JP2004048233A - Antenna system and method for forming antenna element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrawide band small-sized antenna system with a simple configuration adapted to simply and efficiently attain a broadband. <P>SOLUTION: Adjusting sizes W1, W2 in the width direction of an antenna element (loop plate antenna) matches a resonance frequency of the antenna element with a target frequency band. Then a matching circuit with a resonance frequency that is nearly inbetween two resonance points is connected to terminals of the antenna element. Thus, a reflection attenuation of the antenna system at the frequency band is set to be a threshold value or below so as to attain the reception of a broadcast wave with the frequency band in the antenna system. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an antenna device and a method for forming an antenna element, and more particularly to a method for easily widening a band of an antenna device and adjusting a transmission / reception frequency band.
[0002]
[Prior art]
Terrestrial television broadcasting is shifting from analog to digital, and in Japan, digital broadcasting is scheduled to start at the end of 2003. In digital broadcasting, since the UHF band (470 MHz to 770 MHz) is used, an antenna device having a wide band reception frequency is required. In particular, in an antenna device used for digital broadcasting for portable reception, an ultra-wideband small antenna element capable of receiving a UHF band with a size of several centimeters is required due to the external dimensions of the portable reception device.
[0003]
Conventionally, a loop antenna has been known as a wideband small antenna element. However, even in this case, a loop antenna does not have a reception band enough to cover the entire UHF band. Therefore, there is a need to develop an antenna device that can achieve a wider band and a smaller size while using existing antenna elements.
[0004]
In the antenna device described in Japanese Patent Application Laid-Open No. 5-129815, an antenna element whose electric length is set to λ / 2 when a wavelength at a high frequency band used is λ is used. On the other hand, by combining a U-shaped ground plane and a dielectric interposed therebetween, and a transmission line connected to the antenna element and a structure including a dielectric interposed between the transmission line and the ground plane, Broadening of the receiving frequency is attempted. According to such an antenna device, three resonance frequencies can be generated by the above-mentioned structure, and thereby the band width of the antenna device can be widened.
[0005]
[Problems to be solved by the invention]
However, according to such an antenna device, it is necessary to separately provide a structure having a relatively large outer dimension in addition to the antenna element. There is a concern that the external dimensions limit the miniaturization of the receiving device body.
[0006]
Also, since only one resonance phenomenon of the antenna element itself is used, and two resonance phenomena of the structure are separately combined with this, the resonance phenomenon of the antenna element itself is effectively used. It is hard to say, and it is not enough to pursue the simplification of the configuration. The antenna element itself has a myriad of resonance frequencies, and if these resonance frequencies can be matched to the broadcast wave frequency band by adjusting the shape of the antenna element itself, a simpler configuration of the antenna Broadening of the band of the device can be realized.
[0007]
Accordingly, the present invention is to solve such a problem of the conventional device and to provide an ultra-wideband small antenna device capable of easily and efficiently widening a band with a simple configuration.
[0008]
[Means for Solving the Problems]
In view of the above problems, the present invention has the following features.
[0009]
According to a first aspect of the present invention, in the antenna device, an antenna element and a resonance frequency connected to the antenna element and higher than one resonance frequency of the two resonance frequencies of the antenna element and lower than the other resonance frequency. And at least one resonance circuit having the following.
According to the present invention, the resonance point of the resonance circuit can be interposed between the two resonance points of the antenna element, so that the reflection loss in the frequency band between the two resonance points of the antenna element can be reduced by the resonance circuit. Can be suppressed. Thereby, the frequency band of the antenna device can be widened.
[0010]
According to a second aspect of the present invention, in the antenna device according to the first aspect, the resonance circuit has a resonance frequency substantially intermediate between two resonance frequencies of the antenna element.
By thus arranging the resonance point of the resonance circuit almost in the middle between the two resonance points of the antenna element, it is possible to more efficiently suppress the reflection loss in the frequency band between the two resonance points of the antenna element.
