JP2014075650A - Composite antenna - Google Patents

Abstract

Provided are an antenna and a portable wireless device that are small in size, have a wide VSWR characteristic, can be applied to a plurality of communication systems, and are capable of impedance matching and resonance frequency adjustment.
A first antenna element B whose one end is connected to a feeding point S and whose other end is an open end is disposed close to and opposed to the first antenna element B with a predetermined distance, and one end side is connected to the feeding point S. A composite antenna including a second antenna element A connected and having an open end on the other end side and a length longer than that of the first antenna element B, and a series of resonance currents flowing in the first antenna element B It operates in a resonance mode and a parallel resonance mode by a resonance current flowing through the first antenna element B and the second antenna element A, but the second antenna element A does not operate in a series resonance mode, and depends on the series resonance mode. The frequency of the first resonance is higher than the frequency of the second resonance.
[Selection] Figure 1

Description

    The present invention relates to an antenna used in a wireless communication device, and more particularly to a multiband-compatible composite antenna that can be used in a plurality of frequency bands.

    In response to the rapid spread of wireless communication devices such as mobile phones, a plurality of communication systems have been used, and the frequency bands to be used have been diversified. Recent mobile phones are compatible with international roaming and can use a plurality of transmission and reception bands corresponding to domestic and foreign communication systems. In such a case, using an antenna for each high-frequency circuit of a communication system to be used causes an increase in the number of parts including peripheral circuits of the antenna such as a matching circuit, and the wireless communication device becomes expensive, Both weights increase, making them unsuitable for portable use. Therefore, a small antenna that can be connected to a common feeding point in a plurality of communication systems and is compatible with a plurality of communication systems (multiband) has been studied.

  Since there are various communication systems used for wireless communication devices, here, mobile phones that support the LTE band, GSM850 / 900 band, DCS band, PCS band, and UMTS band will be described as examples. LTE and GSM are trademarks or registered trademarks. It is. The uplink / downlink frequency band of each communication system is roughly divided into a low frequency band of 704 MHz to 960 MHz and a high frequency band of 1710 MHz to 2170 MHz. In the low frequency band including the LTE Band17 band and the GSM850 / 900 band, the center frequency (middle of the lower limit frequency and the upper limit frequency) is 832 MHz, the bandwidth is 256 MHz, and the specific bandwidth is about 30.8% [256 MHz. / 832 MHz]. In the high frequency band including the DCS band, the PCS band, and the UMTS Band1 band, the center frequency is 1940 MHz, the bandwidth is 460 Hz, and the specific bandwidth is about 23.7% [460 MHz / 1940 MHz]. If the frequency relationship is seen, the communication system of a high frequency band is about 2 to 2.5 times the communication system of a low frequency band. In order of frequency, it is a frequency band of 704 to 746 MHz in the LTE Band 17 band, 824 to 960 MHz in the GSM850 / 900 band, 1710 to 1880 MHz in the DCS band, 1850 to 1990 MHz in the PCS band, and 1920 to 2170 MHz band in the UMTS band. Depending on the system, some frequency bands may overlap.

  In general, an antenna element that constitutes an antenna (also referred to as a radiation element, a radiation electrode, or a radiation path) has resonance current at a fundamental frequency in resonance in a fundamental mode and resonance at a higher order frequency as resonance in a higher order wave mode. An electric current is generated. The resonance frequency is substantially determined by the length of the antenna element. A monopole antenna known as a classic antenna operates in a series resonance mode, and in principle resonates at a quarter wavelength in a fundamental wave mode. In the next wave mode, resonance occurs at 3 times the fundamental mode, that is, 3/4 wavelength. In the case of a dipole antenna that operates in the parallel resonance mode, the fundamental mode resonates at 1/2 wavelength, and the higher-order mode resonates at 3/2 wavelength.

    In order to make such an antenna compatible with a plurality of communication systems, if the resonance of the fundamental wave mode is set to the low frequency band, the high frequency band corresponds to the resonance of the higher order wave mode. However, since the resonance frequency between the low frequency band and the high frequency band does not have a 1: 3 relationship, it cannot be simply multibanded. Further, VSWR (voltage standing wave ratio), which is one of antenna characteristics, has a problem that the frequency characteristics are narrow to cover a low frequency band or a high frequency band.

  To deal with such a problem, Patent Document 1 discloses a composite antenna that uses a plurality of antenna elements to widen the VSWR frequency characteristic. FIG. 10 shows the configuration. In the figure, current distributions I1 to I3 not shown in Patent Document 1 are shown. This is a code given to explain the operation of the composite antenna described later.

  The composite antenna includes an element 200 (hereinafter sometimes referred to as a common element) standing on the ground plane GND, and elements 201 and 202 (hereinafter referred to as “common elements”) connected to one end side of the element 200 having different lengths. Common element 200 is grounded by element 204 (hereinafter also referred to as a ground element).

