JP2008042600A - Antenna system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an antenna system to inexpensively mass-produce antennas compatible with two-frequency, while achieving wider bandwidth, miniaturization and stable characteristics. <P>SOLUTION: The antenna system has a loop-like element having a first approximately rectangular element to a flat element plane, a second approximately rectangular element opposite to the first element and a pair of rising wires for making the first and the second elements conductive and an insulating support frame in contact with the rear surfaces of flat elements between the first and the second elements and in the elements, a pair of feeding points one of which is connected to a grounding plate are formed with a space approximately at the center part of one long side of an approximate rectangle, rising wires are formed with a space on the opposite long side opposite to a pair of feeding points and the element is further provided with a serial resonance circuit having a resonance point between frequency f1=c/λ and frequency f2=2c/(3λ) when the total length of the element comprised of the first element, the second element and the rising wires is considered as (1/2)λ. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a built-in antenna used in a small wireless communication device such as a portable terminal.

  Until now, the mainstream antenna for wireless portable devices has been a combination of a rod-shaped antenna that can be pulled out of the housing and a built-in antenna inside the device. The bar antenna is not only cumbersome for the user but also restricts the design in the device design. Therefore, in recent years, there is a trend to use only the built-in antenna without using the bar antenna.

  On the other hand, another requirement for antennas of wireless portable devices is to increase the frequency. For example, the frequency band of mobile phones has been expanded not only in Japan but worldwide as well, and many communication systems are employed in each of the 800 MHz to 900 MHz band and the 1.7 GHz to 2.1 GHz band. In addition, in the wireless LAN application, frequencies of 2.4 GHz to 2.5 GHz band and 4.9 GHz to 5.7 GHz band are allocated, which is higher than the low frequency band about twice as high as the cellular phone. A frequency band is assigned.

  Therefore, the requirement for the antenna device of the wireless portable device is that it is built-in type, can support all the required frequency bands, that is, multiple frequency bands, and has a wide band characteristic. If an antenna device having these preferable characteristics can be realized, it can be developed for various uses.

  Conventionally, even if it is a broadband antenna, the ratio band is about several percent at most with respect to the center frequency. Also, since the efficiency of such a small antenna is roughly proportional to its volume, it has been difficult to achieve good characteristics in the frequency band with a small internal antenna.

  A lot of research has been done, but the actual situation is that the development of antennas with good characteristics that can be used in actual machines has not been achieved. For example, a rectangular loop having a short side to long side ratio of 10 or more as a small, wide band, and high gain antenna device that has a wide band even when mounted close to a base plate of a wireless device and is relatively efficient. The antenna has an outer perimeter that is substantially the same as one wavelength at the operating frequency, is placed in parallel to the radio equipment ground plane and in close proximity with a sufficiently small interval compared to the wavelength, and the short side is fed. Folded so as to be close to the part side (see Patent Document 1).

  As a built-in antenna for portable terminals capable of impedance matching over a wide band, strip length 1 having a parallel line of about ½ wavelength with both ends short-circuited, strip interval d, left and right strip widths W1, W2, strip width of short-circuited portion Double-folding of antenna length a, height h of vertical part, and spacing s of folding part after bending the part from about 1/8 wavelength left and right of the feeding point of the folded dipole antenna of W3 vertically and horizontally symmetrically An antenna system having a structure is formed, and the antenna element is arranged close to the tip of a conductor plate having the same width as the antenna length a, and a parallel feeding line is connected to the feeding point of the antenna element to constitute an antenna system. In order to match the input impedance of this antenna element with the characteristic impedance of the balanced feeder, Septum s and the left and right strip width (W1 / W2) adjusts the (see Patent Document 2).

