Patent Publication Number: US-2023155268-A1

Title: Impedance matching film and radio wave absorber

Description:
TECHNICAL FIELD 
     The present invention relates to an impedance matching film and a radio wave absorber. 
     BACKGROUND ART 
     Conventionally, the technology of matching the impedance of the surface of a radio wave absorber to the characteristic impedance of air by using a predetermined film has been known. Meanwhile, hitherto, there have been attempts to provide transparent radio wave absorbers. 
     For example, Patent Literature 1 describes a radio wave absorber in which all of component layers are transparent or translucent. In this radio wave absorber, a full-surface conductor layer, a first dielectric layer, a linear pattern resistive layer, a second dielectric layer, and a pattern layer are stacked in this order. According to this radio wave absorber, the pattern layer which is the outermost layer can satisfactorily receive electromagnetic waves. Since the pattern layer and the second dielectric layer are in contact with each other, leakage of the electromagnetic waves received by the pattern layer, to the second dielectric layer, is large. Since the second dielectric layer and the linear pattern layer are in contact with each other, the linear pattern layer can efficiently convert the electromagnetic waves that have leaked to the second dielectric layer, into heat. 
     Patent Literature 2 describes a visible light transmissive electromagnetic wave absorbing film. The visible light transmissive electromagnetic wave absorbing film has a plastic film and a visible light transmissive metal thin film. A large number of visible light transmissive metal thin films are arranged on at least one surface of the plastic film in a state where the visible light transmissive metal thin films are insulated from each other. 
     A large number of substantially parallel and linear marks are irregularly formed at intervals in at least one direction of each metal thin film. The electric resistance of each metal thin film in at least one side direction is 377±250Ω. The visible light transmissive electromagnetic wave absorbing film can sufficiently absorb electromagnetic wave noise having various frequencies. For example, according to EXAMPLES, the absorption ability for electromagnetic waves of 1 to 6 GHz is evaluated. 
     Patent Literature 3 describes an electromagnetic wave absorber having transparency. In the electromagnetic wave absorber, a reflective layer composed of a thin-line mesh pattern is formed on one surface of a transparent substrate. A transparent solid dielectric layer lies along the reflective layer with an adhesive agent layer interposed therebetween. Furthermore, a frequency selective shielding layer lies along the solid dielectric layer with an adhesive agent layer interposed therebetween. 
     The frequency selective shielding layer is composed of a thin-line pattern of an FSS element formed on one surface of a transparent substrate. A transparent solid dielectric layer lies along the frequency selective shielding layer with an adhesive agent layer interposed therebetween. A frequency selective shielding layer lies along the solid dielectric layer with an adhesive agent layer interposed therebetween. The frequency selective shielding layer is composed of a thin-line pattern of an FSS element formed on one surface of a transparent substrate. The thin-line mesh pattern of the reflective layer and the thin-line pattern of each frequency selective shielding layer have a line width of 15 to 80 μm. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP 2006-179671 A 
         Patent Literature 2: JP 2010-283154 A 
         Patent Literature 3: JP 2009-170887 A 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     It is thought that impedance matching films having transparency will be required for sensing using high-frequency radio waves such as millimeter waves. In addition, it is thought that impedance matching films having transparency will be required for a wide range of technological fields such as 5th generation mobile communication systems (5G) and the Internet of Things (IoT). 
     In order to provide an impedance matching film that can handle high-frequency radio waves and has transparency, it is conceivable to form a plurality of openings at equal intervals in an impedance matching film. In this case, diffraction and interference of light may cause an iridescent pattern on the impedance matching film. It is difficult to say that this is advantageous in terms of the appearance of the impedance matching film. In the technologies described in Patent Literatures 1 to 3, occurrence of such an iridescent pattern is not considered. Meanwhile, in a radio wave absorber including an impedance matching film having a plurality of openings formed at equal intervals therein, the absorption peak frequency of the radio wave absorber may deviate due to a phase shift in the impedance matching film. 
     In view of such circumstances, the present invention provides an impedance matching film that can handle high-frequency radio waves, has transparency, is less likely to cause an iridescent pattern, and is advantageous in terms of reducing deviation of the absorption peak frequency of a radio wave absorber. 
     Solution to Problem 
     The present invention provides an impedance matching film, wherein the impedance matching film has a plurality of openings formed at equal intervals in a specific direction along a main surface of the impedance matching film, the impedance matching film has a sheet resistance of  300  to  700  Ω/□, a size of each opening in the specific direction is 50 μm or more and 1000 μm or less, and a cross-sectional resistance value determined by dividing a specific resistance of a material forming the impedance matching film by a product of a thickness of the impedance matching film and a distance between the nearest openings is 1 MΩ/m or more. 
     In addition, the present invention provides a radio wave absorber including: 
     the above impedance matching film; 
     a reflector for reflecting radio waves; and 
     a dielectric layer disposed between the impedance matching film and the reflector in a thickness direction of the impedance matching film. 
     Advantageous Effects of Invention 
     The above impedance matching film can handle high-frequency radio waves and has transparency. In addition, an iridescent pattern is less likely to occur in the above impedance matching film, and the above impedance matching film is advantageous in terms of reducing deviation of the absorption peak frequency of a radio wave absorber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a plan view showing an example of an impedance matching film according to the present invention. 
         FIG.  1 B  is a cross-sectional view of the impedance matching film taken along a line IB-IB in  FIG.  1 A . 
         FIG.  2 A  is a plan view showing another example of the impedance matching film according to the present invention. 
         FIG.  2 B  is a plan view showing still another example of the impedance matching film according to the present invention. 
         FIG.  2 C  is a plan view showing still another example of the impedance matching film according to the present invention. 
         FIG.  3 A  is a cross-sectional view showing an example of a radio wave absorber according to the present invention. 
         FIG.  3 B  is a cross-sectional view showing a modification of the radio wave absorber according to the present invention. 
         FIG.  3 C  is a cross-sectional view showing another modification of the radio wave absorber according to the present invention. 
