JP2005020289A - Double loop antenna for sharing multiple frequency - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a double loop antenna for sharing multiple frequency which realizes resonance for a plurality of frequencies and suppresses deterioration in antenna efficiency. <P>SOLUTION: A first double loop antenna (402, 602) is provided for resonance to a first frequency formed of at least a pair of the loop antennas electrically connected at one end to the feeding point and at the other end to the grounded conductor. Further, at the internal side of the first double loop antenna, at least one loop antenna is provided for resonance to the frequency higher than the first frequency. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the technical field of dual-loop antennas, and particularly to a multi-frequency dual loop antenna capable of resonating at a plurality of frequencies.
[0002]
[Prior art]
In this type of technical field, an antenna called a double loop antenna is often used from the viewpoint of increasing the antenna gain. This enhances characteristics such as gain and directivity by arranging a plurality of loop antennas having a length of one wavelength symmetrically.
[0003]
FIG. 1 shows a basic principle diagram of a conventional double loop antenna. The twin loop antenna 10 includes a pair of loop antennas 14 connected to a power feeding unit 12 that feeds power through a balanced power feed line. One loop antenna 14 has a length (one wavelength) corresponding to the length of the wavelength with which the antenna should resonate. Further, the dual loop antenna 10 includes a reactance adjustment unit 16 provided along with each loop antenna 14, and this has a function of adjusting the terminal reactance of the antenna. Since one loop antenna 14 has a total length of one wavelength, the phase is 180 degrees different between the vicinity of the power feeding unit 12 and the vicinity of the adjustment unit 16. Accordingly, if power is supplied so that a current flows in the direction of the arrow 18 in the drawing at a certain point in time, a current in the opposite phase (current in the direction of the arrow 20) is generated in the vicinity of the reactance adjustment unit 16. Although the current components in the vertical direction reinforce each other, the current components in the horizontal direction cancel each other, so that the dual loop antenna 10 as a whole functions as a vertically polarized antenna.
[0004]
As shown in FIG. 2, it is also possible to halve the length of the loop antenna by using the principle of mirror image and connecting one end of each loop antenna to a ground conductor. The operating principle of the antenna is the same as that shown in FIG. However, the power supply type in this case is not balanced power supply but unbalanced power supply.
[0005]
On the other hand, with the recent diversification of wireless communication services, services are provided in various frequency bands. Providing a feeding antenna for each of these multiple frequency bands and providing an associated circuit such as a distributor or a mixer in the wireless communication device is disadvantageous from the viewpoint of simplification of the device and cost reduction. It is. For this reason, it is desirable to provide the wireless communication apparatus with an antenna that can resonate with a plurality of frequencies.
[0006]
FIG. 3 shows a conventional dual loop antenna 30 that can resonate at two frequencies. The dual loop antenna 30 includes a pair of first loop antennas 34 that are connected to a power feeding unit 32 that feeds power using a balanced power feed line and resonate at a high frequency (first wavelength). One first loop antenna 34 has a length of the first wavelength. Furthermore, the dual loop antenna 30 has a pair of second loop antennas 36 that resonate at a low frequency (second wavelength) outside the first loop antennas 34. One second loop antenna 36 has a length of the second wavelength. By adopting such a configuration, the double-loop antenna 30 can be selectively tuned to either a low frequency or a high frequency (see, for example, Patent Document 1 for such a double-loop antenna). .)
[0007]
[Patent Document 1]
JP-A-5-63429
[Problems to be solved by the invention]
However, when the configuration as shown in FIG. 3 is adopted, there may be some problems. For example, when the outer second loop antenna 36 is used to tune to a low frequency (first wavelength), the distance between the power supply unit 32 and the second loop antenna 36 is (the first loop antenna 34 is There is a problem that power loss (passage loss) occurs due to the increase in length (compared to the case where there is none), and the antenna efficiency deteriorates. Also, due to the increased distance between the two second loop antennas 36, the directivity of the low-frequency (second wavelength) twin-loop antenna, etc., compared to the case where they are located close to the power feeding unit There is a concern that the characteristics of the antenna may deteriorate and eventually the antenna efficiency may deteriorate.
