the shortage of the frequency. Therefore, in order to use the mobile phone in the dual band, it is necessary to operate the mobile phone in the dual band correspondingly. That is, a dual resonance antenna operating in a dual band is required in addition to a radio circuit for each band in the internal dual band.

As such an antenna, a dual resonance antenna shown in fig. 9 has been proposed. The double resonance antenna has a coil portion 121 wound in a spiral shape, and includes a connection portion 122 formed by bending an upper end of the coil portion 121 downward and penetrating the coil portion 121 along a substantially central axis of the coil portion 121. The end of the connection portion 122 is supplied with power from a power supply portion 124.

Fig. 10 illustrates an equivalent circuit of the dual resonant antenna 114 shown in fig. 9. As shown in fig. 10, a resonance circuit in which an equivalent inductor L101 is connected in parallel with a capacitor 101 is formed to generate a stray capacitance by coupling a coil portion 121 and a connection portion 122 penetrating the coil portion 121 at a high frequency. An equivalent element 125 is equivalently formed on the parallel resonant circuit, an equivalent element 126 is equivalently formed between the parallel resonant circuit and the power supply unit 124, the equivalent element 125 is formed by the coil unit 121, and the equivalent element 126 is formed by the connection unit 122.

In this dual resonance antenna 114, the entire structure of the coil portion 121 and the connection portion 122 operates as an antenna in a low frequency band (first frequency band), the parallel resonance circuit operates as a trap circuit in a high frequency band (second frequency band), and the connection portion 122 becomes an antenna operating in a high frequency band. Thus, the dual resonant antenna 114 will operate in both the first and second frequency bands.

In such a dual resonance antenna, since the antenna operating in the high second frequency band is formed by the linear connection portion 122, the length of the connection portion 122 needs to be set to a length corresponding to the frequency of the second frequency band. However, if the length of the connection portion 122 is set to a length corresponding to the frequency of the second frequency band, the length of the dual resonant antenna 114 becomes long, and it is difficult to reduce the size. The length of the connection portion 122 is shorter than the originally required length to connect the matching circuit showing the double resonance characteristic, thereby miniaturizing the double resonance circuit 114 operating in the first and second frequency bands. The VSWR (voltage standing wave ratio) characteristic of the miniaturized dual resonant antenna 114 connected to such a matching circuit as described above with a length of about 20mm in total length is shown in fig. 11. In the VSWR characteristics shown in fig. 11, the horizontal axis represents the frequency, the 900MHz band (890-960MHz) is the first band in GSM (global system for mobile communications), and the 1.7MHz band (1710MHz-1880MHz) is the second band in DCS (digital cellular system). Referring to fig. 11, the worst value of VSWR in the first frequency band is 3.1 and the worst value of VSWR in the second frequency band is 2.7, there is a problem in that good VSWR cannot be obtained.

The VSWR characteristic shown in fig. 11 is attributed to the fact that the matching circuit shown in fig. 12 is connected between the dual resonant antenna 114 and the power feeding unit 124. In order to obtain a double resonance characteristic, the matching circuit is configured such that the second inductor L112 and the third inductor L113 are connected in series, the capacitor C111 is connected between the connection point of the second inductor L112 and the third inductor L113 and the ground, and the first inductor L111 is connected between the start end of the second inductor L112 and the ground. At this time, the first inductor L111 is about 15nH, the second inductor L112 and the third inductor L113 are about 4.7nH, and the capacitor C111 is about 2 pF. Thus, the dual resonant antenna 114 has a problem that a complicated matching circuit using four or more elements is required.

Disclosure of Invention

Accordingly, an object of the present invention is to provide a dual-resonance antenna that can be miniaturized without impairing electrical characteristics and can realize a simple matching circuit.

In order to achieve the above object, a dual resonance antenna of the present invention includes: a first coil portion; a connecting portion formed by bending one end of the first coil portion and extending substantially along the central axis in the first coil portion; a second coil part connected to the end of the connection part.

In the dual resonance antenna according to the present invention, the first matching reactance element may be connected in series between the end of the second coil portion and the power feeding portion, and the second matching reactance element may be connected between the end of the second coil portion and the ground.

In the second resonance antenna according to the present invention, a pi-type matching circuit or a T-type matching circuit including three reactance elements may be connected between the end of the second coil portion and the feeding portion.

According to the present invention, since the second coil portion is connected to the end portion of the connecting portion extending substantially along the central axis in the first coil portion, the overall length of the dual-resonance antenna can be shortened and downsized, and then, even if such downsizing is performed, the second coil portion can be provided with a length originally necessary. This makes it possible to produce a dual-resonance antenna that can obtain good electrical characteristics. Further, since a matching circuit for obtaining a dual resonance characteristic is not required, the matching circuit for supplying power to the dual resonance antenna can be made into a simple circuit with a small number of parts.

