JP2007124201A - Antenna module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna module capable of suppressing radiation spurious electromagnetic waves caused by a surface wave, thereby reducing distortion in a radiation pattern. <P>SOLUTION: The antenna module is characterized in such that radiation elements (patches 12) are provided to the surface or the inside of an insulation board 11 and an antenna board 1 wherein the surface of surrounding parts of the insulation board 11 is tilted to the rear side toward ends is mounted on a module board 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an antenna module including an antenna substrate that transmits and receives a millimeter-wave band high-frequency signal of 30 GHz or more and a high-frequency circuit that processes the high-frequency signal.

  Microwaves have been used by the general public as carrier waves for wireless devices as represented by mobile phones, but now they are used not only for mobile phones but also as a means of high-capacity data communication such as wireless LAN and Wireless USB. Research and development is underway. However, at present, wireless communication using microwaves has a problem that information transmission speed is slow and large-capacity data such as video and moving images cannot be transmitted. Also, in the future, in the microwave region, the frequency region assigned for communication is narrow, or even if the assigned frequency region is wide like UWB, the transmission power is limited, limiting the possibility of future large-capacity communication. It has been. Therefore, the millimeter wave region of 30 GHz or higher, which is a higher frequency band, has been attracting attention for ultrahigh-speed wireless communication, and research and development have been promoted. In particular, the 60 GHz band has a wide bandwidth all over the world, and is currently put into practical use as a high-capacity high-speed communication means, and is becoming widespread as a communication application between offices replacing optical fibers.

  On the other hand, outside the telecommunications industry, the 77 GHz band has been globally approved as a frequency for inter-vehicle radar, and research and development of radar has been actively promoted so far, and it has been installed in general passenger cars mainly in Europe, and is spreading to the world. is there. Millimeter waves are also being used for military applications and sanitary communication applications, and the millimeter wave market is expected to expand further in the future.

  Here, an antenna is necessary for radio communication or radar to radiate or receive a signal in space. Conventionally, a horn antenna that stably provides excellent characteristics has been used for millimeter wave applications. . Further, when a higher gain is required, a parabolic antenna or a Cassegrain antenna using a horn antenna as a primary radiator has been used.

  However, although the horn antenna has a small loss and a wide band and is excellent in characteristics, there is a problem in making a compact transceiver module having a large volume. Moreover, the horn antenna obtained by metal processing has a difficulty in mass productivity.

  In order to solve these problems, planar antennas such as patch antennas and slot antennas have been used. These antennas can be configured by forming a conductor pattern on a dielectric substrate, and have the advantages of small volume and excellent mass productivity because they do not require special metal processing.

  However, surface waves (electromagnetic waves propagating on the dielectric surface) are generated on the antenna substrate of these planar antennas, and the surface waves propagate to the end of the antenna substrate and are generated from the antenna substrate end by unnecessary electromagnetic waves (caused by surface waves). Unnecessary electromagnetic waves) are radiated, and the radiation pattern radiated from the antenna is distorted. In addition, unnecessary electromagnetic waves caused by surface waves are radiated to a surrounding circuit board or another antenna board, where there is a problem that interference occurs or a semiconductor element malfunctions.

  On the other hand, Non-Patent Document 1 proposes a method for suppressing radiation of unnecessary electromagnetic waves from the antenna substrate. Here, a configuration has been proposed in which a photonic band gap structure designed to suppress the propagation of surface waves is formed in the ground layer, which suppresses the radiation of unwanted electromagnetic waves caused by the surface waves and reduces the antenna radiation pattern. It has been reported that distortion is suppressed and a uniform antenna radiation pattern is obtained. However, in this method, it is necessary to perform an electromagnetic field simulation with a large model shape including a fine and complex photonic bandgap structure to optimize the structure and find a photonic bandgap structure in which surface waves do not propagate. It was cumbersome, time consuming and not useful. Also, from the viewpoint of manufacturing, it is necessary to form a large number of hexagonal metal patterns coupled to the ground with via conductors, which makes the structure complicated and difficult to put into practical use.

  Further, Patent Document 1 proposes a method in which a shield material using a photonic band gap structure is provided between a conductor plate that distorts an antenna radiation pattern and an antenna, and scattering of unnecessary electromagnetic waves by the conductor plate is proposed. However, this method requires a shield member in addition to the antenna substrate, increases the number of parts and the installation process, greatly increases the size of the system, and increases the manufacturing cost.