[0011]
According to a third aspect of the present invention, in the antenna device according to the first or second aspect, based on a current distribution of the antenna element, each of the antenna elements has a resonance frequency matching a predetermined frequency band. The electrical dimensions in the width direction are adjusted.
The current distribution when the antenna element is excited is not uniform in all regions on the antenna element, and the current distribution is uneven at each resonance frequency. The inventors have found that the resonance frequency of the antenna can be controlled by changing the width of the region where the current distribution is dense. Therefore, by adjusting the width dimension of the region, the two resonance frequencies of the antenna can be matched, for example, near the upper and lower limits of the broadcast wave band. By locating the resonance frequency of the resonance circuit between these two resonance points, it is possible to suppress the reflection loss in the frequency band between the two resonance points, and therefore, it is possible to broaden the bandwidth matching the broadcast wave band. It can be realized.
[0012]
According to a fourth aspect of the present invention, in the antenna device according to the third aspect, the antenna element is configured by a rectangular plate-shaped loop antenna having two sets of opposing sides. On the basis of the current distribution, electrical dimensions in the width direction of each side portion are adjusted such that the resonance frequency of the antenna element matches a predetermined frequency band.
[0013]
According to a fifth aspect of the present invention, in the antenna device according to the fourth aspect, at least one pair of side portions among the opposed side portions is constituted by a plurality of branch paths branched in parallel. I do.
By branching predetermined side portions in parallel in this manner, a space can be created between the branch roads. For example, by utilizing this space as an area for arranging components on the receiving device main body side, the size of the receiving device main body can be further reduced. A specific configuration example of such a branch road and characteristics at that time will be described in an embodiment section with reference to FIG.
[0014]
According to a sixth aspect of the present invention, in the antenna device according to the fourth or fifth aspect, a pair of side portions of the antenna element are bent in a direction perpendicular to a plate surface.
In this way, by bending a set of side portions in a direction perpendicular to the plate surface, it is possible to reduce the dimension in the direction parallel to the plate surface while keeping the electrical length of the antenna element the same. Can be further advanced. A specific configuration example when a set of side portions is bent in a direction perpendicular to the plate surface will be described in an embodiment section with reference to FIG.
[0015]
According to a seventh aspect of the present invention, in the antenna device according to any one of the third to sixth aspects, a part of the antenna element meanders in a width direction and / or a direction perpendicular to a plate surface.
In this way, by making a part of the antenna element meander in the width direction and / or the direction perpendicular to the plate surface, it is possible to reduce the dimension in the direction parallel to the plate surface while keeping the electrical length of the antenna element the same. As in the sixth aspect, the size of the receiving apparatus main body can be further reduced. A specific configuration example of such a meandering path will be described in an embodiment with reference to FIG.
[0016]
An eighth aspect of the present invention is an antenna device having a plate-like antenna element in which the electrical dimensions in the width direction of each part are adjusted so that the resonance frequency matches a predetermined frequency band.
[0017]
According to a ninth aspect of the present invention, the resonance frequency of the antenna element is set to a predetermined frequency band by analyzing the current distribution of the antenna element and adjusting the electrical dimension in the width direction of a portion having a large current distribution in the antenna element. A method for forming an antenna element, characterized by matching.
[0018]
The features of the present invention will become more apparent from the following description of embodiments.
[0019]
However, the following embodiments are merely one embodiment of the present invention, and the meanings of the terms of the present invention and each component are not limited to those described in the following embodiments. Absent.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
First, the relationship between the dimension in the width direction (loop element width) of the plate-shaped loop antenna and the resonance frequency of the antenna has been verified, and the verification will be described.
[0021]
FIG. 1 shows a configuration of a plate-like loop antenna used for verification. The loop antenna is set so that its electrical length is λ when the wavelength at 620 MHz, which is the center frequency of the UHF band, is λ. The dielectric constant of the dielectric is 1 (εr = 1), and the distance h between the ground plate and the loop antenna is 15 cm. By setting in this manner, a simulation described later can be performed ignoring the influence of the ground plate.
