MILLIMETER WAVE COMMUNICATION DEVICE

Abstract

Millimeter wave band communication device, including: a substrate (2); a high-frequency circuit element (4) provided on the substrate (2) for a millimeter wave band; and a cover (1) made of a solid material, covering at least part of the high-frequency circuit element (4) and a surface of the substrate (2), wherein the cover (1) is formed by mixing a material with dielectric loss into a base material, characterized by a high-frequency line (3) provided on the substrate surface and connected to the high-frequency circuit element (4) and at its opposite end to an antenna (9); and a groove structure (8) which is formed in the cover (1) in such a way as to prevent contact between the radio frequency line (3) and the cover (1), and whose width at a cross-section which intersects with a radio wave propagation direction of the radio frequency line (3) is less than or equal to a wavelength λ of a millimeter wave operating frequency of the millimeter wave band communication device.

Description

Technical field

[0001] The present invention relates to a communication device and a sensor which use a millimeter wave as the electromagnetic wave. State of the art

[0002] Devices using millimeter waveband frequencies are used for backbone links between radio base stations due to their broadband capability and for scanning devices such as radar due to their high directivity. Newer millimeter wave semiconductor devices are being marketed with surface-mount connections, such as ball grid arrays, in a state where a transmit or receive circuit, or both, are integrated into a single package. Accordingly, these devices rely on the use of a component placement machine and a reflow oven, and cost-effective assembly is achieved even for products designed for the millimeter waveband.

[0003] A millimeter-wave semiconductor device used in a millimeter-wave radar is a device with a wide signal dynamic range and high sensitivity. The main causes of malfunction of the semiconductor device include interference from unwanted external radio waves, and as a measure to suppress unwanted radio waves, a shielding enclosure with a metallic cover is used, as disclosed in PTL 1 to 4. List of reference literature Patent literature PTL 1: JP 2015-119295 A PTL 2: JP 2000-307305 A PTL 3: JP 2002-134987 A PTL 4: JP 2002-124592 B2

[0004] Further prior art is disclosed in US 2009 / 0117386 A1, from which the preamble of claim 1 is derived, and in JP H05-4592 U, US 2014 / 0204550 A1 and US 2004 / 0020674 A1. Summary of the invention: Technical problem

[0005] Millimeter-wave band communication devices described in the prior art use a metallic cover (shielding enclosure) as a measure to suppress unwanted external radio waves. The shielding enclosure reflects radio waves by exploiting a radio wave radiation effect (secondary radiation) due to the high conductivity of metal. The high reflectivity of metal indicates that a room resonance of radio waves is highly likely to occur within the enclosure, and there is a possibility that a receiving circuit or oscillator could be affected by radio waves leaking from the millimeter-wave band circuit itself.

[0006] In PTL 1, the size of the shielding enclosure is adjusted so that a resonant frequency avoids a usable frequency. PTL 2 uses a bandstop filter in a periodic structure of metallic protrusions provided within a space. PTL 3 can suppress the room resonance with a thermoplastic material that absorbs electromagnetic waves (hereinafter referred to as a radio wave absorber). However, since it is difficult to achieve the desired radio wave transmittance with the radio wave absorber alone, a separate metal cover or partition inside an enclosure is required to suppress unwanted radio waves from the outside and to achieve isolation between multiple millimeter-wave band RF circuits.

[0007] In PTL 4, a resistive layer is formed on a dielectric substrate in an area not required for the operation of the millimeter-waveband radio frequency circuit. This reduces the Q-value of the shielding enclosure, thereby minimizing unwanted resonances and vibrations. The radio wave absorber and resistive layer are designed so that radio waves reach a lossy material within a medium. The material used has a low dielectric constant and exhibits a small characteristic impedance difference with air to prevent reflection from any surface of the medium.

