This invention relates to an ultrawideband communication antenna to be used in an ultrawideband (UWB).
Communication using the UWB is a communication method utilizing 20% of a central frequency or a band of 500 MHz or more which is a remarkably wide band ranging from several hundreds of megahertzes to several gigahertzes. Since an output is lower than a noise level of a personal computer, the communication method has various advantages such as capability of sharing with a currently used frequency, capability of high speed communication, applicable to positioning and distance measurement, and simple structure of impulse type circuit without using a carrier wave. Therefore, use of the communication method is expected to be expanded in various fields in near future.
Since the UWB uses the considerably wide band, an antenna using an ultrawideband that has not been utilized in the art, such as that having a full band of 3.1 to 10.6 GHz, a high band of 5 to 10.6 GHz, and a low band of 3.1 to 5 GHz, is required. Such ultrawideband antenna is disclosed in a reference 1 and reference 2.
Since the ultrawideband antenna disclosed on page 35 of the reference 1 and the ultrawideband antenna disclosed in paragraphs [0065] to [0069] and FIGS. 22 and 23 of the reference 2 are flat antenna type, these ultrawideband antennas are not sufficiently downsized though they are reduced in thickness, thereby raising a drawback of limited application. For example, the flat ultrawideband antenna disclosed on page 35 of reference 1 requires a length and a width of 30 mm×40 mm.
As a countermeasure for such drawback, it is considered that downsizing can be achieved by covering a periphery of an antenna element with ceramics having a high complex relative permittivity or by covering a periphery of an antenna element with a resin. The countermeasures take advantage of compression of a wavelength of an electromagnetic wave due to the high complex relative permittivity of the ceramics and the resin. However, in the case of covering the periphery of the antenna element with the ceramics, there are problems of high price and reduced resistance to impact. Also, since it is difficult to obtain a resin of high complex relative permittivity in the case of covering the periphery of the antenna element with the resin, there is a problem that satisfactory downsizing has not been achieved yet. Further, the high complex relative permittivity is considered to be achieved by mixing a magnetic powder with the resin. However, losses of inductive capacity and magnetism will be increased due to the magnetic powder, thereby undesirably causing deterioration in antenna characteristics.
This invention has been accomplished in view of the above-described circumstances, and an object thereof is to provide an ultrawideband communication antenna that is resistant to impact, reduced in losses, and satisfactorily small.
According to an aspect of the invention, there is provided an ultrawideband communication antenna including an antenna element of which at least one part is coated with an insulating resin layer that is mixed with a nonmagnetic metal powder.
The reference numerals used in the drawings denote the followings, respectively:
Hereinafter, an antenna to be used for ultrawideband communication system according to one embodiment of this invention will be described using the drawings.
Both sides of the antenna element 14, i.e. the surface 14a of the antenna 14 close to the substrate 12 and the surface 14b of the antenna element 14 which is the reverse side of the surface 14a, are coated with a first resin layer (resin layer) 24 and a second resin layer (resin layer) 26 each having a constant thickness, and the antenna element 14 is fixed to the surface of the substrate 12 via the first resin layer 24. The antenna element 14 has a width W2 which is smaller than the width W1 of the substrate 12 and larger than the width W3 of the line-like conductor 22, and the length L2 shorter than the length L1. A part of the width of the antenna element 14 close to the line-like conductor 22 is tapered along a direction toward a power supply unit 28, so that an overall shape is like a pentagon.
One end of the line-like conductor 22 is connected to the power supply unit 28 by soldering, and a terminal of the SMA connector 16 is connected to the other end of the line-like connector 22, so that power is supplied from a coaxial cable connector (not shown) connected to the SMA connector 16 to the antenna element 14 via the SMA connector 16 and the line-like conductor 22.
In this embodiment: the substrate 12 has a length (L1+L2) of 31 mm, the width W1 of 10 mm, and a thickness TB of 1.6 mm; the line-like conductor 22 has a length L1 of 22 mm; the antenna element 14 has a length L2 of 9 mm, the width W2 of 5.6 mm, and a thickness TA of 0.1 mm; the first resin layer 24 has a thickness T1 of 0.3 mm; and the second resin layer 26 has a thickness T2 of 1 mm.
The first resin layer 24 and the second resin layer 26 are subjected to the injection molding together with the antenna element 14 that has been placed in a die in advance of the injection molding.
The row material pelletizing machine 32 shown in
The nonmagnetic metal powder 50 is palletized by employing a well-known metal powder production method such as a gas atomizing method, a water atomizing method, and a gas-water atomizing method to achieve the average particle diameter of D50 ranging from about 3 to about 100 μm. In the gas atomizing method, in a cylindrical chamber disposed vertically, a melted raw material is dropped from pores formed on a bottom of a tundish provided at an upper end of the chamber, and an inactive gas is sprayed in the form of a taper around the melted material toward the melted raw material during the dropping to granulate and coagulate the melted material. After that, a metal powder having a desired average particle diameter is obtained by classification from collected metal particles. In the case of employing the gas atomizing method, a relatively spherical metal powder is obtained. In the water atomizing method, in a chamber in which water is stored, a melted raw material is dropped from pores formed on a bottom of a tundish provided at an upper end of the chamber, and a high pressure water is sprayed in the form of a taper around the melted material by using a circular nozzle toward the melted raw material during the dropping to granulate and coagulating the melted material. After drying collected metal particles, a metal powder having a desired average particle diameter is obtained by classification from the collected metal particles. In the case of employing the water atomizing method, a relatively flat metal powder is obtained. In the gas-water atomizing method, a metal powder is obtained in the same manner as in the water atomizing method except for changing the high pressure water to an inactive gas.