[0022]
The loop element width (W1, W2) is set to 10 mm uniformly over the entire length. The lengths L1 and L2 of each side and the gap Lf between the terminals are set to the dimensions shown in the drawing. One end of the loop antenna is excited by a 50Ω signal source, and the other end is terminated by 50Ω.
[0023]
FIG. 2A shows a simulation result obtained by analyzing the loop antenna using the moment method. The horizontal axis in the figure is the frequency of the signal source (unit = GHz), and the vertical axis is the return loss Mag = 10 × log (reflected power / input power). In such a simulation, the analysis was performed ignoring the conductor thickness and conductor loss of the loop antenna. The electromagnetic field analysis using the moment method is described in, for example, “Harrington, RF: Field composition by moment method, Macmillan (1968)”, and is a conventionally well-known analysis method. Here, the description is omitted.
[0024]
FIG. 2B shows an experimental result when the loop antenna having the above configuration is actually excited. In such an experiment, the conductor thickness of the antenna was set to 0.2 mm. Further, unlike the above simulation, the ground is arranged only at the terminal portion. In such an experiment, conductor loss occurs in the loop antenna during excitation. In the above simulation, the analysis is performed ignoring the conductor loss.
[0025]
As shown in FIGS. 2A and 2B, the simulation results and the experimental results show characteristics that are close to each other.
[0026]
In the simulation result of FIG. 2A, several resonance points are observed. Hereinafter, focusing on two resonance points near 430 MHz and 670 MHz near the lower and upper limits of the UHF band, the loop element width will be described. Consider the relationship between and the resonance point.
[0027]
FIG. 3 shows the current distribution on the loop antenna at 430 MHz and 670 MHz. Such a current distribution is based on a simulation result using the above-mentioned moment method. Here, the loop length (electric length) of the loop antenna is の of the wavelength at 430 MHz and one wavelength of the wavelength at 670 MHZ. Hereinafter, the resonance around 430 MHz is called a 波長 wavelength mode, and the resonance around 670 MHz is called a one wavelength mode.
[0028]
As shown in FIG. 3A, in the 波長 wavelength mode, the current distribution on the side including the terminal and the side perpendicular thereto is high. On the other hand, in the one-wavelength mode, the current distribution on the side including the terminal and the side facing the terminal is high as shown in FIG. From the simulation results, the resonance frequency in the half wavelength mode can be controlled by changing the width of the side perpendicular to the side including the terminal (W2 in FIG. 1). Can be controlled by changing the width of the side (W1 in FIG. 1) opposite to the side including. That is, in the 波長 wavelength mode, the current path becomes longer when W2 is made thinner. As a result, the resonance frequency can be reduced. In the one-wavelength mode, the current path becomes longer when W1 is made thinner. As a result, the resonance frequency can be reduced.
[0029]
FIGS. 4B to 4D show simulation results of the resonance frequency when the width dimensions W1 and W2 are changed. The simulation shown in the drawing is a simulation result when the external dimensions L1 and L2 of the loop antenna shown in FIG. 1 are fixed, that is, when the width dimensions W1 and W2 of each side are changed while keeping the opening area of the antenna constant. FIG. 2A shows the simulation result (W1 = W2 = 10 mm) of FIG. 2A as it is for comparison.
[0030]
Of the simulation results in FIGS. 4B to 4D, the resonance frequency in the one-wavelength mode is significantly lower in FIG. 4B than in FIG. 4A, and in FIG. The resonance frequency in the 波長 wavelength mode is significantly lower than that in FIG. This is a result of a logic analysis of the resonance frequency based on the current distribution simulation of FIG. 3, that is, "a reduction in the width of a large side of the current distribution lengthens the current path in the mode and lowers the resonance frequency in the mode." Can also be explained from the result of the logic analysis.
[0031]
As described above, in the plate-like loop antenna of FIG. 1, the resonance frequency of the antenna can be appropriately set by adjusting the width dimensions W1 and W2 of each side.