[0008] In these cases, it is essential to take measures to suppress room resonance when using the metal covering, but the high material costs remain a problem. Furthermore, if a shielding structure using the metal covering has a hole or gap, radio waves will escape, and therefore this hole or gap must be closed as much as possible, which is why finding a way to seal the metal covering also presents a challenge. Solution to the problem

[0009] The problem is solved with a millimeter wave band communication device according to the attached patent claims. Advantageous effects of the invention

[0010] A millimeter wave band communication device capable of suppressing unwanted radio waves from the outside and reducing radio wave radiation leakage from a millimeter wave band high-frequency circuit itself can be provided cost-effectively. Brief description of the drawings [ Fig. 1] Fig. Figure 1 is a perspective view of a millimeter wave band communication device according to a first embodiment of the present invention. [ Fig. 2] Fig. Figure 2 is a perspective view of a groove structure of the first embodiment of the present invention. [ Fig. 3] Fig. Figure 3 is a graph of an analysis result of the permeability of the groove structure according to the first embodiment of the present invention. [ Fig. 4] Fig. Figure 4 is a graph of an analysis result of the transmission loss of a microstrip line provided in the slot structure according to the first embodiment of the present invention. [ Fig. 5] Fig. Figure 5 is a perspective view of a millimeter wave band communication device according to a second embodiment of the present invention. [ Fig. 6] Fig. Figure 6 is a perspective view of a millimeter wave band communication device according to a third embodiment of the present invention. [ Fig. 7] Fig. Figure 7 is a perspective view of a millimeter wave band communication device according to a fourth embodiment of the present invention. [ Fig. 8] Fig. Figure 8 is a perspective view of a millimeter wave band communication device according to a fifth embodiment of the present invention. [ Fig. 9] Fig. Figure 9 is a cross-sectional view of a millimeter wave band communication device according to a sixth embodiment of the present invention. Description of embodiments

[0011] The following sections describe embodiments in detail with reference to the drawings. However, the present invention is not limited to the embodiments described below. It will be understood by those skilled in the art that specific configurations can be modified without deviating from the essence of the present invention.

[0012] In the configurations of the invention described below, the same reference numerals are generally used for identical parts or parts with comparable functions, and their repeated description is omitted.

[0013] The positions, sizes, shapes, areas, and the like of the respective components shown in the drawings, etc., do not always represent the actual positions, sizes, shapes, and areas, in order to facilitate understanding of the invention. Therefore, the present invention is not necessarily limited to the positions, sizes, shapes, areas, and the like disclosed in the drawings, etc.

[0014] In the embodiments described below, instead of a metallic or metal-coated cover, a cover mixed with a dielectric loss material (material with dielectric loss) is used to suppress the transmission of electromagnetic waves. Mixing with the dielectric loss material adjusts the radio wave reflectance of the cover to 90% or less. If the radio wave reflectance depends primarily on the surface properties of the cover, the surface resistance of the cover is increased such that the radio wave reflectance on the cover surface is at least 90% or less, without corresponding to total metallic reflection. It is possible to introduce a loss in reflection by reducing the reflectance of the cover, thereby making it possible to achieve a radio wave attenuation effect through multiple reflections.The damping effect can be calculated by multiplying the reflectance according to the number of reflections.

[0015] If the reflectivity of the cover is reduced, it becomes necessary to increase the cover thickness to mitigate radio wave transmission loss. Increasing the cover thickness leads to an increase in the product's volume and weight, thus increasing manufacturing costs; therefore, a thin cover is desirable. For this reason, the radio wave reflectivity of the cover is preferably 50% or higher.

[0016] Graphite powder, for example, is used as the dielectric loss material, and its shape is not particularly restricted; rather, a flaky, spherical, elliptical, needle-shaped, strand-like or amorphous powder, or a mixed powder with the above shapes, can be used, and its average particle size is set, for example, to 200 µm or smaller.

[0017] The mixing ratio of the dielectric loss material blended in the cover is adjusted to achieve a desired radio wave reflectance. To reduce the radio wave reflectance of the cover to 90% or less, the mixing ratio of the dielectric loss material is adjusted to between 20% and 80%, for example, across the entire cover or as an average mass ratio, and the volume resistivity is set to 20 Ω·cm or higher for the entire cover or an average. Increasing the mixing ratio of the dielectric loss material and decreasing the volume resistivity decreases the radio wave transmittance and increases the reflectance.

[0018] When the composition of the cover is standardized, the radio wave reflectance on the cover surface is set to, for example, 90% or less, and the mixing ratio of the dielectric loss material on the cover surface is set to, for example, 20% to 80%.

[0019] With regard to radio waves generated in or entering the cover, an inner surface of the cover and the printed circuit board are configured to be close together in order to attenuate radio waves through multiple reflections between the cover and the printed circuit board.