  The first antenna element composed of the elements 200 and 201 constitutes an inverted F-type antenna, and the second antenna element composed of the elements 200 and 202 constitutes an inverted L-type antenna, and each antenna is connected to the feeder circuit 203 via a common feeding point S. And is excited by power feeding from the power feeding circuit 203. As is well known, the inverted F-type antenna and the inverted-L type antenna are low profiled by deforming the monopole antenna, and both operate in the series resonance mode.

  By configuring the antenna elements with different lengths, for example, an inverted F-type antenna is adapted to the GSM band (low frequency band), an inverted L-type antenna is adapted to the DCS band (high frequency band), and the low frequency band It is a composite antenna that can be used for high frequency communication systems.

  In addition, it is also described that the VSWR frequency characteristic is widened by resonating the inverted F-type antenna at the frequency f1 and resonating the inverted L-type antenna at the frequency f2, for example, so that the resonance frequency of each antenna is slightly different. ing. According to this configuration, as shown in FIG. 11, the VSWR frequency characteristic exhibits a bimodal characteristic in which two resonances overlap each other, and thus has a low VSWR in a frequency band wider than the single peak characteristic. In the figure, as indicated by the symbol α, a frequency band is generated between the resonance frequencies f1 and f2 where the VSWR waveform overlaps and the VSWR characteristics deteriorate. Hereinafter, the frequency band is referred to as a degradation peak portion. The apparent VSWR at the degradation peak portion increases as the resonance frequencies f1 and f2 move away, and decreases as they approach.

  In Patent Document 2, it is pointed out that even if such a composite antenna has a small VSWR, the radiation efficiency is remarkably deteriorated and is not suitable for practical use. Although the cause of deterioration of radiation efficiency is not clarified, it indicates that the deterioration peak part is directly related.

FIG. 12 shows a composite antenna exemplified in Patent Document 2. This composite antenna has the same basic configuration as that of the composite antenna shown in Patent Document 1, branches from the common element 130 connected to the feed circuit 203 via the feed point s, and has an open end in the same direction. It consists of two inverted L-shaped antennas with horizontal elements 110 and 120 provided.
As shown in the VSWR frequency characteristics of FIG. 13, a plurality of antennas are operated at close resonance frequencies. One of the inverted L antennas is resonated at a frequency within a desired frequency band, and the other inverted L antenna is resonated. Is outside the frequency band and the degradation peak portion is outside the frequency band, thereby preventing deterioration of radiation efficiency within a desired frequency band and widening the VSWR characteristic.

Each of the composite antennas operates a plurality of antennas in a series resonance mode. However, Patent Document 3 discloses a composite antenna corresponding to a plurality of communication systems using both a series resonance mode and a parallel resonance mode. It is disclosed. The structure of this composite antenna is shown in FIG.
This composite antenna includes elements A (A1, A2), B, C, D, E, and F, and is described in Cited Document 1 and Cited Document 2 in that a plurality of antenna elements are formed by a combination of elements. Although it is the same as a composite antenna, it is different in that a parallel resonance mode is used in addition to a series resonance mode.

  The first antenna element by the elements B and E resonates in parallel at a half wavelength of the first frequency, and the second antenna element by the elements A, B, and C resonates in series at a quarter wavelength of the second frequency. The third antenna element composed of elements B, C, and D resonates in parallel at 1/2 wavelength of the third frequency, and the fourth antenna element composed of elements A and D resonates in series at 1/4 wavelength of the fourth frequency. The fifth antenna element by the elements A2, D, and F resonates in parallel at a half wavelength of the fifth frequency, and the elements A1 and F resonate in series at a quarter wavelength of the sixth frequency. The frequency relationship is configured such that the first frequency <the second frequency <the third frequency <the fourth frequency <the fifth frequency <the sixth frequency.

JP 2003-124742 A JP 2009-4847 JP 2005-252480 A

  In developing antennas applicable to a plurality of communication systems, the present inventors studied the operation and problems of the composite antenna shown in FIG. 10 as a model. In the following description, the composite antenna will be described as a transmitting antenna. However, since the antenna has reversibility, it can be appropriately read as receiving transmission and receiving power as receiving power.

Although there is no direct description in Patent Document 1 or Patent Document 2, as described in Patent Document 3, a composite antenna configured using antenna elements having different lengths is basically one series resonance. It is known that parallel resonance occurs at the transition frequency from one to the other series resonance.
When operating in the series resonance mode, a differential mode current is induced in the antenna element, and in a parallel resonance mode, a common mode current is induced. Resonance currents distributed to each element are distributed to three antenna elements at three different frequencies as indicated by arrows indicated as I1, I2, and I3 in a simplified manner.

The first antenna element composed of the common element 200 connected to the power feeding circuit 203 and the horizontal element 201 connected to the common element 200 is formed to a length of ¼ wavelength of the resonance frequency f1. The resonance current generated and operated in the series resonance mode has a current distribution I1 that minimizes the current on the open end side.
The second antenna element composed of the common element 200 connected to the power feeding circuit 203 and the horizontal element 202 connected to the common element 200 is formed to have a length of ¼ wavelength of the resonance frequency f2. The resonance current generated by operating in the series resonance mode has a current distribution I2 that minimizes the current on the open end side.
The third antenna element constituted by the common element 200 and the horizontal elements 201 and 202 operates in the parallel resonance mode, and resonates at a frequency f3 between the frequency f1 and the frequency f2. The generated resonance current has a current distribution I3 that minimizes the current at both open ends.