         FIG.  4    is a cross-sectional view showing another example of the radio wave absorber according to the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     If an impedance matching film has a plurality of openings, this is advantageous in terms of imparting transparency to the impedance matching film. In addition, in order to suppress spatial variations in the transparency and impedance matching of the impedance matching film, it is advantageous to form the plurality of openings at equal intervals along a main surface of the impedance matching film. For example, if such an impedance matching film can handle high-frequency radio waves, the value of the impedance matching film can be further enhanced. Therefore, the present inventors have studied intensively on an impedance matching film that can handle high-frequency radio waves and has a plurality of openings. In the course of this study, the present inventors have noticed that an iridescent pattern occurs in the impedance matching film due to diffraction and interference of light. The present inventors have further studied and found that it is advantageous to increase the sizes of the openings in order to suppress occurrence of an iridescent pattern in the impedance matching film. Meanwhile, the present inventors have noticed that, if the sizes of the openings are increased in the impedance matching film, deviation of the absorption peak frequency of a radio wave absorber tends to be larger. Therefore, the present inventors have conducted a great deal of trial and error, have finally found a condition that can achieve both suppression of occurrence of an iridescent pattern in the impedance matching film and reduction of deviation of the absorption peak frequency of a radio wave absorber, and have conceived of an impedance matching film according to the present invention. As used herein, “transparency” means transparency to visible light, unless otherwise described. 
     Embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments. 
     As shown in  FIG.  1 A  and  FIG.  1 B , an impedance matching film  10   a  has a plurality of openings  11 . The plurality of openings  11  are formed at equal intervals in a specific direction along main surfaces  10   f  of the impedance matching film  10   a . As used herein, the main surfaces  10   f  mean a front surface and a back surface located apart from each other in the thickness direction of the impedance matching film  10   a . Each of the plurality of openings  11  is typically formed as a through hole in the impedance matching film  10   a . The impedance matching film  10   a  has a sheet resistance of  300  to  700  Ω/□. Accordingly, impedance matching for high-frequency radio waves is easily performed. A size G of each opening  11  in the specific direction is 50 μm or more and 1000 μm or less. Accordingly, occurrence of an iridescent pattern is suppressed on the impedance matching film  10   a , and deviation of the absorption peak frequency of a radio wave absorber is easily reduced. A cross-sectional resistance value R s  of the impedance matching film  10   a  is 1 MΩ/m or more. Accordingly, deviation of the absorption peak frequency of a radio wave absorber including the impedance matching film  10   a  is easily reduced. The cross-sectional resistance value R s  is determined by dividing a specific resistance p of the material forming the impedance matching film  10   a  by the product (tW) of a thickness t of the impedance matching film  10   a  and a distance W between the nearest openings  11 . 
     The specific resistance p of the material forming the impedance matching film  10   a  can be determined on the basis of a relationship of Rf=(ρ/t){(G+W)/W}, for example, by taking a fragment having a predetermined dimension from the impedance matching film  10   a  and measuring a sheet resistance Rf of the fragment, the size G of the opening  11 , the distance W between the nearest openings  11 , and the thickness t. The sheet resistance Rf can be measured according to the eddy current method using a non-contact resistance meter. The size G of the opening  11  and the distance W between the nearest openings  11  can be determined by observing the fragment using an optical microscope. In addition, the thickness t of the impedance matching film  10   a  can be determined, for example, by observing a cross-section of the impedance matching film  10   a  using a transmission electron microscope (TEM). Moreover, the specific resistance p of the material forming the impedance matching film  10   a  may be determined by analyzing the material composition of the material, forming a film having the same composition as the material composition, and measuring the sheet resistance and the thickness of the film. 
     The impedance matching film  10   a  desirably has a sheet resistance of  350  Ω/□ or more. In this case, better impedance matching for high-frequency radio waves is easily performed by the impedance matching film  10   a . The sheet resistance of the impedance matching film  10   a  can be measured, for example, according to the eddy current method. 
     The size G of each opening  11  in the specific direction is desirably 100 μm or more, more desirably 150 μm or more, and further desirably 200 μm or more, and may be 250 μm or more, or may be 300 μm or more. The size G of each opening  11  may be 950 μm or less, may be 900 μm or less, or may be 850 μm or less. 
     The cross-sectional resistance value R s  is, for example, 20 MΩ/m or less, and may be 18 MΩ/m or less, may be 16 MΩ/m or less, may be 14 MΩ/m or less, may be 12 MΩ/m or less, may be 10 MΩ/m or less, may be 8 MΩ/m or less, may be 5 MΩ/m or less, or may be 3 MΩ/m or less. 
     The thickness t of the impedance matching film  10   a  is not limited to a specific value as long as the impedance matching film  10   a  has a sheet resistance of  300  to  700  Ω/□ and the cross-sectional resistance value thereof is 1 MΩ/m or more. The thickness t is, for example, 5 nm or more. In this case, the sheet resistance of the impedance matching film  10   a  is less likely to vary over a long period of time, and the impedance matching film  10   a  easily exhibits high durability. 
     The thickness t of the impedance matching film  10   a  may be 10 nm or more or may be 15 nm or more. The thickness t is, for example, 500 nm or less. Accordingly, warpage of the impedance matching film  10   a  is easily suppressed, so that cracks are less likely to occur in the impedance matching film  10   a . The thickness t may be 450 nm or less or may be 400 nm or less. 
     The value of the distance W between the nearest openings  11  is not limited to a specific value as long as the impedance matching film  10   a  has a sheet resistance of  300  to  700  Ω/□ and the cross-sectional resistance value thereof is 1 MΩ/m or more. The value of the distance W may be, for example, 100 μm or less. On the other hand, the value of the distance W is desirably 10 μm or less. Accordingly, in the impedance matching film  10   a , a frame that is in contact with the openings  11  is less likely to be visually recognized when the impedance matching film  10   a  is viewed in a plan view. 
     An opening ratio in the impedance matching film  10   a  is not limited to a specific value as long as the size G of each opening  11  in the specific direction is 50 μm or more and 1000 μm or less, the impedance matching film  10   a  has a sheet resistance of 300 to 700 Ω/□, and the cross-sectional resistance value thereof is 1 MΩ/m or more. The opening ratio in the impedance matching film  10   a  may be, for example, 40% or more. On the other hand, the opening ratio in the impedance matching film  10   a  is desirably 65% or more. Accordingly, the impedance matching film  10   a  easily has high transparency. The opening ratio of the plurality of openings  11  is a ratio Sa/(Sa+Sb) of an opening area Sa of the plurality of openings  11  to a sum Sa+Sb of the opening area Sa of the plurality of openings  11  and an area Sb of the non-opening portion of the impedance matching film  10   a  when the impedance matching film  10   a  is viewed in a plan view. 
