JP2008294809A - Stacked helical antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stacked helical antenna whose frequency reduction is easy. <P>SOLUTION: The stacked helical antenna is equipped with: a plurality of dielectric layers arranged by being stacked; a plurality of first radiation electrodes arranged on any of first surfaces of the plurality of dielectric layers; a plurality of second radiation electrodes arranged on any of second surfaces of the plurality of dielectric layers; a plurality of connection parts for connecting edges of the plurality of first radiation electrodes with edges of the plurality of second radiation electrodes to constitute a helical electrode with the plurality of first, second radiation electrodes; and a first non-supplied electrode which is arranged on a third surface to be boundary of any of the plurality of dielectric layers between the first, second surfaces and is not connected to the helical electrode. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laminated helical antenna used in a wireless communication device.

A technique of a helical antenna having a helical element has been disclosed (see Patent Document 1). The multi-frequency shared antenna 1 is constituted by the helical element 10 and the parasitic helical element 11 electromagnetically coupled to the helical element 10. The helical element 10 is excited in its resonating frequency band. In addition, a current flowing through the helical element 10 is induced in the parasitic helical element 11 arranged substantially coaxially with the helical element 10, and is excited in the resonance frequency band. As a result, the multi-frequency shared antenna 1 operates in two different frequency bands.
JP 2002-118408 A

However, with this technology, it is difficult to lower the frequency band itself that operates. That is, in this technique, the operation is performed only in the frequency band of each of the helical element 10 and the parasitic helical element 11, and by adding the parasitic helical element 11, the operating frequency band of the helical element 10 is lowered. Not that.
In view of the above, an object of the present invention is to provide a laminated helical antenna that can be easily reduced in frequency.

  The laminated helical antenna according to the present invention includes a plurality of dielectric layers arranged in a stacked manner, a plurality of first radiation electrodes arranged on a first surface of any one of the plurality of dielectric layers, , A plurality of second radiation electrodes disposed on a second surface of any one of the plurality of dielectric layers, end portions of the plurality of first radiation electrodes, and a plurality of second radiation electrodes. A plurality of dielectric layers between the first and second surfaces, and a plurality of connection portions constituting a helical electrode together with the plurality of first and second radiation electrodes. And a first parasitic electrode which is disposed on the third surface as a boundary and is not connected to the helical electrode.

  According to the present invention, it is possible to provide a laminated helical antenna that can be easily reduced in frequency.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an exploded perspective view showing a state in which a part of a laminated helical antenna 10 according to an embodiment of the present invention is disassembled. FIG. 2 is an enlarged perspective view showing a state in which a part of the laminated helical antenna 10 (chip antenna 13) is enlarged. 3 and 4 are a front view and a side view, respectively, illustrating a state in which the chip antenna 13 is viewed from the front (free end side) and the side.

  The laminated helical antenna 10 includes an insulating substrate 11, a flat plate ground electrode 12, a chip antenna 13, a feed line 14, a connection portion 15, and a fixed terminal 16.

  The insulating substrate 11 is made of an insulating material such as FR4 (abbreviation of Flame Retardant Type 4 and a flame-retardant printed circuit board material made of a composite material of glass fiber and epoxy resin (relative permittivity ε1r = 4.8)). This is a substantially rectangular flat-plate substrate.

  The flat ground electrode 12 is a substantially rectangular flat conductor made of silver, platinum, copper or the like, and is disposed on the back surface of the insulating substrate 11. Since the feed line 14 and the flat plate ground electrode 12 face each other close to each other, the electric field from the feed line 14 is limited between the flat plate ground electrode 12 and the feed line 14 in the range facing the flat plate ground electrode 12 radiates. Does not function as an electrode.

  The chip antenna 13 has a rectangular parallelepiped shape (substantially flat plate shape) (width W0, length L0, height H0), and includes dielectric members 131 and 132, a helical electrode 133, a parasitic electrode 134, and pads 135 and 136. Have.