Drawings

Fig. 1 illustrates a structure in which a dual resonance antenna, that is, an antenna section of an embodiment of the present invention is mounted in a radio apparatus casing.

Fig. 2 schematically shows an external appearance structure of an antenna unit as a dual resonance antenna according to an embodiment of the present invention.

Fig. 3 schematically shows the structure of an antenna unit as a dual-resonance antenna according to an embodiment of the present invention.

Fig. 4 shows an equivalent circuit of a dual resonance antenna, i.e., an antenna portion, according to an embodiment of the present invention.

Fig. 5 illustrates VSWR characteristics of the dual resonance antenna, i.e., the antenna portion, according to the embodiment of the present invention.

Fig. 6 illustrates a matching circuit of a dual resonance antenna, i.e., an antenna portion, according to an embodiment of the present invention.

Fig. 7 shows another example of a matching circuit of an antenna unit which is a dual-resonance antenna according to an embodiment of the present invention.

Fig. 8 shows another example of a matching circuit of an antenna portion which is a dual resonance antenna according to an embodiment of the present invention.

Fig. 9 schematically shows the structure of a proposed dual resonant antenna.

Fig. 10 shows an equivalent circuit of the proposed dual resonant antenna.

Fig. 11 illustrates VSWR characteristics of the proposed dual resonant antenna.

Fig. 12 shows a matching circuit of a proposed dual resonant antenna.

Detailed Description

Fig. 1 shows an example of a structure in which an antenna portion of a dual resonance antenna according to an embodiment of the present invention is mounted on a chassis of a wireless communication device. Such as the housing of a portable telephone.

An antenna unit 2 is attached to an upper portion of a casing 3 of a portable radio apparatus 1 shown in fig. 1. The antenna part 2 is a dual resonance antenna operating in a dual band. These two frequency bands are, for example, the 800MHz band (810MHz-956MHz) and the 1.4GHz band (1429MHz-1501MHz) in the PDC mode (personal digital cellular telecommunication system), or the 800MHz band (890MHz-960MHz) in the GSM mode and the 1.7GHz band (1710MHz-1880MHz) in the DCS mode.

Fig. 2 shows an example of the external appearance of the antenna unit.

As shown in fig. 2, the antenna unit 2 as a dual-resonance antenna according to the present invention is configured by screwing a metal bottom contact 12 into an opening of a cylindrical antenna cover portion 11 having one closed end. The antenna cover portion 11 is formed by resin molding, and a dual resonance element 14 described later is provided inside the antenna cover portion. The lower end of the dual resonator element 14 is connected to the bottom contact 12. An elongated bar-like mounting portion 13 extends from the lower end of the bottom sub 12. The mounting portion 13 has a screw portion 13a formed in the middle thereof, and the antenna portion 2 is fixed to the housing 3 by inserting the mounting portion 13 into a mounting hole provided in the housing 3 and screwing the screw portion into the mounting hole.

Fig. 3 schematically shows the structure of the dual resonance element 14 provided in the antenna cover part 11.

The double resonance element 14 includes a first coil portion 21 and a second coil portion 23 wound in a spiral shape, and a connection portion 22 which bends an upper end of the first coil portion 21 downward and penetrates the inside of the first coil portion 21 substantially along a central axis. The lower end of the connecting portion 22 is connected to the upper end of the second coil portion 23, and the lower end of the second coil portion 23 is supplied with power from the power supply portion 24. The double resonant element 24 is formed by winding one wire rod in a coil shape and bending the same as shown in fig. 3.

The equivalent circuit of the dual resonant element 14 shown in fig. 3 is illustrated in fig. 4. In order to couple the first coil portion 21 and the connection portion penetrating the first coil portion 21 at a high frequency to generate a stray capacitance, a parallel resonant circuit formed by the first inductor L1 and the capacitor C1 is equivalently formed as shown in fig. 4. The equivalent element 25 formed equivalently by the first coil portion 21 is connected to the parallel resonant circuit, and the second inductor L2 formed equivalently by the second coil portion 23 is connected between the parallel resonant circuit and the power supply portion 24.

In the double-resonance element 14, the entire first coil portion 21, the connection portion 22, and the second coil portion 23 function as an antenna in a low frequency band (first frequency band). Then, by setting the parallel resonant circuit to function as a trap circuit in a high frequency band (second frequency band), the second coil 23 functions as an antenna in the high frequency band (second frequency band). Thus, the dual resonant element 14 is capable of operating in both the first frequency band and the second frequency band.

In the above case, in the first frequency band which is low, since the first coil portion 21 and the second coil portion 23 function as the induction coil, the entire length of the double resonance element 14 can be shortened and the double resonance element 14 can be miniaturized, and in the second frequency band which is high, since the second coil portion 23 functions as the exciting coil, the physical length of the sum of the lengths of the connection portion 22 and the second coil portion 23 can be shortened and the double resonance element 14 can be miniaturized. Even if the size is reduced in this way, the electrical length of the connection portion 22 and the second coil portion 23 can be set to the originally required electrical length, and the electrical properties of the dual resonant element 14 can be improved.