     The opening ratio in the impedance matching film  10   a  is more desirably 70% or more and further desirably 75% or more. The opening ratio in the impedance matching film  10   a  is, for example, 99% or less, and may be 98% or less, or may be 97% or less. 
     The specific resistance p of the material forming the impedance matching film  10   a  is not limited to a specific value as long as the impedance matching film  10   a  has a sheet resistance of  300  to  700  Ω/□ and the cross-sectional resistance value R s  thereof is 1 MΩ/m or more. The specific resistance ρ is, for example, 4×10 −5  to 1×10 −4  Ω·cm. Accordingly, deviation of the absorption peak frequency of the radio wave absorber including the impedance matching film  10   a  is easily reduced more reliably. The specific resistance p is desirably 5×10 −5  to 1×10 −4  Ω·cm. 
     The arrangement of the plurality of openings  11  is not limited to a specific arrangement as long as the plurality of openings  11  are formed at equal intervals in the specific direction along the main surfaces  10   f . For example, the specific direction may include a plurality of alignment directions intersecting each other. For example, in the impedance matching film  10   a , the plurality of openings  11  are arranged such that the centers thereof form a square lattice on the main surfaces  10   f . In other words, in the impedance matching film  10   a , the specific direction includes alignment directions orthogonal to each other. 
     The shapes of the plurality of openings  11  are not limited to specific shapes. For example, in the impedance matching film  10   a , the plurality of openings  11  each have a square shape in a plan view. 
     The material forming the impedance matching film  10   a  is not limited to a specific material as long as the impedance matching film  10   a  has a sheet resistance of  300  to  700  Ω/□ and the cross-sectional resistance value thereof is 1 MΩ/m or more. The material forming the impedance matching film  10   a  may be an inorganic material such as metals, alloys, and metal oxides, or may be an organic material such as electroconductive polymers and carbon nanotubes. 
     The impedance matching film  10   a  may be a film having a plurality of through holes formed therein and having a uniform thickness, or may be a woven fabric. The fiber forming the woven fabric may be an organic material such as electroconductive polymers and carbon nanotubes, or may be an inorganic material such as metals and alloys. 
     As shown in  FIG.  1 B , the impedance matching film  10   a  may be formed, for example, on one main surface of a substrate  22 . In this case, the impedance matching film  10   a  can be provided by an impedance matching film-attached film  15 . The impedance matching film  10   a  may be provided alone without using the substrate  22 . 
     The substrate  22  serves, for example, as a support for supporting the impedance matching film  10   a . The impedance matching film  10   a  in the impedance matching film-attached film  15  can be produced, for example, by forming the plurality of openings  11  by laser processing, etching, or the like in a non-porous film formed on one main surface of the substrate  22  by a film forming method such as sputtering. In some cases, a non-porous film for the impedance matching film  10   a  may be formed by a film forming method such as ion plating or coating (for example, bar coating). 
     The substrate  22  has, for example, a thickness of 10 to 150 μm, and desirably has a thickness of 15 to 100 μm. Accordingly, the flexural rigidity of the substrate  22  is low, and it is possible to suppress wrinkling or deformation of the substrate  22  when forming the impedance matching film  10   a.    
     As for the arrangement and the shapes of the plurality of openings  11 , the impedance matching film  10   a  may be modified into an impedance matching film  10   b  shown in  FIG.  2 A , an impedance matching film  10   c  shown in  FIG.  2 B , or an impedance matching film  10   d  shown in  FIG.  2 C . Each of the impedance matching film  10   b , the impedance matching film  10   c , and the impedance matching film  10   d  is configured in the same manner as the impedance matching film  10   a , except for the portions that are particularly described. The components, of the impedance matching film  10   b , the impedance matching film  10   c , and the impedance matching film  10   d , identical to or corresponding to the components of the impedance matching film  10   a  are indicated by the same reference characters, and the detailed descriptions thereof are omitted. The descriptions given for the impedance matching film  10   a  are also applicable to the impedance matching film  10   b , the impedance matching film  10   c , and the impedance matching film  10   d  unless there is a technical inconsistency. 
     As shown in  FIG.  2 A , in the impedance matching film  10   b , the plurality of openings  11  each have a circular shape in a plan view. In addition, the plurality of openings  11  are arranged such that the centers thereof form a parallelogram lattice on the main surfaces  10   f . The plurality of openings  11  may be arranged so as to form a square lattice. 
     As shown in  FIG.  2 B , in the impedance matching film  10   c , the plurality of openings  11  each have a regular hexagonal shape in a plan view. In addition, the plurality of openings  11  are arranged such that the centers thereof form a parallelogram lattice on the main surfaces  10   f.    
     As shown in  FIG.  2 C , in the impedance matching film  10   d , the plurality of openings  11  each have an equilateral triangle shape in a plan view. In addition, a plurality of the openings  11  having equilateral triangle shapes having the same orientation are arranged such that the centers thereof form a parallelogram lattice on the main surfaces  10   f . Herein, the center of gravity of a planar figure is regarded as the center of an opening having a planar figure shape. 
     The plurality of openings  11  may each have another polygonal shape such as a rectangular shape, or an elliptical shape, in a plan view. The plurality of openings  11  may be arranged such that the centers thereof form another planar lattice such as a rectangular lattice on the main surfaces  10   f . As used herein, the planar lattice means an array of points on a plane that are unchanged as a result of parallel shift for a constant distance in each of two independent directions. 
     As shown in  FIG.  3 A , a radio wave absorber  1   a  can be provided, for example, using the impedance matching film  10   a . The radio wave absorber  1   a  includes the impedance matching film  10   a , a reflector  30  for reflecting radio waves, and a dielectric layer  20 . The dielectric layer  20  is disposed between the impedance matching film  10   a  and the reflector  30  in the thickness direction of the impedance matching film  10   a.    
     The radio wave absorber  1   a  is, for example, a λ/4 radio wave absorber. The radio wave absorber  1   a  is designed such that, when radio waves of a wavelength λ o  to be absorbed by the radio wave absorber  1   a  are incident on the radio wave absorber  1   a , radio waves resulting from reflection on the front surface of the impedance matching film  10   a  (front surface reflection) and radio waves resulting from reflection on the reflector  30  (back surface reflection) interfere with each other. In the λ/4 radio wave absorber, as shown in the following equation (1), the wavelength λ o  of the radio waves to be absorbed is determined according to a thickness t of the dielectric layer and a relative permittivity Er of the dielectric layer. That is, the radio waves of the wavelength to be absorbed can be set by adjusting the relative permittivity and the thickness of the dielectric layer as appropriate. In the equation (1), sqrt(ε r ) means the square root of the relative permittivity ε r . 
       λ o =4 t ×sqrt(ε r )  Equation (1)
 