  The dielectric members 131 and 132 are rectangular parallelepiped members made of a dielectric material having a dielectric constant larger than that of the insulating substrate 11 (for example, a ceramic material such as borosilicate glass-based ceramic (relative permittivity ε2r = 7.5)). is there. The reason why the dielectric constants of the dielectric members 131 and 132 are relatively large is to increase the effective length of the helical electrode 133 and the parasitic electrode 134 to reduce the size thereof. Each of the dielectric members 131 and 132 can be composed of a plurality of dielectric layers.

  The helical electrode 133 includes radiation electrodes 137 (137a, 137b), 138 (138a, 138b), and interlayer connection portions 139 (139a-139c), and functions as a radiation electrode having a substantially helical shape as a whole. The reason why the helical electrode 133 is formed in a helical shape is to effectively use the volume of the chip antenna 13 to secure the line length of the helical electrode 133 and to reduce the frequency of the chip antenna 13. The helical electrode 133 according to this embodiment is a right-handed winding, but may be a left-handed winding.

  Each of the radiation electrodes 137 and 138 is in the vicinity of the upper surface and the lower surface of the chip antenna 13 (in the vicinity of the upper surface of the dielectric member 131, in the vicinity of the lower surface of the dielectric member 132, precisely from the upper and lower surfaces to, for example, 0.1 mm). A strip-shaped flat electrode made of silver, platinum, or copper. One or one of the radiation electrodes 137 and 138 may be arranged on the surface of the dielectric members 131 and 132. The center plane SC is a virtual plane that is equidistant (center) from the radiation electrodes 137 and 138.

  Since the radiation electrodes 137 and 138 constitute a part of the helical electrode 133, the radiation electrodes 137 and 138 are respectively inclined with respect to the side surface of the chip antenna 13 (the radiation electrodes 137 and 138 are arranged on the chip antenna 13). Not perpendicular to the side).

  The radiation electrodes 137 and 138 are divided into radiation electrodes 137a and 137b and radiation electrodes 138a and 138b, respectively. At the feeding end and the free end of the helical electrode 133, radiation electrodes 137b and 138b having shapes different from those of the other radiation electrodes 137a and 138a are disposed due to the connection with the pads 135 and 136. The radiation electrode 137b is connected to the pad 135 through the interlayer connection 139c. The radiation electrode 138b is connected to the pad 136.

  The interlayer connection portion 139 is a kind of via hole made of a conductive material (for example, a conductive paste) disposed through the dielectric members 131 and 132. The interlayer connection portion 139a connects the free end of the radiation electrode 137 and the feeding end of the radiation electrode 138. The interlayer connection portion 139b connects the free end of the radiation electrode 138 and the feeding end of the radiation electrode 137. The interlayer connection portion 139c connects the pad 135 on the power supply end side of the helical electrode 133 and the power supply end of the radiation electrode 137.

  The pads 135 and 136 are disposed on the power supply side and the free end side, respectively, and are connected to the connection portion 15 and the fixed terminal 16 by, for example, a conductor paste. This connection serves not only as an electrical connection but also as a physical connection between the chip antenna 13 and the insulating substrate 11.

  The parasitic electrode 134 is disposed at the interface between the dielectric members 131 and 132 in parallel with the axis of the helical electrode 133 (parallel to the radiation electrodes 137 and 138) and is not connected to the feeder 14 such as silver, platinum, It is a strip-shaped flat electrode made of copper. The parasitic electrode 134 is electromagnetically connected to the helical electrode 133 and contributes to lowering the resonance frequency of the chip antenna 13. Further, it is preferable that the parasitic electrode 134 be separated to some extent from the center plane SC of the helical electrode 133. Details of this will be described later.

The feed line 14 is a substantially linear electrode made of a conductor, for example, silver, platinum, or copper, and having a width of 1.1 mm, for example, and supplies power to the chip antenna 13. The feed line 14 faces the flat plate ground electrode 12.
The feed line 14 is divided by the boundary 18 of the flat plate ground electrode 12, and the feed line 14 on the chip antenna 13 side from the boundary 18 functions as a radiation electrode. The boundary 18 is a virtual line on the upper surface of the insulating substrate 11 corresponding to the boundary 17 on the lower surface of the insulating substrate 11, and does not actually exist on the upper surface of the insulating substrate 11.

