JP2010288175A - Multiband antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multiband antenna in which VSWR characteristics cover wide frequency bands, an intra-band radiation gain is superior and impedance matching is facilitated, and further to provide a wireless apparatus using the multiband antenna. <P>SOLUTION: A multiband antenna includes: a first radiation element that operates under a parallel resonance mode, and a second radiation element which is comprised of a part of the first radiation element and operates under a serial resonance mode. The first radiation element is resonated from an upper limit frequency f1bmax in a frequency band f1b of a first transmitting and receiving system to a lower limit frequency f2bmin in a frequency band f2b of a second transmitting and receiving system. The second radiation element is resonated at a lower frequency than the lower limit frequency f2bmin in the frequency band of the second transmitting and receiving system and at a higher frequency than the upper limit frequency f1bmax in the frequency band of the first transmitting and receiving system. A peak frequency of VSWR between a resonant frequency f1r of the first radiation element and a resonant frequency f2r of the second radiation element is lower than the lower limit frequency f2min or higher than the upper limit frequency f1bmax in the frequency band of the first transmitting and receiving system. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an antenna circuit used in a radio apparatus, and more particularly to a multiband antenna that can be used in a plurality of different frequency bands.

In recent years, wireless devices such as mobile phones have rapidly spread, and the bandwidth used for communication is also wide-ranging. In particular, in recent mobile phones, there are an increasing number of examples in which a plurality of transmission / reception bands are provided in one communication device as called a dual band system, a triple band system, a quad band system, or the like.
The frequency band of the communication system used in the quad-band mobile phone is, for example, GSM850 / 900 band (824 to 960 MHz), DCS band (1710 to 1850 MHz), PCS band (1850 to 1990 MHz), UMTS band (1920 to 2170 MHz). The DCS band, the PCS band, and the UMTS band, which are three consecutive frequency bands, are approximately 2 to 2.5 times the frequency of the GSM band.

Under such circumstances, a multiband antenna capable of supporting a plurality of transmission / reception bands is required as an antenna constituting an antenna circuit built in a wireless device such as a mobile phone.
A radiating element (also referred to as a radiating electrode) that normally constitutes an antenna resonates at a basic frequency and also resonates at a higher frequency. For example, if resonance at a quarter wavelength is set as a fundamental mode, resonance at a quarter wavelength occurs in a higher-order mode. By making good use of such a plurality of resonances, a multiband antenna corresponding to the GSM band, the DCS band, the PCS band, and the UMTS band has been achieved.
Here, a frequency band that includes the frequency that resonates at the lowest frequency (sometimes referred to as a main resonance point) and can be matched with a high-frequency circuit, that is, a frequency band in which the voltage standing wave ratio VSWR is equal to or less than a predetermined numerical value A frequency band including a frequency (sometimes referred to as a higher-order resonance point) that causes higher-order resonance than that is defined as a higher-order frequency band.

  Recent multiband antennas are required to cover the communication system exemplified above, but the frequency bandwidth covered in the fundamental frequency band is 136 MHz in the GSM850 / 900 band, and the specific bandwidth is about 15.3% [136 MHz. / 892 MHz], and the frequency bandwidth covered by the higher-order frequency band is 460 MHz in the DCS band, the PCS band, and the UMTS band, and the specific bandwidth is about 23.7% [460 MHz / 1940 MHz]. Is wide. Therefore, there is a case where a sufficient bandwidth cannot be ensured only by resonance by one radiating element and it is difficult to use.

  In order to deal with such a problem that the bandwidth cannot be obtained, Patent Document 1 discloses that an inverted F antenna and an inverted L antenna having slightly different resonance frequencies are used, and power is directly supplied from a common power supply circuit 203. The antenna can be operated in a wide frequency band, and the antenna has a two-layer structure for the basic frequency band and a high-order frequency band. Disclosed is an operable multiband antenna.

FIG. 3 shows a basic configuration of the multiband antenna disclosed in Patent Document 1. In such a multiband antenna, the two radiating elements 211 and 222 arranged in proximity are operated at slightly different resonance frequencies f1res and f2res, respectively. As shown in FIG. 5, the VSWR characteristic is a bimodal characteristic obtained by superimposing two resonances and has a low VSWR in a wide frequency band. However, since each radiating element resonates independently, the resonance frequency f1res, A region where the VSWR characteristics deteriorate between f2res appears (point A where the VSWR waveforms overlap in FIG. 5). In the figure, f1max and f1min indicate an upper limit frequency and a lower limit frequency in the transmission / reception frequency band of the first transmission / reception system, and f2max and f2min indicate an upper limit frequency and a lower limit in the transmission / reception frequency band of the second transmission / reception system. Indicates the frequency. Here, the transmission / reception frequency band of the first transmission / reception system is relatively higher than the transmission / reception frequency band of the second transmission / reception system.
Although the VSWR characteristic deteriorates at the frequency fA at the point A where the VSWR waveform overlaps, the degree does not significantly affect the power reflection, so it seems that it does not affect the antenna characteristic at first glance. There has been a problem that the radiation gain decreases at the frequency.