  As a built-in antenna for mobile terminals, which is a balanced feed antenna that maintains the self-balanced effect by fixing the strip width to the same level and can perform impedance matching over a wide band, a parallel line of about ½ wavelength with both ends short-circuited is used. The length of the strip is 1, strip distance d, left and right strip widths W1 and W2, and the strip width W3 of the short-circuited portion. Thus, an antenna having a double folded structure having an antenna length a, a height h of the vertical portion, and an interval s of the bent portions is formed, and this antenna element is disposed close to the tip of a conductor plate having the same width as the antenna length a. The antenna system is configured by connecting a balanced or unbalanced feed line to the feed point of this antenna element. In order to match the characteristic impedance of the balanced or unbalanced feed line, the strip width ratio (W1 / W2) of this antenna element is fixed to 1 to maintain the self-balancing action, while the interval s between the bent portions and the vertical portion In addition to the height h, the one in which the strip width W3 of the short-circuit portion and the left and right strip widths W1 = W2 are adjusted (refer to Patent Document 3) has been proposed.

  On the other hand, a microstrip antenna formed using a double-sided printed wiring board, and a loop-shaped antenna conductor layer formed on one side of a substrate, and a dielectric layer made of an insulating material with respect to the antenna conductor layer A ground conductor layer formed on the back side of the ground conductor, and a power feeding portion formed on the same surface so as to be insulated from the ground conductor layer. The antenna conductor layer and the ground conductor layer are grounded via the dielectric layer. And an inductance element that cancels the reactance of the antenna body between the power supply conductor and the antenna conductor layer and widens the bandwidth between the power supply section and the antenna conductor layer through the dielectric layer. A printed antenna (Patent Document 4) provided with a series resonant circuit composed of a capacitance element has been proposed.

JP2002-43826 JP 2004-228917 A JP2004-228918 JP 05-347509 A

  As described above, the antennas of Patent Documents 1 to 3 have advantages such as being less affected by the ground plane (GND) and taking advantage of the advantage of the dipole antenna, and have the effect of widening the bandwidth. The antenna has two double folded structures bent vertically and horizontally at symmetrical positions on the left and right ends of the feeding point of the dipole antenna.

  However, these conventional antennas have the following drawbacks in common. First, the manufacturing process is complicated due to the double folded structure at two locations. Second, the correspondence between the two frequencies is not considered. Thirdly, the design is made under the condition that only the metal plate is used. In other words, the design is in a state of floating in the air. Fourth, in order to stabilize the structure, when a dielectric material such as plastic is inserted and fixed in the folded hollow portion of these antennas, the broadband characteristics realized by the balance of multi-mode resonance are destroyed. In other words, the antenna changes to an antenna having three resonance points apart. In short, the present invention proposes an antenna that does not have a dielectric and is ideal under the ideal conditions for electromagnetic waves, and has a problem in practical use.

  Further, the antenna of Patent Document 4 uses a reactance compensation method for one resonance frequency to widen the bandwidth, and does not correspond to two resonance frequencies. Further, by forming the series resonant circuit on the low-loss double-sided board constituting the printed antenna, the decrease in antenna gain is reduced by reducing the insertion loss of the series resonant circuit.

  The present invention is an antenna based on a folded dipole, and has an object to mass-produce an antenna device that can handle two frequencies, can be widened and reduced in size, and has stable characteristics at low cost. As a result, an antenna device that can be mounted on a mobile phone that is miniaturized year by year can be provided at low cost.

The antenna device according to the invention described in claim 1 is a two-frequency folded dipole antenna in which an antenna element connected to a pair of feed points connected to a ground plate forms a loop from one to the other feed point. An antenna device comprising:
A first antenna element having a substantially rectangular arrangement shape with respect to the plane of the flat element, and a second antenna element provided opposite to the first antenna element and having a substantially rectangular arrangement shape with respect to the plane of the flat element And an antenna element integrally provided with a pair of rising conductors having a predetermined width for conducting the first antenna element and the second antenna element,
An insulating support frame material in contact with the back surfaces of the flat elements of the first antenna element and the second antenna element;
In the antenna element, the pair of feeding points is formed with a gap in the substantially central part of one long side of a substantially rectangular shape,
The pair of rising conductors are formed at intervals on the opposing long sides facing the pair of feeding points,
Each of the pair of rising conducting wires is electrically connected with a gap to a substantially central portion of one long side of the second antenna element parallel to the opposing long side of the first antenna element,
The antenna element includes a frequency f1 = c / λ and a frequency f2 = 2c / (where the total length of the antenna element including the first antenna element, the second antenna element, and the rising conductor is (1/2) λ. And a series resonance circuit having a resonance point between them (3λ).

