JP3976010B2 - Antenna feed circuit - Google Patents

Description

  The present invention relates to an antenna feeding circuit that feeds power to an antenna.

  Conventionally, in an antenna feeding circuit that feeds power to an antenna, a coaxial cable is used as a cable for feeding power to the antenna. When power is supplied by a coaxial cable, a leakage current may occur in the outer conductor portion of the coaxial cable due to unbalanced power supply. In addition, radio waves are radiated by this leakage current, which may adversely affect the radio wave radiation from the antenna.

In order to reduce such a leakage current, for example, Patent Document 1 discloses a technique of attaching a sleeve (super top) to an outer conductor portion of a power feeding coaxial cable connected to an antenna.
Japanese Patent Laid-Open No. 11-17439

  However, in the technique described in Patent Document 1, the sleeve is formed to have a coaxial structure with the feeding coaxial cable, and is connected to a predetermined position of the outer conductor of the coaxial cable. Therefore, for the connection between the outer conductor and the sleeve, the maintenance of the coaxial structure between the coaxial cable and the sleeve, etc., the structure of the antenna feeding circuit is complicated, the number of parts is increased, and the number of parts assembling steps is increased. .

  Therefore, the present invention reduces the radiation of radio waves from the coaxial cable due to current leakage due to unbalanced feeding by devising the arrangement of the coaxial cable in the antenna feeding circuit that feeds the antenna using the coaxial cable. Objective.

  In order to achieve the above object, the invention according to claim 1 is a power feeding circuit including a coaxial cable (40) for feeding power to the antenna (10), and leakage in the coaxial cable in the coaxial cable. Of the portion where the amplitude of the current becomes maximum, the first (a) and second (b) portions are arranged in parallel with each other apart from the feeding point (62) to the antenna of the coaxial cable. This is an antenna feeding circuit.

  In a coaxial cable that feeds power to an antenna, the leakage current generated in the coaxial cable becomes a standing wave, and the distribution of amplitude of the standing wave repeatedly increases and decreases with 1/2 of the transmission wavelength of the radio wave from the antenna as one cycle. The phase of the standing wave changes with the transmission wavelength as one period. Further, the maximum value of the amplitude becomes smaller as the portion where the maximum is separated from the feeding point.

  From the above, out of the portion where the amplitude of the leakage current is maximum away from the feeding point to the antenna, the first and second portions away from the feeding point to the antenna of the coaxial cable are the leakage current. It can be said that this is the part that mainly contributes to the radiation from the coaxial cable. If these portions are adjacent to each other in parallel, the radio wave radiation by the respective currents cancel each other because the leakage currents are in opposite phases. Therefore, radiation from the coaxial cable is reduced.

  In this way, in the antenna feeding circuit that feeds the antenna using the coaxial cable, it is possible to reduce radio wave radiation from the coaxial cable due to current leakage due to unbalanced feeding by devising the arrangement of the coaxial cable. It becomes.

  Note that “parallel” does not need to be strictly parallel, and may be approximately parallel. In other words, the term “parallel” as long as it is within a range that can effectively reduce the influence of radio wave radiation on the antenna due to the leakage current of the coaxial cable.

  In this specification, “the first and second parts are parallel to each other” means that the direction from one end to the other end of the coaxial cable along the coaxial cable is the forward direction. The direction and the forward direction in the second part are the same direction. Therefore, “parallel” in this specification does not include a case where the forward direction in the first part and the forward direction in the second part are opposite.

  Further, “the first and second parts are adjacent to each other in parallel” means that the first and second parts are close to each other and face each other in parallel. The proximity and the right-facing here may be in a range that can effectively reduce the influence on the antenna due to radio wave radiation due to the leakage current of the coaxial cable.

  Further, “away from the feeding point” means “excluding a portion very close to the feeding point”. That is, the first refers to the first of the portions where the amplitude of the leakage current is maximized, excluding the portion where the distance is very small compared to the transmission wavelength.

  The invention according to claim 2 is a power feeding circuit including a coaxial cable (40) for feeding power to the antenna (10), wherein the antenna is fed from a feeding point (62) to the antenna. A portion (a) of the coaxial cable that is separated by ½ of the transmission wavelength of the radio wave from the portion, and a portion (b) of the coaxial cable that is separated from the feeding point of the coaxial cable to the antenna by the transmission wavelength. Are arranged to be adjacent to each other in parallel.

