JP2012169805A - Multiband antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multiband antenna which can deal with a frequency band including LTE and is excellent in a VSWR band, and thus is capable of dealing with multiple transmission and reception systems.SOLUTION: A multiband antenna which can deal with a plurality of transmission and reception systems is configured such that: as a first resonance, a first radiation electrode comprising elements of a first component and a second component and having both terminals being open resonates in parallel at a first frequency f1; as a second resonance, the second component as a second radiation electrode resonates in series at a second frequency f2; as a third resonance, a third component as a third radiation electrode resonates in series at a third frequency f3; as a fourth resonance, the first radiation electrode resonates in parallel at a fourth frequency f4; and as a fifth resonance, the second radiation electrode resonates in series at a fifth frequency f5. The first frequency f1 to the fifth frequency f5 have the following relation: f1<f2<2×f1<f3<f4<f5.

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 response to the rapid spread of wireless communication devices such as mobile phones, the frequency band used by communication systems has become widespread. Especially recently, multiple transmission / reception such as dual-band, triple-band, and quad-band methods are used. The number of mobile phones that support bandwidth has increased. For example, in a mobile phone that supports GSM850 / 900 band, DCS band, PCS band, and UMTS band communication systems, GSM850 / 900 band is 824 to 960 MHz, DCS band is 1710 to 1850 MHz, PCS band is 1850 to 1990 MHz, and UMTS Since the band uses a frequency band of 1920-2170 MHz, an antenna (multiband antenna) that can handle these multiple frequency bands is required.

The antenna elements constituting the antenna [radiating element, radiating electrode, radiation path (also referred to simply as a line)] usually have resonance at a fundamental frequency (fundamental mode) and resonance at a higher order frequency (higher-order mode). Have. For example, in an antenna operating at series resonance, the fundamental mode is ¼ wavelength and the higher order mode is ¾ wavelength. In the case of parallel resonance, the fundamental mode is ½ wavelength and the higher order mode is 3/2 wavelength.
When a multi-band antenna is configured with one antenna element, assuming that fundamental mode resonance by series resonance is obtained, for example, in the GSM850 / 900 band, the DCS band or the like corresponds to higher-order mode resonance. However, the DCS band, PCS band, and UMTS band are about 2 to 2.5 times the frequency of the GSM band, and the plurality of frequency bands are not in a 1: 3 relationship, so it simply supports higher-order mode resonances. Can not. Even in the case of parallel resonance, it is difficult to cope with higher-order mode resonance. In the higher-order mode resonance, the bandwidth for obtaining VSWR (voltage standing wave ratio) is narrow.

  Since the GSM850 / 900 band has a frequency bandwidth of 136 MHz and a center frequency of 892 MHz, the specific bandwidth is about 15.3% [136 MHz / 892 MHz]. Further, since the frequency bandwidth of the DCS band, the PCS band, and the UMTS Band1 band is 460 MHz and the center frequency is 1940 MHz, the specific bandwidth is about 23.7% [460 MHz / 1940 MHz]. In such a frequency band, it is difficult to obtain impedance matching due to resonance by one antenna element, and a sufficient bandwidth cannot be secured.

  In response to such a problem, the present inventor has proposed a multiband antenna shown in FIG. The multiband antenna includes a first radiating element including elements E2 and E3 and operating in a parallel resonant mode, a second radiating element configured by elements E1 and E2 and operating in a series resonant mode, and elements E1 and E3. And a third radiating element configured and operating in a series resonance mode. In the figure, reference numeral 211 denotes a resonant current induced in the second radiating element, reference numeral 222 denotes a resonant current induced in the third radiating element, and a resonant current induced in the third radiating element.

The first frequency of the parallel resonance by the first radiating element is set to be relatively higher than the second frequency of the series resonance by the second radiating element, and the first frequency of the series resonance by the third radiating element is set. The third frequency is set to a relatively higher frequency than the first frequency.
By setting the first frequency within the operating frequency band of the antenna and setting the second and third frequencies outside the band, VSWR degradation that occurs transitively between the resonance in the series resonance mode and the resonance in the parallel resonance mode And the second frequency is set near the lower limit of the operating frequency of the antenna. By using parallel resonance as the main resonance, the frequency capable of impedance matching in the basic mode is widened and the gain is prevented from being lowered. Furthermore, by adding further elements, it is possible to cope with high frequency bands such as DCS band, PCS band and UMTS band.

JP 2010-288175 A

  Recently, the frequency band that the multiband antenna should support has spread to the LTE band. For example, the LTE Band 17 band uses a frequency band of 704 to 746 MHz, and the LTE Band 7 band uses a frequency band of 2500 to 2690 MHz. LTE and GSM are trademarks or registered trademarks.