[0009]
On the other hand, when trying to tune to a high frequency using the inner first loop antenna 34, the outer second loop antenna 36 gives unnecessary impedance (mainly reactance component), and the first loop antenna 34 There is a possibility that the impedance matching is adversely affected and the antenna efficiency is deteriorated. Furthermore, in the configuration of the double loop antenna 30 as shown in FIG. 3, since the loop antennas 34 and 36 are added in series so as to be away from the power feeding unit 32, the overall size of the loop antenna is tuned. As frequency types increase, it increases. Therefore, such a structure is disadvantageous from the viewpoint of miniaturization of the antenna.
[0010]
The present invention has been made to solve at least one of these problems, and an object thereof is to provide a novel multi-frequency dual loop antenna capable of resonating at a plurality of frequencies.
[0011]
Another problem of the present application is to provide a multi-frequency dual loop antenna that can resonate at a plurality of frequencies and can suppress deterioration in antenna efficiency.
[0012]
Another object of the present application is to provide a multi-frequency dual loop antenna that can resonate at a plurality of frequencies and can keep the overall size of the antenna small.
[0013]
[Means for Solving the Problems]
According to one aspect of the present invention, a first frequency (first wavelength) comprising at least one pair of loop elements, one end of which is electrically connected to a feeding point and the other end is electrically connected to a ground conductor. Provided is a multi-frequency dual loop antenna comprising at least one loop antenna that resonates at a frequency (second wavelength) higher than the first frequency inside the resonant first dual loop antenna. . Alternatively, the first dual-loop antenna is provided at least one pair of loop elements, one end of which is electrically connected to the feeding point and the other end is electrically connected to a ground conductor. There is provided a multi-frequency dual loop antenna having a second dual loop antenna that resonates at a second frequency (second wavelength λ _H ) that is higher than the frequency. Since a loop antenna that resonates at a frequency higher than the first frequency is provided inside the first double-loop antenna, it is possible to accommodate the entire antenna by securing a space required for the first double-loop antenna. Become.
[0014]
According to another aspect of the present invention, the length from the branch point of the second double loop antenna branched from the first double loop antenna to the ground conductor among the loop elements forming the second double loop antenna is , And is formed in accordance with a quarter of the wavelength of the first frequency. As a result, when the multi-frequency dual loop antenna operates at the first frequency, the input impedance in the direction branching to the second dual loop antenna becomes very large, and the current in that direction is substantially suppressed. It becomes possible. Therefore, the multi-frequency dual loop antenna can be resonated with the first frequency without deteriorating the antenna efficiency.
[0015]
According to another aspect of the present invention, the length from the feed point to the ground conductor among the loop elements forming the second dual loop antenna is less than half the wavelength of the second frequency. Long formed. More specifically, the second double-loop antenna is formed to have a section extending in parallel with the ground conductor from the branch point by a predetermined length and further extending away from the ground conductor. The length of such a section is not included in the length for determining the second frequency, which is the resonance frequency of the second double-loop antenna, but is a distance set to a quarter length of the first wavelength. (Distance from branch point to ground conductor) is included. Therefore, by appropriately adjusting the length of such a section, it is possible to set various resonance frequencies for the first and second double-loop antennas while suppressing deterioration in antenna efficiency.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
[First embodiment]
FIG. 4 is a diagram showing a twin loop antenna according to the first embodiment of the present application. The dual loop antenna 400 includes a pair of loop antennas (loop elements) 402 that resonate at a first frequency f _L (first wavelength λ _L ). One end of the loop antenna 402, each having an inverted U-shape, is connected to the power supply unit 404, and the other end is connected to the ground conductor unit 406. The two loop antennas 402 are branched at a point P and have a symmetrical shape. The loop antenna 402 has a length substantially equal to λ _L / 2 along the point OPQR. In this embodiment, since the other end of the loop antenna 402 is connected to the ground conductor 406, one loop antenna 402 functions in the same manner as a loop antenna of one wavelength (λ _L ) based on the principle of a mirror image.