Further, Patent Document 2 proposes a method of suppressing the generation of surface waves by changing the height of each element of the array antenna. However, in order to form radiating elements having different heights, unevenness of the antenna substrate is required. In addition, it is a difficult structure for mass production uniformly from the viewpoint of manufacturing, and cannot be practically used.
IEEE Transactions on Microwave Theory and Techniques Vol.47 No11, 1999 pp2059 JP 2004-140560 A JP-A-4-227302

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an antenna module that suppresses the radiation of unnecessary electromagnetic waves caused by surface waves and thereby reduces the distortion of the radiation pattern.

  According to the present invention, a radiation element is provided on the surface or inside of an insulating substrate, and an antenna substrate in which the surface of the peripheral portion of the insulating substrate is inclined toward the back side toward the end is mounted on the module substrate. It is an antenna module characterized by this.

  Radiation of unwanted electromagnetic waves from the end of the antenna substrate due to surface waves (electromagnetic waves propagating on the dielectric surface) has the most adverse effect on the antenna radiation pattern and causes distortion. Can be reduced. This is because the surface wave propagated from the radiating element toward the end of the antenna substrate is reflected by the inclined portion (warp) and attenuates while propagating through the antenna substrate. In addition, this reflection originates in the inclination part (warping) causing the discontinuity of the impedance of the surface wave propagation in the antenna substrate. In addition, even if unwanted electromagnetic waves are radiated from the end of the antenna board, the inclined part (warp) is shaped toward the module board, so the horizontal direction (the antenna board is arranged in parallel to the surface of the module board) The horizontal direction of the antenna board is the direction from the direction parallel to the surface of the module board) to the upward direction (the direction perpendicular to the surface of the module board), and the radiation to the module board side. This is because adverse effects are reduced.

  In the antenna module, a semiconductor element is mounted on the back surface of the insulating substrate, and the semiconductor element and the radiating element are connected.

  This not only suppresses radiation of unwanted electromagnetic waves caused by surface waves from the horizontal direction (direction parallel to the surface of the module substrate) to the upper direction (direction perpendicular to the surface of the module substrate), but also allows the semiconductor element to emit radiation. It is possible to convert the signal transmitted / received from the antenna to a low frequency and transmit it to the module circuit board, and to make the frequency of the unwanted electromagnetic wave radiated from the end of the antenna board different from the frequency in the electric circuit on the module board. it can. As a result, it is possible to suppress adverse effects such as interference with a semiconductor element mounted in the vicinity of the antenna substrate.

  ADVANTAGE OF THE INVENTION According to this invention, the antenna module which suppressed the radiation | emission of the unnecessary electromagnetic wave from the antenna substrate edge part resulting from a surface wave, and reduced the distortion of the antenna radiation pattern by it can be obtained. In particular, when a patch antenna is used as a radiating element, surface waves are likely to be generated, and the present invention that suppresses radiation of unnecessary electromagnetic waves caused by surface waves becomes more effective. In addition, the present invention is effective because a radiation pattern with less distortion of the primary radiation antenna is important even in a structure in which a dielectric lens is disposed so as to cover the radiation element.

FIG. 1 illustrates an antenna module according to an embodiment of the present invention.
The antenna module of the present invention includes an antenna substrate 1 in which a radiating element (patch 12) is provided on the surface or inside of an insulating substrate 11, and the surface of the peripheral portion of the insulating substrate 11 is inclined toward the back surface toward the end. It is mounted on the module substrate 2.

  The material of the insulating substrate 11 constituting the antenna substrate 1 is preferably ceramics in consideration of its reliability when a highly accurate laminated structure or high-density multilayer wiring is required or when a semiconductor element described later is accommodated. On the other hand, an organic material is preferable in view of cost. Examples of ceramics generally include ceramics mainly composed of alumina, aluminum nitride, magnesia, etc., and low-temperature fired ceramics. Especially at high frequencies, loss in transmission lines is large, and it is required to reduce the resistance of the conductor layer in order to suppress the loss. Therefore, low-temperature fired ceramics and organic multilayer substrates that can use copper or silver as the conductor layer are used. preferable. Of these, low-temperature fired ceramics with low dielectric loss and polytetrafluoroethylene organic substrates are preferred.

  Similarly to the insulating substrate 11, the material of the module substrate 2 can be ceramics mainly composed of alumina, aluminum nitride, magnesia, low-temperature fired ceramics, organic multilayer substrates, or the like. In consideration of the manufacturing cost, inexpensive organic substrates such as FR-4 and FR-5 are preferable, and when pursuing high reliability, these are the same in order to match the thermal expansion coefficients of the insulating substrate 11 and the module substrate 2. It is preferable to use a material.