  In a coaxial cable that feeds power to an antenna, for example, when the electrical length of the antenna is 1/4, 1/2, or the like of the transmission wavelength, the first portion away from the feeding point of the coaxial cable to the antenna However, there are many cases where this is in the vicinity of a half wavelength from the feeding point. In such a case, as described above, if the coaxial cable portion separated by ½ wavelength from the feeding point and the coaxial cable portion separated by one wavelength are adjacent to each other in parallel, 1 can achieve the same effect as the power supply circuit in FIG.

  According to a third aspect of the present invention, in the antenna feeding circuit according to the first or second aspect, a portion between the portions of the coaxial cable disposed adjacent to each other in parallel is an S-shape. It is arranged to have a shape.

  In this way, if the portion between the above is S-shaped, there is a portion in the opposite phase that is parallel to that portion, so that the radio waves emitted from that portion are canceled each other, and the antenna radiation The degree of reduction of adverse effects on the product is further improved. The S shape is a concept including an inverted S shape, a crank shape, and the like.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific component as described in embodiment mentioned later.

  Hereinafter, an embodiment of the present invention will be described. FIG. 1 shows an antenna feeding circuit 1 according to this embodiment. The antenna feeding circuit 1 includes an antenna element 10, a conductor substrate 20, a ground 30, and a coaxial cable 40.

  The antenna element 10 has an electrical length corresponding to a quarter wavelength of a transmission or reception radio wave to be used. A short-circuited end 11 that is one end of the antenna element 10 is electrically connected to the ground 30, and a feeding end 12 that is the other end is The conductor land 20 is electrically connected to the electrode land 22. In the present embodiment, the transmission frequency from the antenna element 10 is about 900 MHz, and the transmission wavelength is about 33.3 cm.

  The conductive substrate 20 has a non-conductive portion 21 that electrically isolates the inner side and the outer side of the conductive substrate 20, has an electrode land 22 made of a conductor inside the non-conductive portion 21, and is outside the non-conductive portion 21. A grounding portion 23 that is in electrical contact with the ground 30 is provided.

  The coaxial cable 40 is a power feeding cable for supplying a current for transmission to the antenna element 10 and has a diameter of about 3 mm in this embodiment. The coaxial cable 40 is soldered to the feeding end 12 in the antenna feeding point region 50 surrounded by a square in FIG. 1 and is also soldered to the conductor substrate 20. A part of the coaxial cable 40 is held in an inverted S shape by being bound by the clamp 60.

  FIG. 2 shows an enlarged view of the antenna feeding point region 50 of FIG. The coaxial cable 40 is provided with a central conductor 41, an inner insulator 42, an outer conductor 43, and an outer insulator 44 concentrically from the center. The center conductor 41 is electrically connected to the power feeding end 12 by soldering 53. Further, the outer conductor 43 is connected to the ground portion 23 by soldering 52.

  Since the antenna feeding circuit 1 is configured as described above, the central conductor 41 is electrically connected to the feeding end 12, and the antenna element 10 radiates radio waves by feeding from the central conductor 41. Further, since the coaxial cable 40 is unbalanced, a leakage current is generated in the outer conductor 43 during this radiation.

  The leakage current generated in the outer conductor 43 becomes a standing wave, and the distribution of the amplitude of the standing wave repeatedly increases and decreases with one half of the transmission wavelength as one period, and the phase of the standing wave has one period with the transmission wavelength as one period. Change. Further, the maximum value in the increase or decrease in the amplitude becomes smaller as the portion where the maximum is increased away from the feeding point.

  FIG. 3 shows an example of the distribution of the amplitude and phase of the leakage current value generated in such an outer conductor 43. The amplitude of the standing wave of the leakage current generated in the outer conductor 43 has a distribution like a curve 61. A curve 61 is a curve in two-dimensional coordinates in which the horizontal axis 63 is the distance from the antenna feeding point 62 on the coaxial cable 40 and the vertical axis is the current amplitude, and the amplitude of the leakage current in the corresponding portion of the outer conductor 43. Is shown. However, the amplitude is expressed as a positive value when the phase is positive (for example, 0 ° to 180 °) and as a negative value when the phase is reversed (for example, 180 ° to 360 °). For example, at the point a where the antenna feeding point 62 has a half wavelength, the amplitude is maximum and the phase is reversed. At point c, the amplitude is zero. At point e, the amplitude is maximum and the phase is positive (and the opposite phase is 180 ° different from the phase at point a).

