JP2005210251A - Twin loop antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small twin loop antenna having good radiation efficiency in which the output impedance can be matched with a cable impedance at frequencies in wideband through a simple structure. <P>SOLUTION: The stacked loop antenna comprises two loop elements 120 and 121 facing each other; a parallel line 114 connected with the openings of respective loop elements, an inductor element 122 in the central of the parallel line, and a reflector 113 opposing the surface of the loop elements. Since the antenna output impedance can be matched with the impedance of a coaxial cable 119 connected with an output connector, the stacked loop antenna can be reduced in size using simple components. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a dual loop antenna used for receiving UHF band television waves.

  Conventionally, the twin loop antenna has been widely used as an antenna for television transmission in the UHF band (see, for example, Patent Document 1). FIG. 10 shows a conventional dual loop antenna 101 described in Patent Document 1. A pair of loop elements 102 and 103 having a peripheral length λ for one wavelength are connected to a parallel line 104, and the parallel line is passed through a balanced-unbalanced circuit 105 formed by arranging a conductor line 112 parallel to the coaxial line 106. The antenna is connected to the coaxial line 106 serving as an antenna feeding unit at the center of the line 104. 10A is a front view of the twin loop antenna 101, and FIG. 10B is a side view thereof.

Moreover, as what reduced the shape of the conventional double loop, there existed what was described in patent document 2, for example. FIG. 11 shows a dual loop antenna described in Patent Document 2, in which a balanced line 109 having a changed impedance characteristic is connected to the center output portion of the modified loop elements 107 and 108, and power is fed at the center of the balanced line 109. It is an implementation example of a loop antenna.
JP 2002-223118 A (page 10, FIGS. 16-17) JP 2000-307327 A (page 7, FIG. 1)

  However, the configuration of the conventional double loop antenna shown in FIG. 10 requires a short plate 110 for setting the double loop antenna output impedance, and is placed parallel to the coaxial line to feed the antenna balanced output to the coaxial line. This is a complicated structure requiring a balanced-unbalanced conversion (synonymous with the balun described in Patent Document 1) circuit 105 composed of the conductor wire 112 and the short plate 110. Further, as explained in Patent Document 1, the output impedance of the central portion of the parallel line constituting the double loop antenna is approximately 100 to 200Ω, which is larger than the impedance of 75 ohms of a commonly used normal coaxial cable. is seperated. Therefore, it has been difficult to cover the entire UHF band 470 MHz to 770 MHz of television broadcasting.

  Further, the double loop antenna having the structure shown in FIG. 10 is used as a transmission antenna for television broadcasting, and does not pay much attention to miniaturization of the size and is approximately 1 / of the wavelength λ using the parallel line length L. 2. However, it is necessary to reduce the size for use as a television receiving antenna, and it is important to shorten the parallel line L without degrading performance characteristics such as gain and VSWR which are antenna performance.

  On the other hand, in the configuration in which the two loop elements shown in FIG. 11 are arranged close to each other, the shape of the loop elements 107 and 108 having an annular structure that feeds power to the central part and the shape of the balanced line 109 in which the line interval gradually changes are shown in FIG. 10 is more complicated than the dual-loop antenna structure shown in FIG. 10, and because of the three-layer structure of the reflector 113, the balanced line 109, and the loop elements 107 and 108, which are antenna components, they are in place. There is a problem in mass productivity as a popular household television receiving antenna, such as a complicated support structure for fixing and arranging the TV.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object of the present invention is to provide a small double-loop antenna having a high radiation efficiency by matching the double-loop antenna to a cable impedance over a wide band frequency with a simple structure. .

  In order to solve the above-described conventional problems, the dual loop antenna of the present invention includes two loop elements facing each other, a parallel line connected to each opening of the loop element, and a central part of the parallel line. In addition, an inductor element is connected to the loop element, and a reflecting plate facing the surface of the loop element is provided. The antenna output impedance is matched with the impedance of the coaxial cable connected to the output connector, thereby realizing a miniaturized antenna. ing.

  With this configuration, in the case of the conventional configuration, the parallel line having a length of 1/2 wavelength is shortened to about 1/5 to 1/3 wavelength, no balanced-unbalanced circuit is provided, and a simple structure with a small number of components is used. The antenna output impedance is matched to 75Ω of the coaxial cable, and the antenna output VSWR is made favorable.

  Further, the reflecting plate is curved by bringing the central portion of the reflecting plate closer to the parallel line without reducing the antenna gain.

