JP4136178B2 - Twin loop antenna - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a dual loop antenna that transmits and receives UHF radio waves.
[0002]
[Prior art]
Conventionally, as a horizontally polarized dual-loop antenna used for transmitting UHF band broadcast radio waves, as shown in FIG. 11, a pair of signals having a perimeter of one wavelength of a signal component to be received. The loop antennas 104 and 106 are connected by a pair of feed lines (hereinafter referred to as parallel feed lines) 108 arranged in parallel, and a double loop antenna 102 having a feed point P at the center of the parallel feed line 108 is provided. Known. FIG. 11A is a front view of the twin loop antenna 102, and FIG. 11B is a side view thereof.
[0003]
That is, the horizontally polarized dual-loop antenna 102 is arranged so that the arrangement direction of the pair of loop antennas 104 and 106 coincides with the vertical direction. In each of the loop antennas 104 and 106, the current flows in the same direction on the upper side and the lower side, thereby canceling out the vertical polarization component having the polarization plane along the arrangement direction (vertical direction). Thus, only the horizontal polarization component having the polarization plane along the orthogonal direction is transmitted and received.
[0004]
[Problems to be solved by the invention]
By the way, in the dual loop antenna 102 configured in this way, the directivity changes according to the arrangement interval of the loop antennas 104 and 106. Specifically, as the arrangement interval becomes larger, the side lobe in the vertical plane becomes larger. The level becomes higher. If the side lobe level is high, for example, when receiving radio waves, noise that enters from other than the desired direction (for example, reflected waves from the ground) increases, and when transmitting radio waves, it is unnecessary in other than the desired direction. This is desirable because it is difficult to radiate, and the transmission / reception quality deteriorates.
[0005]
However, in order to efficiently feed power to the loop antennas 104 and 106, the length of the parallel feed line 108 from the feed point P to the connection end of the loop antennas 104 and 106 is set to a signal component line that becomes the target frequency. It is necessary to set the inner wavelength to λL / 4 + n · λL / 2 near λL. That is, there is a problem in that the side lobes cannot be sufficiently reduced because the arrangement interval between the loop antennas 104 and 108 cannot be made smaller than λL / 2.
[0006]
In addition, since the dual loop antenna 102 has a planar configuration, it can be incorporated in building materials and the like, and is considered to be applied to a home antenna. Since the length of 108 is defined, it cannot be sufficiently reduced in size. Furthermore, in order to cover the entire region of the entire UHF band (470 MHz to 770 MHz) with a bandwidth of as much as 300 MHz, the dual loop antenna 102 is generally known to have a wide band (100 MHz or more in the 700 MHz band). However, it is necessary to use three types of dual loop antennas that are divided into the low band, the middle band, and the high band, and are adapted to each area, and the configuration becomes large. It was.
[0007]
Accordingly , an object of the present invention is to provide a double loop antenna capable of reducing the side lobe and reducing the size in order to solve the above problems .
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 is a pair of loop antennas having an annular portion made of a conductor and formed in an annular shape, and two wires for feeding power to the pair of loop antennas. A parallel feed line of the formula, and a dual loop antenna that transmits and receives linearly polarized waves whose plane of polarization is orthogonal to the arrangement direction of the pair of loop antennas, each loop antenna from a center point of the annular portion the circle is a connection point of the pair of points on the ring portion, a pair of feed inlet portion extending toward the center point from the connection point located in the direction along the plane of polarization of the linearly polarized wave look Both ends of the parallel feed lines are connected to a pair of feed introduction sections provided on the pair of loop antennas, respectively, and the parallel feed lines are feed points at equidistant points from the both ends. It is, in the loop antenna -Impedance, by changing the line width ratio A / B is the ratio of the line width A of the the line width B of the annular portion feeding inlet part, is adjusted to match the impedance of the parallel feed line It is characterized by.
[0009]
According to the double-loop antenna of the present invention configured as described above, even if the parallel feed line has the same length as that of the conventional double-loop antenna, the loop antenna is arranged in the arrangement direction (hereinafter simply referred to as the arrangement direction). The total length can be shortened by two loop antenna radii. In addition, since the distance between the loop antennas is narrowed, and the side lobe in the vertical plane is reduced accordingly, when the antenna is used for reception, it is received from outside the desired direction (directivity of the main lobe). When noise reduction is used for transmission, unnecessary radio waves radiated out of a desired direction can be reduced, and transmission / reception quality can be improved.