     The radio wave absorber  1   a  is configured to be able to absorb radio waves in a predetermined frequency range of 20 GHz or more, for example. Examples of the frequency ranges of radio waves that can be absorbed by the radio wave absorber  1   a  are as follows. The following radio waves are under consideration for use as radio waves for 5G in various countries. 
     27.5 to 29.5 GHz 
     27.5 to 28.35 GHz 
     24.25 to 24.45 GHz 
     24.75 to 25.25 GHz 
     37 to 38.6 GHz 
     38.6 to 40 GHz 
     47.2 to 48.2 GHz 
     64 to 71 GHz 
     24.25 to 27.5 GHz 
     40.5 to 43.5 GHz 
     66 to 71 GHz 
     24.75 to 27.5 GHz 
     37 to 42.5 GHz 
     27.5 to 29.5 GHz 
     31.8 to 33.4 GHz 
     37 to 40.5 GHz 
     Other examples of the frequency ranges of the radio waves that can be absorbed by the radio wave absorber  1   a  are as follows. The following radio waves can be used as radio waves for a millimeter wave radar. 
     21.65 to 26.65 GHz 
     60 to 61 GHz 
     76 to 77 GHz 
     77 to 81 GHz 
     94.7 to 95 GHz 
     139 to 140 GHz 
     The radio wave absorber  1   a  has, for example, an absorption peak frequency of 20 GHz or more. This allows absorption of desired high-frequency radio waves. 
     An absorption peak frequency fp is the frequency of a radio wave whose return loss ISI is the maximum for the radio wave absorber  1   a . The return loss ISI is the absolute value of S calculated by the following equation (2). In the equation (2), Po is the power of transmitted radio waves when radio waves are incident on a measurement target at a predetermined incident angle, and P i  is the power of received radio waves in this case. The value of the return loss ISI for the radio wave absorber  1   a  is determined, for example, with the value of the return loss ISI when radio waves are incident on a plate of a reference metal such as aluminum at a predetermined incident angle being regarded as 0 dB. In the radio wave absorber  1   a , front surface reflection of radio waves having the absorption peak frequency fp occurs properly, and the radio wave absorber  1   a  can satisfactorily absorb the radio waves having the absorption peak frequency fp. 
         S [dB]=10×log| P   i   /P   o |  Equation (2)
 
