JP2008166856A - Antenna structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an antenna having less reflection loss in a very wide band. <P>SOLUTION: The antenna is provided with: a dielectric substrate 11; a plurality of sector-like antenna conductors 1, 2 disposed in linear symmetry or rotational symmetry on one surface of the dielectric substrate; an arc-like conductor 9 disposed in linear symmetry and short-circuiting the plurality of sector-like antenna conductors; and a plurality of power feeding conductors 3, 4 disposed in linear symmetry. The plurality of sector-like antenna conductors are disposed so that their apexes may oppose with each other near a rotary center, the one ends of the plurality of power feeding conductors are connected to near the apexes of the sector-like antenna conductors respectively, the other ends of the power feeding conductors are each power feeding ends 5, 6, and the arc-like conductor is disposed on the opposite side of the power feeding ends of the power feeding conductors with the apexes of the sector-like antenna conductors sandwiched. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an antenna structure, and more particularly to an ultra-wideband small antenna structure.

  In recent years, short-range wireless interfaces such as wireless LAN and Bluetooth (trademark) have come to be widely used, but the ultra wideband wireless system (UWB) that enables higher-speed transmission attracts attention as the next system. . Although the specification is being studied in each country, a relatively large output is recognized in the United States as 3.1 to 10.6 GHz as the use frequency. In any case, since this UWB system uses a very wide band frequency, high-speed wireless transmission of 100 Mbps or more is possible, but it is not easy to realize an antenna for transmitting such a wide band signal. Even if a normal antenna is phase-matched, such a broadband antenna cannot be realized.

There is an antenna structure described in the following Patent Document 1 as an antenna structure that reduces reflection loss in a very wide range.
JP, 2005-130292, A An antenna structure given in patent documents 1 is constituted on one side on a dielectric substrate, the dielectric substrate, a plurality of antenna conductors which are pseudo self-complementary on the surface, and the antenna conductor A plurality of feeding conductors symmetric with respect to the symmetry axis of the antenna, and a gap of 1/10 or less of the wavelength in vacuum at the operating frequency is provided at the center of rotational symmetry between the plurality of antenna conductors. It is what.

In addition, as a broadband antenna, one in which two antenna conductors of a bow tie antenna are short-circuited has been reported (Non-Patent Document 1). FIG. 9 is an explanatory diagram thereof. FIG. 9A shows the topology of a fan-shaped loop antenna, and FIG. 9B shows the topology of a combination of two fan-shaped loop antennas. In these figures, the center of the fan-shaped conductor is a feeding point. (C) shows an antenna structure realized on the ground plane using half of the antenna of (b). In FIG. 9, the blacked-out portion shows the conductor.
Nader Behdad and Kamal Sarabandi, "A Compact Antenna for Ultrawide-Band Applications" IEEE TRANSACTION ON ANTENNAS AND PROPAGATION, VOL.53, NO.7, JULY 2005, pp2185-2192

  The antenna structure described in Patent Document 1 is based on a self-complementary structure. In the self-complementary structure, a plurality of antenna conductors are symmetrical with respect to the symmetry axis, and the antenna conductor overlaps with the antenna conductor itself when rotated 180 ° with respect to the symmetry point, and the antenna conductor is patterned when rotated 90 °. It is a structure that overlaps with no part. Theoretically, the self-complementary structure can realize a broadband antenna, but the size of the antenna conductor must be infinite. Such an antenna structure cannot actually be realized, and the antenna conductor must be accommodated within a predetermined range (referred to as “pseudo” self-complement in Patent Document 1). Therefore, the characteristics are slightly deteriorated.

  Since the antenna structure described in Non-Patent Document 1 (FIG. 9C) is a three-dimensional structure, it was difficult to mount. Although the structure of FIG. 9B can be realized in a plane, there is a drawback that it is difficult to extract a signal from the feeding point at the center because the periphery of the feeding point is surrounded by a conductor. If the feed line is placed on the same surface of the antenna conductor, it will be short-circuited with the short-circuit line, and even if the feed line is connected to the via after being pulled out from the feed point to the other surface via the via, Therefore, the operation of the antenna is deteriorated because the short-circuit wire or the antenna conductor intersects with the feed line. In order to avoid this, it is conceivable to increase the thickness of the dielectric, but this has the disadvantage of increasing the cost of the material.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an antenna structure capable of realizing a good broadband characteristic while using an antenna conductor having a finite size.