The VSWR characteristics with respect to frequency of the miniaturized, total length of about 20mm dual resonant element 14 is shown in fig. 5. In FIG. 5, the 900MHz band (890-960MHz) in the GSM mode is used as the first band, and the 1.7GHz band (1710MHz-1880MHz) in the DCS mode is used as the second band. Referring to fig. 5, the VSWR of the frequency at the beginning of the first band may be about 1.3, the VSWR of the frequency at the end may be about 1.8, and the worst value of the VSWR of the first band may be about 1.8. In addition, the VSWR of the frequency at the start of the second band may be about 1.3, the VSWR of the frequency at the end may be about 2.4, and the worst value of the VSWR of the second band may be about 2.4. It is thus understood that good VSWR can be obtained at frequencies at both ends of the first frequency band and the second frequency band.

In addition, the VSWR characteristic shown in fig. 5 interposes the matching circuit shown in fig. 6 between the double resonance element 14 and the power feeding portion 24. The matching circuit is configured such that the capacitor 11 is connected between the double-resonant element 14 and the power supply unit 24, and the inductor L11 is connected between the double-resonant element 14 and the ground. At this point, inductor L11 is about 8.2nH and capacitor 11 is about 5 pF. Although only single resonance can be obtained by the two reactance elements, since the two resonance elements 14 themselves exhibit resonance characteristics, a matching circuit can be simply constituted by the two reactance elements, and thus good electrical characteristics can be obtained.

The matching circuit is an example of the matching circuit shown in fig. 6, but the configuration of the matching circuit differs depending on the environmental conditions of the dual resonant element 14 such as the configuration of the housing 3 and the specification such as the antenna length. For this reason, another example of the matching circuit is shown in fig. 7(a), (b), and (c).

The matching circuit section shown in fig. 7(a), (b), and (c) has a simple structure in which only a single resonance characteristic can be obtained by using two reactance elements. The matching circuit shown in fig. 7(a) is configured such that the inductor 12 is connected between the double resonant element 14 and the power supply unit 24, and the capacitor C12 is connected between the double resonant element 14 and the ground. The matching circuit shown in fig. 7(b) is configured such that a capacitor C14 is connected between the double-resonant element 14 and the power feeding unit 24, and a capacitor C13 is connected between the double-resonant element 14 and the ground. The matching circuit shown in fig. 7(c) is configured such that an inductor L13 is connected between the double resonant element 14 and the feeding unit 24, and an inductor L14 is connected between the double resonant element 14 and the ground.

Fig. 8(a) and (b) show another example of the matching circuit.

The matching circuits shown in fig. 8(a) and (b) each have a simple structure in which only single resonance can be obtained by using three reactance elements. The matching circuit shown in fig. 8(a) is a pi-type circuit, and is configured such that a second reactance X2 is connected between the double-resonant element 14 and the feeding portion 24, a first reactance X1 is connected between the double-resonant element 14 and the ground, and a third reactance X3 is connected between the feeding portion 24 and the ground. The matching circuit shown in fig. 8(b) is a T-type circuit, and is configured such that a fourth reactance X4 and a sixth reactance X6 are connected in cascade between the double-resonant element 14 and the feeding unit 24, and a fifth reactance X5 is connected between the connection point of the fourth reactance X4 and the sixth reactance X6 and the ground.

Among the above matching circuits, which matching circuit can obtain good electrical performance can be selected according to the environmental conditions of the dual resonant element 14, the specification of the antenna length, and the like.

In the present invention, as described above, the second coil portion is connected to the end portion of the connecting portion extending substantially along the central axis line of the first coil portion, so that the overall length of the dual-resonance antenna can be shortened, the dual-resonance antenna can be miniaturized, and even if the dual-resonance antenna is miniaturized, the second coil portion can be maintained at the originally required length. Thereby making it possible to manufacture a dual resonance antenna capable of having good electrical characteristics. Further, since a matching circuit capable of obtaining a double resonance characteristic is not required, a simple circuit can be configured in which the number of components of the matching circuit for feeding the double resonance antenna is reduced.

Claims (3)

1. A dual-resonant antenna, comprising: a first coil portion; bending one end of the first coil part and extending a connecting part along the approximate central axis in the first coil part; and a second coil portion connected to an end of the connecting portion.

2. The dual resonance antenna according to claim 1, wherein a first matching reactance element is connected in series between the end of the second coil portion and the feeding portion, and a second matching reactance element is connected between the end of the second coil portion and a ground.

3. The dual resonance antenna as claimed in claim 1, wherein a pi-type matching circuit or a T-type matching circuit composed of three reactance elements is connected between the end of the second coil portion and the feeding portion.