[0020] For example, if a millimeter-wave band radio frequency (MMRF) circuit configured to use a semiconductor chip is mounted on a printed circuit board (PCB) surface, the height of any outer form of the cover configured to enclose the MMRF circuit must be greater than or equal to the height of the MMRF circuit. If the cover is an integrally formed solid material, it can be brought close enough to the PCB to be in tight contact by providing a concave portion (cavity) in the cover that corresponds to a convex portion of the MMRF circuit, and the MMRF circuit being enclosed and covered by this concave portion.

[0021] On the other hand, it is desirable to provide a groove such that the cover does not come too close to a radio wave transmission line, since a millimeter wave signal is attenuated simply by bringing the cover, which is mixed with the dielectric loss material, close to the transmission line. The deepest part of the groove is preferably set to more than four times the thickness of a dielectric material from which the line formed on the printed circuit board consists, and the width of the groove is preferably set to be less than or equal to a spatial wavelength λ of a usage frequency.

[0022] The concave section or groove described above can be produced easily and cost-effectively by integrally forming the cover from a resin or the like mixed with the dielectric loss material.

[0023] A metal layer that reflects radio waves for coverage is formed on the circuit board, and part of it can be used as ground (GND) for a millimeter wave band radio frequency circuit. First embodiment<1. Overall structure of the millimeter wave band communication device>

[0024] Fig. Figure 1 is a perspective view of a millimeter-wave band communication device according to a first embodiment of the present invention. Here, 1 represents a cover, 2 represents a printed circuit board, 3 represents a radio frequency line, 4 represents a millimeter-wave band radio frequency circuit (active element), 5 represents a concave section of the cover, 6 represents a passive element, 7 represents an inner layer conductor, 8 represents a groove structure of the cover, and 9 represents an antenna. A millimeter wave generated by the millimeter-wave band radio frequency circuit 4, for example, has a wavelength of approximately 4 mm at 76 GHz.

[0025] The high-frequency line 3 and the antenna 9 are formed on the surface of the printed circuit board 2, and the inner layer conductor 7 is formed in an inner layer of the printed circuit board 2, with a portion of this conductor layer serving as the ground electrode (GND electrode) for the high-frequency line 3. The cover 1 is located on the surface of the printed circuit board 2. The GND electrode is typically configured to provide shielding to prevent the entry of external radio waves from the side of the printed circuit board 2. The shielding serves to reflect radio waves from both sides (front and back) of the printed circuit board 2. The high-frequency line 3 connects the millimeter-wave band radio frequency circuit 4 to the antenna 9. With this configuration, millimeter waves generated by the millimeter-wave band radio frequency circuit 4 are radiated by the antenna 9. <2. Cover Structure>

[0026] The cover 1 consists of a material in which a resin is mixed with a dielectric loss material such as graphite. The cover 1 can be easily produced, for example, by mixing a thermoplastic resin with the dielectric loss material and injection molding the mixture. The graphite can be scaly, spherical, elliptical, needle-shaped, or strand-like. Additionally, it can be amorphous or a mixed powder containing the above forms. Although uniform properties can be achieved with a fine dielectric loss material, the average particle diameter of the dielectric loss material is set to 200 µm or less in the present embodiment for the sake of simplicity of production.In the present embodiment, the mixing ratio of the dielectric loss material mixed in the cover is uniformly distributed with a mass ratio between 20% and 80%, and a surface resistance is set to 20 Ω or higher.

[0027] When injection molding is carried out with a graphite mixing ratio exceeding 80%, the specific on-resistance is 10 Ω·cm or less, and while the radio wave shielding effect of the cover increases, the surface resistance also decreases proportionally to the specific on-resistance, resulting in a reflectance on the cover surface close to 1 and essentially total reflection of radio waves.

[0028] While a cover close to total internal reflection is preferable for shielding radio waves outside the cover 1, it hardly eliminates room resonance, since virtually no radio wave is attenuated when reflected within the cover 1 (one side on which the millimeter-wave band radio frequency circuit 4 is located). Therefore, in the present embodiment, attenuation when the radio wave is reflected within the cover is increased by adjusting the mixing ratio of the cover's dielectric loss material to 80% or less, intentionally reducing the reflectance on the cover surface to 90% or less. Furthermore, room resonance is eliminated by multiple reflection attenuation caused by the multiple reflections of radio waves.

[0029] For multiple reflection attenuation, it is advantageous to reduce the distance between radio wave-reflecting surfaces surrounding the millimeter-wave band radio frequency circuit 4. In the example shown in Fig. As shown in Figure 1, the cover 1 has a thickness T in a direction perpendicular to the printed circuit board 2, and a concave section 5 is provided to cover a high-frequency circuit element such as the millimeter-wave band high-frequency circuit 4.