  The connection portion 15 is a conductor, for example, a substantially flat conductor made of silver, platinum, or copper, and is formed integrally with the feed line 14 and is helically connected to the feed line 14 via the pad 135 and the interlayer connection portion 139c. The electrode 133 is electrically connected.

The fixed terminal 16 is a conductor, for example, a substantially flat conductor made of silver, platinum, or copper, and is connected to the open end side of the helical electrode 133 via a pad 136.
The connection portion 15 and the fixed terminal 16 function as a pad for fixing the chip antenna 13 to the insulating substrate 11. The chip antenna 13 is connected to the insulating substrate 11 and electrically connected to the chip antenna 13 by connecting the connecting portion 15 and the fixed terminal 16 with, for example, a conductive paste.
The fixed terminal 16 functions as a radiation electrode that radiates electromagnetic waves together with the helical electrode 133. The fixed terminal 16 adds a line length to the helical electrode 133, shifts the radiation characteristic of the laminated helical antenna 10 to the low frequency side, and achieves a wider band.

(Antenna characteristics)
Hereinafter, a change in characteristics of the laminated helical antenna 10 due to the addition of the parasitic electrode 134 will be described.
Here, the reference values of the width W0, the length L0, and the height H0 of the chip antenna 13 are set to 1.6 mm * 3.2 mm * 1 mm. The fixed terminal 16 has a width of 1.6 mm and a length of 1.0 mm.
5, FIG. 6 and FIG. 8 to FIG. 13 are graphs showing frequency characteristics of the laminated helical antenna 10, respectively. The horizontal and vertical axes of the graph correspond to the frequency [GHz] and the reflectance [dB], respectively.
Tables 1 to 4 show the length L [mm], the width W [mm], the distance t [mm], the number of turns N [times], the center frequency F0 [MHz], and the bandwidth BW [MHz]. ]. Of these, Table 2 also represents the distance Δt (= t−0.5) from the center plane SC of the helical electrode 133.

The distance t means the distance from the bottom surface of the chip antenna 13 (helical electrode 133) to the parasitic electrode 134, and corresponds to the position of the parasitic electrode 134.
Bandwidth BW is VSWR (Voltage Standing Wave Ratio (ratio of peak and valley of voltage amplitude distribution generated on transmission line where reflected wave is generated due to impedance mismatch)) = 2. It is defined by the difference between the minimum frequency fL that becomes 0 and the maximum frequency fH, and is represented by BW = fH−fL.

(1) Presence / absence of parasitic electrode 134 Each of graphs G00, G01, G02 in FIG. 5 corresponds to the following case.
Graph G00: When neither parasitic electrode 134 nor fixed terminal 16 is connected Graph G01: When only fixed terminal 16 is connected Graph G02: Both parasitic electrode 134 and fixed terminal 16 are connected If

In contrast to the case of only the helical electrode 133 (graph G00), the resonance frequency (peak) is shifted somewhat to the low frequency side by connecting the fixed terminal 16 and increasing the electrode length (graph G01). Furthermore, by connecting the parasitic electrode 134, the resonance frequency (peak) moves to the low frequency side (graph G02).
As described above, it can be seen that the resonance frequency moves to the low frequency side by adding the parasitic electrode 134.

(2) Position of parasitic electrode 134 Table 1 corresponds to graphs G10 to G14 in FIG.

FIG. 7 shows the correspondence between the distance Δt (= t−0.5) from the center plane SC of the helical electrode 133 and the change amount (frequency change amount) ΔF0 (= F0 (Δt) −F0 (0)) of the center frequency F0. It is a graph showing a relationship. Table 2 corresponds to FIG.

  It can be seen that the center frequency F0 moves to the low frequency side by shifting the position of the parasitic electrode 134 from the center plane SC (t = 0.5 mm) of the helical electrode 133. In the graph of FIG. 7, it can be seen that the distance Δt = 0 and the left and right are almost symmetrical, and the sign of the distance Δt (whether it moves up or down the center plane SC) has little effect on the frequency change amount ΔF0.