  As described above, according to the dual-loop antenna of the present invention, the antenna dimensions can be reduced by a configuration composed of simple components without requiring a short plate and a balanced-unbalanced circuit having a complicated configuration, and the antenna gain can be reduced. Without lowering, it is possible to realize an antenna having a broadband frequency characteristic with good VSWR matched to the coaxial cable impedance.

  Moreover, the intensity | strength for withstanding a wind-pressure load can be increased by curving a reflecting plate.

The best mode for carrying out the present invention will be described below with reference to the drawings.
(Embodiment 1)
FIG. 1 is a configuration diagram of a double-loop antenna according to Embodiment 1 of the present invention. In FIG. 1, the same components as those in FIGS. 10 and 11 are denoted by the same reference numerals, and description thereof is omitted.

  In FIG. 1, a loop element 120 and a loop element 121 that are close to the wavelength λ of the frequency used by the outer peripheral length are coupled to each other by a parallel line 114 having the same planar shape and each opening being formed of two conductors. Further, one side of the central portion of the parallel line 114 is connected to the central conductor of the coaxial cable 119 via the inductance element 122, and the other side of the parallel line is connected to the outer conductor of the coaxial cable 119 to output the double loop antenna. An antenna reception signal is guided to the connector 123. Further, the reflecting plate 113 is arranged to face the surface of the two loop elements so that the distance D is closer to λ / 4 than the surface of the loop element, and is configured as a reflective element of the antenna. The size of the reflector is such that the width is slightly longer than one half of the wavelength, the height covers the entire two loop elements having one wavelength or more, and the radio wave is efficiently reflected with a minimum area.

  The loop element support plate 124 fixes the loop elements 120 and 121 and the parallel line 114, the support body 125 keeps the loop element on the same plane with the loop element support plate 124, and the hollow support base 126 is the support body 125. The loop element surface is opposed to the reflector 113 in parallel with the support metal fitting 127 interposed therebetween. Further, the support fitting 127 has a structure in which the double loop antenna is attached to the antenna attachment mast 130 by the holding fitting 128 and the fixing screw 129. Note that the loop element support plate 124 and the support 125 are made of a dielectric material and do not affect the electrical characteristics of the antenna.

  According to this configuration, the loop element 120 and the loop element 121 serve as antennas having the maximum radiation directivity in the loop axis direction, and the output impedance Zr of the loop element is 100 in the UHF band from 470 MHz to 770 MHz used in television broadcasting. -300Ω balanced output.

  Furthermore, the impedance Zb when the loop element 120 side or the loop element 121 is viewed from the center of the parallel line is determined by Zr, the characteristic impedance Z0 of the parallel line 114, and the length of the parallel line, and is arranged vertically symmetrical in FIG. The impedance Za on the antenna radiating element side as viewed from the center of the parallel line by the loop element and the parallel line is ½ of the impedance Zb.

In the conventional double loop antenna shown in FIG. 10, the impedance Zr of the loop element opening is set to Zr = 200Ω by the short plate 110, and the impedance Z0 of the coaxial cable is obtained by the impedance conversion effect by the λ / 4 length of the parallel line 104. Was consistent with. For example, when the coaxial cable impedance is 100Ω, the impedance ZL of the parallel line is determined by the relationship of ZL ² = 2ZrZ0.

  However, in the configuration according to the present invention shown in FIG. 1, the short plate is eliminated and the length of the parallel line is shortened. Therefore, the loop element impedance is made capacitive by eliminating the short plate without designing by this method. Further, by using a shorter parallel line length and adding a single inductor element 122 as a matching element to the center of the parallel line 114, the antenna output impedance is matched with the normally used 50Ω or 75Ω coaxial impedance. ing.

  The impedance Zr of the loop element having no impedance adjusting short plate is determined by the loop length and the conductor diameter W, and is 100 to 300Ω in the television broadcast band (470 MHz to 770 MHz), but exhibits a little capacitive property.

  As an actual measurement example, the output impedance characteristic Zr of the loop element in the UHF TV band (470 MHz to 770 MHz) is shown in the 75Ω standard Smith chart of FIG. It shows with.

  The parallel line impedance ZL is increased to about 300Ω, and the parallel line length is set to 1/5 to 1 / 3λ. The length of the parallel line is short, and the impedance Za at the center of the parallel line is Smith at the lower limit frequency of use of 470 MHz. Proximity setting can be realized on a constant 75Ω circle on the chart. Zb shown on the Smith chart of FIG. 2 is a value in which the impedance Zr of the loop element is rotated around the parallel line impedance ZL, and Za has a relationship of half of Zb.