     The radio wave absorber  1   a  exhibits, for example, a return loss of 10 dB or more, and desirably exhibits a return loss of 20 dB or more, in a predetermined frequency range of 20 GHz or more. 
     The reflector  30  is not limited to a specific form as long as the radio waves to be absorbed can be reflected. The reflector  30  is, for example, a transparent conductive film. In this case, the reflector  30  has transparency, and the entire radio wave absorber  1   a  is easily made transparent. The material forming the transparent conductive film may be an inorganic material such as metals including aluminum, etc., alloys, and metal oxides, or may be an organic material such as electroconductive polymers and carbon nanotubes. The reflector  30  may be an opaque conductive film. The material forming such a conductive film may be an inorganic material such as metals including aluminum, etc., alloys, and metal oxides, or may be an organic material such as electroconductive polymers and carbon nanotubes. 
     The transparent conductive film has, for example, a plurality of openings  31  formed regularly along main surfaces of the transparent conductive film. This configuration allows the reflector  30  to properly reflect radio waves to be absorbed and makes it easier for the reflector  30  to have desired transparency. The transparent conductive film may be a non-porous film. 
     In the case where the reflector  30  has the plurality of openings  31 , the impedance matching film  10   a  may be a film having a plurality of through holes formed therein and having a uniform thickness, or may be a woven fabric. The fiber forming the woven fabric may be an organic material such as electroconductive polymers and carbon nanotubes, or may be an inorganic material such as metals and alloys. 
     The shapes of the plurality of openings  31  in the reflector  30  are not limited to specific shapes. Each of the shapes of the plurality of openings  31  may be, for example, a triangular shape, a quadrilateral shape such as a square shape and a rectangular shape, a hexagonal shape, another polygonal shape, a circular shape, or an elliptical shape in a plan view. 
     The arrangement of the plurality of openings  31  in the reflector  30  is not limited to a specific arrangement. The plurality of openings  31  may be arranged such that, for example, the centers of the plurality of openings  31  form a planar lattice such as a square lattice and a parallelogram lattice. 
     The dielectric layer  20  has, for example, a relative permittivity of 2.0 to 20.0. In this case, it is easy to adjust the thickness of the dielectric layer  20 , and it is easy to adjust the radio wave absorption performance of the radio wave absorber  1   a . The relative permittivity of the dielectric layer  20  is, for example, a relative permittivity at 10 GHz measured according to the cavity resonance method. 
     The dielectric layer  20  is formed, for example, from a predetermined polymer. The dielectric layer  20  contains, for example, at least one polymer selected from the group consisting of ethylene-vinyl acetate copolymer, vinyl chloride resin, urethane resin, acrylic resin, acrylic urethane resin, acrylic-based elastomer, polyethylene, polypropylene, silicone, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyimide, and cycloolefin polymer. In this case, it is easy to adjust the thickness of the dielectric layer  20 , and the production cost of the radio wave absorber  1   a  can be kept low. The dielectric layer  20  can be produced, for example, by hot-pressing a predetermined resin composition. 
     The dielectric layer  20  may be formed as a single layer, or may be formed of a plurality of layers made of the same material or different materials. In the case where the dielectric layer  20  has n layers (n is an integer equal to or greater than 2), the relative permittivity of the dielectric layer  20  is determined as follows, for example. A relative permittivity ε i  of each layer is measured (i is an integer from 1 to n). Next, ε i ×(t i /T) is obtained by multiplying the measured relative permittivity ε i  of each layer by the ratio of a thickness t 1  of the layer to a total thickness T of the dielectric layer  20 . The relative permittivity of the dielectric layer  20  can be determined by adding up ε i ×(t i /T) of all the layers. 
     As shown in  FIG.  3 A , the dielectric layer  20  includes, for example, a first layer  21 , a second layer  22 , and a third layer  23 . The first layer  21  is disposed between the second layer  22  and the third layer  23 . The first layer  21  contains, for example, at least one polymer selected from the group consisting of ethylene-vinyl acetate copolymer, vinyl chloride resin, urethane resin, acrylic resin, acrylic urethane resin, polyethylene, polypropylene, silicone, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyimide, and cycloolefin polymer. 
     In the radio wave absorber  1   a , the second layer  22  serves as a substrate for the impedance matching film  10   a . The second layer  22  is disposed, for example, at a position closer to the reflector  30  than the impedance matching film  10   a  is. As shown in  FIG.  3 B , the second layer  22  may be disposed at a position farther from the reflector  30  than the impedance matching film  10   a  is. In this case, the dielectric layer  20  is composed of the first layer  21  and the third layer  23 . In this case, the impedance matching film  10   a  and the dielectric layer  20  are protected by the second layer  22 , and the radio wave absorber  1   a  has high durability. In this case, for example, the impedance matching film  10   a  may be in contact with the first layer  21 . The material of the second layer  22  is, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), acrylic resin (PMMA), polycarbonate (PC), polyimide (PI), or cycloolefin polymer (COP). Among them, the material of the second layer  22  is desirably PET in terms of the balance among good heat resistance, dimensional stability, and manufacturing cost. 
     In the radio wave absorber  1   a , the third layer  23  supports the reflector  30 , for example. In this case, the reflector  30  may be produced, for example, by forming a film on the third layer  23  using a method such as sputtering, ion plating, or coating (for example, bar coating). Furthermore, the plurality of openings  31  may be formed by laser processing, etching, or the like. As shown in  FIG.  3 A , the third layer  23  is disposed, for example, at a position closer to the impedance matching film  10   a  in the radio wave absorber  1   a  than the reflector  30  is, and forms a part of the dielectric layer  20 . As shown in  FIG.  3 C , the third layer  23  may be disposed at a position farther from the impedance matching film  10   a  than the reflector  30  is. In this case, for example, the reflector  30  is in contact with the first layer  21 . 
     As the material of the third layer  23 , for example, the materials exemplified as the material of the second layer  22  can be used. The material of the third layer  23  may be the same as or different from the material of the second layer  22 . The material of the third layer  23  is desirably PET in terms of the balance among good heat resistance, dimensional stability, and manufacturing cost. 
     The third layer  23  has, for example, a thickness of 10 to 150 μm, and desirably has a thickness of 15 to 100 μm. Accordingly, the flexural rigidity of the third layer  23  is low, and it is possible to suppress wrinkling or deformation of the third layer  23  when forming the reflector  30 . The third layer  23  may be omitted in some cases. 
     The first layer  21  may be composed of a plurality of layers. In particular, in the case where the first layer  21  is in contact with at least one of the impedance matching film  10   a  and the reflector  30  as shown in  FIG.  3 B  or  FIG.  3 C , the first layer  21  can be composed of a plurality of layers. 