It can be seen that by shifting the position of the parasitic electrode 134 by 0.2 mm or more from the center plane SC of the helical electrode 133 (| Δt | ≧ 0.2), the center frequency F0 can be greatly moved to the low frequency side. Considering the thickness (t0) of the chip antenna 13, the ratio (shift ratio) R (= | Δt / t0 |) of this shift amount is 0.2 mm / 1.0 mm = 0.2. The shift ratio R is preferably 0.2 or more. In the range of R <0.2, the change amount ΔF0 of the center frequency F0 is relatively small.
As described above, since the radiation electrodes 137 and 138 are within a range of 0.1 mm from the top and bottom surfaces of the chip antenna 13, the upper limit of the absolute value of the distance Δt in FIG. .4 (range in which the parasitic electrode 134 and the radiation electrodes 137 and 138 do not contact each other).

  In the above, the shift ratio R is defined based on the thickness t0 of the chip antenna 13. On the other hand, instead of the shift ratio R, a shift ratio R1 (= | Δt / t1 |) based on the distance t1 between the radiation electrodes 137 and 138 can be used. Even in this case, it can be said that the amount of change ΔF0 of the center frequency F0 is relatively small in the range of R1 <0.2. This is because the parasitic electrode 134 is disposed in the vicinity of the upper and lower surfaces of the chip antenna 13, so that the distance t 1 between the radiation electrodes 137 and 138 is substantially equal to the thickness t 0 of the chip antenna 13.

(3) Size of parasitic electrode 134 FIGS. 8 and 9 are graphs showing frequency characteristics of the laminated helical antenna 10 when the length L and width W of the parasitic electrode 134 are changed, respectively.

無給電電極１３４の長さＬ，幅Ｗを大きくすることで，中心周波数Ｆ０が低周波側に移行することが判る。 Tables 3 and 4 correspond to FIG. 8 (graphs G30 to G33) and FIG. 9 (graphs G40 to G43), respectively.

It can be seen that the center frequency F0 shifts to the low frequency side by increasing the length L and the width W of the parasitic electrode 134.

(4) Number of parasitic electrodes 134 The resonance frequency of the laminated helical antenna 10 can be lowered even if a plurality of parasitic electrodes 134 are provided.
FIG. 10 is a front view showing a state in which the chip antenna 23 of the laminated helical antenna 20 according to the modification of the present invention is viewed from the front (free end side), and corresponds to FIG. The chip antenna 23 has two parasitic electrodes 234a and 234b instead of the parasitic electrode 13. Three layers of dielectric members 231 to 233 are arranged corresponding to the parasitic electrodes 234a and 234b. The parasitic electrodes 234a and 234b are disposed substantially symmetrically (so that the distance from the central plane SC is substantially equal) with respect to the central plane SC of the chip antenna 23 (helical electrode 133).

FIG. 11 is a graph showing the frequency characteristics of the laminated helical antenna 20 when the length L of the chip antenna 23 (helical electrode 133) is changed. The graphs G51 to G53 in FIG. 11 correspond to the length L of the parasitic electrode 134 = 2.2, 1.4, and 0.6 mm, respectively. At this time, the width W of the parasitic electrode 134 is 0.2 mm, the distance t is 0.2 mm, and the number of turns N is 6.75.
Table 5 corresponds to the graphs G51 to G53 in FIG.

Even if there are a plurality of parasitic electrodes 134, the center frequency F0 can be lowered. Even if the two parasitic electrodes 134 are arranged symmetrically with respect to the axis of the helical electrode 133, the center frequency F0 shifts to the low frequency side.
Further, by comparing the graph G11 in FIG. 6 with the graph G51 in FIG. 11 (the length L, the width W, and the distance t are equal), by increasing the number of the parasitic electrodes 134 from one to two, It can be seen that the center frequency F0 decreases somewhat.