  When the antenna is operated in the series resonance mode, the antenna is designed to radiate not only from the antenna element constituted by each element but also from the ground plane. For example, in a mobile phone, the radiation efficiency is improved by increasing the apparent antenna volume by using the radiation from the metal part of the housing. On the other hand, it is known that in the parallel resonance mode, a resonance current flows through the antenna element, but almost no current flows through the feeding point and the ground plane, so that the VSWR frequency characteristic tends to be a narrow band.

  In the case of the series resonance mode, a differential mode current is induced in each antenna element, and in the case of the parallel resonance mode, a common mode current is induced, but in fact, they are not clearly separated according to the frequency. Not simple. In particular, when the resonance frequencies of the two series resonance modes are close to each other, in the transition frequency band in which the resonance modes change, currents having different phases in both modes are mixed and strengthened or weakened. For this reason, it has been inferred that the radiation efficiency of the composite antenna of Patent Document 1 is lowered even if the VSWR is not so large in the frequency band where the series resonance mode is changed to the parallel resonance mode.

  Based on such inference, even if the degradation peak portion α is outside the use frequency band as in Patent Document 2, and the frequency band where the low VSWR is widened, the radiation gain is degraded to some extent. It is thought that the area will remain. In order to remove the degradation peak portion α from the predetermined frequency band, it is necessary to greatly separate the resonance frequencies of the two series resonance modes. In this case, it is not possible to increase the bandwidth of the VSWR characteristics.

  Also in Patent Document 3, when the resonance frequencies of the two series resonance modes are close to each other, for the same reason, it is considered that the radiation efficiency is lowered in the frequency band where the series resonance mode is changed to the parallel resonance mode. It is difficult to set parallel resonance at an adjacent frequency, and the degree of freedom in setting the resonance frequency is limited.

  In addition, since both of the composite antennas extend the antenna element using the series resonance mode in the same direction, it is difficult to obtain isolation between the antenna elements in the basic mode, and further, a mirror image current flowing on the ground plane is not obtained. In order to achieve the same phase, if the design change of the other antenna element, such as the length, is affected, the impedance of the other antenna element is affected, disturbing the matching, and the resonance frequency also fluctuates, making the antenna design difficult. Problems remained.

  The present invention is proposed in view of such circumstances, and is an antenna and a portable device that are small in size, have a wide VSWR characteristic, are compatible with a plurality of communication systems, and are capable of impedance matching and resonance frequency adjustment. An object is to provide a wireless device.

  The present invention is a composite antenna that includes linear antenna elements having different lengths and that can be used in one series resonance mode and one parallel resonance mode as a fundamental mode resonance, and is a pair of first antennas Each antenna element has an element and a second antenna element, and each antenna element is connected to a common feeding point on the start end side and is open to the end side, and is extended side by side from the start end side to the end side to form an electric field coupling. The composite antenna is characterized in that one antenna element that does not operate in the series resonance mode is used as a resonance frequency adjusting means in the parallel resonance mode.

  When multiple antenna elements are placed close to each other and electric field coupled, the resonance in the fundamental mode of the composite antenna is reduced by one differential current in one of the two series resonance modes by each antenna element. Resonance and one parallel resonance mode resonance. In the present invention, the resonance frequency of the parallel resonance mode is adjusted without affecting the resonance of the series resonance mode by using one antenna element that does not operate in the series resonance mode as a resonance frequency adjusting means of the parallel resonance mode. I can do it.

  In the present invention, it is preferable to provide an opposing portion with a narrower element spacing on the terminal side of the paired antenna elements so that the electric field coupling generated between the elements is different between the starting end side and the terminal end side. By strengthening the coupling on the terminal side, the antenna element operates in a series resonance mode by the first antenna element having a relatively short length and a parallel resonance mode by the first and second antenna elements. In this case, the resonance frequency of the parallel resonance mode appears on the lower frequency side than the resonance of the series resonance mode. The relatively short antenna element can be used as the resonance frequency adjusting means in the series resonance mode.

  According to the composite antenna of the present invention, resonance in the same resonance mode does not occur at adjacent frequencies, so there is no need to consider isolation between antenna elements, and impedance matching with the feeding circuit and setting of the resonance frequency are also possible. It becomes easy.

  In the present invention, the first antenna element having one end connected to the feeding point and the other end open to the first antenna element is disposed in close proximity to the first antenna element with a predetermined interval, and one end is connected to the feeding point. A composite antenna including a second antenna element having an open end on the end side and a length longer than that of the first antenna element, the series resonance mode by a resonance current flowing through the first antenna element, and the first antenna element The antenna operates in a parallel resonance mode based on a resonance current flowing in one antenna element and the second antenna element, but the second antenna element does not operate in a series resonance mode, and the frequency of the first resonance in the series resonance mode is the parallel resonance mode. The composite antenna is characterized in that the frequency is higher than the frequency of the second resonance due to the mode.