The corresponding frequency band required for multiband antennas is expanding. Although the multiband antenna of Patent Document 1 is compatible with a wideband frequency, the VSRW band is not sufficient in the main resonance in the parallel resonance mode to support the fundamental mode frequency band including LTE. There's a problem.
The frequency of the parallel resonance in the fundamental mode by the first radiating element that is the main resonance is adjusted by the length of the elements constituting the second radiating element and the third radiating element. Of course, if the length of the element is changed, the frequency of the two series resonances also changes.
For example, it is possible to provide resonance at the second frequency within the LTE frequency band by using series resonance by the second radiating element. However, adjustment is difficult, and a desired VSWR can be obtained in the main resonance or higher-order mode. There is a problem that the obtained frequency band becomes narrow. For this reason, it has been difficult for conventional multiband antennas to support frequency bands including LTE.
Therefore, an object of the present invention is to provide a multiband antenna that can support a frequency band including LTE, is excellent in the VSWR band, and can support a plurality of transmission / reception systems.

  The present invention is a multiband antenna corresponding to a plurality of transmission / reception systems, in which one end side is connected to a feeding point and the other end side is an open end, one end side is connected to the feeding point, and the other end side is open. A second element having an element length shorter than that of the first element and extending in the same direction as the first element, one end connected to the feeding point, and the other end opened A third element which is an end, has an element length shorter than that of the second element, and extends at least partially in the same direction as the second element; A short-circuit line for grounding the third element directly or through an impedance element is provided, and the multiband antenna is configured as a first resonance by a first open end composed of elements of the first element and the second element. One radiation electrode resonates in parallel at the first frequency f1, and the second As a vibration, the second element serves as a second radiation electrode in series resonance at the second frequency f2, and as a third resonance, the third element serves as a third radiation electrode in series resonance at the third frequency f3. As the fourth resonance, the first radiation electrode resonates in parallel at the fourth frequency f4, and as the fifth resonance, the second radiation electrode resonates in series at the fifth frequency f5, and the first frequency f1 to the first resonance The fifth frequency f5 is a multiband antenna characterized by having a relationship of f1 <f2 <2 × f1 <f3 <f4 <f5.

  According to the present invention, a multiband antenna having excellent VSWR band characteristics in a frequency band including LTE as well as high frequency bands such as GSM850 / 900 band, DCS band, PCS band, and UMTS band and capable of supporting a plurality of transmission / reception systems. Can be provided easily.

It is a figure for demonstrating the example of 1 structure of the multiband antenna of this invention. It is a figure for demonstrating the operation | movement in the 1st frequency of the multiband antenna of this invention. It is a figure for demonstrating the operation | movement in the 2nd frequency of the multiband antenna of this invention. It is a figure for demonstrating the operation | movement in the 3rd frequency of the multiband antenna of this invention. It is a figure for demonstrating the operation | movement in the 4th frequency of the multiband antenna of this invention. It is a figure for demonstrating the operation | movement in the 5th frequency of the multiband antenna of this invention. It is a figure for demonstrating the other structural example of the multiband antenna of this invention. It is an external appearance perspective view which shows the structural example by the metal plate of the multiband antenna of this invention. It is a figure which shows the frequency characteristic of VSWR of the multiband antenna of this invention. It is a Smith chart which shows the impedance characteristic between 100 MHz-1700 MHz of the multiband antenna of this invention. It is a Smith chart which shows the impedance characteristic between 1700 MHz-2500 MHz of the multiband antenna of this invention. It is a Smith chart which shows the impedance characteristic between 2500 MHz-3300 MHz of the multiband antenna of this invention. It is a figure for demonstrating the structure of the conventional multiband antenna.

The basic structure of the multiband antenna of the present invention will be described with reference to FIG.
The multiband antenna 1 includes a first element el1, a second element el2, and a third element el3, and each element is excited by power supply from a common power supply circuit 200, and includes at least first to fifth elements. Resonance is generated, so that it can cope with a plurality of transmission / reception systems. In addition, the frequency of each resonance becomes a high frequency in order of the 1st-5th.

  When two elements having different lengths are connected to the power feeding circuit 200, it is known that series resonance occurs at a frequency corresponding to each length and parallel resonance occurs at a frequency between the two frequencies. In operation, a resonance current in the parallel resonance mode is generated in addition to the series resonance mode.

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, since almost no current flows through the feeding point and the ground plane, there is a problem that the radiation efficiency and gain are lowered 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.

  However, when the present inventors are diligently researching, when elements having different lengths are arranged close to each other, a resonance current based on series resonance is not induced in one element, and series resonance on a relatively low frequency side is caused. It was found that it no longer developed. In such a state, the frequency of the series resonance and the frequency of the parallel resonance can be easily adjusted, and the length of the element necessary for the resonance can be shortened by the parasitic capacitance formed between the elements. It has been found.