  According to a second aspect of the present invention, there is provided an antenna apparatus comprising: a pair of feeding points according to the first aspect; a first antenna element; a second antenna element; and a pair of rising conductors; The series resonant circuit is formed by cutting off an excess portion from a thin metal plate.

  An antenna device according to a third aspect of the present invention further includes a capacitor of a series resonance circuit composed of two flat plates in which the same conductive plate constituting the flat element is opposed to the antenna element according to the second aspect. It is characterized by that.

  According to a fourth aspect of the present invention, there is provided an antenna device according to any one of the first to third aspects, wherein the first antenna element and the second antenna element have a shape and distance having electromagnetic coupling with each other. It is characterized by being.

  The antenna device according to the invention described in claim 5 is characterized in that the distance between the first antenna element and the second antenna element described in claim 4 is 4 mm or more and 12 mm or less.

  An antenna device according to a sixth aspect of the present invention is directed to a part of the outer peripheral edge of the first antenna element or the second antenna element according to any one of the first to fifth aspects toward an opposing antenna element. It is characterized by having a bent edge.

  As described above, the present invention is an antenna device configured to be mass-produced, can handle two frequencies, can be widened and reduced in size, and has stable characteristics. For example, an antenna device that can be mounted on a mobile phone that is miniaturized year by year can be provided at low cost.

  In the antenna of the folded dipole antenna of Patent Documents 1 to 3, the antenna has various electromagnetic field distributions between the front and back elements, and several resonances can be achieved by optimizing the antenna shape and element dimensions. It is shown that the points gather around a certain frequency, and as a result, the antenna characteristic becomes a wide band.

  However, these studies have been made on folded antennas in the air, and were conducted under conditions where no dielectric was present. For example, when an antenna element is arranged on the surface of a substrate material such as a printed circuit board, the substrate material has a relative dielectric constant larger than 1, and the electromagnetic field distribution of each resonance mode indicating the resonance point is greatly different. As a result of the influence of the relative permittivity of the material being different, the characteristics change to an antenna having several resonance points. As a result, the original broadband characteristic of the folded antenna is destroyed.

  In addition, it is necessary to have a stable structure that is fixed to a dielectric material such as plastic in order to be mounted as a single component of a small portable device and to perform good operation even under vibrations or shocks. The above research results still have problems.

  Therefore, the antenna device of the present invention is an antenna device composed of a two-frequency folded dipole antenna in which an antenna element connected to a pair of feed points connected to a ground plate forms a loop from one to the other feed point. A first antenna element having a substantially rectangular arrangement shape with respect to the plane of the flat element, and a first antenna element provided opposite to the first antenna element and having a substantially rectangular arrangement shape with respect to the plane of the flat element. An antenna element integrally including two antenna elements, a pair of rising conductors having a predetermined width that conducts the first antenna element and the second antenna element, and the first antenna element and the second antenna element. An insulating support frame material in contact with the back surfaces of the flat elements. In the tenor element, the pair of feeding points is formed with a gap at a substantially central portion of one long side of a substantially rectangular shape, and the pair of rising points is spaced on the opposing long sides facing the pair of feeding points. A conductive wire is formed, and each of the pair of rising conductive wires is electrically connected to a substantially central portion of one long side of the second antenna element parallel to the opposing long side of the first antenna element with a gap therebetween; When the total length of the antenna element composed of the first antenna element, the second antenna element, and the rising conductor is (1/2) λ, the frequency is f1 = c / λ and the frequency f2 = 2c / (3λ). And a series resonance circuit having a resonance point between them.