  As the radiating element, a structure in which a patch conductor 12 is provided on the surface of the insulating substrate 11 is shown, and a plurality of patch conductors 12 are provided in the drawing. Although the patch conductor 12 shown in the figure is provided on the surface of the antenna substrate 1, it may have a structure (structure provided inside) where the surface of the patch conductor 12 is covered with a dielectric layer and not exposed, for example. In addition to the patch antenna, a structure such as a slot antenna or a dielectric resonator antenna may be used. However, patch antennas are easier to design and feed structures are simpler than slot antennas and dielectric resonator antennas. If there are patch conductors on the surface layer, antenna characteristics can be predicted by measuring their dimensions. A patch antenna is preferable because it enables easy product selection. In addition, since the generation of surface waves is remarkable in the patch antenna as compared with the slot antenna and the dielectric resonator antenna, the effect of the present invention is great.

  In the drawing, the power supply line to the radiating element (patch conductor 12) is omitted, but a slot, stripline, coaxial, or the like can be used, and the power supply method is not particularly limited. Further, the number of radiating elements is not particularly limited.

  The antenna substrate 1 has a structure in which the surface of the peripheral portion of the insulating substrate is inclined toward the back surface toward the end portion.

  Specifically, an arc shape as shown in FIG. 2, a shape having a flat portion and an inclined portion as shown in FIG. 3, or a shape where the central portion of the antenna substrate 1 is recessed as shown in FIG. 4. Although not shown in the drawings, a shape in which the thickness gradually decreases toward the end portion can be mentioned, but considering the manufacturing surface, a structure having a substantially constant thickness is preferable as shown in FIGS.

  Note that the peripheral portion refers to a region indicated by a distance a in FIGS.

  Here, in FIG. 2, the patch conductor 12 as a radiating element is formed on the surface of the insulating substrate 11, but the patch conductor 12 that is closest to the end portion of the insulating substrate 11 is high in the central portion. And b / a is 0.5% (for example, 25 μm / 5 mm) where b is the difference between the height of the surface end of the insulating substrate 11 and b and the distance from the patch conductor 12 to the surface end of the insulating substrate 11 is a. ) Or more. However, when a is equal to or longer than the wavelength λ in the air of the signal transmitted and received from the antenna substrate 1, a = λ. The length b is preferably 0.2 mm or less. If the ratio b / a is increased and the length b is greater than 0.2 mm, there is a risk of substrate destruction during mounting if the insulating substrate 11 is a ceramic substrate, and surface mounting if the insulating substrate 11 is an organic substrate. This is because there is a risk that defects such as inability to join the solder of the solder may occur.

  As described above, the surface of the peripheral portion of the insulating substrate 11 is inclined toward the back surface toward the end portion, thereby suppressing emission of unnecessary electromagnetic waves due to surface waves propagating through the antenna substrate 1, particularly Horizontal direction (antenna substrate 1 is arranged in parallel with the surface of module substrate 2, antenna substrate 1 horizontal direction is a direction parallel to the surface of module substrate 2) upward direction (a direction perpendicular to the surface of module substrate 2) ) Can be suppressed and distortion of the antenna radiation pattern can be reduced. This is because the surface wave is reflected by the inclined portion (warp) and attenuates while propagating again through the substrate, and the antenna substrate 1 is inclined to the back surface side so that the surface end of the antenna substrate 1 is lower than the radiation element. Due to the shape, unnecessary electromagnetic waves that have been attenuated but could not be extinguished are emitted to the module substrate side and scattered by the module substrate.

  Note that the structure in which the surface of the peripheral portion of the insulating substrate 11 is inclined toward the back side toward the end is preferably formed over the entire region of the peripheral portion of the insulating substrate 11, but is not limited to the entire region. You may form only in the area | region which wants to suppress the radiation | emission of a surface wave.

Below, the formation method of the inclination shape (warp shape) shown in FIGS. 2-4 is demonstrated.
For example, when the insulating substrate 11 is a ceramic substrate, an inclined shape can be obtained by firing with a surface on which the radiating element (patch conductor 12) is formed facing down and a spacer at the end of the insulating substrate 11. This is because the ceramic substrate is softened at a high temperature and the central portion of the antenna substrate is lowered due to gravity.