In response to such a decrease in the radiation gain in widening the band, Patent Document 2 proposes to move the point A outside the frequency band to be used.
The configuration of the antenna of Patent Document 2 is shown in FIG. The two radiating elements 211 and 222 are conductors having different lengths, one end being connected to the common power feeding circuit 203 and the other end being an open end, and extending in the same direction in parallel with the ground plane GND formed on the circuit board 202. It is formed as a pattern and is configured as two inverted L antennas each operating in a series resonance mode.
Then, one radiating element is resonated at a frequency within a desired frequency band, and the other radiating element is at a lower frequency band outside the desired frequency band, and the degradation peak of the radiating gain that is between the resonant frequencies of the radiating elements. The part is set to be in a frequency band lower than outside the desired frequency band. With such a configuration, the frequency band in which the VSWR is lower than that of the multiband antenna of Patent Document 1 is narrowed, but the radiation gain in the desired frequency band is improved. In addition, the low VSWR frequency band and the radiation gain are improved as compared with the case of a single radiating element.

JP 2003-124742 A JP 2009-4847

FIG. 1 shows a simplified model of a multiband antenna having a plurality of radiating elements, such as Patent Document 1 and Cited Document 2. This multiband antenna is configured to include a common conductor E1 standing on the ground plane GND and horizontal conductors E2 and E3 connected to one end side of the common conductor E1, and the open end side just extends in the opposite direction. This is equivalent to a T-type monopole structure in which two inverted L antennas are combined.
The other end side of the common conductor E <b> 1 serves as a power feeding end and is connected to the power feeding circuit 203. The horizontal conductors E2 and E3 have different lengths and are connected to the common conductor E1 to form radiating elements each having a quarter wavelength, and resonate at frequencies f1res and f2res to operate in a series resonance mode. .

  Each of the multiband antennas 201 configured as shown in FIGS. 1 to 3 is excited by feeding from a common feeding circuit 203. When a plurality of radiating elements having different lengths are connected to the power feeding circuit 203, a parallel resonance occurs in principle between two series resonances. For this reason, in the multiband antenna, a resonance current in the parallel resonance mode is generated in addition to the series resonance mode in different frequency bands of the high-frequency signal. Although this parallel resonance mode is not described in Patent Document 1, Patent Document 2 suggests the parallel resonance mode, assuming that antenna characteristics deteriorate when current directions in the two antennas are not aligned.

In these multiband antennas, the resonance current distributed in the radiating elements is distributed at three different paths at different frequencies, as indicated by arrows indicated as I1, I2, and I3 in each figure. Become.
The first path I1 is a path formed by a first radiating element including a common conductor E1 connected to the power feeding circuit 203 and a horizontal conductor E2 connected to the common conductor E1, and has a length that resonates at a predetermined wavelength (frequency f1res). The current distribution of the series resonance mode is such that the current is minimized on the open end side.
The second path I2 is a path formed by the second radiating element including the common conductor E1 connected to the power feeding circuit 203 and the horizontal conductor E3 connected to the common conductor E1, and has a length that resonates at a predetermined wavelength (frequency f2res). The current distribution of the series resonance mode is such that the current is minimized on the open end side.
The third path I3 is a path formed by the horizontal conductors E2 and E3, and resonates at a wavelength (f3res between the frequencies f1res and f2res) different from that of the first and second radiating elements, and the current is minimum at both open ends. The current distribution of the parallel resonance mode is as follows.

In general, an antenna operating in a series resonance mode is designed to radiate not only from a radiating element but also from a ground plane. For example, in a mobile phone, radiation efficiency is improved by increasing the apparent antenna volume by using radiation from a metal part of a casing.
On the other hand, in the parallel resonance mode, a conductor pattern between one end of the first radiating element 211 (E1, E2) and one end of the second radiating element 222 (E1, E3) is used as the third radiating element 233 (E2, E3). In this operation mode, since almost no current flows through the feeding point and the ground plane, there is a problem that radiation efficiency and gain are reduced when a sufficiently large radiation element cannot be secured. Therefore, a series resonance mode with excellent radiation efficiency is used exclusively for a small antenna, and a parallel resonance mode that resonates only with a radiating element has not been used much.

Further, the frequency fres3 of the parallel resonance generated at the transition frequency from one series resonance to the other series resonance is specified by the change in reactance of the Smith chart and compared with the VSWR characteristic, the VSWR waveform by the two series resonances fres1 and fres2 is compared. Agrees well with the frequency fA at the point A where the two overlap.
Therefore, it is assumed that the deterioration of the radiation gain at the point A where the VSWR waveforms overlap is strongly influenced by the antiresonance (parallel resonance mode).

  As described above, in the conventional multiband antenna, the radiation efficiency may decrease in the frequency band where the series resonance mode is changed to the parallel resonance mode. Therefore, the overlapping part (parallel resonance) of the VSWR waveform is moved and set to resonate at a frequency that is lower than the desired frequency band, and only the series resonance mode with good radiation efficiency is used. Although it can be said that it is an effective method to improve the reduction of the radiation gain in the frequency band, there are still some problems.