  For this reason, the configuration of the antenna device is only the position where the vertical / horizontal double-folded structure faces the feeding point, and a printed wiring board is used as a support frame member and printed on this board. Although it is possible to form the antenna element by cutting off the excess portion from the thin metal plate, it is suitable for mass production and can be manufactured at low cost. Therefore, as a preferable aspect, an antenna element composed of a pair of feeding points, a first antenna element, a second antenna element, and a pair of rising conductors is formed by cutting off an excess portion from a thin metal plate. It is.

  That is, by forming the element by removing portions other than the flat element such as die-cut molding, there is one vertical / horizontal double folded portion, so that there is an advantage that manufacture is easy, and it is suitable for mass production. It also has the advantage. As a method for removing portions other than the flat element, there are stamping molding by press, laser processing molding, etching molding, water jet molding and the like, but stamping molding by press is suitable for mass production. For example, mass production is performed by forming the first antenna element, the second antenna element, and the rising conductor integrally by punching and then bending and inserting an insulating support frame material or insert molding. Can do. In any case, since there is one vertical / horizontal double folded portion, there is an advantage that manufacture is easy.

  Further, as the series resonant circuit of the present invention, a commercially available capacitor may be connected to the first antenna element or the second antenna element. However, the capacitance of the capacitor constituting the series resonant circuit of the present invention is very low at 1 pF or less. Low. For this reason, when using a commercially available capacitor | condenser, the device, such as arrange | positioning in series, is required. Therefore, as a preferred embodiment, the antenna element is further provided with a capacitor of a series resonance circuit composed of two flat plates facing the same conductive plate constituting the flat element. Thus, a capacitor having a capacity can be produced along with the production of the first and second antenna elements. Specifically, a structure in which the support frame material of the antenna device of the present invention is simply removed is obtained by performing punching molding with a structure that forms a capacitor of a series resonance circuit in the punching die of the antenna element. be able to. As the capacitor in this case, a capacitor composed of two flat plates opposed to the same conductive plate constituting the flat element is suitable.

  In the present invention, as described above, it is necessary to hold the first antenna element and the second antenna element at a constant distance in order to change the electromagnetic field distribution by folding back vertically and horizontally. There is. Therefore, preferably, a support frame member is provided that supports the back surfaces of the flat elements of the first antenna element and the second antenna element at a certain distance.

  The support frame material may be integrated when the antenna element formed in advance and associated with the series resonance circuit is bent, or the antenna element associated with the series resonance circuit is insert-molded as an insert metal. At this time, it may be formed of a resin.

  Now, the antenna device of the present invention is a kind of folded dipole antenna, but it is considered to have characteristics of a folded loop antenna because of its configuration. When the distance between the folded elements is large and the electromagnetic coupling between the elements has an appropriate electromagnetic coupling, resonance occurs at substantially equal intervals. Each resonance frequency is such that one of a pair of feeding points is connected to a relatively large ground plane (ground plate), so that the total length of the antenna element is (1/2) λ (where λ is the wavelength) due to the mirror image effect. Then, the resonance frequencies corresponding to (1/2) λ, 1λ, (3/2) λ, and 2λ from the smaller side. (Refer to FIG. 7 described later)