     The first layer  21  may have adhesiveness, or may not necessarily have adhesiveness. In the case where the first layer  21  has adhesiveness, an adhesive layer may be disposed in contact with at least one of both main surfaces of the first layer  21 , or adhesive layers may not necessarily be disposed in contact with both main surfaces of the first layer  21 , respectively. In the case where the first layer  21  does not have adhesiveness, adhesive layers are desirably disposed in contact with both main surfaces of the first layer  21 , respectively. In the case where the dielectric layer  20  includes the second layer  22 , even if the second layer  22  does not have adhesiveness, adhesive layers may not necessarily be disposed in contact with both main surfaces of the second layer  22 , respectively. In this case, an adhesive layer can be disposed in contact with one main surface of the second layer  22 . In the case where the dielectric layer  20  includes the third layer  23 , even if the third layer  23  does not have adhesiveness, adhesive layers may not necessarily be disposed in contact with both main surfaces of the third layer  23 , respectively. In this case, an adhesive layer can be disposed in contact with at least one main surface of the third layer  23 . Each adhesive layer contains, for example, a rubber-based adhesive agent, an acrylic-based adhesive agent, a silicone-based adhesive agent, or a urethane-based adhesive agent. The thickness of each adhesive layer containing the adhesive agent is not limited to a specific value, and is, for example, 3 to 50 μm, and desirably 5 to 30 μm. 
     The radio wave absorber  1   a  may contain at least one of a dielectric loss material and a magnetic loss material. In other words, the radio wave absorber  1   a  may be a dielectric loss radio wave absorber or a magnetic loss radio wave absorber. The dielectric layer  20  may contain at least one of a dielectric loss material and a magnetic loss material. The material forming the impedance matching film  10   a  may be magnetic. 
     The radio wave absorber  1   a  can be modified in various respects. For example, the radio wave absorber  1   a  may be modified into a radio wave absorber  1   b  shown in  FIG.  4   . The radio wave absorber  1   b  is configured in the same manner as the radio wave absorber  1   a  except for the portions that are particularly described. The components, of the radio wave absorber  1   b , identical to or corresponding to the components of the radio wave absorber  1   a  are indicated by the same reference characters, and the detailed descriptions thereof are omitted. The descriptions given for the radio wave absorber  1   a  are also applicable to the radio wave absorber  1   b  unless there is a technical inconsistency. 
     As shown in  FIG.  4   , the radio wave absorber  1   b  further includes an adhesive layer  40   a . In the radio wave absorber  1   b , the reflector  30  is disposed between the dielectric layer  20  and the adhesive layer  40   a.    
     For example, the radio wave absorber  1   b  can be adhered to a predetermined article by pressing the radio wave absorber  1   b  against the article with the adhesive layer  40   a  brought into contact with the article. Accordingly, a radio wave absorber-attached article can be obtained. 
     The adhesive layer  40   a  contains, for example, a rubber-based adhesive agent, an acrylic-based adhesive agent, a silicone-based adhesive agent, or a urethane-based adhesive agent. The radio wave absorber  1   b  may further include a release liner(not shown). In this case, the release liner covers the adhesive layer  40   a . The separator is typically a film that can maintain the adhesive strength of the adhesive layer  40   a  when covering the adhesive layer  40   a  and that can easily be peeled from the adhesive layer  40   a . The release liner is, for example, a film made of polyester resin such as PET. By peeling the release liner, the adhesive layer  40   a  becomes exposed, allowing the radio wave absorber  1   b  to be adhered to an article. 
     EXAMPLES 
     Hereinafter, the present invention will be described in more detail by means of Examples. The present invention is not limited to the following Examples. First, evaluation methods for the Examples and Comparative Examples will be described. 
     [Tem Observation] 
     Cross-sectional observation samples of a non-porous film according to each of the Examples and the Comparative Examples and an alloy film in an alloy film-attached film according to each of the Examples and the Comparative Examples were prepared using a focused ion beam processing observation apparatus (product name: FB-2000A, manufactured by Hitachi High-Tech Corporation). Then, the cross-sectional observation samples were observed using a field emission transmission electron microscope (product name: HF-2000, manufactured by Hitachi High-Tech Corporation), and the thickness of the non-porous film according to each of the Examples and the Comparative Examples was measured. The thickness of the non-porous film was regarded as the thickness of the alloy film in the alloy film-attached film according to each of the Examples and the Comparative Examples. The results are shown in Table 1. 
     [Specific Resistance, Sheet Resistance, and Cross-Sectional Resistance Value] 
     The sheet resistance of the alloy film in the alloy film-attached film according to each of the Examples and the Comparative Examples was measured by the eddy current method according to JIS Z 2316 using a non-contact type resistance measurement device NC-80LINE manufactured by NAPSON CORPORATION. Meanwhile, the sheet resistance of the non-porous film according to each of the Examples and the Comparative Examples was measured in the same manner. The product of the thickness of the non-porous film measured as described above and the sheet resistance of the non-porous film measured as described above was obtained to determine the specific resistance of the material forming the non-porous film. The specific resistance of the material forming the non-porous film was regarded as the specific resistance of the material forming the alloy film in the alloy film-attached film according to each of the Examples and the Comparative Examples. In each of the Examples and the Comparative Examples, a cross-sectional resistance value R s  was determined by dividing the specific resistance of the material forming the alloy film, by the product of the thickness of the alloy film and the distance between the nearest openings in the alloy film-attached film. The results are shown in Table 1. 
     [Appearance Check] 
     In a state where the alloy film-attached film of the sample according to each of the Examples and the Comparative Examples was irradiated with light from a white light source, whether or not an iridescent pattern was observed was checked. When an iridescent pattern was not observed, the film was evaluated as “A”, and when an iridescent pattern was observed, the film was evaluated as “X”. In addition, whether or not an alloy frame of the alloy film-attached film of each sample can be visually recognized was visually checked. When the alloy frame was not recognized, the film was evaluated as “A”, and when the alloy frame was recognized, the film was evaluated as “X”. The results are shown in Table 1. 
     [Radio Wave Absorption Performance] 
     With reference to JIS R  1679 :  2007 , radio waves having frequencies of 60 to 90 GHz were made incident at an incident angle of 0° on the sample according to each of the Examples and the Comparative Examples fixed to a sample holder, using a vector network analyzer manufactured by ANRITSU CORPORATION, and a return loss ISI at each frequency was determined according to the above equation (2). Instead of the sample according to each of the Examples and the Comparative Examples, an aluminum plate was fixed to the sample holder, a return loss ISI when radio waves were incident perpendicularly on the plate was regarded as 0 dB, and the return loss ISI of each sample was determined. The plate had a face dimension of 30 cm square, and the thickness of the plate was 5 mm. For each sample, the maximum value of the return loss ISI and the frequency (absorption peak frequency fp) at which the maximum value was exhibited were determined. When the maximum value of the return loss ISI is 10 dB or more, the sample can be evaluated to have good radio wave absorption performance. In addition, a shift amount [%] from 77 GHz which is the frequency of radio waves to be absorbed having the absorption peak frequency in each sample was determined according to the following equation (3). The results are shown in Table 1. 
       Shift amount[%]=100×( fp− 77)/77  Equation (3)
 