[0010]
Further, as a result of repeating various experiments, the present inventors have determined that the impedance of the loop antenna is the ratio of the line width B of the loop antenna ring portion to the line width A of the feed introduction portion, as shown in FIG. It was found that it can be adjusted by changing A / B.
[0011]
In the graph shown in FIG. 10, the target frequency is 585 MHz (center frequency when a phase change of 440 MHz to 770 MHz is considered), the circumference of the loop antenna is λ, and the wavelength of the signal that is the target frequency is λ. The result of measuring the voltage standing wave ratio (VSWR) with a measurement device with an input terminal impedance of 75Ω attached to the tip of the power feeding introduction part through a 1: 4 balun, set to 26λ. It is. The closer the impedance of the loop antenna is to a pure resistance of 300 (= 75 × 4) Ω, the closer to VSWR = 1 (that is, a state where the impedance is perfectly matched).
[0012]
In other words, according to the twin loop antenna of the present invention, the impedance of the loop antenna can be adjusted only by changing the line width ratio A / B of the loop antenna, for example, by adjusting the line width of the feeding introduction portion. It is possible to easily design a double-loop antenna in which impedance matching with the parallel feeder is taken.
[0013]
Moreover, in the conventional horizontally polarized dual loop antenna, as shown in FIG. 11B, the impedance of the loop antenna is adjusted by providing the receiving end short circuit SC at both ends of the loop antennas 104 and 106 in the arrangement direction. However, in the double loop antenna of the present invention, the receiving end short circuit SC can be omitted, and the device configuration can be simplified.
[0014]
The line width ratio A / B is preferably set in a range of 1 ≦ A / B ≦ 3 as described in claim 2.
[0015]
Further, when power is supplied to the loop antenna through the power supply introduction unit (hereinafter referred to as a central power supply type), the circumference length Lc of the loop antenna is set to the center wavelength of the target frequency to be transmitted and received as described in claim 3. Is preferably set to 1.1λ ≦ Lc ≦ 1.4λ.
[0016]
That is, in the end feed type that feeds power from one end, such as a conventional horizontally polarized dual loop antenna, the circumference of the loop antenna is approximately equal to one wavelength of the signal component that becomes the target frequency. It is known that when this is set, the reactance component of the impedance is almost zero, and it is close to a pure resistance that can easily achieve impedance matching. In other words, the center feeding type loop antenna used in the present invention can be regarded as a semi-annular end feeding type loop antenna connected in parallel. Excellent characteristics are obtained in the vicinity of the wavelength.
[0017]
According to a fourth aspect of the present invention, in the twin-loop antenna according to any one of the first to third aspects, a reflector is disposed on the back side of the loop antenna, and the parallel feed lines are the loop antenna and the reflector. It is characterized by being wired between.
[0018]
According to a fifth aspect of the present invention, in the dual loop antenna according to the fourth aspect, the loop antenna is configured such that both end portions of the parallel feeding line are connected to the feeding introduction portion without contacting the annular portion. It is characterized in that the wiring is inclined with respect to the arrangement surface.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1A is a plan view showing the overall configuration of a double loop antenna for transmitting and receiving UHF band radio waves according to this embodiment, and FIG. 1B is a side view thereof.
[0022]
As shown in FIG. 1, the twin loop antenna 2 of the present embodiment includes a pair of loop antennas 4 and 6 formed in an annular shape, and each loop antenna 4 and 6 has a center point of the loop antenna. A pair of power feeding introduction portions 4b and 6b are extended from the pair of connection points on the annular portions 4a and 6a facing each other toward the center point.
[0023]
The loop antennas 4 and 6 are arranged so that the wiring direction (X direction in the figure) of the power feeding introduction portions 4b and 6b is orthogonal to the arrangement direction of the loop antennas 4 and 6 (Y direction in the figure). The feeding introduction portions 4 b and 6 b of the loop antenna are connected to each other by a two-wire parallel feeding line 8.
[0024]
In addition, a reflector 10 is disposed on the back side of the loop antennas 4 and 6, and the parallel feeder 8 is wired between the loop antennas 4 and 6 and the reflector 10. Further, the parallel feeding line 8 is provided with a feeding point P at the center thereof.
In the twin loop antenna 2 of the present embodiment, the dimensions of each part are set as follows with the center frequency 620 [MHz] of the UHF band radio wave to be transmitted and received as the target frequency.
[0025]
That is, the parallel feed line 8 has an impedance at the target frequency of 150 [Ω] at the feed point P to which the coaxial cable for feeding (characteristic impedance: 75 [Ω]) is connected, and the loop antennas 4 and 6 are connected. Both ends are set to 300 [Ω], and the impedance between them is continuously changed.