  In the antenna device of the present invention, when the total length of the antenna element including the first antenna element, the second antenna element, and the rising conductor is (1/2) λ, the frequency c / λ and the frequency 2c / (3λ) (Where c is the speed of light), the antenna element is provided with a series resonance circuit having a resonance point. This series resonance circuit has a capacitive property on the lower frequency side than the resonance frequency and an inductive property on the higher frequency side. As a result, the series resonant circuit works capacitively with respect to the resonance point of the frequency c / λ, so that the function is the same as when a capacitor is added to the antenna device, and the resonance point is on the frequency 2c / (3λ) side. Move (resonance frequencies 1 ′ and 2 ′ in FIG. 7 move to 1 and 2). In addition, since this series resonance circuit works inductively for resonance frequencies greater than 2c / (3λ), the same action is obtained when a coil is added to this antenna, and the resonance point moves to the 1λ side (described above). 7, the resonance frequencies 3 ′ and 4 ′ move to 3 and 4). As a result, the two resonance points of the frequency c / λ and the frequency 2c / (3λ) approach each other. The two resonance points are brought close to each other so as to have a double resonance characteristic, thereby enabling a wide band (see FIG. 9 described later).

  In the first place, in the present invention, the area of the antenna is set to a size that can be stored in a portable device (specifically, 40 mm × 10 mm). Assuming that this area exists on the same plane as the front of the portable device, the thickness direction of the portable device was assumed to be the height direction of the antenna. That is, (gain of antenna) × (frequency bandwidth) is proportional to the volume of the antenna. Therefore, in order to obtain performance when the area is limited to a small size, the height of the antenna must be increased.

  In addition, in the antenna device excluding the series resonance circuit, it is preferable to resonate at substantially equal frequency. Therefore, it is desirable that the distance between the folded elements is large and the electromagnetic field coupling between the elements is weakened. Therefore, as a preferable aspect, at least the first antenna element and the second antenna element have a shape and distance having electromagnetic coupling with each other, and more preferably, the distance between the first antenna element and the second antenna element is The coupling of the electromagnetic field distribution between the elements is weakened by 4 mm or more and 12 mm or less. If it is shorter than 4 mm, the frequency band of 800 MHz cannot be obtained, and the performance of the antenna is extremely lowered. Further, if the distance is longer than 12 mm, the electromagnetic field coupling between the elements becomes extremely weak and cannot be covered by the series resonance circuit.

  In addition, the external shape of a 1st antenna element and a 2nd antenna element is changed according to the distance of a 1st antenna element and a 2nd antenna element. In the present invention, in order to correspond to at least two frequency bands of a small size that can be mounted on a mobile phone and a frequency band of 800 MHz to 900 MHz and a frequency band of 1.7 GHz to 2.1 GHz, first, 800 MHz to 900 MHz. This is because the approximate length of the antenna element length corresponding to 1 / 2λ is determined from the frequency band. Specifically, according to changing the distance between the first antenna element and the second antenna element to 4 mm to 12 mm, the outer width of the first antenna element and the second antenna element is set to 40 mm ± 10 mm, The depth may be 10 mm ± 5 mm.

  As another preferable aspect of the present invention, a bent edge that is bent toward an opposing antenna element is provided on a partial outer peripheral edge of the first antenna element or the second antenna element. As a result, even when the coupling of the electromagnetic field distribution between the elements such that the distance between the first antenna element and the second antenna element exceeds 6 mm is extremely weakened, the electromagnetic coupling is performed between the antenna element facing the bent edge. Can be strengthened.

  Further, the bending edge may be only one edge of the first and second antenna elements having a substantially rectangular shape, as long as it produces a coupling of the electromagnetic field distribution between the elements and a good resonance frequency can be obtained. May be included. In addition, in order to improve the coupling | bonding of electromagnetic field distribution, the device which enlarges the width | variety of the flat element of an antenna element may be performed.

  FIG. 1 is an explanatory diagram showing the configuration of the antenna device of the present invention. FIG. 7A is a developed view of the antenna element, and FIG. b is an explanatory view showing a combination of the antenna element and the supporting frame member of FIG. FIG. 2 is an explanatory view showing a state in which the antenna device shown in FIG. 1 is connected to a ground plate (equipotential surface).

  As shown in FIG. 2, the antenna device 10 of the present invention connects the feeding point 17 of the pair of feeding points 11 and 17 to the ground plate 40 that is an equipotential surface, and connects the feeding point 11 to the feeding signal source 18. This is a two-frequency folded dipole antenna in which an antenna element forms a loop from one feeding point to the other.