The injection molding machine 56 shown in
Hereinafter, evaluation tests wherein various materials were used as the nonmagnetic metal powder and a mixing ratio of the nonmagnetic metal powder was changed are shown together with the results.
In Test Example 1, antenna samples 10a and 10b were obtained in the same manner as in the case of obtaining the antenna 10 described in the foregoing except for using materials shown in Table 1 for the first resin layer 24 and the second resin layer 26. Referring to Tables 1 to 4, each of the complex specific inductive capacities was measured by using a measurement frequency of 4 GHz. Also, a value of an added amount of each of materials (metal components) shown in Tables 1 and 2 is based on wt % (% by weight).
As shown in
Shown in
An antenna sample 10c and an antenna sample 10d were produced in the same manner as in the production method of the above-described antenna 10 except for using materials shown in Table 2 as the first resin layer 24 and the second resin layer 26.
As shown in
Shown in
An antenna sample 10e and an antenna sample 10f were produced in the same manner as in the production method of the above-described antenna 10 except for using materials shown in Table 3 as the first resin layer 24 and the second resin layer 26.
As shown in
Shown in
An antenna sample 10g and an antenna sample 10h were produced in the same manner as in the production method of the above-described antenna 10 except for using materials shown in Table 4 as the first resin layer 24 and the second resin layer 26. In Test Example 4, the metal powders were flat and had large particle diameters, and a volumetric charge ratio of the antenna sample 10h was increased.
As shown in
Shown in
In Test Example 5, antenna samples 10i, 10j, and 10k were produced by using the same materials (component of metal powder: Ni-3.5Fe-3.5B-3Mo-3Cu-3.8Si-0.5C; magnetism of metal powder: nonmagnetic; metal powder production method: gas atomizing method; metal powder average particle diameter; average particle diameter of metal powder: 50 μm; resin: PPS resin). Shapes of the antenna samples 10i, 10j, and 10k were the same as those of the antenna samples 10a and 10c, and volumetric charge ratios (%: volumetric ratio) of the antenna samples 10i, 10j, and 10k were changed from one another as showed in Table 5.
As shown in
VSWR=|Vmax|/|Vmin|=(1+|Γ|)/(1−|Γ|)
In the above expression, Γ is a reflection coefficient and Γ=reflected wave voltage VR/traveling wave voltage VF
Shown in
As described above, according to the antenna 10 of this embodiment, the antenna element is covered with the first resin layer 24 and the second resin layer 26 having the high complex specific inductive capacities since the antenna element 14 is coated with the insulating first resin layer 24 and the second resin layer 26 with which the nonmagnetic metal powder is mixed. Therefore, it is possible to largely reduce the size due to the compression of wavelength of electromagnetic wave. Also, since the nonmagnetic metal powder 50 is used, the first resin layer 24 and the second resin layer 26 are free from a loss of magnetism generated therein, thereby realizing the antenna in which the loss is maintained to a low level.
Also, according to the antenna 10 of this embodiment, since the antenna element 14 is formed of the flat conductor, and since the first resin layer 24 and the second resin layer 26 cover one surface of the antenna element 14, it is possible to make the antenna thinner as a whole, thereby achieving the downsizing. For comparison, the length and the width of the flat monopole antenna shown in Picture 2 of reference 1 is 40×30 mm, and the length and the width of the antenna 10 of this embodiment is 31×10 mm which is largely downsized.
Also, according to the antenna 10 of this embodiment, since the nonmagnetic metal powder 50 is mixed at the ratio of 10 to 50 vol % with respect to the first resin layer 24 and the second resin layer 26, the complex specific inductive capacities of the first resin layer 24 and the second resin layer 26 are favorably increased to enable the large downsizing.
Further, according to the antenna 10 of this embodiment, the antenna element 14 is formed of the flat conductor, and the first resin layer 24 and the second resin layer 26 are provided with the complex specific inductive capacities in the range of 8 to 90 in the planar direction of the flat conductor. Therefore, it is possible to achieve the wavelength compression effect, thereby realizing the largely downsized flat antenna.
Also, according to the antenna 10 of this embodiment, since the first resin layer 24 and the second resin layer 26 cover the antenna element 14 at a constant thickness and are injection-molded together with the antenna element 14 that has been placed in the die 72 in advance of the injection molding, it is possible to simultaneously perform the molding and fixing, thereby achieving the advantages of high mass productivity and low production cost.
The antenna 10 of this embodiment achieves good characteristics in the frequency band of 3 to 5 GHz that is used in the UWB communication system.