The first problem is that the radiation characteristic of the antenna changes between the state of being arranged on the circuit board and the state of being arranged in the housing in order to set the main mode of resonance to series resonance.
The inverted L antenna and inverted F antenna are configured as quarter wavelength antennas. As is well known, this antenna has a predetermined antenna characteristic based on a current flowing through a radiating element excited by power feeding and a mirror image current based on a radiating element image mapped onto the ground plane. In addition, it is possible to obtain antenna characteristics with an effective length (1/2 wavelength) that is twice as long. Therefore, it can be said that it is easily affected by the ground plane.
In order to suppress fluctuations in the radiation characteristics, it is necessary to design in consideration of the housing structure in which the antenna is disposed. However, since the antenna design and the housing design are usually performed separately, it is difficult to perform the optimum design. In addition, since the design of the housing places particular emphasis on design, it is difficult to consider the effects on the antenna, so even if excellent radiation characteristics are obtained when placed on the circuit board, the wireless device in the state placed inside the housing The apparatus has a problem that desired characteristics cannot be obtained.

  Because it is easy to be affected by the ground plane, even if the antenna design is performed in consideration of the housing structure, and the radiation efficiency is improved by increasing the apparent antenna volume using the radiation from the metal part of the housing, In some cases, the effective radiation efficiency of the antenna is greatly impaired by the influence of a nearby human body.

Further, as shown in FIG. 1, in the structure in which the first radiating element 211 and the second radiating element 222 extend in opposite directions, the horizontal conductors E2 and E3 of the first radiating element 211 and the second radiating element 222 are reversed. Phase current flows. For this reason, the radiation at the horizontal conductor portion is reduced, and the effective radiation is mainly the radiation obtained by the common conductor E1 standing on the ground plane GND and connected to the feeder circuit.
Therefore, in order to obtain excellent radiation efficiency and gain, the length of the common conductor E1 standing on the ground surface must be increased. However, particularly in a small mobile communication device such as a mobile phone, the space in which the antenna is arranged is restricted by the housing, so that it is actually difficult to obtain a sufficient length of the conductor portion. There was a problem that efficiency and gain could not be obtained. This is the second problem.

  Further, as in the prior art, when two radiating elements that resonate in the same mode are extended in the same direction, there is a third problem that it is difficult to obtain isolation between the radiating elements. In this configuration, the mirror image current flowing on the ground plane is in phase, so if one of the radiating elements is changed in length or other design changes, the impedance of the other radiating element is affected and the matching is disturbed. It was a factor that made design difficult.

  In either case, if the horizontal conductor portions of the first radiating element 211 and the second radiating element 222 are arranged near the ground plane, sufficient radiation characteristics cannot be obtained, and the VSWR characteristic is narrowed. There were also four problems.

  In addition, for the purpose of multibanding, a radiating element is required for each of the fundamental frequency band and the higher-order frequency band, and there has been a fifth problem that hinders downsizing of the multiband antenna.

  Therefore, in the present invention, in a small multiband antenna having a plurality of radiating elements, the VSWR characteristics are wide in the frequency band, the radiation gain within the band is excellent, the impedance matching is easy, and the radiation characteristics are An object of the present invention is to provide a radio apparatus using the same that is hardly affected by the human body.

The first invention includes at least two transmission / reception systems in which the frequency bands are close to each other and the center frequency of the frequency band f1b of the first transmission / reception system is relatively higher than the center frequency of the frequency band f2b of the second transmission / reception system. A corresponding multi-band antenna,
A first radiating element that operates in a parallel resonant mode; and a second radiating element that is configured by a part of the first radiating element and operates in a series resonant mode, wherein the first radiating element is a frequency band f1b of the first transmission / reception system. Resonates between the upper limit frequency f1bmax at the lower limit frequency f2bmin in the frequency band f2b of the second transmission / reception system,
The second radiating element resonates at a frequency lower than the lower limit frequency f2bmin in the frequency band of the second transmission / reception system or higher than the upper limit frequency f1bmax in the frequency band of the first transmission / reception system,
The peak frequency of VSWR between the resonance frequency f1r of the first radiating element and the resonance frequency f2r of the second radiating element is lower than the lower limit frequency f2min or the upper limit frequency f1bmax in the frequency band of the first transmission / reception system. Is a multiband antenna characterized by high frequency.

In the present invention, the first radiating element operating in the parallel resonant mode has a T-shaped antenna structure with both ends open, and the second radiating element operating in the series resonant mode is an inverted L antenna configured by a part of the first radiating element. A structure is preferable.
The first radiating element is composed of horizontal conductors E2 and E3 connected to a common conductor E1 erected on the ground plane GND. The horizontal conductors E2 and E3 are formed to have different lengths, and the total length of the horizontal conductors E2 and E3 is the lower limit frequency f2bmin in the frequency band f2b of the second transmission / reception system from the upper limit frequency f1bmax in the frequency band f1b of the first transmission / reception system. It is the length which resonates in between (basic frequency band). Preferably, the frequency at which the VSWR caused by the first radiating element is minimized is set to a length that is a substantially intermediate frequency from the frequency f1bmax to the frequency f2bmin.