  In the present invention, the open ends of the first antenna element and the second antenna element may be folded back toward the feeding point. According to such a configuration, it is easy to fit in a limited space such as in a housing of a mobile phone or the like.

  In the present invention, it is preferable to further increase the number of antenna elements. As with the first and second antenna elements, the added third antenna element has one end connected to the feeding point, the other end is an open end, and is configured to be short in length to operate in the series resonance mode. The frequency of the third resonance by the three antenna elements is set to a frequency higher than twice the frequency of the second resonance.

  According to the present invention, it is an object of the present invention to provide a composite antenna and a portable wireless device that are small in size, have a wide VSWR characteristic, are compatible with a plurality of communication systems, and are capable of impedance matching and resonance frequency adjustment. . The wireless device using the composite antenna of the present invention is small in size and can use a plurality of communication systems.

It is a figure for demonstrating the composite antenna which concerns on one Example of this invention. It is a figure which shows the VSWR frequency characteristic of the composite antenna which concerns on one Example of this invention. It is a figure for demonstrating the composite antenna which concerns on the other Example of this invention. It is a figure which shows the VSWR frequency characteristic of the composite antenna which concerns on one Example of this invention. It is a figure for demonstrating the composite antenna which concerns on the other Example of this invention. It is a figure which shows the VSWR frequency characteristic of the composite antenna which concerns on one Example of this invention. It is a figure for demonstrating the composite antenna used as the basis of this invention. It is a figure for demonstrating the VSWR frequency characteristic of the composite antenna used as the basis of this invention. It is a figure for demonstrating the VSWR frequency characteristic of the composite antenna used as the basis of this invention. It is a figure for demonstrating the conventional composite antenna. It is a figure which shows the VSWR frequency characteristic of the conventional composite antenna. It is a figure for demonstrating the other conventional composite antenna. It is a figure which shows the VSWR frequency characteristic of the other conventional composite antenna. It is a figure for demonstrating the other conventional composite antenna.

  Before describing the composite antenna of the present invention, the composite antenna that is the basis thereof will be described with reference to FIG. This figure shows an electromagnetic field simulation model of the composite antenna. An antenna is formed along the upper side of a rectangular substrate of length Lmm × width Wmm × thickness Tmm, and a ground plane GND is formed except for a portion where an antenna element is provided. The horizontal element a and the elements b (b1, b2) extending substantially in parallel with the ground plane GND and with the gap G in the same direction, the common elements c (c1, c2) connected to the feeder circuit 203, and the element b for grounding d.

  This model is based on a dielectric substrate having a length of 1100 mm, a width of 600 mm, and a thickness of 0.6 mm, and includes a region where the ground surface on the upper side is not formed in the drawing, and an antenna is disposed on one main surface side of the region. The substrate 300 is made of a resin material having a relative dielectric constant εr = 4.5 and a dielectric loss (dielectric loss tangent) tan δ = 0.005. Each element has a width of 1 mm and a thickness of 0.15 mm, and is an integrated copper strip line. In the figure, the length of each element indicated by a lower case alphabetic code is based on the center line. The interval G does not include the element width. The composite antenna shown here includes an antenna element A composed of elements a, c1, and c2, an antenna element B composed of elements b1, b2, and c2, and an antenna composed of elements a, c1, b1, and b2. The element C is a combination of three antennas. Note that L1 = 83 mm, L2 = 87 mm, and W = 1.5 mm.

(Examination 1)
Table 1 shows the verification conditions by simulation based on such conditions, and Tables 2 and 3 summarize the results. FIG. 8 shows the VSWR frequency characteristics under condition 2. In this examination, the antenna element B on the side close to the ground plane GND is configured to be short, and the antenna element A on the side far from the ground plane GND is configured to be long.

  Table 2 shows resonance frequencies and resonance modes in the fundamental wave mode. The resonance frequency is a peak frequency at which the VSWR frequency characteristic shows a bottom value, the frequency band indicates a band of VSWR ≦ 3 including the resonance frequency, and when VSWR exceeds 3, it is indicated by a symbol *. Table 3 shows resonance frequencies and resonance modes in the higher-order wave mode.

  The resonance mode is determined based on the distribution of current induced in each antenna element, its intensity, and balance. For example, the series resonance is a case where a resonance current flows predominantly in one antenna element, and the parallel resonance is a case where a resonance current having an equal current intensity flows in both antenna elements. In the current distribution, a resonance current flows through both antenna elements, but there may be a clear difference in current intensity. Such a state is shown in the table as series> parallel as a state in which parallel resonance and series resonance are mixed (resonance mixed state).