[0026]
Specifically, as a pair of feed lines constituting the parallel feed line 8, one having a line width of 10 [mm] is used, the line spacing at the feed point P of both feed lines is Wp = 2 [mm], both ends In this section, the line interval is Wt = 15 [mm], and the wiring is inclined so as to gradually widen from the feeding point P toward both ends. The total length of the parallel feeding line 8 is set so that the length Lpt = 16 [cm] from the feeding point P to both ends, that is, the distance between the center points of both loop antennas 4 and 6 is 32 [cm]. Has been. The distance 32 [cm] between the center points is set from the gain and sidelobe characteristics.
[0027]
Further, Lc = 61 [cm] so that the circumferential length Lc of the annular portions 4a and 6a of each loop antenna is 1.26 times the wavelength λ of the signal component that is the target frequency (hereinafter referred to as the target wavelength). (Diameter 19.4 [cm]), and further, the line width (hereinafter referred to as “introduction line width”) A of the feeding introduction portions 4b and 6b of the loop antenna and the line width (hereinafter referred to as element) of the annular portions 4a and 6a. B) (referred to as width) is set to A = 30 [mm] and B = 10 [mm] (accordingly, A / B = 3) so as to match the impedances at both ends of the parallel feeder 8.
[0028]
Further, the distance between the formation surface of the loop antennas 4 and 6 and the reflector 10 is Wh = λ / 4 (= 12.1 [cm]), and the distance between the formation surface of the loop antennas 4 and 6 and the parallel feed line 8. Is set to Wg = λ / 50 (= 9.7 [mm]) or less.
Next, the result of measuring the characteristics of the double-loop antenna 2 of the present embodiment configured as described above will be described.
[0029]
As a comparative example, as shown in FIG. 2B, an end feeding type double loop antenna 32 in which the circumference of the loop antennas 34 and 36 is set to 1λ (= 48.4 [cm]) is also used. Similar measurements were made. However, even in the dual loop antenna 32 of the comparative example, in order to facilitate impedance matching at the feeding point P, the line spacing gradually increases from the feeding point P toward both ends as the parallel feeding line 38 as in the present embodiment. The one set to spread was used.
[0030]
FIG. 3 is a graph showing a result of measuring directivity on a horizontal plane along the wiring direction of the power feeding introduction portions 4b and 6b and a vertical plane along the arrangement direction of the loop antennas 4 and 6, and FIG. It is a graph showing the result of having measured operation gain, standing wave ratio, front-to-back ratio, and half value angle about the whole field of UHF band.
[0031]
As shown in FIG. 3, the directivity in the horizontal plane is almost the same in the present example and the comparative example, whereas the directivity in the vertical plane is the same as that of the present example with respect to the comparative example. In the loop antenna 2, the intensity of the side lobe is maximum (in the case of 770 MHz), which is reduced from −3 dB to −10 dB, that is, 7 dB.
[0032]
Further, as shown in FIG. 4, in the dual loop antenna 2 of the present embodiment, the operation gain and the standing wave ratio are improved in the low band (470 to 560 MHz) as compared with the comparative example, and the UHF band Almost uniform characteristics are obtained over the entire region.
Next, for the double loop antenna 2 of the present embodiment and the twin loop antennas 2a, 2b, 2c of the modification of the present embodiment shown in FIG. It shows in FIG. 6, FIG.
[0033]
As a modification, as shown in FIG. 5, a parallel feed line 8 a in which the line interval between a pair of feed lines is set in the same manner as the parallel feed line 8 of the embodiment is reflected across the loop antennas 4 and 6. Two loop antennas 2a (Modification 1) provided on the opposite side of the plate 10 and a pair of feed lines are fixed to 2 [mm] so that the parallel feed line 8a has a uniform impedance of 150 [Ω]. The pair of feed lines are arranged at a constant line interval of 15 [mm] so that the double loop antenna 2b (Modification 2) wired in parallel at intervals and the parallel feed line 8c have a uniform impedance of 300 [Ω]. A twin-loop antenna 2c (Modification 3) wired in parallel was used.
[0034]
However, the line width of the pair of feed lines constituting the parallel feed lines 8a, 8b, and 8c is 10 [mm], and the ends and loops of the parallel feed lines 8a, 8b, and 8c are set in each of the twin loop antennas 2a, 2b, and 2c. The antennas 4 and 6 were determined as impedance matching.