  In addition, the arrow in the coaxial cable 40 indicates the normal / reverse of the leakage current amplitude and phase of the outer conductor 43 in each part of the coaxial cable 40 (the left direction is normal and the right direction is reverse). Moreover, the arrow described along the horizontal axis 63 shows the amplitude of the leakage current of the outer conductor 43 at a distance from the feeding point 62 in the coaxial cable.

  Such a leakage current becomes a source of radio wave radiation. However, as described above, the maximum value of the leakage current attenuates as the distance from the antenna feeding point 62 of the coaxial cable 40 increases, and is ignored compared to the current on the antenna element 10 at a position several wavelengths away from the antenna feeding point 62. As much as possible, the influence of the radio wave radiation at the position on the radio wave radiation of the antenna element 10 may be ignored. However, in the portion close to the antenna feeding point 62, particularly in the portion where the leakage current is maximum, the radio wave radiation due to the leakage current is not negligible with respect to the radio wave radiation of the antenna element 10.

  Therefore, in the present embodiment, in order to cancel and reduce the influence of radio wave radiation due to such leakage current, as shown in FIG. 1, from the portion close to the antenna feed point 62, that is, from the antenna feed point 62, as shown in FIG. A portion corresponding to about one wavelength is bound by a clamp 60, and the portion is held in an inverted S shape.

  A state in which the coaxial cable 40 is held in the inverted S shape is schematically shown in FIGS. 4 to 6 indicate the same portions as the points a to e on the coaxial cable 40 in FIG. That is, point a is a part away from the feeding point 62 by 1/2 of the transmission wavelength, point b is a part away from the feeding point 62 by 5/8 of the transmission wavelength, and point c is 6 / of the transmission wavelength from the feeding point 62. A point separated by 8 is a point d separated from the feeding point 62 by 7/8 of the transmission wavelength, and a point e is separated from the feeding point 62 by one transmission wavelength.

  As shown in FIGS. 4 to 6, a point a to a point e are in an inverted S shape (or a crank shape). This shape is maintained by the clamp 60 binding three points, the middle part between the points a and b, the middle part between the points c and d, and the part away from the feeding point by 1/8 wavelength from the point e. The 4 to 6, the coaxial cable 40 has an angular shape so as to be bent, but is actually bent with a curvature radius of about 5 mm.

  The arrow in FIG. 4 has shown the magnitude | size of the amplitude of the leakage current in each point a-point e. In addition, the arrows in FIG. 5 indicate the magnitude of the amplitude and phase of the leakage current at points a to e.

  By holding the coaxial cable 40 in such a shape, the point a portion and the point e portion are adjacently arranged in parallel. That is, when the direction from the feeding point 62 to the other end of the coaxial cable 40 along the coaxial cable 40 is the forward direction, the forward direction at the point a and the forward direction at the point e are substantially the same direction, The point a and the point e are close to each other (for example, 1/10 or less of the transmission wavelength) and face each other. “Directly facing” means that when the point a portion is projected onto the point e perpendicular to the above-described forward direction, the point a substantially overlaps the point e portion.

  At this time, as described above, the point a is located at a position away from the antenna feeding point 62 by ½ wavelength, and the portion of the portion where the amplitude of the leakage current flowing through the outer conductor 43 of the coaxial cable 40 is maximized. Among these, it is a portion corresponding to the first position away from the antenna feeding point 62. Further, as described above, the point e is located at a position away from the antenna feeding point 62 by one wavelength, and the antenna feeding is included in the portion where the amplitude of the leakage current flowing through the outer conductor 43 of the coaxial cable 40 is maximized. This is a portion corresponding to the second position away from the point 62.

  As described above, these two parts are the parts of the maximum amplitude, and the amplitude becomes smaller as the distance from the antenna feeding point 62 becomes smaller. Therefore, the two parts are the parts mainly contributing to the radiation from the coaxial cable due to the leakage current. I can say that. If these portions are adjacent to each other and parallel to each other, the radio wave radiation by the respective currents cancel each other because the currents are in opposite phases. Therefore, radiation from the coaxial cable is reduced.