  Further, the shrinkage rate of the metallization formed on the ceramic substrate is controlled by changing the metallization composition, and the metallization that is difficult to shrink is formed on the side of the plurality of dielectric layers on which the radiation element (patch conductor 12) is formed. Thus, an inclined shape can be obtained. Here, the metallization is not necessarily formed on the surface on which the radiating element (patch conductor 12) is formed, and may be formed on the inner layer closer to the radiating element side from the thickness center of the ceramic substrate. Further, a metallization that easily contracts from the thickness center of the ceramic substrate to the inner layer on the opposite side of the radiating element may be formed. Examples of methods for controlling the shrinkage rate of metallization include changing the particle size of the conductor powder, changing the amount of organic components in the metallized paste, adding glass powder and ceramic powder in addition to the conductor powder, and changing the particle size thereof. .

  In addition, the shrinkage rate during firing of the dielectric layer may be controlled, and the dielectric layer on the radiating element side may be configured to be difficult to contract, and a dielectric layer that is easily contracted to the side opposite to the radiating element (patch conductor 12) It may be arranged. The change in the shrinkage rate of the dielectric layer includes methods such as changing the particle size of the powder, changing the amount of organic components, and changing the crystallization temperature by changing the composition, in the same way as controlling the shrinkage rate of metallization.

  Alternatively, the antenna substrate 1 may be pre-processed into a shape corresponding to FIGS.

  On the other hand, when the insulating substrate 11 is an organic substrate, there are a method using a dielectric layer having a different shrinkage ratio at the time of thermosetting, a press working, a method of bonding to a substrate having a desired inclined shape (warped shape), and the like.

  The antenna substrate 1 formed in this manner is mounted on the module substrate 2 having a circuit pattern formed on the surface, thereby forming an antenna module.

  FIG. 1 shows a configuration in which an antenna substrate 1 is mounted on a module substrate 2 with solder balls 3. Other mounting methods include gold ribbon, gold wire bonding, LGA type, PGA type using pins, etc., but solder mounting with low cost and excellent characteristic stability is preferable. As described above, the power supply line to the radiating element (patch conductor 12) is omitted in the figure, but the power supply method is not particularly limited.

  FIG. 5 shows an antenna module obtained by adding a semiconductor element to the antenna module described above. That is, an antenna module having a structure in which a semiconductor element 4 is mounted on the back surface of an insulating substrate 11 constituting the antenna substrate 1 and the semiconductor element 4 and a radiation element (patch conductor 12) provided on the surface are connected. It has become. The mounting portion of the semiconductor element 4 has a recessed shape and a cavity is formed. The cavity is covered with a sealing cap 5 and is protected from moisture and dust. As a form of this sealing, the shape provided with cavities as described above may be used, or resin sealing may be used.

  Such a structure not only suppresses radiation of unwanted electromagnetic waves caused by surface waves from the horizontal direction (direction parallel to the surface of the module substrate) to the upward direction (direction perpendicular to the surface of the module substrate), but also a semiconductor element. The signal transmitted and received from the radiating element can be converted to a low frequency and transmitted to the module circuit board, and the frequency of the unwanted electromagnetic wave radiated from the end of the antenna board is different from the frequency in the electric circuit on the module board. Can be made. As a result, it is possible to suppress adverse effects such as interference with a semiconductor element mounted in the vicinity of the antenna substrate.

  Although not shown, the semiconductor element 4 is connected to the radiating element (patch conductor 12) directly or via another semiconductor element or a device such as a filter. In order to connect the radiating element (patch conductor 12) and the semiconductor element 4, a transmission line such as a microstrip line, a strip line, a via conductor, a coplanar line, a slot line, or a laminated waveguide is generally used. However, the track is not particularly limited. Considering the ease of routing the line, a microstrip line and a strip line are preferable, and a laminated waveguide is preferable from the viewpoint of low transmission loss. Further, instead of via conductors, slots may be used for electromagnetic connection to reduce signal loss.

  Although only one semiconductor element is mounted in FIG. 5, a plurality of semiconductor elements may be mounted as amplifiers, modulators / demodulators, signal processing elements, multipliers, etc., regardless of the number of mounted semiconductor elements. A frequency converter and a local oscillator may be mounted in the antenna substrate so that the frequency of the signal transmitted and received by the antenna is different from the frequency transmitted and received by the antenna substrate and the module substrate. Note that when the signal is directly input to the oscillator and modulated, the frequency converter is not necessary. As the oscillator, various forms such as a case where the local oscillator and the multiplier are separately configured, a case where the local oscillator and the multiplier are formed together, a case where other elements such as a frequency converter are included, and a case where a Gunn diode is used can be adopted.