     Example 1 
     DC magnetron sputtering was performed using an Al (aluminum) target material and an Si (silicon) target material and using argon gas as a process gas, to form an Al—Si alloy film on a PET film. In the DC magnetron sputtering, discharge involving the Al (aluminum) target material and discharge involving the Si (silicon) target material were performed simultaneously. Thus, a non-porous film according to Example 1 was formed on the PET film. The specific resistance of the material forming the non-porous film according to Example 1 was 4.8×10 −5  Ω·cm. The non-porous film had a thickness of 30 nm. Next, using a metal laser patterning machine, a plurality of square-shaped openings were formed at equal intervals in the non-porous film according to Example 1 so as to form a square lattice, to obtain an alloy film-attached film according to Example 1. In a plan view of the alloy film-attached film according to Example 1, the size of each opening in the direction in which the plurality of openings were arranged at equal intervals was 220 μm, and the distance between the nearest openings was 10 μm. The alloy film in the alloy film-attached film can function as an impedance matching film. 
     DC magnetron sputtering was performed using an ITO target material containing 10 weight % of SnO 2  and using argon and oxygen as process gases, to form an ITO film on a PET film. Then, the ITO film was annealed under the condition of a temperature of 150° C. for 1 hour to polycrystallize the ITO, to obtain a reflector-attached film. The sheet resistance of the reflector of the reflector-attached film was 20 Ω/□. Next, an acrylic resin having a relative permittivity of 2.6 was molded so as to have a thickness of 560 μm, to obtain an acrylic resin layer A. The alloy film-attached film according to Example 1 was put on the acrylic resin layer A such that the alloy film of the alloy film-attached film according to Example 1 was in contact with the acrylic resin layer A. Next, the reflector-attached film was put on the acrylic resin layer A such that the ITO in the reflector-attached film was in contact with the acrylic resin layer A. Thus, a sample according to Example 1 was obtained. 
     Example 2 
     A non-porous film according to Example 2 was formed on a PET film and an alloy film-attached film according to Example 2 was obtained, in the same manner as Example 1 except for the following. In DC magnetron sputtering, the ratio of the discharge power of the discharge involving the Si (silicon) target material to the discharge power of the discharge involving the Al (aluminum) target material was adjusted such that the specific resistance of the material forming the non-porous film according to Example 2 was 5.0×10 −5  Ω·cm. In addition, the conditions of the DC magnetron sputtering were adjusted such that the thickness of the alloy film in the alloy film-attached film according to Example 2 was 50 nm. Next, using a metal laser patterning machine, a plurality of square-shaped openings were formed at equal intervals in the non-porous film according to Example 2 so as to form a square lattice, to obtain an alloy film-attached film according to Example 2. In a plan view of the alloy film-attached film according to Example 2, the size of each opening in the direction in which the plurality of openings were arranged at equal intervals was 600 μm, and the distance between the nearest openings was 10 μm. 
     A sample according to Example 2 was obtained in the same manner as Example 1, except that the alloy film-attached film according to Example 2 was used instead of the alloy film-attached film according to Example 1. 
     Example 3 
     A non-porous film according to Example 3 was formed on a PET film and an alloy film-attached film according to Example 3 was obtained, in the same manner as Example 1 except for the following. In DC magnetron sputtering, the ratio of the discharge power of the discharge involving the Si (silicon) target material to the discharge power of the discharge involving the Al (aluminum) target material was adjusted such that the specific resistance of the material forming the non-porous film according to Example 3 was 1.0×10 −4  Ω·cm. In addition, the conditions of the DC magnetron sputtering were adjusted such that the thickness of the alloy film in the alloy film-attached film according to Example 3 was 5 nm. Next, using a metal laser patterning machine, a plurality of square-shaped openings were formed at equal intervals in the non-porous film according to Example 3 so as to form a square lattice, to obtain an alloy film-attached film according to Example 3. In a plan view of the alloy film-attached film according to Example 3, the size of each opening in the direction in which the plurality of openings were arranged at equal intervals was 50 μm, and the distance between the nearest openings was 10 μm. 
     A sample according to Example 3 was obtained in the same manner as Example 1, except that the alloy film-attached film according to Example 3 was used instead of the alloy film-attached film according to Example 1. 
     Example 4 
     A non-porous film according to Example 4 was formed on a PET film and an alloy film-attached film according to Example 4 was obtained, in the same manner as Example 1 except for the following. In DC magnetron sputtering, the ratio of the discharge power of the discharge involving the Si (silicon) target material to the discharge power of the discharge involving the Al (aluminum) target material was adjusted such that the specific resistance of the material forming the non-porous film according to Example 4 was 5.0×10 −5  Ω·cm. In addition, the conditions of the DC magnetron sputtering were adjusted such that the thickness of the alloy film in the alloy film-attached film according to Example 4 was 5 nm. Next, using a metal laser patterning machine, a plurality of square-shaped openings were formed at equal intervals in the non-porous film according to Example 4 so as to form a square lattice, to obtain an alloy film-attached film according to Example 4. In a plan view of the alloy film-attached film according to Example 4, the size of each opening in the direction in which the plurality of openings were arranged at equal intervals was 200 μm, and the distance between the nearest openings was 100 μm 
     A sample according to Example 4 was obtained in the same manner as Example 1, except that the alloy film-attached film according to Example 4 was used instead of the alloy film-attached film according to Example 1. 
     Comparative Example 1 
     A non-porous film according to Comparative Example 1 was formed on a PET film and an alloy film-attached film according to Comparative Example 1 was obtained, in the same manner as Example 1 except for the following. In DC magnetron sputtering, the ratio of the discharge power of the discharge involving the Si (silicon) target material to the discharge power of the discharge involving the Al (aluminum) target material was adjusted such that the specific resistance of the material forming the non-porous film according to Comparative Example 1 was 1.0×10 −4  Ω·cm. In addition, the conditions of the DC magnetron sputtering were adjusted such that the thickness of the alloy film in the alloy film-attached film according to Comparative Example 1 was 5 nm. Next, using a metal laser patterning machine, a plurality of square-shaped openings were formed at equal intervals in the non-porous film according to Comparative Example 1 so as to form a square lattice, to obtain an alloy film-attached film according to Comparative Example 1. In a plan view of the alloy film-attached film according to Comparative Example 1, the size of each opening in the direction in which the plurality of openings were arranged at equal intervals was 20 μm, and the distance between the nearest openings was 10 μm. 
     A sample according to Comparative Example 1 was obtained in the same manner as Example 1, except that the alloy film-attached film according to Comparative Example 1 was used instead of the alloy film-attached film according to Example 1. 
     Comparative Example 2 
     A non-porous film according to Comparative Example 2 was formed on a PET film and an alloy film-attached film according to Comparative Example 2 was obtained, in the same manner as Example 1 except for the following. In DC magnetron sputtering, the ratio of the discharge power of the discharge involving the Si (silicon) target material to the discharge power of the discharge involving the Al (aluminum) target material was adjusted such that the specific resistance of the material forming the non-porous film according to Comparative Example 2 was 5×10 −5  Ω·cm. In addition, the conditions of the DC magnetron sputtering were adjusted such that the thickness of the alloy film in the alloy film-attached film according to Comparative Example 2 was 50 nm. Next, using a metal laser patterning machine, a plurality of square-shaped openings were formed at equal intervals in the non-porous film according to Comparative Example 2 so as to form a square lattice, to obtain an alloy film-attached film according to Comparative Example 2. In a plan view of the alloy film-attached film according to Comparative Example 2, the size of each opening in the direction in which the plurality of openings were arranged at equal intervals was 1500 μm, and the distance between the nearest openings was 50 μm 
     A sample according to Comparative Example 2 was obtained in the same manner as Example 1, except that the alloy film-attached film according to Comparative Example 2 was used instead of the alloy film-attached film according to Example 1. 
     Comparative Example 3 
     A non-porous film according to Comparative Example 3 was formed on a PET film and an alloy film-attached film according to Comparative Example 3 was obtained, in the same manner as Example 1 except for the following. In DC magnetron sputtering, the ratio of the discharge power of the discharge involving the Si (silicon) target material to the discharge power of the discharge involving the Al (aluminum) target material was adjusted such that the specific resistance of the material forming the non-porous film according to Comparative Example 3 was 5.0×10 −5  Ω·cm. In addition, the conditions of the DC magnetron sputtering were adjusted such that the thickness of the alloy film in the alloy film-attached film according to Comparative Example 3 was 50 nm. Next, using a metal laser patterning machine, a plurality of square-shaped openings were formed at equal intervals in the non-porous film according to Comparative Example 3 so as to form a square lattice, to obtain an alloy film-attached film according to Comparative Example 3. In a plan view of the alloy film-attached film according to Comparative Example 3, the size of each opening in the direction in which the plurality of openings were arranged at equal intervals was 1000 μm, and the distance between the nearest openings was 50 μm 
     A sample according to Comparative Example 3 was obtained in the same manner as Example 1, except that the alloy film-attached film according to Comparative Example 3 was used instead of the alloy film-attached film according to Example 1. 
     Comparative Example 4 
     A non-porous film according to Comparative Example 4 was formed on a PET film and an alloy film-attached film according to Comparative Example 4 was obtained, in the same manner as Example 1 except for the following. In DC magnetron sputtering, the ratio of the discharge power of the discharge involving the Si (silicon) target material to the discharge power of the discharge involving the Al (aluminum) target material was adjusted such that the specific resistance of the material forming the non-porous film according to Comparative Example 4 was 5.0×10 −5  Ω·cm. In addition, the conditions of the DC magnetron sputtering were adjusted such that the thickness of the alloy film in the alloy film-attached film according to Comparative Example 4 was 100 nm. Next, using a metal laser patterning machine, a plurality of square-shaped openings were formed at equal intervals in the non-porous film according to Comparative Example 4 so as to form a square lattice, to obtain an alloy film-attached film according to Comparative Example 4. In a plan view of the alloy film-attached film according to Comparative Example 4, the size of each opening in the direction in which the plurality of openings were arranged at equal intervals was 800 μm, and the distance between the nearest openings was 5 μm. 
     A sample according to Comparative Example 4 was obtained in the same manner as Example 1, except that the alloy film-attached film according to Comparative Example 4 was used instead of the alloy film-attached film according to Example 1. 
     Comparative Example 5 
     A non-porous film according to Comparative Example 5 was formed on a PET film and an alloy film-attached film according to Comparative Example 5 was obtained, in the same manner as Example 1 except for the following. In DC magnetron sputtering, the ratio of the discharge power of the discharge involving the Si (silicon) target material to the discharge power of the discharge involving the Al (aluminum) target material was adjusted such that the specific resistance of the material forming the non-porous film according to Comparative Example 5 was 5.0×10 −5  Ω·cm. In addition, the conditions of the DC magnetron sputtering were adjusted such that the thickness of the alloy film in the alloy film-attached film according to Comparative Example 5 was 100 nm. Next, using a metal laser patterning machine, a plurality of square-shaped openings were formed at equal intervals in the non-porous film according to Comparative Example 5 so as to form a square lattice, to obtain an alloy film-attached film according to Comparative Example 5. In a plan view of the alloy film-attached film according to Comparative Example 5, the size of each opening in the direction in which the plurality of openings were arranged at equal intervals was 600 μm, and the distance between the nearest openings was 10 μm. 
     A sample according to Comparative Example 5 was obtained in the same manner as Example 1, except that the alloy film-attached film according to Comparative Example 5 was used instead of the alloy film-attached film according to Example 1. 
     As shown in Table 1, no iridescent pattern was observed in the sample according to each Example. On the other hand, in the sample according to Comparative Example 1, an iridescent pattern was observed. Therefore, it was suggested that each of the sizes of the openings formed at equal intervals being 50 μm or more in the impedance matching film is advantageous in terms of suppressing occurrence of an iridescent pattern. In the sample according to each Example, the shift amount was 10% or less. On the other hand, in each of the samples according to Comparative Examples 2, 3, and 5, the shift amount exceeded 10%. Therefore, it is suggested that the cross-sectional resistance value R s  being 1 MΩ/m or more in the impedance matching film is advantageous in reducing deviation of the absorption peak frequency. It is difficult to say that the samples according to Comparative Examples 2 and 4 had good radio wave absorption performance. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                   
                 Sheet 
                 Specific resistance 
                   