  The second radiating element is configured in an inverted L antenna structure by a horizontal conductor E2 connected to the common conductor E1 or a horizontal conductor E3 connected to the common conductor E1. The total length of the common conductor E1 and the horizontal conductor E2 and the total length of the common conductor E1 and the horizontal conductor E3 resonate at a frequency lower or higher than the fundamental frequency band, and the resonance frequency f1r of the first radiating element The peak frequency of VSWR between the resonance frequency f2r of the second radiating element is set to a length outside the fundamental frequency band.

When the two horizontal conductors extend in the same direction in parallel with the ground plane and are arranged close to each other as in the cited document 2, the series resonance mode of the second radiating element is caused by mutual interference of the radiating elements. In some cases, only one resonance is visible.
In this case, it is preferable that the second radiating element is resonated at a frequency lower than the fundamental frequency band, and the peak frequency at which the VSWR deteriorates is outside the fundamental frequency band and lower than the lower limit frequency f2min.

Further, like the multiband antenna shown in FIG. 2, the ground conductor GE may be connected to the horizontal conductor of the first radiating element. Such a configuration is equivalent to a structure in which an inverted F antenna that operates in the series resonance mode and an inverted L antenna that operates in the series resonance mode are equivalent, and impedance adjustment is easy.
Also in this case, the first radiation element by the horizontal conductors E2 and E3 is operated in the parallel mode, and the second radiation constituted by the horizontal conductor E2 connected to the common conductor E1 or the horizontal conductor E3 connected to the common conductor E1. The element is resonated at a frequency lower than or higher than the fundamental frequency band, and the peak frequency of VSWR between the resonance frequency f1r of the first radiating element and the resonance frequency f2r of the second radiating element is outside the fundamental frequency band. The configuration is as follows. Therefore, the operation and characteristics are different from the antenna of the cited document 1 having the same configuration at first glance.

  In the configuration of the two horizontal conductors E2 and E3, the open end side may be extended in different directions like the multiband antenna shown in FIG. 1, or folded back halfway like the multiband antenna shown in FIG. May be extended in the same direction. If the horizontal conductor is extended in the same direction substantially parallel to the ground plane, the length of the radiating element in the extension direction can be reduced.

  Each conductor is composed of an electrode pattern formed on the surface of the resin substrate or a strip electrode erected on the resin substrate.

Further, if the folded portion is formed in at least one of the horizontal conductors E2 and E3, the frequency of the higher-order resonance can be reduced. Therefore, the fundamental frequency band (the frequency band f1b of the first transmission / reception system and the second transmission / reception system) can be reduced. It is possible to operate in a higher-order frequency band (third frequency band f3b) that is a relatively higher frequency than the frequency band f2b), and thus a multiband antenna corresponding to at least three transmission / reception systems. The frequency of the higher-order resonance can be adjusted by the capacitance generated between the opposing conductors and the ground plane by folding.
If a folded portion is formed in each of the horizontal conductors E2 and E3, it is possible to operate in the third frequency band f3b and the fourth frequency band f4b, thereby providing a multiband antenna corresponding to at least four transmission / reception systems. I can do it. Therefore, there is no need to prepare radiating elements corresponding to the fundamental frequency band and the higher-order frequency band, and the multiband antenna can be made compact.

  If a multi-band antenna is used as a radio communication device, it can contribute to miniaturization and high performance of the radio communication device. The wireless communication device includes a power feeding circuit connected to the multiband antenna and a control circuit for controlling the power feeding circuit.

According to the present invention, in a small multi-band antenna, the VSWR characteristic is wide frequency band, excellent in radiation efficiency and gain within the band, impedance matching is easy, and the radiation characteristic is less influenced by the housing and the human body. In addition, it is possible to provide a wireless device using the same.
In addition, since the multiband antenna of the present invention has a wide band and is excellent in efficiency and gain within the band, a wireless device using the antenna can reduce battery consumption, extend communication time, and expand a communication area. The call quality such as can be improved.

It is a figure for demonstrating the example of 1 structure of a multiband antenna. It is a figure for demonstrating the other structural example of a multiband antenna. It is a figure for demonstrating the other structural example of a multiband antenna. It is a figure for demonstrating the other structural example of a multiband antenna. It is a VSWR characteristic figure of the conventional multiband antenna. It is a figure which shows the VSWR characteristic of the multiband antenna which concerns on one Example of this invention. It is a perspective view for demonstrating the structure of the multiband antenna which concerns on one Example of this invention. It is a front view for demonstrating the structure of the multiband antenna which concerns on one Example of this invention. It is a back view for demonstrating the structure of the multiband antenna which concerns on one Example of this invention. It is an expanded view for demonstrating the structure of the multiband antenna which concerns on one Example of this invention. It is an expanded view for demonstrating the structure in the fundamental frequency band of the multiband antenna which concerns on one Example of this invention. It is an expanded view for demonstrating the structure in the high frequency band of the multiband antenna which concerns on one Example of this invention. It is a figure which shows the VSWR characteristic of the multiband antenna which concerns on one Example of this invention. It is a figure which shows the other VSWR characteristic of the multiband antenna which concerns on one Example of this invention. It is a figure which shows the VSWR characteristic of the multiband antenna which concerns on a comparative example. It is a figure which shows the average antenna gain characteristic of the multiband antenna which concerns on the Example and comparative example of this invention.