Also, according to the antenna 10 of this embodiment, since the antenna element 14 is the flat antenna (monopole type) that is connected to one end of the strip type waveguide, the antenna 10 has the advantage that it is possible to be further downsized.
Though one embodiment of this invention has been described based on the drawings in the foregoing, this invention is applicable to other modes.
For example, though the surfaces of the antenna element 14 are covered with the first resin layer 24 and the second resin layer 26 in the foregoing embodiment, it is possible to achieve the effect of downsizing when one of the surfaces of the antenna element 14 is covered with the first resin layer 24 or the second resin layer 26.
Though the shape of the antenna 10 is pentagon-shaped in the foregoing description, the shape may be another one, and the antenna 10 may be linear or comb-like.
Also, though the length L1 of the microstrip is longer than the length L2 of the antenna element 14 in the foregoing embodiment, the length L1 may be the same as the length L2 of the antenna element 14 or may be shorter than the length L2 of the antenna element 14. The lengths L1 and L2 may be changed depending on the required radiation property of the antenna element 14.
Note that the foregoing embodiment has been descried only by way of example, and it is possible to practice this invention in modes to which various alternations and modifications are added based on the knowledge of person skilled in the art.
In addition, the nonmagnetic metal powder means a metal powder having a magnetic characteristic that a loss of magnetism generated when used in the frequency band of the UWB is satisfactorily small to avoid troubles, and, even when magnetized, the magnetic substance may be used as the nonmagnetic metal powder insofar as the loss is remarkably small. In general, metal powders excluding a so-called ferromagnetic substance may be used, and gold, silver, aluminum, copper, alloys thereof, a silicon steel, and metal powders obtained by plating these metals, which are excellent in electroconductivity, may preferably be used.
The more the ratio of the nonmagnetic metal powder is increased in the resin layer, the more the nonmagnetic metal powder contributes to an increase in complex relative permittivity of the resin layer, and it is possible to add the nonmagnetic metal powder until the ratio reaches to that at which a reduction in insulating property of the resin layer starts due to contact between metal powder particles. However, when the ratio of the nonmagnetic metal powder with respect to the resin layer is less than 10 vol %, the increase in complex relative permittivity of the resin layer becomes insufficient, thereby failing to contribute to the large downsizing of the ultrawideband communication antenna. Also, when the ratio of the nonmagnetic metal powder with respect to the resin layer exceeds 50 vol %, the complex relative permittivity becomes too large to keep compatibility with the air, thereby reducing a radiation property. In terms of the complex relative permittivity of the resin layer, it is difficult to satisfactorily contribute to the downsizing when the complex relative permittivity in the planar direction of the antenna element is 8 or less. Further, the upper limit of the complex relative permittivity is set to 90 due to limitation in production. When the ratio of the nonmagnetic metal powder with respect to the resin layer exceeds 50 vol % (40 vol % when a flat powder is used), fluidity of the resin in performing the injection molding is deteriorated to prevent satisfactory molding.
Uniformity of the complex relative permittivity of the nonmagnetic metal powder tends to be reduced with a reduction in particle diameter due to distribution of dispersion. and tends to be reduced with an increase in particle diameter due to contact between particles and the like. Therefore, the particle diameter of the nonmagnetic metal powder may preferably be in the range of 3 to 100 μm. The nonmagnetic metal powder is not limited to a spherical powder and may be a flat powder. Also, the particle diameter of the nonmagnetic metal powder in this specification means an average particle diameter (D50).
The ultrawideband communication antenna is not limited to a monopole antenna and may be an antenna of a different type such as a dipole antenna, and the antenna is not necessarily a flat antenna.
A polyphenylene sulfide (PPS) resin may preferably be used for the resin layer in view of its satisfactory heat resistance to a solder welding temperature, and insulating resins such as a PET resin, an epoxy resin, a nylon resin, a polycarbonate resin, and a phenol resin that satisfy a certain strength in accordance with usage, an insulating property, heat resistance to solder welding temperature, and the like may also be used. Also, a fiber reinforced resin in which a fiber is added may be used.
The inventor of these embodiments has conducted extensive researches in view of the above-described circumstances to find that addition of a nonmagnetic metal powder to a resin for covering an antenna element makes it possible to: reduce a loss coefficient tan δ (=ε″/ε′, wherein ε′ and ε″ are a real part and an imaginary part) of inductive capacity of the resin in a wavelength band of the UWB to 0.05; reduce a loss coefficient tan δ (=μ″/μ′, wherein μ′ and μ″ are a real part and an imaginary part) of magnetism generated in the resin layer due to the use of the nonmagnetic metal powder; and maintain losses of the antenna to low levels. Accordingly, a specific inductive capacity of the resin layer is considerably increased to make it possible to obtain an ultrawideband communication antenna that is resistant to impact and largely reduced in size as well as possible to maintain the losses of the antenna to favorably low levels. These embodiments have been accomplished based on the above findings.
While the present invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
The present application is based on Japanese Patent Application No. 2006-217588 filed on Aug. 9, 2006, Japanese Patent Application No. 2007-44784 filed on Feb. 24, 2007, and the contents thereof are incorporated herein by reference.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
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