[0032]
The above simulation and logic analysis can be applied to antenna elements other than the plate-shaped loop antenna shown in FIG. That is, also in the antenna elements other than the above, the length of the current path of each mode is changed by adjusting the line width according to the analyzed current distribution, whereby the resonance frequency of the mode is reduced or increased. You can easily guess.
[0033]
FIG. 5 shows a configuration example in which a matching circuit is connected between terminals of the plate-shaped loop antenna. Such a matching circuit has a resonance frequency that fills a valley between two resonance frequencies of the half-wave mode and the one-wavelength mode of the plate-shaped loop antenna.
[0034]
FIG. 6 shows a specific configuration example of the matching circuit. In the figure, C1 and C2 are capacitances, L11, L12 and L21 are inductances, and T is an input / output terminal of the antenna. By setting the values of the capacitances C1 and C2 and the inductances L11, L12 and L21 to predetermined values, for example, a resonance frequency substantially at the center between two resonance frequencies of the half-wave mode and the one-wave mode is set to the loop antenna. You can have.
[0035]
FIG. 7 shows a measurement result of a frequency-return loss characteristic when the matching circuit is applied to the loop antenna. Here, the widthwise dimensions W1 and W2 of the loop antenna were set to the values shown in FIG. 4B. Further, the resonance frequency of the matching circuit is set to a frequency substantially intermediate between the half wavelength mode and the one wavelength mode. In this way, by filling the valley between the resonance points of each mode with the resonance points of the matching circuit, it is possible to secure a return loss of −7 db or less in the frequency range of 470 MHz to 770 MHz. Thus, a wide band digital television broadcast in the UHF band can be received by the small loop antenna having the dimensions shown in FIG.
[0036]
8 and 9 show modified examples of the above-described plate-shaped loop antenna.
[0037]
FIG. 8A shows the side including the terminal and the side opposite to the terminal meandering in a direction parallel to the plate surface. According to such a configuration, while the electrical length of the side including the terminal and the opposite side is the same as that of FIG. 1, the shape and size of the antenna in the horizontal direction of FIG. 1 can be made smaller than that of FIG. 1. it can. The meandering direction may be a direction perpendicular to the plate surface. In addition to the meandering of the side including the terminal and the side facing the terminal as shown in FIG. 8A, the side perpendicular to the side including the terminal may be meandered, or all sides may be meandered.
[0038]
FIG. 8B is a diagram in which a side perpendicular to the side including the terminal is branched in parallel. According to such a configuration, an opening (space) can be provided in each of the branched side portions, and such an opening portion can be used as a component arrangement space on the receiving device main body side. When the side is branched in this way, the width direction dimension of the side contributing to the adjustment and control of the resonance frequency is W2 (including the width dimension of the space portion) shown in FIG. Therefore, such a configuration example is suitable for use when it is necessary to set the width dimension of the side large in relation to the resonance frequency to be set. Note that the number of branch roads is not limited to two as shown in FIG. 3B, and three or more branch roads may be formed. In addition, a branch path may be formed not only on the side perpendicular to the side including the terminal but also on the side including the terminal and the side opposite thereto.
[0039]
FIG. 9 is obtained by bending a side perpendicular to the side including the terminal in a direction perpendicular to the plate surface. According to such a configuration, it is possible to reduce the shape and size of the antenna in the horizontal direction in FIG. The side to be bent may be a side perpendicular to the side including the terminal as shown in the figure, or may be a side including the terminal and a side opposed thereto.
[0040]
Although various embodiments according to the present invention have been described above, the present invention is not limited to such embodiments, and various other modifications are possible.