  An antenna structure according to the present invention includes a dielectric substrate, a plurality of fan-shaped antenna conductors arranged in line symmetry and rotational symmetry on one surface of the dielectric substrate, and the plurality of fan-shaped antennas arranged in line symmetry. An arc-shaped conductor that short-circuits between the conductors, and a plurality of power supply conductors arranged in line symmetry, and the plurality of fan-shaped antenna conductors are arranged opposite to each other in the vicinity of the rotation center, One end of each of the feeding conductors is connected in the vicinity of the apexes of the plurality of fan-shaped antenna conductors, the other end of the plurality of feeding conductors is a feeding end, and the arcuate conductor is the plurality of fan-shaped conductors. The antenna conductors are arranged on opposite sides of the feeding ends of the plurality of feeding conductors with the apex of the antenna conductor interposed therebetween.

  The angles of the apexes of the plurality of fan-shaped antenna conductors are each 120 degrees.

The arc-shaped conductor short-circuits the outer periphery of the plurality of fan-shaped antenna conductors.
The arcuate conductor connects the first portion provided outside the outer periphery of the plurality of fan-shaped antenna conductors and the first portion to the outer periphery of the plurality of fan-shaped antenna conductors, respectively. A plurality of second parts may be included.
Alternatively, the arc-shaped conductor short-circuits substantially the middle of the radius of the plurality of fan-shaped antenna conductors.

  The plurality of power supply conductors may be wider at the power supply end than the apexes of the plurality of fan-shaped antenna conductors.

  The plurality of feeding conductors are provided on a surface of the dielectric substrate different from the surface on which the plurality of fan-shaped antenna conductors are provided, and the apexes of the plurality of fan-shaped antenna conductors and the plurality of feeding antennas are provided. The conductors may be connected by vias.

  According to the present invention, it is possible to realize an antenna with little reflection loss in a very wide band range.

Embodiment 1 of the Invention
An antenna according to Embodiment 1 of the present invention will be described with reference to the drawings.
FIG. 1A is a plan view of an antenna structure according to Embodiment 1 of the invention. 1 and 2 are fan-shaped antenna conductors constituting the antenna (the angle is 120 degrees, but is not limited to this angle), and 3 and 4 are feeding conductors having one end connected to the antenna conductors 1 and 2, respectively. is there. Reference numerals 5 and 6 denote ends of the feeding conductors 3 and 4 opposite to the antenna conductors 1 and 2, respectively. Signals whose phases are shifted from each other by 180 degrees are fed from these portions (feed ends) 5 and 6. The antenna conductors 1 and 2 and the feeding conductors 3 and 4 are line symmetric with respect to the symmetry axis AS. Reference numeral 9 denotes an arcuate conductor which is arranged symmetrically with respect to the symmetry axis AS and which short-circuits the plurality of fan-shaped antenna conductors 1 and 2 at their outer peripheries P and Q. The arcuate conductor 9 is arranged on the opposite side of the plurality of feeding conductors 3 and 4 with the rotational symmetry point PS as the center, and shorts the plurality of fan-shaped antenna conductors 1 and 2 there. In the example of FIG. 1, the arcuate conductor 9 has the same shape as the outer periphery (arc) of the fan-shaped antenna conductors 1 and 2, and short-circuits the outermost edges P and Q of the fan-shaped antenna conductors 1 and 2. ing.

  The arcuate conductor 9 that short-circuits the antenna conductors 1 and 2 does not adversely affect the differential operation because the odd mode becomes the eigenmode as long as the shape is symmetrical. Therefore, the width of the arcuate conductor 9 may not be constant. In FIG. 1, the outermost peripheries P and Q of the antenna conductors 1 and 2 are connected, but the portions may be short-circuited.

  A symmetrical point PS exists between the antenna conductors 1 and 2, and the antenna conductors 1 and 2 are rotationally symmetric with respect to the symmetrical point PS. That is, when the two fan-shaped conductors 1 and 2 are rotated 180 degrees around the symmetry point PS, they coincide with the fan-shaped conductors 1 and 2 in FIG.

  FIG.1 (b) is sectional drawing (aa arrow sectional drawing of the figure (a)) of the antenna structure which concerns on Embodiment 1 of invention. Reference numeral 11 denotes a dielectric substrate. The antenna conductors 1 and 2 and the feeding conductors 3 and 4 are formed on the same surface of the dielectric substrate 11.