Although the basic structure of the multiband antenna of the present invention is the same as the conventional structure, here, a multiband antenna having a structure in which a ground conductor is provided on the T-shaped antenna shown in FIG. 4 will be described as an example.
This multiband antenna includes a common conductor E1, parallel conductors E2 and E3 that are connected to one end of the common conductor E1 and open at the other end and are substantially parallel to the ground plane GND, and between the parallel conductor E3 and the ground plane. A ground conductor GE to be connected is provided.
The parallel conductors E2 and E3 extend substantially parallel to the ground plane GND and in the opposite directions, respectively, and the sum of their lengths is substantially ½ of the wavelength λ1 of the resonance frequency f1r that resonates in parallel within the fundamental frequency band. Thus, the first radiating element 233 operating in the parallel resonance mode is configured. The current distribution when the first radiating element 233 resonates in parallel is 0 (zero) at both ends, and is maximum at the center. Therefore, in the central portion of the first radiating element 233, the voltage is substantially 0 (zero), and the impedance is in a short state. Accordingly, the ground conductor GE to be grounded is preferably connected in the vicinity of a portion where the voltage becomes 0 (zero) during power feeding. Further, the impedance of the first radiating element 233 can be adjusted by adjusting the position of the connection point between the ground conductor GE and the parallel conductor E2.

The common conductor E1 and the parallel conductor E2, and the common conductor E1 and the parallel conductor E3 function as the second radiating element 211 and the third radiating element 222 that operate in the series resonance mode. The sum of the lengths of the common conductor E1 and the parallel conductor E2 is approximately ¼ of the wavelength λ2 of the resonance frequency f2r in series resonance outside the fundamental frequency band. Further, the sum of the lengths of the common conductor E1 and the parallel conductor E3 is approximately ¼ of the wavelength λ3 of the resonance frequency f3r in series resonance outside the fundamental frequency band.
FIG. 6 is a diagram showing the VSWR characteristics of the multiband antenna of the present invention. The resonance frequency f2r and the resonance frequency f3r may be relatively higher, but the frequency is outside the fundamental frequency band f1b, and one of them is always lower than the lower limit frequency f2min in the fundamental frequency band f2b. It is set so that the other is higher than the upper limit frequency f1max. When only one resonance frequency in the series resonance mode appears, the resonance frequency is set to be lower than the lower limit frequency f2min in the fundamental frequency band f2b.
In FIG. 6, the resonance frequency f2r is set to be lower than the lower limit frequency f2min in the frequency band f2b of the second transmission / reception system, and the VSWR appearing in the frequency band between the series resonance frequency and the parallel resonance frequency is deteriorated. A is also set to a frequency lower than the lower limit frequency f2min. The resonance frequency f3r is higher than the upper limit frequency f1max in the frequency band f1b of the first transmission / reception system, but is not shown.

In the present embodiment, the parallel conductors E2 and E3 extend in the opposite direction. For example, the parallel conductor E2 may be folded back so as to extend in the same direction as the parallel conductor E3, or the parallel conductor E3 may be turned into the parallel conductor E2. It may be folded back to extend in the same direction. Further, it may be configured to be folded back in multiple directions so that the parallel conductors E2 and E3 extend in different directions by folding in the opposite direction. According to such a configuration, the multiband antenna can be configured in a small size, and a multiband antenna corresponding to at least three transmission / reception systems can be obtained by adjusting the frequency of higher-order resonance.
Further, the parallel conductors E2 and E3 are arranged close to each other to cause mutual interference, so that the high-frequency current is concentrated on one of the second radiating element 211 and the third radiating electrode 222, and resonance in the series resonance mode is reduced. You may only see one. In the series resonance in this case, it is preferable that the second antenna is resonated at a frequency lower than the fundamental frequency band, and the peak frequency at which the VSWR deteriorates is on the low frequency side outside the fundamental frequency band.

In the prior art, parallel resonance that occurs in a multiband antenna is set as an unnecessary mode. However, in the present invention, the parallel resonance mode is set as the main operation mode of the antenna, and the resonance frequency of the series resonance mode is outside the fundamental frequency band. The frequency fA of the VSWR degradation peak that occurs transitively between the resonance in the resonance mode and the resonance in the parallel resonance mode is set to be outside the fundamental frequency band.
The resonance generated in the radiating element operating in the series resonance mode exhibits sharper resonance characteristics than the resonance generated in the first radiating element 233 operating in the parallel resonance mode, and therefore, is near the lower limit frequency f2bmin or the upper limit frequency f1bmax of the fundamental frequency band. Even if the resonance frequency is set so as to be, the frequency fA of the VSWR degradation peak can be outside the fundamental frequency band f1b.

  Since the parallel resonance mode is the main mode of operation, even if the horizontal conductor of each radiating element is placed close to the ground plane, the degree to which the electrical characteristics are reduced is less than that of the series resonance mode. For this reason, the common conductor E1 connected to the power feeding circuit can be formed short and a low-profile multiband antenna can be obtained.