[0041]
For example, in the above-described embodiment, a plate-shaped loop antenna has been described as an example. However, the present invention is applicable to a dipole-type rod-shaped antenna in addition to the plate-shaped loop antenna. In such a case, a matching circuit having a resonance frequency that fills a gap between the resonance frequencies of the dipole antenna is connected to a terminal of the antenna. In the above description, the simulation analysis of the current distribution and the like is performed using the moment method, but the simulation can be performed by another analysis method. Further, the shape, dimensions, and configuration of the matching circuit of the antenna element described above are merely examples, and the antenna element and the matching circuit can be configured with other shapes, dimensions, and configurations.
[0042]
Further, in the above-described embodiment, the band is widened by using two resonance points of the antenna element. However, by matching three or more resonance points to a predetermined frequency band, the band of the antenna device can be widened. You may make it aim. Further, the matching circuit may have two or more resonance points in addition to one having one resonance point. For example, the two resonance points of the matching circuit may be located between the two resonance points of the antenna element. Alternatively, when the matching circuit has two resonance points, each resonance point is set to the resonance point of the antenna element. Positioning may be performed so as to fill the gap between the three resonance points.
[0043]
Various changes can be made to the embodiments of the present invention as appropriate within the scope of the technical idea of the present invention.
[0044]
【The invention's effect】
As described above, according to the present invention, the band of the antenna device is broadened while using a plurality of resonance points. Therefore, the number of resonance circuits connected to the antenna element can be limited, and thus the size of the antenna device can be reduced. Can be further advanced. In addition, since the resonance point is appropriately shifted by changing the width direction dimension of the antenna element based on the current distribution, it is possible to easily form the antenna element matched to the target frequency band, Along with the simplification of the configuration, it is possible to reduce the number of parts and simplify the forming process.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration example of an antenna device according to an embodiment; FIG. 2 is a diagram illustrating verification results (simulation and actual measurement) of the antenna device; FIG. 3 is a diagram illustrating a current distribution (simulation) of the antenna device; FIG. 4 shows a verification result (simulation) of the antenna device. FIG. 5 shows another configuration example of the antenna device according to the embodiment. FIG. 6 shows a configuration example of a matching circuit of the antenna device. FIG. 7 shows a verification result (actual measurement) of the antenna device. FIG. 8 shows another configuration example of the antenna element according to the embodiment. FIG. 9 further shows an antenna element according to the embodiment. Diagram showing another configuration example [Explanation of reference numerals]
L11, L12, L21 Inductance C1, C2 Capacitance

Claims (9)

An antenna element and at least one resonance circuit connected to the antenna element and having a resonance frequency higher than one resonance frequency and lower than the other resonance frequency among two resonance frequencies of the antenna element. An antenna device characterized by the above-mentioned. In claim 1,
The antenna device according to claim 1, wherein the resonance circuit has a resonance frequency substantially intermediate between two resonance frequencies of the antenna element. In claim 1 or 2,
The antenna device according to claim 1, wherein an electrical dimension in a width direction of each part of the antenna element is adjusted based on a current distribution of the antenna element so that a resonance frequency of the antenna element matches a predetermined frequency band. In claim 3,
The antenna element is configured by a rectangular plate-shaped loop antenna having two sets of opposing sides, and based on a current distribution of the antenna element, a resonance frequency of the antenna element is set to a predetermined frequency band. The electrical size of each of these side portions in the width direction is adjusted so as to match. In claim 4,
An antenna device, wherein at least one set of the side portions facing each other is constituted by a plurality of branch paths branched in parallel. In claim 4 or 5,
An antenna device, wherein one set of side portions of the antenna element is bent in a direction perpendicular to a plate surface. In any one of claims 3 to 6,
An antenna device, wherein a part of the antenna element meanders in a width direction and / or a direction perpendicular to a plate surface. An antenna device having an antenna element, wherein an electrical dimension in a width direction of each part is adjusted based on a current distribution of the antenna element so that a resonance frequency of the antenna element matches a predetermined frequency band. . Analyzing the current distribution of the antenna element and adjusting the electrical dimension in the width direction of a portion of the antenna element having a large current distribution to match the resonance frequency of the antenna element to a predetermined frequency band. A method for forming an antenna element.

Images