[0030] A distance D between the top of the concave section 5 of the cover 1 (a surface of the cover 1 facing the printed circuit board 2) and the printed circuit board 2 is configured for multiple reflection attenuation to be less than the thickness T, and the number of reflections is increased by increasing the distance D between the top, which is a reflective surface, and the substrate. If the cover 1 has a bulk shape of an essentially rectangular parallelepiped, as in Fig. As shown in Figure 1, the length and width of the cover 1 are approximately 3 to 5 cm as exemplary dimensions. Furthermore, the thickness T of the cover 1 is approximately 2 mm, and the distance D is greater than the height H of the millimeter-wave band high-frequency circuit 4 and less than the thickness T.

[0031] It is desirable to use a resin or ceramic mixed with graphite as a binder (base material) in the cover, and to use an insulating material so that the specific thermal resistance of the cover can be modified with the graphite. Various known materials, such as a phenolic resin, can be used for the resin serving as the binder of cover 1, and the manufacturing process is not limited to injection molding.

[0032] Regarding the dielectric loss material in the cover 1, achieving a reflectance of 90% or less does not necessarily require a uniform concentration. For example, the concentration of the dielectric loss material may decrease towards the circuit board 2, or it may have a higher concentration in a center of thickness and a lower concentration in a section closer to the surface. It is also possible to achieve high reflection of radio waves outside the cover and low reflection of radio waves inside the cover by providing an appropriate distribution of the dielectric loss material concentration. Furthermore, it is also possible to shield radio waves inside the cover while minimizing reflection of radio waves on the surface of the cover. <3. Structure of the concave section of the cover (cavity) >

[0033] As described above, cover 1 of the in Fig. The cover 1 of the millimeter-wave band communication device shown in Figure 1 is essentially a solid material (base material, bulk material) and has a rectangular parallelepiped shape with a predetermined thickness T in the vertical direction of the printed circuit board 2. As described above, the cover 1 is provided with the concave cover section (cavity) 5, which is configured to accommodate the millimeter-wave band radio frequency circuit 4 and the passive element 6. Due to the millimeter-wave band radio frequency circuit 4 and the passive element 6 being mounted on the printed circuit board 2, the surface of the printed circuit board 2 is uneven, and the distance between the inner surface of the cover 1 and the printed circuit board 2 is reduced by arranging the convex section of the millimeter-wave band radio frequency circuit 4 within the concave section on the cover 1, thus facilitating multiple reflections.Furthermore, the cover 1 and the circuit board 2 are in close contact with each other to prevent radio waves from entering the cavity from the outside. Since the cover 1 is integrally shaped as described above, an outer surface and a back surface (a face of the concave cover section 5) of the cover 1 are continuous surfaces. <4. High-frequency transmission line and slot structure>

[0034] A millimeter wave signal generated by the millimeter-wave band radio frequency circuit 4 is guided to the antenna 9 via the radio frequency line 3. It is desirable to provide a groove 8 such that the cover 1 is not too close to the radio frequency line 3, since a millimeter wave signal is attenuated simply by bringing the cover 1, which contains dielectric loss material, into close proximity with the radio frequency line 3. On the other hand, it is desirable to design the structure so that external radio waves cannot enter the cavity 5 via the groove 8, or that unwanted radio waves cannot escape via the groove 8.For this purpose, the deepest part of the groove 8 is preferably set to more than four times the thickness of a dielectric from which the high-frequency line 3 formed on the circuit board 2 is formed, and a width of the groove 8 is preferably set such that it is less than or equal to a spatial wavelength λ of a usage frequency.

[0035] Fig. Figure 2 is a schematic view representing the groove structure 8 provided in the cover 1 mixed with the dielectric loss material. A cross-section of the groove structure 8 has a rectangular shape. In the present embodiment, the groove depth is set to four times or more the thickness of the dielectric section of the high-frequency conductor provided on the printed circuit board 2, and the groove width is set to less than or equal to a wavelength of the operating frequency. Although the groove is rectangular in the present invention, it can also be configured with a circular arc cross-section, a shape obtained by cutting a portion of an ellipse, triangular, polygonal, with a free-form surface or cross-section, or by a complex combination of these shapes.