  In FIG. 1 (a), an arcuate conductor 9 (hereinafter sometimes referred to as "short-circuit metal" or "short-circuit line") is provided above the plurality of antenna conductors 1 and 2, so that a plurality of antenna conductors are provided. 1 and 2 are short-circuited in direct current (DC). On the other hand, there is no short-circuit metal on the lower side, and the feed lines 3 and 4 are drawn between the plurality of antenna conductors 1 and 2.

  According to the antenna structure according to the first embodiment of the invention, the self-complementary antenna structure is generally provided when there is no short-circuit wire 9, but the antenna conductors 1 and 2 are short-circuited, so that a short circuit occurs in DC and the antenna is It does not operate, but when the frequency increases due to the inductance of the short circuit wire, it will not be short circuited and will begin to operate as an antenna.

When the antenna structure according to Embodiment 1 of the present invention is compared with the antenna structure described in Patent Document 1, the following points are different.
(1) The first embodiment of the invention includes the arc-shaped conductor (short-circuit metal) 9 whereas the patent document 1 does not include (2) The antenna conductors 1 and 2 of the first embodiment of the invention are fan-shaped. In contrast, Patent Document 1 has a triangular point (3) The angle of antenna conductors 1 and 2 of Embodiment 1 of the invention is 120 degrees, whereas Patent Document 1 has 90 degrees.

When the antenna structure according to the first embodiment of the invention is compared with the antenna structure described in Non-Patent Document 1, the following points are different.
(4) While the first embodiment of the invention includes the feeding conductors 3 and 4 provided on the same plane as the antenna conductors 1 and 2, the non-patent document 1 does not clearly indicate the feeding conductor (non- (The power supply and the flow of Patent Document 1 are merely schematically drawn)
(5) The antenna structure of the first embodiment of the invention is open (either the antenna conductor 1 or 2 or the short-circuit metal 9 from the feeding point located at the center of the fan-shaped antenna conductors 1 and 2 to the outside of the antenna). The line of non-patent document 1 is closed while the line can be drawn without touching

  FIG. 2 shows the characteristics (◯ mark) of the antenna structure according to the first embodiment of the invention and the characteristics (× mark) of the comparative example. FIG. 2 is obtained by computer simulation. The comparative example has the structure shown in FIG. In the comparative example, antenna conductors 1 and 2 are short-circuited on both sides thereof. In this structure, since it is difficult to arrange the antenna feed line in the above point (5), it cannot be put into practical use (computer simulation is possible). The comparative examples are for reference only.

  In the antenna structure of the comparative example, the feeding point is surrounded by metal, and thus crosses the line. By pulling the feed line to the back of the substrate with vias and crossing with the short-circuit metal 9 through the dielectric, it is possible to avoid short-circuiting at low frequencies, but in the high-frequency band, the antenna short-circuit metal and the feed line cross at the crossing part. As a result, the antenna is capacitively coupled to deteriorate the antenna characteristics. Such an inconvenience can be avoided with the antenna structure according to the first embodiment of the invention.

  FIG. 2 shows that the antenna conductors 1 and 2 have an angle of 120 degrees sandwiching the fan-shaped portion with a radius of 21 mm, and the antenna conductor is made of copper on a substrate having a relative dielectric constant of 3.5 and a thickness of 0.1 mm. A simulation was performed as a fabricated product.

  FIG. 2A shows a comparison of input impedance. According to the figure, both the antenna structure according to the first embodiment of the invention and the antenna structure of the comparative example have a substantially constant input impedance at 3 GHz or more, and both exhibit substantially the same characteristics. That is, for both the antenna structure according to the first embodiment of the invention and the antenna structure of the comparative example, the input impedance is 3 GHz or higher, and the real part has a constant value of 160Ω and the imaginary part has a constant value of 0Ω.

  FIG. 2B shows the reflection loss when the antenna of the antenna structure according to the first embodiment of the invention and the antenna of the comparative example are connected to a differential terminal having an impedance of 160Ω. All indicate that a reflection loss of 2 GHz or more and -10 dB or less is obtained. Both satisfy the reflection loss (-10 dB or less) normally required for an antenna, and an extremely wide antenna characteristic of 2 GHz to 15 GHz is realized. This reflection characteristic is in a practically acceptable range.

  As described above, the antenna structure according to the first embodiment of the present invention has almost no influence on the operation of the antenna even if the feed line is provided, and can obtain broadband characteristics with the same performance as the antenna. Has characteristics.