  As shown in FIG. 1, the antenna element is mainly composed of a flat element having a width of 1 mm and a plate thickness of 0.1 mm, and a first conductor formed by conducting wires 12 and 16 whose arrangement shape with respect to the plane of the flat element is substantially rectangular. An antenna element 10a, a second antenna element 10b formed in parallel to the first antenna element 10a, and formed from a conductive wire 14 having a substantially rectangular arrangement with respect to the plane of the flat element, and these first antenna elements 10a and the second antenna element 10b are provided with a pair of rising conductors 13 and 15 having a height of 6 mm. This antenna element was formed by punching a metal plate having a thickness of 0.1 mm.

  The flat element 14a on the side facing the pair of feeding points 11 and 17 of the second antenna element 10b has a width of 6 mm, which is wider than other places. This is for strengthening electromagnetic coupling between the first and second antenna elements.

  The pair of rising conductors 13 and 15 are formed on the opposing long sides facing the feeding points 11 and 17 of the first antenna element with a space therebetween, and each of the pair of rising conductors 13 and 15 corresponds to the first antenna element 10a. The second antenna element 10b parallel to the opposing long side is electrically connected to a substantially central portion of one long side with a gap.

  That is, since the first and second antenna elements 10a and 10b are grounded antennas having one of the feeding points connected to the ground plate, the first and second antenna elements 10a and 10b are opposed to the conductor 12 starting from the feeding point 11 of the first antenna element 10a. The path length from the conducting wire 16 of the first antenna element 10a through the conducting wire 14 of the second antenna element 10b, through the conducting wire 14 of the second antenna element 10b, through the other rising conducting wire 15 to the conducting point 16 of the first antenna element 10a. (That is, the total circumference) is (1/2) λ that resonates at a substantially lower frequency, so that the resonance frequencies are 2c / λ, c / λ, 2c / (3λ), and c / (2λ). The antenna can be operated.

  The first antenna element 10a includes a series resonance circuit having a resonance point between the frequency c / λ and the frequency 2c / (3λ). In the series resonance circuit of the present invention, since the loop antenna has a specific inductance, a capacitor may be provided for the specific inductance. Specifically, a capacitor 20 is provided that is composed of two flat plates that are branched into a conductive wire 12 and a conductive wire 16 and are opposed to the same conductive plate constituting the element.

  As shown in FIG. 1b, the first antenna element 10a and the second antenna element 10b are opposed to each other by turning up the antenna element shown in FIG. A support frame member 30 having a thickness of 6 mm for supporting the back surfaces of the flat elements of the first antenna element 10a and the second antenna element 10b at a distance of 6 mm is disposed. In the figure, the antenna element has a width a of 40 mm, a depth b of 10 m, and a height c of 6 mm.

  FIG. 3 is an explanatory diagram of the configuration of the capacitor portion, and includes an enlarged view in which a part is enlarged. FIG. 4 is a diagram showing frequency characteristics of the antenna device excluding the capacitor 20 constituting the series resonance circuit in the antenna device shown in FIG. FIG. 5 is a Smith chart of FIG. 6 is a diagram showing frequency characteristics of the antenna device shown in FIG. FIG. 7 is a Smith chart of FIG.

  As shown in FIG. 3, the shaded part is composed of two conductive plates 21 and 22 separated from the center part, and the gap part is capacitive and functions as a capacitor 20. In addition, an LC series resonance circuit is formed as a whole by being incorporated in the loop antenna.

  By adding the series resonance circuit as described above to the folded antenna device, as described above, it is possible to widen the band using the principle of the double resonance characteristic. The antenna element was formed by punching metal plates 21 and 22 having a thickness of 0.1 mm including the capacitor 20 portion.