[0017]
The dual loop antenna 400 includes a pair of loop antennas (loop elements) 408 that resonate at a second frequency f _H (second wavelength λ _H ) that is higher than the first frequency. One end of the loop antenna 408, each having an inverted U shape, is also connected to the power feeding unit 404, and the other end is connected to the ground conductor 406. The two loop antennas 402 are branched at a point A and have a symmetrical shape. The loop antenna 408 has a length substantially equal to λ _H / 2 along the point OABC. Since the other end of the loop antenna 408 is also connected to the ground conductor 406, one loop antenna 408 functions in the same manner as a loop antenna of one wavelength (λ _H ) by the principle of mirror image. As shown in the figure, the branch point of the first and second dual loop antennas 402 and 408 is located at a location (point A) separated from the power supply unit 404 by a predetermined distance, that is, the loop antennas 402 and 408 are OA. The part indicated by is shared.
[0018]
During operation, a current is supplied from the power supply unit 404 to each loop element. By using an outer loop antenna 402, it can be made to resonate the twin loop antenna 400 to the first frequency f _L. Further, by using the inner loop antenna 408, it is possible to resonate the twin loop antenna 400 higher than the first frequency f _L second frequency f _H.
[0019]
According to the present embodiment, the double loop antenna 408 is provided inside the outer double loop antenna 402, and the size of the entire double loop antenna is determined by the size of the outer loop antenna 402. According to the present embodiment, since the two types of double loop antennas 402 and 408 are connected in parallel to the power supply unit, the size of the double loop antenna is larger than that in the conventional case where they are connected in series. Can be suppressed. Thus, according to the present embodiment, a multi-frequency dual loop antenna capable of keeping the size of the entire antenna small can be obtained.
[0020]
By the way, the inner loop antenna 408 is provided closer to the power feeding unit 404 than the outer loop antenna 402. For this reason, when the outer loop antenna 402 is resonated at the first frequency f _L (first wavelength λ _L ), the hatched portion (the portion along ABC) in the inner loop antenna 408 is the outer loop antenna. There is a possibility that an extra impedance (particularly a capacitive component) is added to 402, and the antenna efficiency is deteriorated. However, as will be explained below, this problem is solved by adjusting the hatched portion to an appropriate length.
[0021]
FIG. 5 shows a distributed constant line with one end shorted to ground potential. When a high-frequency signal is applied to this line from point A, if the length of the line is set to ¼ of the signal wavelength, the input impedance viewed from point A becomes infinite. That is, the high frequency signal does not flow on the line.
[0022]
Utilizing such properties, the length of the inner loop antenna 408 shown in FIG. 4 is defined. That is, the length of the hatched portion (ABC) is set to ¼ (λ _L / 4) of the wavelength of the first frequency at which the outer loop antenna resonates. In this way, when the outer loop antenna 402 is resonated at the first frequency f _L , the input impedance from the point A to the B and C sides becomes infinite, and the current flowing through the inner loop antenna 408 is substantially equal. Becomes zero, and the outer loop antenna 402 can be efficiently fed. Thus, if the length of the inner loop antenna 408 can be adjusted appropriately, a double loop antenna capable of resonating at a plurality of frequencies without degrading the antenna efficiency can be obtained.
[0023]
Note that when the inner loop antenna 408 is resonated at the second frequency f _H (second wavelength λ _H ), the inventor of the present application has a negligible deterioration in antenna efficiency due to the outer loop antenna 402. It has been confirmed by such studies. This is presumed to be because the current flowing into the outer loop antenna 402 connected in parallel to the power feeding unit is negligibly small in a situation where the inner loop antenna 408 close to the power feeding unit 404 has reached a resonance state. Is done. Incidentally, in the conventional dual loop antenna 30 as shown in FIG. 3, the loop antennas 34 and 36 are connected in series unlike the embodiment of the present application. For this reason, there is a concern that the current from the power supply section 32 always flows to both the inner loop antenna 34 and the outer loop antenna 36, and the antenna efficiency is greatly deteriorated.
[0024]
[Second Embodiment]
FIG. 6 is a diagram showing a twin-loop antenna according to the second embodiment of the present application. Similar to the first embodiment, the dual-loop antenna 600 includes a pair of loop antennas 602 that resonate at the first frequency f _L (first wavelength λ _L ). One end of each loop antenna 602 is connected to the power feeding unit 604, and the other end is connected to the ground conductor unit 606. The two loop antennas 602 are branched at a point P and have a symmetrical shape. The loop antenna 602 has a length substantially equal to λ _L / 2 along the point OPQR.