Embodiment 2 of the Invention
According to the simulation results of FIG. 2, the antenna structure of FIG. 1 should be terminated with an input impedance of 160Ω. However, in practice, it is rarely terminated with an input impedance of 160Ω, and normally the antenna is terminated with a coaxial cable (unbalanced 50Ω) or differential 100Ω. Without impedance matching, the signal will be attenuated. In order to avoid this, a differential impedance matching circuit is required when terminated differentially, and an impedance matching circuit and a balanced / unbalanced conversion circuit (balun) are required when terminated with a coaxial cable.

  By adjusting the dimensional shape of the feeder lines 3 and 4 without changing the shape of the antenna conductors 1 and 2, it is possible to match the terminal impedance. 4 and 5 are plan views of an antenna structure according to Embodiment 2 of the invention. In this figure, the same or corresponding parts as those in the embodiment of the present invention are denoted by the same reference numerals.

  In FIG. 4, when the width of the end 5 of the power feeding conductor 3 is compared with the width of the other end (end on the antenna conductor 1 side), the width increases monotonously from the end on the antenna conductor 1 side toward the end 5. . The same applies to the width of the end 6 of the power supply conductor 4 and the width of the other end (end on the antenna conductor 1 side). The inclination may change depending on the location, or may change partially discontinuously. In short, it is only necessary that the width gradually narrows or widens from one end to the other end, and does not widen in the middle of becoming narrower.

  Alternatively, as shown in FIG. 5, the power supply conductor 3 may be composed of power supply conductors 3-1 and 3-2 having different widths. The same applies to the power supply conductor 4.

  In the second embodiment of the present invention, since the widths of the power supply conductors 3 and 4 are as described above, the output impedance of the LSI connected to the power supply conductors 3 and 4 is lower than the input impedance of the antenna. However, the external signal source impedance can be matched to the antenna.

  When the output impedance of the LSI is higher than the input impedance of the antenna, contrary to the case described above, that is, the width of the feeding conductors 3 and 4 is wide at the portion connected to the antenna, What is necessary is just to comprise so that it may become narrow by 6.

  According to the second embodiment of the present invention, it is possible to sufficiently maintain the broadband property of the antenna by performing impedance matching. The impedance matching circuit needs to design the impedance of the feed line to the desired impedance, but in this case the input impedance of the antenna is higher than the impedance of the feed point, so the line width of the pair of feed lines is narrower on the antenna side. This can be realized by adjusting the line width to a high impedance as the width and a low impedance with the feeding side as a thick line. Further, when unbalanced power feeding is performed, the balun function is also achieved. Since there is no ground plane in the vicinity of the feed line, the current flows in the opposite direction between the lines from the law of current continuity, which also serves as a balun.

Embodiment 3 of the Invention
In the first embodiment of the present invention, the antenna conductors 1 and 2 and the feeding lines 3 and 4 are provided on one surface of the dielectric substrate 11, but the feeding lines 3 and 4 are provided on a different surface from the antenna conductors 1 and 2. You may make it provide. FIG. 6 shows an example of the third embodiment of the invention. In these drawings, the same reference numerals are given to the same or corresponding parts as those of the embodiment of the present invention.

  6A is a plan view of an antenna structure according to Embodiment 3 of the invention, and FIG. 6B is a cross-sectional view taken along the line bb. The power feeding conductors 3 and 4 are provided on the back surface of the dielectric substrate. For this purpose, vias 24 and 25 are provided for connecting the antenna conductors 1 and 2 and the feeding conductors 3 and 4. Signals whose phases are shifted from each other by 180 degrees are fed from the portions 5 and 6.

Embodiment 4 of the Invention
FIG. 7 shows an antenna structure according to the fourth embodiment of the present invention. In the figure, the same reference numerals are given to the same or corresponding parts as those of the embodiment of the invention.

  7 includes a first portion 9 ′ provided slightly outside the outer periphery of the plurality of fan-shaped antenna conductors 1 and 2, and the first portion 9 ′ as a plurality of fan-shaped antenna conductors. It consists of 2nd part P 'and Q' for connecting with the outer periphery of 1 and 2, respectively. The second portions P ′ and Q ′ are provided not in the ends of the plurality of fan-shaped antenna conductors 1 and 2 but in the middle of the arcs, and the first portion is formed between the second portions P ′ and Q ′. Is short-circuited at the portion 9 '. Since the first portion 9 ′ is slightly larger than the plurality of fan-shaped antenna conductors 1 and 2, it does not contact the plurality of fan-shaped antenna conductors 1 and 2 except for the second portions P ′ and Q ′.