  As shown in FIGS. 4 to 7, the resonance point 1 (marker 1) to the resonance point 4 (marker 4) are resonance points of the antenna device of the present invention. The resonance point 1 ′ to the resonance point 4 ′ are resonance points when the series resonance circuit 20 is not added. In FIG. 4, the series resonant circuit has a resonance point between 2 'and 3'. Since this resonance circuit works capacitively with respect to the resonance point of 2 ', it becomes the same function as adding a capacitor to this loop antenna, and the resonance point moves to 2. On the other hand, since the resonance circuit works inductively with respect to the resonance point of 3 ', it becomes the same function as adding a coil to this loop antenna, and the resonance point moves to 3.

  As a result, the two resonance points approach each other. Two resonance points are brought close to each other so as to have a double resonance characteristic, thereby enabling a wide band. Next, in FIG. 4, the resonance point 3 ′ and the resonance point 4 ′ move to the marker 3 and the marker 4, respectively. This is due to the inductive nature of the series resonant circuit. This inductivity is larger when it is far from the resonance point. Therefore, the amount of movement from 4 'to 4 is larger than the amount of movement from 3' to 3. Therefore, the resonance points 3 ′ and 4 ′ are approximated by a resonance circuit. From the above results, it is possible to widen the bandwidth because of the double resonance characteristics.

  Next, the change of the reactance component is considered by the Smith chart. 5 and 7, the imaginary component of the impedance of the resonance point 1 (marker 1) is 50Ω to −6Ω, and the imaginary component of the impedance of the resonance point 2 (marker 2) is 127Ω to 23Ω. It shows the same characteristics as. On the other hand, the imaginary component of the impedance of the resonance point 3 (marker 3) is −55 to −6Ω, and the imaginary component of the impedance of the resonance point 4 (marker 4) is −66Ω to 22Ω. Show.

  The amount of change between the marker 3 and the marker 4 is 49Ω for the marker 3 and 89Ω for the marker 4. The change amount of the marker 4 is larger than the change amount of the marker 3. This is because of the characteristics of the series resonant circuit as described above. As described above, it can be seen from the Smith chart results that the change in reactance of these markers is the result of inserting a series resonance circuit having a resonance point between the markers 2 and 3.

  As a result, a wideband antenna having a return loss of -5 dB or less over a wide band from 1.44 GHz to 2.65 GHz is realized. On the Smith chart, since the inside of the circle of return loss −5 dB in FIG. 7 is less than or equal to return loss −5 dB, the frequency of the locus inside this circle is the band.

  FIG. 8 is a development view showing the configuration of another antenna element. FIG. 9 is a developed view showing the configuration of still another antenna element. FIG. 10 is a development view showing a configuration of still another antenna element.

  As shown in FIG. 1, the conductor width of one of the vertically opposed elements is made several times wider than the other to improve the coupling of the electromagnetic field distribution between the first and second antenna elements. As an example of improving the coupling of the electromagnetic field distribution between such antenna elements, there is a case of bending. 8 and 9, the alternate long and short dash line means that it is bent in the direction of the lower element.

  As shown in FIG. 8, the antenna element 81 according to this embodiment is bent at one place in the case of FIG. 8, and is bent to form a bent edge 82. The antenna element 91 of FIG. 9 is bent at three places to form a bent edge 92. Further, the two long sides 93 and 94 of the second antenna element 90b can be widened. In this case, it is bent into a box shape. Increasing the conductor width or bending to form a bent edge means increasing the capacitance between elements (strengthening the coupling), which increases the distance between the elements and reduces the capacitance (weak coupling). ) Also means that it is made up for. Also, at the capacitor addition position, as shown in FIG. 10, the capacitor 120 may be disposed at a location near the one feeding point 107 side of the antenna element 101.