[0025]
In addition, the dual loop antenna 600 includes a pair of loop antennas 608 that resonate at a second frequency f _H (second wavelength λ _H ) that is higher than the first frequency f _L. One end of each loop antenna 608 is also connected to the power feeding unit 604, and the other end is connected to the ground conductor unit 606. The two loop antennas 602 are branched at a point A and have a symmetrical shape. As shown, the loop antennas 602 and 608 share a portion indicated by OA (a conductive element having a predetermined length). Further, the inner loop antenna 608 according to the present embodiment extends in parallel with the ground conductor portion 606 from the branch point A (AB), bends away from the ground conductor portion 606 (BC), and again becomes the ground conductor portion 606. After extending in parallel (CD), it has a shape (DE) toward the ground conductor.
[0026]
During operation, a current is supplied from the power feeding unit 604 to each loop antenna. By using the outer loop antenna 602, the double-loop antenna 600 can resonate with the first frequency. In addition, by using the inner loop antenna 608, the twin-loop antenna 600 can resonate at a second frequency higher than the first frequency.
[0027]
In the present embodiment, the inner loop antenna 608 has a shape that extends in parallel to the ground conductor portion 606 from the branch point A and reaches the ground conductor portion (point E) via the bending points B, C, and D. In order for the inner loop antenna 608 to resonate at the second frequency f _H , the length of the portion along OA and BCDE (the portion excluding AB of the entire OABCDE) is substantially equal to λ _H / 2. Cost. In other words, the total length OABCDE of the inner loop antenna 608 is longer than λ _H / 2 by AB. Thus, although the length of the portion indicated by AB functions as a feed line for the inner loop antenna 608, it should be noted that it is not a factor that determines the resonance frequency (resonance wavelength) of the loop antenna 608. Further, when the outer loop antenna 602 that resonates at the first frequency f _L is used, in order to prevent the inner loop antenna 608 from generating an extra impedance component, the line from the branch point A to the point E can be prevented. The length (length of ABCDE) needs to be equal to λ _L / 4. That is, it should be noted that the length of the portion indicated by AB becomes a factor for forming a short stub of λ _L / 4.
[0028]
Thus, while not a factor in determining the second frequency f _H that resonates, by providing a section AB as a factor to form a short stub of the lambda _{L /} 4 to the inside of the loop antenna, the design of the antenna The degree of freedom to do is greatly expanded. In the example shown in FIG. 4, since the length of the OABC portion is λ _H / 2 and the length of the ABC portion that is a part of the length is λ _L / 4, the first and second It is difficult to arbitrarily select the wavelengths λ _L and λ _H. On the other hand, in this embodiment, by changing the length of the section AB, it is possible to arbitrarily select various combinations of wavelengths (λ _L , λ _H ) without deteriorating the antenna efficiency. Become.
[0029]
FIG. 7 shows a simulation example regarding the voltage standing wave ratio (VSWR) and the frequency of the twin loop antenna. The horizontal axis indicates the frequency. The vertical axis indicates the voltage standing wave ratio or the return loss, and the return loss increases as it goes upward along the vertical axis, and the return loss decreases as it goes downward along the vertical axis. This simulation has been performed for conventional twin loop antenna may resonate only at a low frequency f _L (. Having a shape as shown in FIG. 2). As shown in the graph, return loss at the resonance frequency f _L is very small, it can be seen to provide excellent antenna efficiency near that frequency.
[0030]
Figure 8 also, as similar to FIG. 7 shows a simulation example of the reflectance and the frequency of the bi-loop antenna, this simulation, conventional twin loop antenna may resonate only at a high frequency f _H that (shown in Figure 2 Have a shape of As shown in the graph, it can be seen that the return loss becomes very small at the resonance frequency f _H , and excellent antenna efficiency is provided in the vicinity of the frequency.