[0036] Fig. Figure 3 shows the result of an analysis of the radio wave transmittance of the groove structure using an electromagnetic field simulator HFSS (a tool for the design of high-frequency devices offered by Ansoft, Inc. of the USA as software for the numerical calculation of electromagnetic fields). The horizontal axis represents the width of the groove structure 8, and the vertical axis represents a radio wave attenuation value when the radio waves are introduced from the front and back of the groove structure 8.

[0037] A cover was provided on a 130 µm dielectric resin, corresponding to printed circuit board 2, and radio waves were introduced from the front and back of the groove. A radio wave frequency of 76 GHz (wavelength λ ≈ 3.89 mm) was assumed. The groove structure had a rectangular cross-section, a depth of 0.8 mm (more than four times the dielectric thickness of 130 µm), and a width of 3.0 mm (from 0.6 mm to 8 mm). The groove length was 8 mm. An aluminum alloy (metal cover) and a resin (graphite cover) containing 50 wt% graphite were compared as materials for forming the groove in the cover. The covering containing 50% graphite by mass corresponds to one with a specific on-resistance of approximately 1M Ω·cm, a reflectance of 0.89, a relative dielectric constant of 21, and an electrical loss of 0.34 as electrical properties.Measurement results obtained through a transmission line method of the Keysight 85071E material measurement software (trade name) were used.

[0038] When aluminum is used for the cover, radio waves are easily transmitted through the groove structure, and the transmission loss reaches a maximum of -44 dB at a width corresponding to the cutoff frequency in the waveguide, = 1.8 mm (λ / 2 accordingly). The cutoff frequency of the metal waveguide is, incidentally, c / (a waveguide width*2), as is generally known (where c is the speed of light). In the case of the metal cover, a radio wave also occurs, which is transmitted not only in the groove structure 8 but also in the 130 µm resin that forms the circuit board 2. If a ground conductor of the circuit board 2 and the metal cover are not connected without a gap, a radio wave leak occurs.

[0039] Regarding the metal cover, the graphite-mixed metal inside the groove structure and between the cover and the circuit board is subject to multiple reflection attenuation, and the signal is attenuated by -20 dB at a width of 2.8 mm, by -60 dB at a width of 1.8 mm, and by -90 dB at a width of 1.5 mm or less. These results indicate that the spatial propagation of radio waves is significantly suppressed by multiple reflection attenuation when the groove width of the cover is less than or equal to a wavelength, and that the transmission level of the cover is attenuated by -90 dB or less in the case of the graphite-mixed cover.

[0040] Fig. 4 represents a result of the analysis of the influence of the slot structure width on the microstrip line, which was obtained by using the high-frequency line 3 (in the data from Fig. 4 the microstrip line was used) on circuit board 2 in the in Fig. The groove structure 8 shown in Figure 2 is provided for. For the high-frequency line 3, a coplanar line, a grounded coplanar line, or a differential line can be used in addition to a microstrip line. With a groove width of less than 3.0 mm, an influence of the cover groove structure near the microstrip line can be detected. Although the transmission loss of the microstrip line increases under the influence of the dielectric loss material, the increased amount of transmission loss is only 0.7 dB at a groove width of 1.5 mm. Therefore, the influence of the transmission loss can be essentially neglected when the groove width is 1.5 mm or more.

[0041] When a signal with a frequency below microwave is connected to the millimeter-waveband high-frequency circuit 4 and the passive element 6, a conductor layer located in an inner layer of the printed circuit board (PCB) is used as a conductor to connect an outer layer conductor of the PCB 2 to an inner layer conductor via a via through a ground (GND) layer of the PCB 2. As the GND layer is traversed by the via, a conductor ablation structure of less than half the size of a wavelength λ of the operating frequency is provided in the GND layer.

[0042] Since the concave section 5 and the groove structure 8 are provided in the cover 1, which is mixed with the dielectric loss material, and which is mounted on the circuit board 2 in the millimeter-wave band communication device of the present invention, as shown in Fig. As shown in Figure 1, it is possible to suppress the irradiation of the millimeter-wave radio frequency circuit 4 by an antenna sidelobe, to suppress leakage radio waves emitted by the millimeter-wave radio frequency circuit 4 itself, to suppress room resonance in the concave section of the cover in which the millimeter-wave radio frequency circuit 4 is housed, and to suppress crosstalk from the millimeter-wave radio frequency circuit 4 to the passive element 6, etc., while simultaneously suppressing the penetration of unwanted radio waves from outside into the millimeter-wave radio frequency circuit 4, thereby reducing unwanted radio waves that cause malfunctions. Therefore, the millimeter-wave communication device 10 enables communication by utilizing high-performance receiver sensitivity and highly sensitive sampling, while drastically reducing the occurrence of unwanted interference or the like.