(5) Direction of Parasitic Electrode 134 FIG. 12 is a perspective view of the chip antenna 33 of the laminated helical antenna 30 according to the comparative example of the present invention, and corresponds to FIG. The chip antenna 33 has three parasitic electrodes 334 (334a to 334c) instead of the parasitic electrode 13. Note that the radiation electrode 137a is not shown for easy viewing. The parasitic electrodes 334a to 334c do not come into contact with the radiation electrodes 137a and 137b in the vertical direction of the chip antenna 33 (helical electrode 133) (in the vertical direction of the radiation electrodes 137 and 138) and substantially symmetrical to the center plane SC. Is arranged.
Graphs G60, G61, and G62 in FIG. 13 represent frequency characteristics of the laminated helical antenna 30 when the number of parasitic electrodes 334 is 0, 1, and 3, respectively.
As shown in this figure, it can be seen that when the parasitic electrode 134 is arranged in the vertical direction of the chip antenna 13, the center frequency F0 is hardly lowered.

(Other embodiments)
Embodiments of the present invention are not limited to the above-described embodiments, and can be expanded and modified. The expanded and modified embodiments are also included in the technical scope of the present invention.
(1) When power is supplied to the chip antenna 13, various transmission lines can be used. In the above-described embodiment, power is transmitted by a so-called microstrip line in which the feeder 14 and the flat plate ground electrode 12 face each other in close proximity. Instead, a so-called coplanar line in which the feeder 14 is arranged on the same plane as the flat plate ground electrode 12 may be used.

(2) It is possible to dispose other elements on the insulating substrate 11. For example, other antennas, switches for switching antennas, filters (bandpass filters, etc.), crystal resonators, ICs for reception (integrated circuits), ICs for transmission, and ICs for high frequency amplification.

1 is a perspective view of a laminated helical antenna according to an embodiment of the present invention. 1 is an enlarged top view of a laminated helical antenna according to an embodiment of the present invention. 1 is an enlarged front view of a laminated helical antenna according to an embodiment of the present invention. 1 is an enlarged side view of a laminated helical antenna according to an embodiment of the present invention. It is a graph showing an example of the frequency characteristic of a laminated | stacked helical antenna. It is a graph showing an example of the frequency characteristic of a laminated | stacked helical antenna. It is a graph showing distance (DELTA) t from the center surface of a helical electrode, and frequency change amount (DELTA) F0 correspondence relationship. It is a graph showing an example of the frequency characteristic of a laminated | stacked helical antenna. It is a graph showing an example of the frequency characteristic of a laminated | stacked helical antenna. It is a front view of the lamination type helical antenna concerning the modification of the present invention. It is a graph showing an example of the frequency characteristic of a laminated | stacked helical antenna. It is a perspective view of the lamination type helical antenna concerning the comparative example of the present invention. It is a graph showing an example of the frequency characteristic of a laminated | stacked helical antenna.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Laminated helical antenna 11 Insulating substrate 12 Flat ground electrode 13 Chip antenna 14 Feed line 15 Connection part 16 Fixed terminal 17 Boundary 18 Boundary 131, 132 Dielectric member 133 Helical electrode 134 Parasitic electrode 135, 136 Pad 137 (137a, 137b ), 138 (138a, 138b) Radiation electrode 139 (139a-139c) Interlayer connection

Claims (5)

A plurality of dielectric layers arranged on top of each other;
A plurality of first radiation electrodes disposed on a first surface of any of the plurality of dielectric layers;
A plurality of second radiation electrodes disposed on a second surface of any of the plurality of dielectric layers;
The plurality of first radiation electrodes and the plurality of second radiation electrodes are connected to each other, and a plurality of first and second radiation electrodes constitute a helical electrode. The connection of
A first parasitic electrode that is disposed on a third surface between the first and second surfaces, which is a boundary of any one of the plurality of dielectric layers, and is not connected to the helical electrode;
A laminated helical antenna characterized by comprising: 2. The stacked helical antenna according to claim 1, wherein the parasitic electrode is substantially parallel to a central fourth surface of the first and second surfaces. The multilayer helical antenna according to claim 2, wherein a distance between the third and fourth surfaces is 0.2 times or more a distance between the first and second surfaces. A second parasitic electrode disposed on a fifth surface of the plurality of dielectric layers between the first and third surfaces;
The laminated helical antenna according to any one of claims 1 to 3, further comprising: 5. The stacked helical antenna according to claim 4, wherein a distance between the third and fourth surfaces is substantially equal to a distance between the fourth and fifth surfaces.

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