[0031]
FIG. 9 also shows a simulation example regarding the reflectance and frequency of the dual loop antenna. This simulation has been performed for may resonate in higher frequency f _H as well as the low frequency f _L double loop antenna (. Having a shape as shown in FIG. 4). However, the length (ABC) after the branch point of the inner loop antenna is not adjusted to λ _L / 4. As shown in the graph, and return loss is reduced at the resonance frequency f _L and f _H, it is found to provide excellent antenna efficiency in the vicinity of the high frequency f _H. However, due to the length of the inner loop antenna is not properly adjusted, return loss in the vicinity low frequency f _L is seen to be increased as compared with the case shown in FIG. Therefore, the antenna efficiency is deteriorated accordingly.
[0032]
FIG. 10 also shows a simulation example regarding the reflectance and frequency of the dual loop antenna. This simulation is performed for a double loop antenna that resonates not only at the low frequency f _L but also at the high frequency f _H, and the length after the branch point of the inner loop antenna is adjusted to λ _L / 4 (see FIG. 6 has a shape as shown in FIG. As shown in the graph, the resonance frequency f _L and has become very small return loss in both f _H, to provide excellent antenna efficiencies even at low frequency f _L around not only the high frequency f _H I understand.
[0033]
In the present embodiment, the inner loop antenna is provided with the adjustment section as in the section AB (FIG. 6). However, such an adjustment section may be provided on the outer loop antenna. That is, the shape of the outer loop antenna can be made as shown by OABCD in FIG. 6, and furthermore, such an adjustment unit can be provided on both the inner and outer antennas. In any case, (a) the lengths of the inner and outer loop antennas are set so as to resonate at their resonance frequencies (set according to the resonating wavelength), and (b) the inner loop antennas. loop antenna, since one end may be satisfied conditions such to form a distributed constant line having a length of lambda _{L /} 4 shorted (short stub of λ _{L /} 4) in the ground conductor.
[0034]
In the embodiment described above, the outer loop antenna and the inner loop antenna are formed so as to share the OA portion, but the present invention is not limited to such an embodiment. For example, as shown in FIG. 11, the inner and outer loop antennas may be branched separately from the feeding point O. In this case, the length of the OPQR portion in the outer loop antenna is set equal to λ _L / 2, the length of the OABC portion in the inner loop antenna is set equal to λ _H / 2, and the length of the OABC portion The length is set to λ _L / 4. In addition, it is possible to expand the degree of freedom of design by introducing a portion like section AB in FIG. 6 into the example shown in FIG. Further, like the OP and OA portions in FIG. 11, the loop element may be formed by a broken line that bends at an angle other than a right angle. The length of the loop element can be adjusted by changing the bending angle. This can also contribute to increasing the degree of design freedom.
[0035]
In the embodiment of the present application, the shape of the loop antenna (OPQR, OABC, OABCDE) forming the double loop antenna is formed to have a quadrangular or polygonal shape, but this is not essential to the present invention. It is also possible to adopt other shapes consisting of straight lines and curves. For example, it is also possible to form a loop antenna in accordance with a part of the circumference. However, from the viewpoint of reducing the area occupied by the twin loop antenna, it is desirable to employ a polygonal line element as in the present embodiment. Conversely, it is preferable to make the shape of the loop antenna circular from the viewpoint of enclosing a large area.
[0036]
In the dual loop antenna according to the embodiment of the present application, the outer loop antenna and the inner loop antenna are formed substantially in the same plane. However, this is not essential to the present invention. For example, it is possible to form a dual loop antenna so that the inner loop antenna and the outer loop antenna are located in different planes. However, it is preferable to form both the inner and outer loop antennas on the same plane from the viewpoint of ease of manufacturing.
[0037]
Although the double loop antenna according to the embodiment of the present invention is formed so as to resonate at two types of high and low frequencies, it is also possible to form the double loop antenna so as to resonate at a frequency of three or more frequencies as necessary. is there.
[0038]
The double loop antenna according to the embodiment of the present application can be provided at any place where the ground conductor portion can be secured. For example, the vehicle body can be a ground conductor, and the loop antenna can be formed on the window glass like a defogger pattern. In addition to the window glass, it is also possible to form a dual-loop antenna as an outdoor antenna such as a roof top antenna, roof side antenna, trunk lid antenna, or as an in-vehicle antenna (indoor antenna). is there.