  According to the examination results using the electromagnetic field simulation by the present inventors, in the fundamental wave mode, the series resonance of the antenna element A appears, but the antenna element B shorter than the antenna element A has a resonance current based on the series resonance. As a result, the resonance in the fundamental wave mode is caused by the series resonance (f1) on the low frequency side and the parallel resonance by the antenna element C on the higher frequency side than the series resonance. (F2) only (conditions 1 and 2). In addition, in the VSWR frequency characteristics, the resonance in the series resonance mode has a wider band than the parallel resonance mode, and the resonance in the series resonance mode has a wider band as the resonance band on the high frequency f2 side becomes narrower.

  As the interval G between elements increases, the parallel resonance on the high frequency f2 side in the fundamental wave mode greatly decreases the band of the VSWR frequency characteristic, and the resonance current flows through both antenna elements. An unstable current distribution with increasing current intensity was obtained (Condition 3).

  In the higher-order wave mode, series resonance (f3) on the low frequency side and parallel resonance (f4) by the antenna element C on the higher frequency side than the series resonance occurred (conditions 1 and 3). In condition 1, since the frequency band with VSWR of 3 or less is 3.06 GHz to 3.56 GHz, the f3 frequency band and f4 frequency band in Table 3 are divided into two frequency bands with reference to the degradation peak portion appearing in the frequency band. Separately shown.

The resonance state of such a composite antenna is different from a resonance mode that occurs in the order of series resonance, parallel resonance, and series resonance as conventionally known. It is considered that the degree of coupling between elements and the close proximity of resonance frequencies have an effect.
Also, considering the bandwidth of the VSWR frequency characteristics, it is difficult to use such a composite antenna as it is. Further, when the current distribution of the antenna element B appears strongly in the mixed resonance state (condition 3), the length of the other antenna element is the same as in the case where the two antenna elements using the series resonance mode are extended in the same direction. When the design change was made, matching was disturbed by affecting the impedance of the other antenna element.

(Examination 2)
In this examination, the antenna element B on the side close to the ground plane GND is long and the antenna element A on the far side is short. The verification conditions by simulation are summarized in Table 3, and the results are summarized in Table 4. In FIG. S. W. R characteristic is shown.
It is a figure showing the conditions of the simulation of a composite antenna.

  In the composite antenna of this configuration, a resonance mode similar to that of the composite antenna of Study 1 appears, and series resonance of the antenna element B appears. However, a resonance current based on series resonance is hardly induced in the antenna element A shorter than the antenna element B. The series resonance on the high frequency side does not appear, and the resonance in the fundamental mode includes the series resonance mode on the low frequency side by the antenna element B and the parallel resonance mode having a higher resonance frequency than the series resonance mode by the antenna element C. It became 2 mode. Similarly, in the VSWR frequency characteristics, the resonance in the series resonance mode is wider than the resonance in the parallel resonance mode, but the resonance in the series resonance mode is narrower than in Study 1, and the resonance in the parallel resonance mode is from Study 1. Was also broadband. Further, as the element spacing G narrowed, the series resonance band narrowed and the series resonance band widened. In addition, the resonance in the higher-order wave mode is similar to the condition 1 in that series resonance by the antenna element B and parallel resonance by the antenna element C occur, and the frequency band where the VSWR is 3 or less is 450 MHz to 530 MHz.

  The resonance frequencies f1 and f2 in the fundamental wave mode are set according to the lengths of the antenna element A and the antenna element B. However, since resonance in the series resonance mode does not occur in one of the antenna elements, the length of the antenna element is adjusted. Can be performed without considering the influence of the other antenna element, and the resonance frequency f1 on the low frequency side can be easily determined. When changing the resonance frequency in the series resonance mode, the length of the antenna element in which the resonance current is induced may be changed. Further, when changing the resonance frequency in the parallel resonance mode, it is only necessary to change the length of the antenna element in which no resonance current is induced in the series resonance mode, and the resonance frequency can be easily adjusted independently. When the resonance frequency of the fundamental wave mode is changed, the resonance frequencies f3 and f4 in the higher-order wave mode are increased or decreased accordingly.

  The composite antenna obtained in this study has wide and practical VSWR frequency characteristics in the fundamental wave mode and the higher-order wave mode. However, when examining whether the LTE Band 17 band on the low frequency side can be handled in the series resonance mode and the GSM850 / 900 band on the high frequency side in the parallel resonance mode, the LTE Band 17 band has a narrow frequency band of 42 MHz and the VSWR If the frequency band of the series resonance mode having a wide frequency characteristic can be used, it can be adequately handled. However, the GSM850 / 900 band has a frequency band of 136 MHz, and the band of the VSWR frequency characteristic obtained in the parallel resonance mode is narrow. Looking at VSWR as 3 or less, the frequency band cannot satisfy the GSM850 / 900 frequency band.