[0035]
In the double loop antenna 2 of the present embodiment, as shown in FIG. 6A, when parallel feeding lines are inclined and the impedance of the line is continuously changed, the entire area of the UHF band is covered. The standing wave ratio is 2 or less, indicating excellent characteristics.
Further, in the dual loop antenna 2a of the first modification in which the parallel feeding lines are wired on the front side of the loop antennas 4 and 6, as shown in FIG. 6B, the characteristics on the high frequency side are slightly deteriorated. As with the dual loop antenna 2 of the example, the standing wave ratio is 2 or less over the entire region of the UHF band, indicating excellent characteristics.
[0036]
On the other hand, in the two loop antennas 2b and 2c of the second modification and the third modification having parallel feeding lines 8b and 8c in which a pair of feeding lines are wired in parallel, as shown in FIGS. 7 (a) and (b), In both cases, the characteristics on the high frequency side are degraded. That is, it can be seen from the simulation results shown in FIGS. 7 and 8 that the characteristics of the double-loop antenna can be broadened by using a parallel feed line whose impedance changes continuously.
[0037]
As described above, the twin-loop antenna 2 of the present embodiment uses the center feed type loop antennas 4 and 6, and therefore, compared with the conventional double loop antenna using the end feed type loop antenna. The arrangement interval of the loop antennas 4 and 6 can be reduced.
[0038]
As a result, in the dual loop antenna 2 of the present embodiment, not only the total length along the arrangement direction of the loop antennas 4 and 6 can be reduced, but also the side lobe level in the directivity in the vertical plane becomes low. It is possible to reduce reception of unnecessary signal components (that is, noise) from a direction other than the desired direction, such as a reflected wave from, and at the time of transmission, the input power can be efficiently radiated in the desired direction, so that transmission / reception quality can be improved. . This effect can be obtained in the same way with the twin-loop antennas 2a to 2c of the respective modifications.
[0039]
Further, in the dual loop antenna 2 of the present embodiment, the impedance matches the external feed line at the feed point P and the loop antennas 4 and 6 at both ends, and both ends (loop antennas 4 and 6 from the feed point P). ) Is used, the parallel feed line 8 is set so that the impedance continuously changes, so that the frequency characteristic of the parallel feed line 8 is widened. It is possible to send and receive radio waves in all areas of the band and radio waves of terrestrial digital broadcasting currently planned. This effect can be obtained in the same manner with the dual loop antenna 2a of the first modification.
[0040]
For this reason, according to the double loop antenna 2 of a present Example, it can be used suitably as a receiving antenna of the television broadcast electric wave for home use which a miniaturization is strongly requested | required, for example.
In this embodiment, the length from the feeding point P of the parallel feeding line 8 to both ends where the loop antennas 4 and 6 are connected is Lpt = 16 [mm]. Can be set to any length as long as they are set to match the impedances of the external feed line and the loop antennas 4 and 6, respectively.
[0041]
Here, FIG. 8 shows a double loop antenna (see FIG. 2 (a)) using a center feed type loop antenna and a double loop antenna (see FIG. 2 (b)) using an end feed type loop antenna. It is a graph showing the result of having changed the length of each parallel feeder 8 and 38, and having measured the operation gain of both. As a parameter, the distance d from the feeding point P to the center point of the loop antenna was used.
[0042]
As shown in the figure, when any type of loop antenna is used, the operation gain decreases as the distance d (loop interval) is reduced. However, the center feed type double loop antenna is of the end feed type. The rate at which the gain decreases is smaller than that of the twin loop antenna.
[0043]
That is, when using the central feeding type loop antennas 4 and 6 and the parallel feeding line 8 whose impedance changes continuously as in the present embodiment, the loop interval can be arbitrarily set, so the degree of freedom in design. When the loop interval is made close to reduce the side lobe, a larger operating gain can be obtained than when the end feed type loop antennas 34 and 36 are used, and the balance is better. Characteristics can be obtained.
[0044]
In the above-described embodiment, the arrangement direction is configured as a double loop antenna that transmits and receives radio waves composed of horizontally polarized waves by matching the arrangement direction in the vertical direction. However, by arranging the arrangement direction in the horizontal direction, that is, FIG. It is good also as a double loop antenna which transmits / receives the electromagnetic wave which consists of a vertically polarized wave by using the double loop antenna 2 shown to (a) in the state rotated 90 degrees.
[0045]
Moreover, in the said Example, in order to change the impedance of the parallel feed line 8, the line interval of a pair of feed line which comprises the parallel feed line 8 is changed. The line width may be changed.