  Za shown here has a lower limit operating frequency that is substantially on the 75 Ω constant circle of the Smith chart. By connecting a single inductor element 122 in series, the entire operating frequency band (470-770 MHz) is Smith chart. It will be closer to the center circle. That is, by reducing the antenna VSWR, ideal characteristics are obtained in which no loss occurs in connection with the transmission cable.

  FIG. 3 shows an example of actual measurement in the above described embodiment of the VSWR when there is no inductor element 122 and when it is present. In particular, the performance improvement effect at the low frequency 470 MHz is remarkable. In addition, since the impedance Za at the central portion of the parallel line is close to the coaxial impedance, the value of the inductor element 122 is small, and the parallel line is a balanced line that does not radiate electromagnetic waves, so it does not operate as an antenna. The obtained VSWR performance value can achieve a good value without requiring a balanced-unbalanced conversion circuit.

  In the present embodiment, the central conductor 135 of the coaxial cable 119 is connected to the parallel line 114 via the inductor element 122. However, the inductor element 122 may be realized by deforming the central conductor of the coaxial cable.

  FIG. 4 is a structural example of a connection portion between the coaxial cable 119 and the parallel line 114, and realizes an inductor element 122 obtained by modifying the central conductor of the coaxial cable. That is, the inductor element 122 is formed by an extension of the central conductor 135 of the coaxial cable, and the tip end portion of the inductor element made of the central conductor of the coaxial cable is crimped and connected to the bent connection terminal 132.

  The connection fitting 133 is connected by being sandwiched between the central portions of the parallel lines 114, and is connected to the connection terminals 132 by screws 131. On the other hand, the outer conductor 137 of the coaxial cable 119 is connected to the other end of the parallel line 114 at the center by the connecting fitting 138 having the same shape as the connecting fitting and the screw 131 by crimping the coaxial outer conductor 137 through the pinching connection terminal 134. Has been. Further, although the inductor element 122 is shown in a coil shape, the shape can be modified as long as the inductance value is required.

  According to such a configuration, the electrical connection between the coaxial cable and the parallel line can be easily assembled with a small number of components, which is effective in mass production.

  In the case of the antenna element 139 shown in FIG. 5 in which the loop element and the parallel line are formed of an integral conductor, the connecting line 133 and 138 can be used to connect the parallel line part. Further, the antenna element 139 having the same wire diameter W as the loop element and the conductor wire diameter of the parallel line has an advantage in the simultaneous processing and the like from the viewpoint of mass production.

The dielectric loop element support 124 that fixes the loop element 120 and the parallel line 114 not only has the effect of maintaining the impedance of the parallel line at a constant value, but in particular, the loop shape and the parallel line are integrally formed by a conductor line. In the case of the antenna element 139 shown in FIG. 5, the antenna element 139 also has an important role of firmly fixing including the loop shape and holding the loop surface in a plane.
(Embodiment 2)
FIG. 6 is a configuration diagram of a double loop antenna according to the second embodiment of the present invention. In FIG. 6, the same components as those in FIGS. 1 and 10 are denoted by the same reference numerals and description thereof is omitted.

  In FIG. 6, the reflecting plate 140 has a curved surface that is close to the loop element surface at the center where the two loop elements face each other. Furthermore, the flat portion of the reflector near the center of the loop element is disposed at a position of λ / 4 from the loop element surface, so that the twin-loop antenna of this embodiment has high gain antenna performance.

  According to such a configuration, not only the strength against wind pressure is increased due to the curved surface of the reflecting plate, but also the antenna gain performance is slightly improved compared to the flat plate without causing deterioration of the antenna characteristics VSWR. Occurs.

  As shown in FIG. 7A, the loop element having an outer circumference of λ length has the maximum electromagnetic field radiation characteristic in the Z direction perpendicular to the loop element surface. It is known that this antenna radiation characteristic pattern is close to the characteristic in which two dipole elements having a length of λ / 2 arranged at an interval of λ / 4 are excited in phase.

  FIG. 7B shows an antenna including two dipole elements 142 equivalent to the loop element 120. In order to increase the gain performance by using a reflector for the dipole antenna, the wave in the direction of arrival of the electromagnetic wave and the reflected wave are preferably in the same phase, and the axis of the dipole is focused as shown in FIG. The reflection curved surface to be formed may be the shape of the reflection plate 143, and the focal length may be set to λ / 4.