As the element spacing G is narrowed, the VSWR frequency characteristic due to the parallel resonance mode becomes narrower, while the VSWR frequency characteristic due to the series resonance mode becomes broader. Although it is possible to increase the bandwidth of the VSWR frequency characteristic of the mode, the spread of the VSWR frequency characteristic due to the parallel resonance mode is small compared to the narrowing of the VSWR frequency characteristic due to the series resonance mode.
Further, if the VSWR frequency characteristic of condition 8 is satisfied, it is possible to satisfy the bandwidth (256 MHz) of LTE Band 17 band and GSM 850/900 band, but assuming that it is actually installed in a wireless communication device, The resonance frequency may fluctuate due to the influence of parasitic reactance due to interference with other components, and the frequency band covered by the series resonance mode including the fluctuation of the resonance frequency due to disturbance is not sufficient. In the first place, the wider the gap G, the smaller the size of the antenna is hindered, making it unsuitable for use in a small wireless communication device.

(Examination 3)
Therefore, the present inventors have further studied a composite antenna using two resonance modes, and the low frequency band is supported by a relatively narrow parallel resonance mode, and the high frequency band is handled by a relatively wide series resonance mode. We have conducted extensive research on complex antennas.
As a result, the distance between the elements extending in the same direction of the antenna element is widened on the feeding circuit side so that coupling is relatively sparse on the starting end (feeding circuit) side, and narrowed on the terminal end (opening end) side, and on the open end side The series resonance on the low frequency side disappears but the series resonance on the high frequency side appears, and as a result, the resonance in the fundamental wave mode has a resonance frequency band lower than the series resonance mode and the series resonance mode. It was found that the parallel resonance mode appears in 2 modes.

  FIG. 1 is a diagram showing the conditions for simulation of a composite antenna according to an embodiment of the present invention. The difference from the composite antenna in the examinations 1 and 2 is that a part of the antenna element is bent in a crank shape, and the interval between the antenna elements is made different between the interval G2 on the feeding side and the interval G1 on the open end side, The point is that G2 <G1.

  The verification conditions by simulation are summarized in Table 6, and the results are summarized in Tables 7 and 8. FIG. 2 shows the VSWR frequency characteristics under condition 9.

  Table 7 shows resonance frequencies and resonance modes in the fundamental wave mode. The resonance frequency is a peak frequency at which the VSWR frequency characteristic shows a bottom value, and the frequency band is a band of VSWR ≦ 3 including the resonance frequency. Table 8 shows resonance frequencies and resonance modes in the higher-order wave mode. Note that the f3 frequency band and f4 frequency band in Table 8 are also divided into two frequency bands based on the degradation peak portion appearing in the frequency band as in Study 1.

According to the examination result using the electromagnetic field simulation, the resonance current based on the series resonance of the antenna element A is hardly induced in the fundamental wave mode, while the antenna element B shorter than the antenna element A is based on the series resonance. The point where the resonance current is induced is different from those in the studies 1 and 2.
The resonance frequencies f1 and f2 can be set according to the lengths of the antenna element A and the antenna element B, and the resonance in the series resonance mode does not occur in the relatively long antenna element A. The resonance frequency f1 of the parallel resonance mode on the low frequency side can be determined. When changing the resonance frequency in the series resonance mode, the length of the antenna element B in which the resonance current is induced may be changed.

The condition 9 and the condition 11 are different from each other in the close facing portion on the open end side of the antenna element. In the condition 9, the facing length is 10 mm at the interval G2 = 0.5 mm, and in the condition 11, the distance is 30 mm. It has become. If the opposing length is long, the band of the VSWR frequency characteristic of the parallel resonance is widened, and the VSWR frequency characteristic of the series resonance is narrowed. In addition, the frequency band of the series resonance tends to be narrower than the frequency band of the parallel resonance is widened.
Further, the condition 9 and the condition 10 have different antenna element intervals G2. When the interval G2 is narrowed, the resonance frequency of the parallel resonance mode is lowered and the VSWR frequency band is narrow. On the other hand, the resonance frequency of the series resonance mode is also lowered, but the VSWR frequency band is widened.

  The VSWR frequency characteristic of the composite antenna obtained in this study has a relationship that the VSWR frequency characteristic by the parallel resonance mode is a narrow band, and the VSWR frequency characteristic by the series resonance mode is a wide band. If so, the LTE Band 17 band on the low frequency side can be sufficiently handled in the parallel resonance mode, and the GSM850 / 900 band on the high frequency side in the series resonance mode.

  In the high-order wave mode, as in the resonance in the fundamental wave mode, parallel resonance by the antenna element C occurs on the low frequency side, and series resonance by the antenna element B occurs on the high frequency side. In the case of close coupling at the open end side, the mode of resonance occurring in the higher-order mode may differ depending on conditions such as the distance G between the elements and the length of the elements to be closely opposed to each other. . For example, in the condition 10, unlike the resonance in the fundamental wave mode, the low frequency side series resonance (f3) by the antenna element A and the parallel resonance (f4) by the antenna element C on the higher frequency side than the series resonance occurred. . In some cases, series resonance (f3) on the low frequency side by the antenna element A and series resonance (f4) by the antenna element B on the higher frequency side than the series resonance may occur. Thus, although the resonance of the higher-order wave mode is various, the VSRW frequency band exceeds 300 MHz and a relatively wide band resonance is obtained, and the radiation efficiency is not significantly deteriorated.