[0043] In the millimeter-wave band communication device of the present invention, which is in Fig. As shown in Figure 1, the concave cover section 5 and the groove structure 8 are provided as a means of reducing the distance between the cover surface and the printed circuit board (PCB) in order to effectively achieve multiple reflection attenuation through the cover 1 and the PCB 2. In practice, however, a resin cover with a flat inner surface and no concave section 5 or groove structure 8 can also be used, provided the cover is small and exhibits low radio wave attenuation, since multiple reflection attenuation can always be achieved with the dielectric loss material.

[0044] Since the cover of the present invention is not a radio wave shield that uses metallic radiation (total internal reflection), but rather radio waves are attenuated by moderate multiple reflection attenuation between the cover and the printed circuit board, it is not necessary to connect the cover to the ground (GND) of the printed circuit board. Therefore, there is no need to close a gap to the printed circuit board, to braze, to apply a conductive adhesive, etc., as is the case when mounting a metal cover, and the cover can be attached using simple means such as screws, pins, fittings, clamps, and insulating adhesive. If the cover is manufactured using a molding technique, significant cost savings are achieved with regard to both the manufacturing and assembly costs of the cover. Second embodiment

[0045] Fig. Figure 5 is a perspective view of a millimeter-wave band communication device according to a second embodiment of the present invention. Here, 1 represents a cover, 2 represents a printed circuit board, 3 represents a microstrip line, 4 represents a millimeter-wave band radio frequency circuit, 5 represents a concave section of the cover, 6 represents a passive element, 7 represents an inner layer conductor, 8-2 represents a slot structure provided with a choke structure, and 9 represents an antenna.

[0046] The differences from the first embodiment are described below. The groove structure 8-2 is a groove structure provided in the cover 1, which is mixed with 20% or more of a dielectric loss material. If the width of the groove is narrowed to suppress radio wave propagation, a side effect is an increase in microstrip line loss, as shown in Fig. 3 and Fig. Figure 4 shows that in this example, a choke structure is arranged in a slot structure to locally narrow the cross-sectional area, although the width of the slot structure is less than or equal to a wavelength λ of a usage frequency, in order to enhance a radio wave attenuation effect in the slot structure itself while simultaneously reducing the influence on the microstrip line. Third embodiment

[0047] Fig. Figure 6 is a perspective view of a millimeter-wave band communication device according to a third embodiment of the present invention. Here, 1 represents a cover, 2 represents a printed circuit board, 3 represents a microstrip line, 4 represents a millimeter-wave band radio frequency circuit, 5 represents a concave section of the cover, 6 represents a passive element, 7 represents an inner layer conductor, 8 represents a groove structure of the cover, 9 represents an antenna, and 11 represents a dielectric lens (lens antenna).

[0048] The dielectric lens 11 is connected to the antenna 9 provided on the circuit board 2 to increase the directivity of the antenna 9. The dielectric lens 11 is an insulator and focuses radio waves onto a curved lens surface to narrow the angle. Although neither the cover nor the lens is formed from a single material, since the insulator is made of a different material than the cover, which has favorable radio wave transmittance, it is possible to integrate both the cover and the lens using a dual-mold process or a composite-mold process, in which a variety of materials are formed using a single mold.If only the section of the dielectric lens 11 through which the transmitted radio waves are collected is shaped with the material for the lens antenna, and a circumference of the lens is held and fixed with a material on the cover 1 side, it is possible to eliminate a gap between the cover 1 and the dielectric lens 11 and to cause the radio waves emitted by the antenna 9 to propagate efficiently without leaking out of the lens. Fourth embodiment

[0049] Fig. Figure 7 is a perspective view of a millimeter-wave band communication device according to a fourth embodiment of the present invention. Here, 1 represents a cover, 2 represents a printed circuit board, 3 represents a microstrip line, 4 represents a millimeter-wave band radio frequency circuit, 5 represents a concave section of the cover, 6 represents a passive element, 7 represents an inner layer conductor, 8 represents a groove structure of the cover, 9 represents an antenna, and 12 represents a waveguide horn antenna.