  Further, when the ground plane GND is close, the radiation in the series resonance mode set outside the fundamental frequency band is reduced as compared with the parallel resonance mode that is the main operation mode, and the VSWR is also increased. Further, it is possible to prevent the unnecessary radiation of the high frequency signal outside the fundamental frequency band by the third radiating element 222. Further, the operating frequency band in the parallel resonance mode can be further broadened by making the operating frequency band in the series resonance mode narrower by being close to the ground plane GND.

  Furthermore, by configuring the parallel conductors E2 and E3 by folding, a multiband antenna corresponding to at least three transmission / reception systems can be obtained.

The common conductor E1, the parallel conductors E2 and E3, and the ground conductor GE are formed on a printed board such as FR4 (glass epoxy resin board) with a low resistance Cu thin plate by a known method such as etching, alumina, or other A ceramic substrate made of a dielectric ceramic material may be formed of a good conductor such as low resistance Au, Ag, or Cu by a known method such as printing or etching, or may be formed of a conductor thin plate made of Cu or phosphor bronze. Also good. If the radiation electrode is formed of an alloy such as phosphor bronze which is easy to process but is not easily deformed by an external force, it is possible to form the radiation electrode in a free shape regardless of the support.
Further, the radiation electrode formed on the printed circuit board or the ceramic body may be configured to be mounted on another printed circuit board having a ground surface, or may be configured in combination with a conductive thin plate.

Hereinafter, the multiband antenna according to the present invention will be described in detail. 7 is a perspective view of the multiband antenna, FIG. 8 is a plan view of the multiband antenna viewed from the DA direction, and FIG. 9 is a plan view of the multiband antenna viewed from the DB direction. In FIG. 9, the printed circuit board 100a is omitted.
The multiband antenna according to the embodiment of the present invention includes a common conductor E1 (conductor elements e4a and e4b) that is connected to the feeder circuit 203 via the feeder line kl and is erected from the ground plane GND, and substantially parallel to the ground plane GND. The first parallel conductor E2 (conductor elements e2, e3a, e3b, e3c, e3d, e3e) and the second parallel conductor E3 (conductor elements e1a, e1b, e1c, e1d, e1e, e1f, e1g, e1h, e1i, e1j), a third parallel conductor E4 (conductor elements e6a, e6b), and a ground conductor GE (conductor elements e5a, e5b).

  The multiband antenna is composed of conductor elements provided on another printed circuit board 100b, which are arranged on one side of the printed circuit board 100a. The printed circuit board 100a is provided with a ground pattern serving as a ground plane GND and a feed line kl. The printed circuit board 100a is a copper-clad double-sided conductor board (glass epoxy board), but a ground pattern is not formed on both sides of the printed circuit board 100a.

  The printed circuit board 100b disposed substantially parallel to the printed circuit board 100a at a predetermined distance includes a common conductor E1 and first parallel conductors E2 (conductor elements e2, e3a, e3b, e3c, e3d, e3e) The second parallel conductor E3 (conductor elements e1a, e1b, e1c, e1d, e1e, e1f, e1g, e1h, e1i, e1j), the third parallel conductor E4 (conductor elements e6a, e6b), and the first parallel conductor E3 A grounding conductor GE (conductor elements e5a, e5b) connected to is formed.

  Connected to one end of a conductor element e4a to be the common conductor E1, orthogonal to the extending direction, the conductor element e1a extends in the left direction and the conductor element e2 extends in the right direction in FIG. The end of the conductor element e2 is connected to a conductor element e3a extending in the same direction, and a ground conductor e5a constituting a ground conductor GE extending in parallel with the conductor element e4a is connected between the conductor elements e2 and e3a. ing. The conductor elements e4a and e5a are connected to the feed line kl and the ground plane GND formed on the printed circuit board 100a through the conductor elements e4b and e5b, respectively.

The end of the conductor element e1a is connected so that the conductor element e1b extends in the right direction and the conductor element e6a extends in the left direction in FIG. 7 orthogonal to the extending direction. One end of the end portion of the conductor element e6a is a free end and is connected to the conductor element e6b extending substantially parallel to the conductor element e1a. The end portion of the conductor element e1b is connected to the conductor element e1d formed on the back surface through the conductor element e1c formed on the side surface to the side of the printed circuit board 100b.
On the back side of the printed circuit board 100b, an integral belt-like conductor (a hatched portion in FIGS. 8 and 9) made of a U-shaped conductor thin plate is erected. In this example, a thin plate-like Cu sheet metal having a thickness of 0.2 mm and a width of 1 mm was used for the strip-shaped conductor. The strip-shaped conductor is connected to the conductor element e1d with a brazing material such as solder, connected to the conductor element e1e extending to the printed circuit board 100a side, and the end of the conductor element e1e, and the conductor extending between the two printed circuit boards 100a and 100b. The element e1f is connected to the end of the conductor element e1f, and is composed of a conductor element e1h formed on the back surface of the printed circuit board 100b and a conductor element e1g connected by a brazing material. The conductor element e1f is formed longer than the total length of the conductor elements e1a, e2, e3a.
The conductor element e1h is formed on the surface via the conductor element e1i formed on the side surface, and one end of the conductor element e1h is connected to the conductor element e1j having a free end.