(Examination 4)
FIG. 3 is a diagram showing conditions for another antenna simulation of the present invention. The difference from the antenna shown in FIG. 1 is that the antenna element having the longer actual length is arranged closer to the ground plane GND than the antenna element having a relatively shorter actual length. Table 9 shows the verification conditions by simulation based on such conditions, and Table 10 shows the results. In FIG. S. W. R characteristic is shown.

  In the case of Study 4, similarly to Study 3, a resonance current based on series resonance is induced in the antenna element having a short length in the fundamental wave mode, and on the other hand, no series resonance on the relatively high frequency side appears, and as a result, Resonance occurred in the frequency order of parallel resonance and series resonance. Further, the VSWR frequency characteristic of Study 4 is wider than that of Study 3, and in the resonance modes of Conditions 12 and 13, the LTE Band 17 band on the low frequency side is the parallel resonance mode and the frequency band is high frequency. The GSM850 / 900 band on the side can be sufficiently handled in the series resonance mode. Further, although the resonance in the higher-order wave mode depends on the conditions, parallel resonance by the antenna element C occurs on the low frequency side as in the resonance in the fundamental wave mode, and the series by the antenna element B occurs on the high frequency side. Resonance occurred and the VSWR frequency band was a wide band exceeding 400 MHz.

  Hereinafter, the composite antenna according to the present invention will be described in detail. FIG. 5 is a diagram for explaining a configuration example of a composite antenna. The composite antenna 1 is configured as a composite antenna for a mobile phone corresponding to the LTE Band 17 band, GSM 850/900 band, DCS band, PCS band, UMTS band, and LTE Band 7 band. The uplink / downlink frequency band of the LTE Band7 band is 2500 MHz to 2690 MHz.

  This composite antenna has outer dimensions of a width Wa of 10 mm, a length of Wb of 46.5 mm, and a height of Wc of 6.5 mm, and is composed of a conductive thin plate having a thickness of 0.1 mm made of phosphor bronze supported by a polycarbonate resin. In the figure, the outline of the component part made of polycarbonate resin is shown by a broken line, and is shown in a transparent manner so that the mounting state of the composite antenna can be easily understood.

  Standing on a printed circuit board 1 made of a copper-clad double-sided conductor board (glass epoxy board), the three antenna elements el1, el2, and el3 are connected to the feed circuit via connection points (feed points). One ends of the antenna elements el1, el2, and el3 are open ends. In the printed circuit board 600, a ground pattern is not formed in a portion overlapping the composite antenna 1. In order to clarify the structure in the following description, the X axis, the Y axis, and the Z axis are taken with reference to the printed circuit board 600 on which the composite antenna is mounted.

  The antenna element consists of a single conductor and is bent. The element 501 rising from the printed circuit board 600 in the Z direction is provided on the first longitudinal side surface of the composite antenna, and one end side is connected to a feeding point S that is connected to the feeding circuit. The end on the rising side is located on the upper surface of the composite antenna which is a horizontal portion with respect to the printed circuit board 600 and is connected to the element 502 extending in the Y-axis direction. Further, the element 502 is bent on the upper surface, and is connected to an element 503 extending in parallel with the ground surface of the printed circuit board 600 in the X-axis direction to constitute an antenna element el3.

  An element 510 extending in the X-axis direction and in a direction opposite to the element 503 branches from the element 502 on the upper surface of the composite antenna. The element 510 reaches the first short side surface of the composite antenna, falls down, extends in the Z direction, and is connected to the element 531. Further, the element 531 is bent to the vicinity of the lower surface on the first short side surface, and extends in the Y-axis direction away from the feeding point S toward the second long side surface facing the first long side surface. Connected. The element 532 is a lower end of the second long side surface, and extends in the X direction from the first short side surface side to the second short side surface side facing the first short side surface; Connected. The end side of the element 533 is bent at the second longitudinal side surface and is connected to an element 534 that rises and extends in the Z direction. The element 534 reaches the upper surface, and is connected to the element 535 extending in the Y direction toward the ground surface on the upper surface. The element 535 is further bent on the upper surface, and extends in parallel with the ground surface of the printed circuit board 600 in the X-axis direction and is connected to the element 536 that approaches the feeding point S, thereby constituting the antenna element el2.

  An element 505 branched from the element 510 on the upper surface of the composite antenna in the Y-axis direction toward the second longitudinal side surface falls on the second longitudinal side surface, extends in the Z direction, and is connected to the element 521. Further, the element 521 is bent to reach the vicinity of the element 533 on the second long side surface, and is spaced in parallel with the element 533 constituting the antenna element el2 from the first short side surface side to the second short side surface side. Connected to the element 522 extending in the X direction. The end side of the element 522 is bent at the second longitudinal side surface, rises and approaches the element 534 in parallel with the element 534 in the Z direction, and is connected to the element 523 that rises and extends in the Z direction. The element 523 reaches the upper surface, and is connected to the element 524 extending in the Y direction toward the ground surface on the upper surface. The element 524 is further bent on the upper surface, is bent, and extends in parallel with the ground surface of the printed circuit board 600 in the X-axis direction and is connected to the element 525 that approaches the feeding point S, thereby constituting the antenna element el1.