[0050] The horn antenna 12 is connected to the antenna 9 provided on the circuit board 2 to increase the directivity of the antenna 9. The horn antenna 12 can be made with a resin mixed with a dielectric loss material in a high ratio corresponding to that of the cover 1. The horn antenna 12 and the cover 1 can be integrated to simplify holding and mounting the horn antenna, as in the lens antenna of the third embodiment. A resin with a graphite content exceeding 80% by mass, to suppress attenuation caused by multiple reflections on an inner surface of the horn antenna, can be produced by a double-mold process, similar to the lens antenna. Fifth embodiment

[0051] Fig. Figure 8 is a transparent perspective view of a millimeter-wave band communication device according to a fifth embodiment of the present invention. Here, 1 represents a cover, 2 represents a printed circuit board, 3 represents a microstrip line, 4 represents a millimeter-wave band radio frequency circuit, 5 represents a concave section of the cover, 6 represents a passive element, 7 represents an inner layer conductor, 8 represents a groove structure of the cover, 12 represents a horn antenna, 13 represents a gap, 14 represents a slot, and 15 represents a through-hole contact. The microstrip line 3, the gap 13, and the slot 14 are formed on the printed circuit board 2, and the microstrip line 3 uses the inner layer conductor 7 as the ground conductor, while the gap 13 is provided within the inner layer conductor 7 of the ground conductor.

[0052] A millimeter wave signal transmitted by the millimeter wave band radio frequency circuit 4 is propagated via the microstrip line 3, the gap 13, and the slot 14 to the horn antenna 12 on the opposite side of the circuit board 2. When a millimeter wave propagates from the microstrip line 3 to the gap 13, the microstrip line is connected to the gap by a through-hole 15. However, the microstrip line, from which a ground conductor is hollowed out through the through-hole 15 and the gap 13, is inductive and has a structure from which radio waves can easily radiate and escape. The concave section 5 of the cover 1 is provided in a conductor transition between the microstrip line and the gap. The concave section 5 of the cover 1 covers the conductor transition, thereby reducing radiation leakage. Sixth embodiment

[0053] Fig.Figure 9 is a cross-sectional view of a millimeter-wave band communication device according to a sixth embodiment of the present invention. Here, 1 represents a cover, 2 represents a printed circuit board, 3 represents a microstrip line, 5 represents a concave section of the cover, 7 represents an inner layer conductor, 8 represents a groove structure of the cover, 12 represents a horn antenna, 16 represents a waveguide structure mimicking the interior of the printed circuit board, and 17 represents a stub line with a length of λ / 4. The microstrip line 3 is connected to the stub line 17, which is arranged at an upper part of the waveguide structure 16. A groove with a depth of λ / 4 is formed in the concave cover section 5, which is arranged in the waveguide structure 16 and the stub line 17.The concave cover section 5 serves as a λ / 4 backshort of the waveguide, so that the line transition from the microstrip line 3 to the waveguide structure 16 is efficient via the stub line 17.

[0054] As described in detail above, in the first to sixth embodiments, the cover 1, which is mixed with the dielectric loss material in a high mixing ratio, consists of the material that exhibits reflection loss while suppressing radio wave transmission. Since the millimeter-wave band radio frequency circuit 4 provided in the printed circuit board 2 is housed in the concave cover section 5, unwanted radio waves from the outside are suppressed by the radio wave transmission of the cover 1. The unwanted radio waves that are reflected and penetrate the gap between the cover 1 and the printed circuit board 2 are attenuated and removed by multiple reflections between the printed circuit board 2 and the cover 1.The insulation between the concave cover sections 5, which cover the millimeter wave band radio frequency circuit 4, is the radio wave transmittance of the cover 1 itself, and the radio waves radiated and escaped from the millimeter wave band radio frequency circuit 4 itself are attenuated and removed by multiple reflections due to the internal reflection of the concave cover section 5.

[0055] Signal transmission to antenna 9 and to the outside is carried out via a conductor provided in the groove 8 of the cover 1. Although radio wave propagation is possible directly through the groove structure of the cover 1, it is possible to suppress radio wave propagation by increasing the multiple reflection attenuation in the groove space by limiting the width of the groove 8 to λ or less, and it is possible to obtain sufficient isolation between the circuits.