  The conductor element e3b is connected to the end of the conductor element e3a, orthogonal to the extending direction, and the conductor element e3b extends rightward in FIG. The conductor element e3b extends to the side of the printed circuit board 100b and is connected to the conductor element e3d formed on the back surface through the conductor element e3c formed on the side surface. The conductor element e3d is formed longer than the conductor elements e1c and e1i, extends under the strip-shaped conductor, its end extends in the left direction in FIG. 9, and the end is connected to the conductor element e3e having a free end. To do. Each conductor element excluding the belt-like conductor is composed of a Cu thin plate formed by etching or the like. In this embodiment, the thickness of the Cu thin plate in each part of the printed circuit boards 100a and 100b is 0.1 mm and the width is 1 mm. The interval between the printed circuit boards 100a and 100b is 5 mm.

FIG. 10 is a diagram in which a multiband antenna is developed on a plane. 11 is a diagram for explaining the operation of the multiband antenna of FIG. 10 in the fundamental frequency band, and FIG. 12 is a diagram for explaining the operation of the multiband antenna of FIG. 10 in the higher frequency band. It is.
The operation in the fundamental frequency band is mainly a parallel resonance mode by the first radiating element 233. As shown in FIG. 11, in this embodiment, the first radiating element 233 includes a common conductor E1 including conductor elements e4a and e4b and a feed line kl, a horizontal conductor E2 including conductor elements e1a to e1j, and a conductor element. The horizontal conductor E3 comprised by e2, e3a-e3e is provided. Although the horizontal conductors E2 and E3 are folded back several times, the basic configuration is equivalent to a T-type antenna. The total length of the horizontal conductor E2 and the horizontal conductor E3 is a length that causes parallel resonance at a frequency within the fundamental frequency band (824 MHz to 960 MHz).

  The second radiating element 211 includes a common conductor E1 including the conductor elements e4a and e4b and the feed line kl, a horizontal conductor E2 including the conductor elements e1a to e1j, a ground conductor GE including the conductor elements e5a and e5b, A conductor element e2 that connects the horizontal conductor E2 and the ground conductor GE is provided. The horizontal conductor E2 has a structure that is folded back several times, but the basic configuration is equivalent to an inverted F-type antenna. The total length of the horizontal conductor E2 and the ground conductor GE is such that the series resonance occurs at a frequency outside the fundamental frequency band (824 MHz to 960 MHz). In this embodiment, the resonance frequency is lower than 824 MHz. Yes.

  The horizontal conductor E2 and the horizontal conductor E3 are arranged close to each other, and in the VSWR characteristic diagrams of FIGS. 13 to 15 described later, resonance by the horizontal conductor E3 is not confirmed, and only one resonance in the series resonance mode is caused by mutual interference. I couldn't see it.

In the high-order frequency band, the operation is performed in the parallel resonance mode by the third radiating element 244 and the series resonance mode by the fourth radiating element 255. As shown in FIG. 12, in this embodiment, the third radiating element 244 includes a common conductor E1 including conductor elements e4a and e4b and a feed line kl, a conductor element e1a, and a horizontal conductor composed of the conductor elements e6a and e6b. E4 and a horizontal conductor E3 including conductor elements e2 and e3a to e3d are provided. Note that the conductor element e3e constituting the horizontal conductor E3 is not visible at a high-order frequency. The horizontal conductors E3 and E4 have a structure that is folded back several times, but the basic configuration is equivalent to a T-type antenna like the first radiating element. The total length of the horizontal conductor E2 and the horizontal conductor E3 is a length that causes parallel resonance at a frequency within a high-order frequency band (1710 MHz to 2170 MHz).
In the embodiment, in the printed circuit board 100b, capacitive coupling is achieved by arranging a part of the horizontal conductor E2 (conductor elements e1h to e1j) and a part of the horizontal conductor E3 (conductor elements e3b to e3d) close to each other. Is strengthened. With such a configuration, the resonance frequency of the third radiating element 244 can be lowered, and the resonance frequency can be adjusted without changing the length of the horizontal conductors E3 and E4.

  The fourth radiating element 255 includes a common conductor E1 including the conductor elements e4a and e4b and the feed line kl, a conductor element e1a, a horizontal conductor E4 including the conductor elements e6a and e6b, and conductor elements e5a and e5b. A grounding conductor GE and a conductor element e2 that connects the horizontal conductor E2 and the grounding conductor GE are provided. Although the horizontal conductor E4 has a structure that is folded back several times, the basic configuration is equivalent to an inverted F-type antenna, like the second radiating element 222. The total length of the horizontal conductor E4 and the ground conductor GE is also a length that causes series resonance at a frequency within the fundamental frequency band (1710 MHz to 2170 MHz).