  An element 506 branched from the element 510 on the upper surface of the composite antenna in the Y-axis direction toward the first longitudinal side surface falls on the first longitudinal side surface and extends in the Z direction, and is connected to the ground pattern GND of the printed circuit board 600. It connects with the element 540 to do. With such a configuration, an antenna having an inverted F antenna structure and an inverted L antenna structure is combined.

  Each antenna element el1, el2 extends in the same direction, and after being bent at a plurality of locations, the end portion faces the feeding point side. The lengths of the antenna element el1 are 77.5 mm, and the antenna element el2 is 81.5 mm. The elements 524 and 525 constituting the antenna element el1 are close to each other in parallel with the elements 535 and 536 constituting the antenna element el2, so that the antenna element el1 and the antenna element el2 are close to each other on the second long side surface and the top surface. The elements 521 and 522 of the antenna element el1 on the feeding point side and the elements 531, 532 and 533 of the antenna element el2 are provided away from the side surfaces different from each other, and the electric field coupling at the part is weakened. . In this example, the distance on the open end side close to the antenna element was 0.5 mm, and the distance was 1.5 mm or more in other parts.

  The antenna element el3 is formed extending toward the open end side of the antenna element el1 and the antenna element el2. Its length is 30.5 mm. The open end portion is in a region surrounded by the antenna element el1 in three directions, and is opposed to the adjacent antenna element el1 with an interval of 1.9 mm or more so as to reduce interference.

  As a result of confirming the current distribution of the obtained composite antenna, as the resonance of the fundamental mode, the first resonance due to the parallel resonance of the antenna element el1 and the antenna element el2 is in the LTE Band17 band, and the second resonance due to the series resonance of the antenna element el1. Is in the GSM850 / 900 band, the third resonance due to the series resonance of the antenna element el3 is in the LTE Band7 band, and the fourth resonance due to the parallel resonance of the antenna element el1 and the antenna element el2 is performed as DCS / PCS as the higher-order mode resonance. In the band, the fifth resonance due to the series resonance of the antenna element el1 was obtained in the UMTS band.

  The composite antenna was connected to a network analyzer via a 50 ohm coaxial cable, and the VSWR characteristics were measured. FIG. 6 shows the VSWR frequency characteristics at 600 MHz to 2.200 MHz. According to the composite antenna of the present invention, it can be seen that the frequency band in which each resonance appears in the band of each transmission / reception system and the VSWR value is 3 or less covers the band of each transmission / reception system.

1 Composite antenna 501,502,503,504,504,506,521,522,523,524,525,531,532,533,534,535,536,540 Element 203 Feed circuit 300, 600 Board, printed circuit board el1, el2, el3 Antenna element S Feeding point

Claims (7)

A composite antenna having linear antenna elements of different lengths and usable in one series resonance mode and one parallel resonance mode as a fundamental mode resonance,
Each antenna element has a first antenna element and a second antenna element that are coupled to each other, and each antenna element is connected to a common feeding point on the start end side and is open to the end side, and is arranged at intervals from the start end side to the end side. And extend
A composite antenna, wherein one antenna element that does not operate in a series resonance mode is used as a resonance frequency adjusting means in a parallel resonance mode. The composite antenna according to claim 1,
A composite antenna comprising a pair of a first antenna element and a second antenna element, each having a facing portion with a narrower element spacing on the terminal side. The composite antenna according to claim 2,
A composite antenna, wherein a resonance frequency of a parallel resonance mode is lower than a resonance frequency of a series resonance mode. The composite antenna according to claim 2 or 3,
A composite antenna characterized in that a relatively short antenna element of the paired first antenna element and second antenna element operates in a series resonance mode and is used as a resonance frequency adjustment means in the series resonance mode. antenna. A first antenna element having one end connected to the feeding point and the other end opened to the first antenna element close to and spaced from the first antenna element with a predetermined distance, one end connected to the feeding point, and the other end is an open end. A composite antenna comprising a second antenna element having a length longer than that of the first antenna element,
It operates in a series resonance mode by a resonance current flowing through the first antenna element and a parallel resonance mode by a resonance current flowing through the first antenna element and the second antenna element, but the second antenna element operates in a series resonance mode. Without
The composite antenna according to claim 1, wherein the frequency of the first resonance in the series resonance mode is higher than the frequency of the second resonance in the parallel resonance mode. A composite antenna according to any one of claims 1 to 5,
A composite antenna, wherein an open end side of the antenna element is folded back toward a feeding point side. The composite antenna according to any one of claims 1 to 6,
A third antenna element having a shorter length than the paired first and second antenna elements, having one end connected to the feeding point and the other end open, and having a resonance frequency of resonance in the series resonance mode A composite antenna having a frequency higher than twice the frequency.

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