  In the case of two dipole elements equivalent to the loop element shown in FIG. 8B, the reflection position is lowered in the curved portion indicated by the broken line and the focal point position becomes two, so that the reflecting plate is made a conventional plane. The shape of the reflector 144 is used.

  On the other hand, since the dual loop antenna has two loop elements, it is equivalent to four dipole elements arranged at the positions shown in FIG. Therefore, in order to increase the antenna gain performance, if the reflectors having the structure shown in FIG. 8B are arranged up and down and the shape of the reflector 145 is on the extended line of the curved surface of the reflector, the reflected wave can be obtained. Reaches the dipole element with maximum efficiency.

  That is, the antenna gain performance can be increased by making the reflecting plate of the dual loop antenna curved.

  In general, a metal plate is used as the reflection plate. However, since the wavelength λ is around 500 mm at the television broadcast frequency, several conductor rods or wire mesh conductors may be used. FIG. 9 shows an embodiment of a double loop antenna that realizes the same role as the reflector by using a conductor rod. The number of the conductor rods 146 can be reduced by arranging them at intervals of at least λ / 4 or less at the position of the reflector plate longer than λ / 2 and having a curved surface.

  Note that the antenna gain is almost maximized at the position of λ / 4 from the loop element surface, but the antenna VSWR does not change greatly even if the reflector is moved away from the loop surface from the position of λ / 4. On the other hand, when the reflector is brought closer, the antenna can be reduced in size, but the impedance of the loop element changes greatly, resulting in a narrow-band dual-loop antenna.

  In order to realize a small, narrow-band, dual-loop antenna in which the reflector and the loop surface are close to each other, it is easy to increase the characteristic impedance by increasing the interval between the parallel lines and to further reduce the value of the inductor element. realizable.

  The dual loop antenna according to the present invention can reduce the size of the antenna with simple components, can realize an antenna having a wide frequency characteristic with a good VSWR matched to the coaxial cable impedance, and can withstand a wind pressure load. Since the strength can be increased, it is useful as a receiving antenna for television broadcasting.

Configuration diagram of loop antenna in Embodiment 1 of the present invention Characteristic explanatory drawing of Embodiment 1 of this invention The figure which shows the example of a characteristic of Embodiment 1 of this invention The figure which shows the example of a connection of a parallel track and a coaxial track Diagram showing an antenna element including a loop element Configuration diagram of a dual loop antenna according to Embodiment 2 of the present invention Illustration of loop antenna characteristics Illustration of reflector shape Implementation configuration diagram with the reflector replaced with a conductor rod Configuration diagram of a conventional dual loop antenna Configuration diagram of a conventional dual loop antenna

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Twin loop antenna 102 Loop element 103 Loop element 104 Parallel line 105 Balance-unbalance conversion circuit 106 Coaxial line 107 Loop element 108 Loop element 109 Balance line 110 Short board 112 Conductor line 113 Reflector 114 Parallel line 119 Coaxial cable 120 Loop element 121 Loop element 122 Inductor element 123 Output connector 124 Loop element support plate 125 Support body 126 Support base body 127 Support metal fitting 128 Holding metal fitting 129 Fixing screw 130 Mast 131 Screw 132 Connection terminal 133 Connection metal fitting 134 Interposing connection terminal 135 Central conductor 137 External conductor 138 Connection bracket 139 Antenna element 140 Reflector 142 Dipole element 143 Reflector 144 Reflector 145 Reflector 146 Conductor bar 147 Holding material

Claims (4)

Two loop elements in which open portions of the loop curve face each other, a parallel line connected to an opening of the two loop elements, an inductor element connected to a central part of the parallel lines, and the two loops A twin loop antenna having a reflector disposed opposite to a surface of an element. The inductor element is formed of a central conductor at the end of a coaxial cable, has a connection terminal at the end of the central conductor, and further connects a pin connection terminal to the outer conductor of the coaxial cable, and the pin connection with the connection terminal The double loop antenna according to claim 1, wherein each of the terminals is connected at the center of the parallel line. The two loop elements and the parallel line are formed in an antenna element made of the same conductor wire, the antenna element is held in a predetermined shape by a dielectric support, and the antenna element end is connected, The twin-loop antenna according to claim 1, wherein the twin-loop antenna is connected to a coaxial cable via an inductor element. The dual-loop antenna according to claim 1, wherein the reflecting plate is curved by bringing the reflector close to the loop element surface at the opposite center of the two loop elements.

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