[0056] Furthermore, the balance between transmittance and reflection is adjusted by selecting the mixing ratio of the dielectric loss material in the resin, and transmittance is controlled by increasing or decreasing the thickness of the cover. It is not necessary to electrically connect the cover to the ground (GND) of the circuit board, as the electromagnetic wave is suppressed by the multiple reflection attenuation between the cover and the circuit board, which differs from the shielding effect of a metal cover. Therefore, it is sufficient for the cover 1 to be physically in contact with the circuit board 2, and the cover 1 can be easily mounted by screwing, pinning, or using an insulating adhesive or similar method, resulting in extremely low assembly costs compared to a metal cover.

[0057] The present invention is not limited to the embodiments described above and includes various modifications. For example, some configurations of a particular embodiment can be replaced by configurations of another embodiment, and a configuration of another embodiment can be added to the configuration of a particular embodiment. Furthermore, with respect to some configurations of each embodiment, configurations of the respective embodiments can be added, deleted, or replaced. Industrial applicability

[0058] The present invention is applicable to a communication device and a sensor that use a millimeter wave as an electromagnetic wave. List of reference symbols 1 cover 2 circuit boards 3 High-frequency line (microstrip line) 4 millimeter wave band high-frequency circuit 5 concave section of the cover 6 passive element 7 inner layer conductors 8 groove structure 8-2 Groove structure with throttle structure 9 Antenna 1 millimeter wave band communication device 11 dielectric lens 12 Horn antenna 13 gaps 14 slots 15 through-contacts 16 Waveguide structure 17 branch lines

Claims

[1] Millimeter-wave band communication device, comprising: a substrate (2); a high-frequency circuit element (4) provided on the substrate (2) for a millimeter wave band; and a cover (1) made of a solid material, covering at least part of the high-frequency circuit element (4) and a surface of the substrate (2), wherein the cover (1) is formed by mixing a material with dielectric loss into a base material, characterized by a high-frequency line (3) provided on the substrate surface and connected to the high-frequency circuit element (4) and at its opposite end to an antenna (9); and a groove structure (8) which is formed in the cover (1) in such a way as to prevent contact between the radio frequency line (3) and the cover (1), and whose width at a cross-section which intersects with a radio wave propagation direction of the radio frequency line (3) is less than or equal to a wavelength λ of a millimeter wave operating frequency of the millimeter wave band communication device. [2] Millimeter wave band communication device according to claim 1, wherein the material with dielectric loss is graphite. [3] Millimeter wave band communication device according to claim 1, wherein the radio wave reflection coefficient of the cover (1) is set to 90% or less. [4] Millimeter wave band communication device according to claim 1, wherein the radio wave reflection coefficient of the cover (1) is set to between 50% and 90%. [5] Millimeter wave band communication device according to claim 1, wherein the cover (1) is integrally formed with a resin as the base material. [6] Millimeter wave band communication device according to claim 1, wherein the mixing ratio of the material with dielectric loss mixed with the cover (1) is between 20% and 80% over the entire cover or in an average mass ratio. [7] Millimeter wave band communication device according to claim 1, wherein the cover (1) has a specific on-resistance of 20 Ω·cm or higher. [8] Millimeter wave band communication device according to claim 1, wherein the concentration of the material with dielectric loss is lower on a side of the cover (1) opposite the substrate (2). [9] Millimeter wave band communication device according to claim 1, wherein the concentration of the material with dielectric loss is higher on one side of the cover (1) which is closer to a thickness center. [10] Millimeter-wave band communication device according to claim 1, wherein the cover (1) is a rectangular parallelepiped, has a thickness T in a direction perpendicular to the substrate (2) and has a concave section (5) covering the high-frequency circuit element (4), and a distance D between a ceiling of the concave section (5) of the cover (1) and the substrate (2) is less than the thickness T and greater than a height H of the high-frequency circuit element. [11] Millimeter wave band communication device according to claim 1, further comprising: a dielectric lens (11) consisting of an insulator, wherein the cover (1) and the dielectric lens (11) are formed integrally. [12] Millimeter wave band communication device according to claim 1, wherein a horn antenna (12) is configured by mixing a resin with a material having dielectric loss, wherein the cover (1) and the horn antenna (12) are configured integrally. [13] Millimeter wave band communication device according to claim 10, wherein the concave section (5) of the cover (1) is adjusted to have a depth of λ / 4 to act as a backshort of a line transition of the high frequency line (3).

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