  As described above, in the antenna device of the present invention, the element of the folded loop antenna and the series resonance circuit can be integrally formed by cutting off an excess portion from the metal thin plate. Since the series resonance circuit is a distributed constant circuit and is incorporated into a part of the antenna, an external circuit is not required by incorporating the capacitor portion into the element. This eliminates the need for chip parts and their mounting work, and can reduce costs. In the present embodiment, since the capacitance component is configured using the air gap, a very low capacitance (1 pF or less) can be easily configured. This is particularly effective when it cannot be realized with a chip capacitor or has a large allowable range.

It is explanatory drawing which shows the structure of the antenna apparatus of this invention. FIG. 7A is a developed view of the antenna element, and FIG. b is an explanatory view showing a combination of the antenna element and the supporting frame member of FIG. It is explanatory drawing which shows the state which connected the antenna apparatus shown in FIG. 1 to the ground plate (equipotential surface). It is explanatory drawing of a structure of a capacitor | condenser part, and is provided with the enlarged view which expanded a part. FIG. 2 is a diagram showing frequency characteristics of the antenna device excluding a capacitor constituting a series resonance circuit in the antenna device shown in FIG. 1. It is a Smith chart of FIG. It is a diagram which shows the frequency characteristic of the antenna apparatus shown in FIG. It is a Smith chart of FIG. It is an expanded view which shows the structure of another antenna element. It is an expanded view which shows the structure of another antenna element. It is an expanded view which shows the structure of another antenna element.

Explanation of symbols

10: Antenna device,
10a ... 1st antenna element,
10b ... the second antenna element,
11, 17 ... feeding point,
12, 16 ... Lead wire,
14 ... Lead wire,
13, 15 ... Rising conductor,
18 ... a power supply signal source,
20: Capacitor (series resonant circuit),
21, 22 ... guide plates,
30: Support frame material,
40 ... ground plate,
81, 91, 101 ... antenna elements,
82, 92 ... bent edges,
90b ... the second antenna element,
93, 94 ... long side,
107 ... feeding point,
120 ... capacitor,

Claims (6)

An antenna device comprising a folded dipole antenna corresponding to two frequencies in which an antenna element connected to a pair of feeding points connected to a ground plate forms a loop from one to the other feeding point,
A first antenna element having a substantially rectangular arrangement shape with respect to the plane of the flat element, and a second antenna element provided opposite to the first antenna element and having a substantially rectangular arrangement shape with respect to the plane of the flat element And an antenna element integrally provided with a pair of rising conductors having a predetermined width for conducting the first antenna element and the second antenna element,
An insulating support frame material in contact with the back surfaces of the flat elements of the first antenna element and the second antenna element;
In the antenna element, the pair of feeding points is formed with a gap in the substantially central part of one long side of a substantially rectangular shape,
The pair of rising conductors are formed at intervals on the opposing long sides facing the pair of feeding points,
Each of the pair of rising conducting wires is electrically connected with a gap to a substantially central portion of one long side of the second antenna element parallel to the opposing long side of the first antenna element,
The antenna element includes a frequency f1 = c / λ and a frequency f2 = 2c / (where the total length of the antenna element including the first antenna element, the second antenna element, and the rising conductor is (1/2) λ. 3λ) (where λ is the wavelength and c is the speed of light), and an antenna device comprising a series resonance circuit having a resonance point.   The antenna element composed of the pair of feeding points, the first antenna element, the second antenna element, and the pair of rising conductors is formed by cutting off an excess portion from a thin metal plate. The antenna device according to claim 1.   3. The antenna device according to claim 2, further comprising a series resonance circuit capacitor including two flat plates facing the same conductive plate constituting the flat element.   The antenna device according to any one of claims 1 to 3, wherein the first antenna element and the second antenna element have a shape and a distance that have appropriate electromagnetic coupling with each other.   The antenna apparatus according to claim 4, wherein a distance between the first antenna element and the second antenna element is 4 mm or more and 12 mm or less. The antenna according to any one of claims 1 to 5, further comprising a bent edge that is bent toward a facing antenna element on a peripheral edge of a part of the first antenna element or the second antenna element. apparatus.

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