  In addition, when the portion between the point a and the point e has an inverted S-shape, there is an antiphase portion that is parallel to the portion between the points. It is between point b and point c and between point d and point e in FIGS. This is because there is a point where the phase is switched between the point a and the point e, and a portion swelled to the right (corresponding to between the points b to c) and a portion swelled to the left (points). is equivalent to between the point d and the point e). Thus, the radio waves emitted from the portion bulging to the right and the portion bulging to the left are canceled each other, and the degree of reduction in the adverse effect on the radiation of the antenna is further improved.

  In this way, in an antenna feeding circuit that feeds an antenna using a coaxial cable, by devising the arrangement of the coaxial cable, radio wave radiation from the coaxial cable due to current leakage due to unbalanced feeding is reduced, and thus the antenna It is possible to reduce the adverse effect on the radiation of the element 10.

  Moreover, it can be said that the leakage current generated in the outer conductor 43 seems to be effectively canceled by canceling the radio wave radiation from the outer conductor 43 in this way. The arrows in FIG. 6 indicate the reverse of the amplitude and phase of the effective leakage current after being effectively canceled. The currents at points a and e cancel each other, and the current between points b and c and the current between points d and e cancel each other.

  In the above-described embodiment, the transmission wavelength is not limited to 900 MHz, and can be applied to any frequency.

  In addition, depending on the type of antenna, the portion that is 1/2 wavelength away from the feeding point and the portion that is 1 wavelength away are not necessarily the maximum point of the amplitude of the leakage current. For example, a maximum point of amplitude may occur at a position very close to the feeding point, that is, a position that is far away from the feeding point by a very small distance compared to the transmission wavelength. In such a case, among the portions of the coaxial cable where the amplitude of the leakage current flowing through the coaxial cable is maximized, the first and second portions away from the feeding point of the coaxial cable to the antenna are What is necessary is just to arrange | position so that it may mutually become parallel.

  Further, it is not always necessary to have a crank shape or an S shape. The factor that contributes most to the reduction of radio wave radiation from the coaxial cable 40 is that the point a and the point e are parallel. Therefore, for example, as long as the point a and the point e are parallel, a shape other than the S-shape (for example, a spiral shape) may be used.

1 is a configuration diagram of an antenna feeding circuit 1 according to an embodiment of the present invention. 4 is an enlarged view of an antenna feeding point region 50. FIG. 6 is a diagram for explaining a distribution of leakage current generated in an outer conductor 43 of the coaxial cable 40. FIG. It is a figure which shows arrangement | positioning of the coaxial cable 40, and the amplitude of the leakage current in each part. It is a figure which shows the magnitude | size and direction of the leakage current in arrangement | positioning of the coaxial cable 40, and each part. It is a figure which shows the magnitude | size and direction of the effective leakage current in arrangement | positioning of the coaxial cable 40, and each part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Antenna feed circuit, 10 ... Antenna element, 11 ... Short-circuit end, 12 ... Feed end,
20 ... conductive substrate, 21 ... non-conducting part, 22 ... electrode land, 23 ... grounding part,
30 ... Ground, 40 ... Coaxial cable, 41 ... Center conductor, 42 ... Insulator,
43 ... Outer conductor, 44 ... External insulator, 50 ... Antenna feed point region, 52 ... Soldering,
53 ... Soldering, 60 ... Clamp, 61 ... Curve, 62 ... Antenna feeding point, 63 ... Horizontal axis.

Claims (3)

A feeding circuit comprising a coaxial cable (40) for feeding power to an antenna (10),
Of the portion of the coaxial cable where the amplitude of the leakage current flowing through the coaxial cable is maximized, the first (a) and the second (b) away from the feeding point (62) of the coaxial cable to the antenna. The antenna feeding circuit is characterized in that the portions are arranged so as to be adjacent to each other in parallel. A feeding circuit comprising a coaxial cable (40) for feeding power to an antenna (10),
A portion (a) of the coaxial cable that is separated from a feeding point (62) of the coaxial cable to the antenna by a half of a transmission wavelength of a radio wave from the antenna, and a feeding point of the coaxial cable to the antenna To the coaxial cable portion (b) separated by the transmission wavelength from each other and arranged adjacent to each other in parallel. 3. The antenna according to claim 1, wherein a portion between the portions of the coaxial cable disposed so as to be adjacent to each other in parallel is disposed so as to have an S-shape. Power supply circuit.

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