In this case, the parallel feed line only needs to have a narrower line width as the impedance is higher, and when such a parallel feed line is applied to the above embodiment, the one having a shape as shown in FIG. 9 may be used. .
[0046]
Further, in the above embodiment, the line width ratio between the introduction line width A and the element width B of the loop antenna is set to be A / B = 3. What is necessary is just to set so that it may match with the impedance in the both ends of the parallel feeder 8.
[0047]
When applied to a home receiving antenna or the like, in order to reduce the thickness of the device, the reflector 10 can be made closer to the loop antennas 4 and 6, that is, the distance between them can be set to Wh <λ / 4. Conceivable. However, since the impedances of the loop antennas 4 and 6 change according to the interval Wh, in order to match the impedances of the two, it is necessary to set the line width ratio A / B lower as the two are brought closer. Thus, considering the case where the distance between the reflecting plate 10 and the loop antennas 4 and 6 is made closer, the line width ratio A / B of the loop antennas is in the range of 1 ≦ A / B ≦ 3. It is preferable to set.
[0048]
Furthermore, in the above embodiment, the interval between the formation surface of the loop antennas 4 and 6 and the parallel feed line 8 is set to Wg = λ / 50 or less, but it may be set to Wg> λ / 50.
[Brief description of the drawings]
FIG. 1 is a front view, a side view, and an enlarged view of each part showing an overall configuration of a twin-loop antenna of an embodiment.
FIG. 2 is an explanatory diagram showing a schematic configuration of a double loop antenna of an example and a comparative example used for characteristic measurement.
FIG. 3 is a graph showing the results of measuring directivity for examples and comparative examples.
FIG. 4 is a graph showing the results of measuring various frequency characteristics for examples and comparative examples.
FIG. 5 is an explanatory diagram illustrating a schematic configuration of a modified example of the embodiment.
FIG. 6 is a graph showing the results of measuring the frequency characteristics of the standing wave ratio for Examples and Modifications.
FIG. 7 is a graph showing a result of measuring a frequency characteristic of a standing wave ratio for a modified example.
FIG. 8 is a graph showing a result of measuring a characteristic of an operation gain with respect to a loop interval.
FIG. 9 is an explanatory diagram showing a modification of the parallel power feed line.
FIG. 10 is a graph showing a result of measuring a characteristic of a standing wave ratio with respect to a line width ratio of a loop antenna.
FIGS. 11A and 11B are a front view and a side view showing an overall configuration of a conventional horizontally polarized dual loop antenna. FIGS.
[Explanation of symbols]
2, 2a to 2c ... double loop antenna 4, 6 ... loop antenna 4a, 6a ... annular part 4b, 6b ... feeding introduction part 8, 8a to 8c ... parallel feeding line 10 ... reflector

Claims (5)

A pair of loop antennas made of a conductor and having an annular part formed in an annular shape,
A two-loop parallel feeding line that feeds power to the pair of loop antennas, and a dual-loop antenna that transmits and receives linearly polarized waves whose plane of polarization is orthogonal to the arrangement direction of the pair of loop antennas,
Wherein each loop antenna, and a connection point of a pair of points on the annular portion positioned in the direction along the plane of polarization of the linear polarized waves as viewed from the center point of the annular portion, the central from the connection point A pair of power supply introduction portions extending toward the point,
Both ends of the parallel feed line are respectively connected to a pair of feed introduction portions provided in the pair of loop antennas, and the parallel feed line is a feed point at a point equidistant from the both ends .
The impedance of the loop antenna is matched with the impedance of the parallel feeding lines by changing a line width ratio A / B which is a ratio of the line width B of the annular portion and the line width A of the feeding introduction portion. A double-loop antenna characterized by being adjusted as follows .   2. The double loop antenna according to claim 1, wherein the line width ratio A / B is set in a range of 1 ≦ A / B ≦ 3. Circumference length Lc of the loop antenna as the center wavelength of the target frequency for transmitting and receiving lambda, claim 1 or claim 2 double loop wherein it is set to 1.1λ ≦ Lc ≦ 1.4λ antenna.   A reflector is arranged on the back side of the loop antenna,
  The dual loop antenna according to any one of claims 1 to 3, wherein the parallel feeding line is wired between the loop antenna and the reflector.   Both ends of the parallel feed lines are wired so as to be inclined with respect to the arrangement plane of the loop antenna so as to be connected to the feed introduction part without being in contact with the annular part. The double loop antenna according to claim 4.

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