  Based on such knowledge, when a sufficiently large radiating element cannot be secured, even if the actual length of the component is short, the apparent length is estimated to be long. The problem of gain degradation can be improved.

In the present embodiment, the first element el1 includes elements a, d, e, and f, the second element el2 includes elements b, e, and f, and the third element el3 includes elements c, g, and f. Become. Moreover, the short circuit line becomes the element h. The short circuit line may be grounded via an impedance element.
Element a is set to be slightly longer than element b. The difference in length between the element a and the element b is substantially the difference in length between the first element el1 and the second element el2. The main part of each element is ideally arranged substantially parallel to the ground plane GND, and is configured to extend in the same direction.

  The first element el1 is arranged close to the second element el2, and constitutes a first radiating element that resonates in parallel at the first frequency f1 by the elements a, b, and d. The total length is substantially half of the wavelength λ1 of the first frequency f1, and as shown in FIG. 2, the elements a, b, and d constituting the first radiating element include A resonance current Ip1 is induced. In an ideal state, the third element el3 side has a high impedance and is not visible from the power feeding side, so is indicated by a dotted line.

  The current distribution Ip1 at the time of parallel resonance is 0 (zero) at both ends thereof, and is maximum at the center. Therefore, in the central portion of the first radiating element, the voltage is substantially 0 (zero), and the impedance is in a short state. The element h constituting the grounded short-circuit line is connected in the vicinity of a portion where the voltage becomes 0 (zero) during power feeding.

FIG. 3 is a diagram showing a resonance state at the second frequency f2. The second element el2 functions as a second radiating element, and a resonance current Is1 is induced in the components b, e, f, g, and h. The second element el2 is formed to have a length approximately ¼ of the wavelength λ2 that resonates at the second frequency f2, and has a current distribution in a series resonance mode in which the current is minimized on the open end side. In the ideal state, the first element el1 and the third element el3 have high impedance and are not visible from the power supply side, and are shown by dotted lines. However, the third element el3 is coupled to the second element el2 and is connected in series. A resonant current of resonance may be induced. The current in that case is smaller than the current due to the main resonance.
Moreover, the impedance of the second radiating element can be adjusted by adjusting the position of the short-circuit line.

FIG. 4 is a diagram showing a resonance state at the third frequency f3. The frequency f3 is set to a frequency exceeding twice the first frequency f1. The third element el3 functions as a third radiating element, and a resonance current Is2 is induced in the components c, f, g, and h. The third element el3 is formed to have a length substantially ¼ of the wavelength λ3 that resonates at the third frequency f3, and has a current distribution in a series resonance mode in which the current is minimized on the open end side.
In the ideal state, the first element el1 and the second element el2 have high impedance and are not visible from the power feeding side, and are shown by dotted lines. When the third frequency f3 is a frequency close to a higher-order resonance frequency at which the first element el1 and the second element el2 can resonate, a resonance current of higher-order series resonance is also induced in each element. Is smaller than the current due to the main resonance.

FIG. 5 is a diagram showing a resonance state at the fourth frequency f4. A resonance current Ip2 in a higher-order parallel resonance mode is induced in the first radiating element.
In the ideal state, the third element el3 has a high impedance and is not visible from the power feeding side, so is shown by a dotted line. When the third element el3 is coupled to the second element el2, a series resonance resonance current may be induced, but is smaller than the current due to the main resonance.

FIG. 6 is a diagram showing a resonance state at the fifth frequency f5. A resonance current Is3 in a higher-order series resonance mode is induced in the second radiating element.
In the ideal state, the first element el1 and the third element el3 have high impedance and are not visible from the power feeding side, and are indicated by dotted lines. However, the first-order radiating element and the third radiating element are connected in series. A resonance current due to resonance may be induced. In this case, the resonance current is smaller than the current due to the main resonance.

The spacing between the elements can be adjusted as appropriate so as to exhibit the desired antenna characteristics, but the spacing between the adjacent elements and the antenna characteristics tend to be approximately the following.
When the distance between the first element el1 and the second element el2 is reduced and the coupling is strengthened, the band of the VSWR at the first frequency is narrowed and the band of the VSWR at the second frequency f2 is widened. Further, the fifth resonance moves to the low frequency side.
When the distance between the second element el2 and the third element el3 is reduced and the coupling is increased, the third resonance moves to the low frequency side, and the gain at the second frequency f2 decreases.

In the present embodiment, the first element el1 and the second element el2 are linear and extend in the same direction, but can be configured by curves or meandering. Further, it may be bent and folded back so that the tip side extends in the same direction. Furthermore, the tip end side of the folded second element el2 may be opposed so as to be coupled with the third element el3.
According to such a configuration, the multiband antenna can be configured in a small size. In addition, a wideband multiband antenna can be obtained by utilizing resonance in the path of the second element el2 and the third element el3.