  The short-circuit metal 9 in FIG. 7 is longer than that in FIG. The impedance can be changed by adjusting this length.

  The antenna structure according to the fourth embodiment of the present invention has the same effects as those of the above-described embodiments of the present invention.

Embodiment 5 of the Invention
FIG. 8 shows an antenna structure according to the fifth embodiment of the present invention. In the figure, the same reference numerals are given to the same or corresponding parts as those of the embodiment of the invention.

  The arcuate conductor 9 ″ in FIG. 8 is smaller than the plurality of fan-shaped antenna conductors 1 and 2 (in FIG. 8, approximately half the radius of the plurality of fan-shaped antenna conductors 1 and 2), and the middle is short-circuited. is doing. In FIG. 8, P ″ and Q ″ are connection points between the plurality of fan-shaped antenna conductors 1 and 2 and the arcuate conductor 9 ″.

  The antenna structure according to the fifth embodiment of the present invention has the same effects as those of the above-described embodiments of the present invention.

  The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the invention described in the claims, and these are also included in the scope of the present invention. Needless to say.

1A is a plan view of an antenna structure according to Embodiment 1 of the invention, and FIG. 1B is a cross-sectional view taken along the line aa. It is a graph which shows the characteristic by the antenna structure which concerns on Embodiment 1 of invention, and the characteristic of a comparative example. It is a top view of the antenna structure of a comparative example. It is a top view of the antenna structure which concerns on Embodiment 2 of invention. It is a top view of the other antenna structure which concerns on Embodiment 2 of invention. It is a top view of the antenna structure which concerns on Embodiment 3 of invention. It is a top view of the antenna structure which concerns on Embodiment 4 of invention. It is a top view of the antenna structure which concerns on Embodiment 5 of invention. It is explanatory drawing of the conventional antenna structure.

Explanation of symbols

1, 2 Fan-shaped antenna conductor 3, 4 Feeding conductor (feeding line)
5, 6 Feeding end 9, 9 ″ Arc conductor (short-circuit metal, short-circuit wire)
9 'first portion of arc-shaped conductor 11 dielectric substrate 24, 25 via P', Q 'second portion of arc-shaped conductor

Claims (7)

  A dielectric substrate, a plurality of fan-shaped antenna conductors arranged line-symmetrically and rotationally symmetrically on one side of the dielectric substrate, and an arc-shaped short circuit between the plurality of fan-shaped antenna conductors arranged symmetrically A plurality of feeding conductors arranged in line symmetry, and the apexes of the plurality of fan-shaped antenna conductors are arranged opposite to each other in the vicinity of the rotation center, and one ends of the plurality of feeding conductors are respectively Connected near the apexes of the plurality of fan-shaped antenna conductors, the other end of the plurality of power supply conductors is a power supply end, and the arcuate conductor sandwiches the apexes of the plurality of fan-shaped antenna conductors An antenna structure, wherein the antenna structure is disposed on a side opposite to a feeding end of the plurality of feeding conductors.   2. The antenna structure according to claim 1, wherein an angle of a vertex of each of the plurality of fan-shaped antenna conductors is 120 degrees.   The antenna structure according to claim 1, wherein the arc-shaped conductor short-circuits the outer periphery of the plurality of fan-shaped antenna conductors.   The arcuate conductor connects the first portion provided outside the outer periphery of the plurality of fan-shaped antenna conductors and the first portion to the outer periphery of the plurality of fan-shaped antenna conductors, respectively. The antenna structure according to claim 1, comprising a plurality of second portions.   2. The antenna structure according to claim 1, wherein the arc-shaped conductor short-circuits substantially the middle of the radii of the plurality of fan-shaped antenna conductors.   2. The antenna structure according to claim 1, wherein the plurality of power supply conductors are wider at the power supply end than the apexes of the plurality of fan-shaped antenna conductors.   The plurality of feeding conductors are provided on a surface of the dielectric substrate different from the surface on which the plurality of fan-shaped antenna conductors are provided, and the apexes of the plurality of fan-shaped antenna conductors and the plurality of feeding antennas are provided. The antenna structure according to claim 1, wherein the conductors are connected by vias.

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