A multiband antenna of a comparative example in which the second radiating element 211 has series resonance at a frequency within the fundamental frequency band (824 MHz to 960 MHz) was manufactured with the same configuration.
Table 1 summarizes the dimensions of each conductor. Since the conductor element is formed with a width, the length is based on a line segment that bisects the width of the conductor element. When the end portion is connected to another conductor element, the intersection of each bisector is used as a reference, and when the end portion is a free end, the free end portion of the bisector is used as a reference for the length.

The VSWR characteristics and average antenna gain characteristics of the obtained multiband antennas of Examples and Comparative Examples were evaluated. The performance evaluation of the multiband antenna will be described. A measurement antenna was provided at a position 3 m away from the multiband antenna in the anechoic chamber, the measurement antenna was connected to a network analyzer via a 50Ω coaxial cable, and the antenna characteristics were measured. Specifically, in a printed circuit board configured with a multiband antenna, X is a direction in which the common conductor extends, Y is a direction in which the horizontal conductor extends in a direction perpendicular to the common conductor, and a direction perpendicular thereto, that is, the surface of the printed circuit board. A direction perpendicular to Z was defined as Z, and an average gain and VSWR in the XY, ZX, and ZY planes were measured.
13 and 14 are VSWR characteristic diagrams according to the embodiment of the present invention, and FIG. 15 is a VSWR characteristic diagram according to a comparative example. FIG. 16 shows average antenna gain characteristics of the examples and comparative examples showing the VSWR characteristics. Here, the average antenna gain characteristic is an omnidirectional average antenna gain of a multi-band antenna, and means an antenna gain measured and averaged in all directions of X, Y, and Z, and the unit is expressed in dBi.

  In each of the VSWR characteristic diagrams of FIGS. 13 to 15, the dotted line indicates that the VSWR value is 3. The frequency band having a VSWR value of 3 or less on the low frequency side including the fundamental frequency band is within the fundamental frequency band indicated by the markers 1 and 2 and the resonance frequency (not shown) of the first radiating element and the second radiating element. The multiband antenna of the comparative example in which the resonance frequency of the first and second radiating elements is adjusted so that the overlapping portion A of the resonance frequency f2r and the VSWR waveform is located is wider than the embodiment. However, in the average antenna gain characteristic shown in FIG. 16, the average antenna gain is remarkably lowered at the frequency including the overlapping portion A. Further, when looking at the VSWR characteristics of the first and second embodiments, the VSWR value in the fundamental frequency band can be reduced as the resonance frequency f2r of the second radiating element is closer to the lower limit frequency of the fundamental frequency band indicated by the marker 1. And the average antenna gain has increased.

E1 Common conductor E2, E3 Horizontal conductor GE Ground conductor

Claims (6)

A multiband antenna corresponding to at least two transmission / reception systems in which the frequency bands are close to each other and the center frequency of the frequency band f1b of the first transmission / reception system is higher than the center frequency of the frequency band f2b of the second transmission / reception system. There,
A first radiating element that operates in a parallel resonant mode; and a second radiating element that is configured by a part of the first radiating element and operates in a series resonant mode, wherein the first radiating element is a frequency band f1b of the first transmission / reception system. Resonates between the upper limit frequency f1bmax at the lower limit frequency f2bmin in the frequency band f2b of the second transmission / reception system,
The second radiating element resonates at a frequency lower than the lower limit frequency f2bmin in the frequency band of the second transmission / reception system or higher than the upper limit frequency f1bmax in the frequency band of the first transmission / reception system,
The peak frequency of VSWR between the resonance frequency f1r of the first radiating element and the resonance frequency f2r of the second radiating element is lower than the lower limit frequency f2min or the upper limit frequency f1bmax in the frequency band of the first transmission / reception system. Multiband antenna characterized by high frequency.   The first radiating element that operates in the parallel resonance mode has a T-shaped antenna structure with both ends open, and the second radiating element that operates in the series resonance mode has an inverted L antenna structure configured by a part of the first radiating element; The multiband antenna according to claim 1, wherein:   The first radiating element is composed of a common conductor erected on the ground surface and two horizontal conductors connected to the common conductor, and the first horizontal conductor and the second horizontal conductor are formed to have different lengths, The total length of the first radiating element is a length that resonates between an upper limit frequency f1bmax in the frequency band f1b of the first transmission / reception system and a lower limit frequency f2bmin in the frequency band f2b of the second transmission / reception system. The multiband antenna according to claim 1 or 2.   The second radiating element is configured by the first horizontal conductor or the second horizontal conductor connected to the common conductor, and the total length of the common conductor and the first horizontal conductor and the total length of the common conductor and the second horizontal conductor are: The multiband antenna according to claim 3, wherein the multiband antenna has a length that resonates at a low frequency of a lower limit frequency f2bmin or a frequency higher than an upper limit frequency f1bmax.   The multiband antenna according to claim 3 or 4, wherein at least one of the first horizontal conductor and the second horizontal conductor is folded in the middle and extended in the same direction. The second radiating element is folded to configure a third radiating element that resonates between the frequency band f1b of the first transmission / reception system and the third frequency band f3b that is relatively higher in frequency than the frequency band f2b of the second transmission / reception system. The multiband antenna according to claim 1, wherein the multiband antenna is provided.

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