The elements that make up each element are formed on a printed circuit board such as FR4 (glass epoxy resin board) using a low resistance Cu thin plate by a known technique such as etching, or a ceramic made of alumina or other dielectric ceramic material. It can also be formed on a substrate with a good conductor such as Au, Ag, or Cu by a known method such as printing or etching. Moreover, you may comprise with the conductor thin plate which consists of Cu or phosphor bronze.
If the element is formed of an alloy such as phosphor bronze which is easy to process but is not easily deformed by an external force, it can be formed into a free shape regardless of the support.
The elements formed on the printed circuit board or the ceramic body may be mounted on another printed circuit board having a ground surface, or may be configured in combination with a conductor thin plate.

Embodiments of the multiband antenna according to the present invention will be described below.
FIG. 7 is a diagram for explaining a configuration example of a multiband antenna. Moreover, the structural example by a metal plate is shown in the perspective view of FIG. Although this multiband antenna is supported by polycarbonate resin, it is omitted in the drawing. As for the external dimensions, the width is 10 mm, the length is 46.5 mm, and the height is 6.5 mm.

The multiband antenna includes a first element el1, a second element el2, and a third element el3 that are connected to the power feeding circuit 200 via a connection point (feeding point) A, and a printed circuit board ( It is composed of a thin conductor plate having a thickness of 0.1 mm and made of phosphor bronze provided upright on one side.
The printed circuit board is a copper-clad double-sided conductor board (glass epoxy board), but the ground pattern is not formed on both sides of the part overlapping the multiband antenna.

  The first element el1 and the second element el2 extend in the same direction with respect to the feeding point A, and after being bent at a plurality of locations, the end portion faces the feeding point A side. The length of the first element el1 was 81.5 mm, and the length of the second element el2 was 77.5 mm. In the present embodiment, the proximity portion is provided on the end side, and the distance between the elements is 0.5 mm. In other parts, it is formed with an interval of 1.5 mm.

  A third element el3 is formed toward the end portions of the first element el1 and the second element el2. The length was 30.5 mm. The end portion is in a region surrounded by the second element el2 in three directions, and the distance between the adjacent second element el2 is 1.9 mm on the end portion side of the second element el2 and on the side close to the feeding point. 2.0 mm.

  With this configuration, the first resonance is in the LTE Band 17 band, the second resonance is in the GSM850 / 900 band, the third resonance is in the DCS / PCS band, the fourth resonance is in the UMTS band, and the fifth resonance is in the LTE Band 7 band. A multiband antenna.

The obtained multiband antenna was connected to a network analyzer via a 50Ω coaxial cable, and VSWR characteristics were measured.
FIG. 9 shows the VSWR characteristics at 100 MHz to 3300 MHz. In the VSWR characteristic diagram, the dotted line indicates that the VSWR value is 4. As impedance characteristics at each frequency, FIG. 10 shows a Smith chart at 100 MHz to 1700 MHz, FIG. 11 shows a Smith chart at 1700 MHz to 2500 MHz, and FIG. 12 shows a Smith chart at 2500 MHz to 3300 MHz.

  According to the multiband antenna of the present invention, the frequency band in which each resonance appears in the band of each transmission / reception system and the VSWR value is 4 or less covers the band of each transmission / reception system.

DESCRIPTION OF SYMBOLS 1 Multiband antenna 200 Feed circuit el1 1st element el2 2nd element el3 3rd element

Claims (1)

A multi-band antenna corresponding to a plurality of transmission / reception systems,
A first element whose one end side is connected to the feeding point and whose other end side is an open end; one end side is connected to the feeding point; the other end side is an open end; and the element length is shorter than the first element; and A second element extending side by side in substantially the same direction as the first element, one end side is connected to the feeding point, the other end side is an open end, the element length is shorter than the second element, and A third element extending at least partially aligned in the same direction as the second element, and a short-circuit line for grounding the first to third elements directly or via an impedance element on the feeding point side,
In the multiband antenna, as a first resonance, a first radiating electrode having both ends open constituted by elements of the first element and the second element resonates in parallel at a first frequency f1, and a second resonance The second element serves as a second radiation electrode in series resonance at the second frequency f2, and as the third resonance, the third element serves as a third radiation electrode in series resonance at the third frequency f3. As the fourth resonance, the first radiation electrode resonates in parallel at the fourth frequency f4, and as the fifth resonance, the second radiation electrode resonates in series at the fifth frequency f5,
The first frequency f1 to the fifth frequency f5 have a relationship of f1 <f2 <2 × f1 <f3 <f4 <f5.

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