                   
                   
                 Distance 
               
               
                   
                 resistance of 
                 of material forming 
                 Cross-sectional 
                 Thickness of 
                 Size of 
                 between 
               
               
                   
                 alloy film 
                 alloy film 
                 resistance value R s   
                 alloy film 
                 opening 
                 openings 
               
               
                   
                 [Ω/□] 
                 [Ω · cm] 
                 [MΩ/m] 
                 [nm] 
                 [μm] 
                 [μm] 
               
               
                   
               
               
                 Ex. 1 
                 397 
                 4.8 × 10 −5   
                 1.6 
                 30 
                 220 
                 10 
               
               
                 Ex. 2 
                 610 
                 5.0 × 10 −5   
                 1.0 
                 50 
                 600 
                 50 
               
               
                 Ex. 3 
                 300 
                 1.0 × 10 −4   
                 1.0 
                 5 
                 50 
                 10 
               
               
                 Ex. 4 
                 300 
                 5.0 × 10 −5   
                 1.0 
                 5 
                 200 
                 100 
               
               
                 Comp. Ex. 1 
                 300 
                 1.0 × 10 −4   
                 20 
                 5 
                 20 
                 10 
               
               
                 Comp. Ex. 2 
                 310 
                 5.0 × 10 −5   
                 0.2 
                 50 
                 1500 
                 50 
               
               
                 Comp. Ex. 3 
                 210 
                 5.0 × 10 −5   
                 0.2 
                 50 
                 1000 
                 50 
               
               
                 Comp. Ex. 4 
                 805 
                 5.0 × 10 −5   
                 1.0 
                 100 
                 800 
                 5 
               
               
                 Comp. Ex. 5 
                 305 
                 5.0 × 10 −5   
                 0.5 
                 100 
                 600 
                 10 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                 Presence/absence 
                 Visual 
                 Absorption peak 
                   
                   
               
               
                   
                 Opening ratio 
                 of iridescent 
                 recognition of 
                 frequency fp 
                 Shift amount 
                 Return loss 
               
               
                   
                 [%] 
                 pattern 
                 frame 
                 [GHz] 
                 [%] 
                 [dB] 
               
               
                   
               
               
                 Ex. 1 
                 91.5 
                 A 
                 A 
                 74.2 
                 −3.6 
                 36.5 
               
               
                 Ex. 2 
                 96.7 
                 A 
                 X 
                 81.8 
                 6.2 
                 25.8 
               
               
                 Ex. 3 
                 69.4 
                 A 
                 A 
                 78.7 
                 2.2 
                 13.9 
               
               
                 Ex. 4 
                 44.4 
                 A 
                 X 
                 80.6 
                 4.7 
                 23.1 
               
               
                 Comp. Ex. 1 
                 44.4 
                 X 
                 X 
                 77.4 
                 0.52 
                 18.5 
               
               
                 Comp. Ex. 2 
                 93.7 
                 A 
                 X 
                 84.8 
                 10.1 
                  5.0 
               
               
                 Comp. Ex. 3 
                 90.7 
                 A 
                 A 
                 90 or more 
                 16.8 or more 
                 — 
               
               
                 Comp. Ex. 4 
                 98.8 
                 A 
                 A 
                 81.5 
                 5.8 
                  6.9 
               
               
                 Comp. Ex. 5 
                 96.7 
                 A 
                 A 
                 90 or more 
                 16.8 or more 
                 —