[0039]
【The invention's effect】
As described above, the multi-frequency dual loop antenna according to the present invention can resonate with a plurality of frequencies while suppressing deterioration of the antenna efficiency. It is also possible to keep the size of the entire antenna small.
[0040]
[Brief description of the drawings]
FIG. 1 shows a principle diagram of a twin-loop antenna.
FIG. 2 is a diagram showing another twin-loop antenna.
FIG. 3 is a diagram showing a conventional double loop antenna capable of resonating at two frequencies.
FIG. 4 is a diagram showing a twin-loop antenna according to the first embodiment of the present application.
FIG. 5 is a diagram showing a distributed constant line whose one end is short-circuited to a ground potential.
FIG. 6 is a diagram showing a twin-loop antenna according to a second embodiment of the present application.
FIG. 7 is a diagram showing a simulation example regarding the reflectance and frequency of a twin-loop antenna.
FIG. 8 is a diagram showing a simulation example regarding the reflectance and frequency of a dual-loop antenna.
FIG. 9 is a diagram illustrating a simulation example regarding the reflectivity and frequency of a dual-loop antenna.
FIG. 10 is a diagram showing a simulation example regarding the reflectance and frequency of a twin-loop antenna.
FIG. 11 is a diagram showing a modification of the dual loop antenna.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Double loop antenna 12 Feed part 14 Loop antenna 16 Termination reactance part 30 Double loop antenna 32 Feed part 34 High frequency loop antenna 36 Low frequency loop antenna 400 Double loop antenna 402 Low frequency loop antenna 404 Feed part 406 Ground Conductor portion 408 High-frequency loop antenna 600 Double-loop antenna 602 Low-frequency loop antenna 604 Feed portion 606 Ground conductor portion 608 High-frequency loop antenna

Claims (12)

Inwardly of the first double-loop antenna resonating at a first frequency consisting of at least one pair of loop elements, one end of which is electrically connected to the feed point and the other end is electrically connected to the ground conductor. A multi-frequency dual loop antenna comprising at least one loop antenna that resonates at a frequency higher than one frequency. A first double loop antenna resonating at a first frequency comprising at least one pair of loop elements, one end of which is electrically connected to the feeding point and the other end of which is electrically connected to the ground conductor;
It is provided inside the first twin loop antenna, and is composed of at least one pair of loop elements in which one end is electrically connected to the feeding point and the other end is electrically connected to a ground conductor. A multi-frequency dual loop antenna comprising a second dual loop antenna resonating at a second frequency which is a high frequency. The multi-frequency dual loop antenna according to claim 2, wherein a branch point of the second dual loop antenna branched from the first dual loop antenna is located at a predetermined distance from the feed point. Of the loop elements forming the second double-loop antenna, the length from the branch point to the ground conductor is formed in accordance with a quarter of the wavelength of the first frequency. The multi-frequency dual loop antenna according to claim 3. Of the loop elements forming the second double-loop antenna, a length from the feeding point to the ground conductor is longer than a half of the wavelength of the second frequency. The multi-frequency dual loop antenna according to claim 3. At least one of the first or second dual-loop antenna is formed to have a section extending in parallel with the ground conductor from the branch point by a predetermined length and further extending away from the ground conductor. The multi-frequency dual loop antenna according to claim 3. The multi-frequency dual loop antenna according to claim 2, wherein a branch point of a second dual loop antenna branched from the first dual loop antenna is positioned at the feeding point. Of the loop elements forming the second double-loop antenna, a length from the feeding point to the ground conductor is formed in accordance with a quarter of the wavelength of the first frequency. The multi-frequency dual loop antenna according to claim 7. Of the loop elements forming the second double-loop antenna, a length from the feeding point to the ground conductor is longer than a half of the wavelength of the second frequency. The multi-frequency dual loop antenna according to claim 7. At least one of the first or second dual-loop antenna is formed to have a section extending in parallel with the ground conductor from the branch point by a predetermined length and further extending away from the ground conductor. The multi-frequency dual loop antenna according to claim 7. The multi-frequency dual loop antenna according to any one of claims 1 to 10, wherein the ground conductor is connected to a vehicle body. The multi-frequency dual loop antenna according to any one of claims 1 to 11, wherein the first and second dual loop antennas are provided on a window glass of a vehicle.

Images