  Even in a structure in which a dielectric lens is arranged so as to cover the radiating elements, distortion of the primary radiating antenna is suppressed and a uniform radiation pattern can be obtained by the present invention, so that it is not necessary to design a lens in consideration of the distortion. Thus, the design time is shortened, and it is not necessary to design the lens by approximating the radiation pattern of the distorted portion. Further, by suppressing the emission of unnecessary electromagnetic waves, variations in the radiation characteristics due to changes in the surrounding conditions and the emission conditions of unnecessary electromagnetic waves are suppressed, and antenna characteristics with high process capability can be obtained.

  In order to evaluate the antenna characteristics of the antenna module of the present invention, a finite element method simulation was performed.

  The insulating substrate constituting the antenna substrate is a substrate made of polytetrafluoroethylene having a relative dielectric constant of 2.2, and the size is 17 mm wide × 8 mm long. As shown in FIG. 6, a patch conductor 12 and a microstrip line 13 that feeds power are provided on the surface layer of the insulating substrate 11, and a ground layer 15 is provided on the back surface. Further, as shown in FIG. 7 for the coordinate system and FIG. 8 for the overall model configuration diagram, power is supplied to the microstrip line 13 from the WR-12 rectangular waveguide 6 via the slot 14. A module substrate (20 mm × 8 mm) 2 is disposed below the antenna substrate 1, and the upper surface of the module substrate 2 is covered with a conductor (not shown). The rectangular waveguide 6 has an inner diameter of 1.548 mm in the X direction and 3.098 mm in the Y direction, and is disposed through the module substrate 2. And air was provided above the upper surface of the module substrate 2, and the side surface and upper surface of the air were set as radiation boundary conditions. The size of air in the xy direction is the same as that of the module substrate 2. The center of the antenna substrate 1 is a connection portion between the microstrip line 13 and the patch conductor 12. The length of the microstrip line 13 is 2.4 mm, the width is 0.06 mm, the slot 14 is 0.2 mm × 1.4 mm, and the center of the slot 14 in the X direction is 0.8 mm from the end of the microstrip line 13. is there. The antenna substrate 1 has a thickness of 0.5 mm for the upper layer sandwiched between the patch conductor 12 and the slot 14 and 0.4 mm for the lower layer.

  The patch antenna is fed from the rectangular waveguide 6 because a broadband structure can be easily created by simulation. In practice, the module substrate 2 is joined to the antenna substrate 1 by surface mounting or the like, and a signal fed from the joined portion is fed to the antenna via a microstrip line, a slot line, a strip line, or the like. When the semiconductor element 4 is mounted on the antenna substrate 1 and frequency conversion is performed by the semiconductor element 4, a signal transmitted from the module substrate 2 to the antenna substrate 1 is radiated from the radiating element (patch conductor 12). The frequency may be lower than that of the signal, and the antenna substrate 1 and the module substrate 2 can be easily joined by the conventional surface mounting technology.

  The radiation pattern in the φ = 0 ° (E plane) direction (on the XY plane) was calculated using the above model. The gain result of Co-Poralization is shown in FIG. The horizontal axis is the angle θ (angle formed with the Z axis), and the vertical axis is the gain. The solid line is outside the claimed scope of the present invention, and the dotted line is the result of the antenna substrate structure shown in FIG. Here, the values of a and b shown in FIG. 10 were set to b / a = 0.2 mm / 4.286 mm = 4.67%. When a is equal to or greater than the wavelength λ in the air of the signal transmitted / received from the antenna substrate 1, a = λ is set, as shown in FIG.

  According to the results shown in FIG. 9, the gains at ± 90 ° on the solid line were −2.49 dB and −3.94 dB, but −7.48 dB and −7. It can be reduced to 11 dB. Further, the depression of the radiation pattern in the 0 degree direction is reduced, the side lobe near 60 degrees can be reduced, and a radiation pattern with less unevenness is obtained.

Table 1 shows the gain at ± 90 ° when b / a shown in FIG. FIG. 11 is a plot of this.

  From this result, the samples 2 to 6 within the scope of the present invention are inclined as compared with the sample 1 outside the scope of the present invention in which the surface of the peripheral portion of the insulating substrate is not inclined toward the back surface toward the end. It can be seen that better results are obtained, and in particular, b / a is preferably 0.5% or more.

It is explanatory drawing of one Embodiment of the antenna module of this invention. It is explanatory drawing of an example of the antenna board | substrate 1 shown in FIG. It is explanatory drawing of the other example of the antenna board | substrate 1 shown in FIG. It is explanatory drawing of the other example of the antenna board | substrate 1 shown in FIG. It is explanatory drawing of other embodiment of the antenna module of this invention which mounted the semiconductor element 4 on the back surface of the insulated substrate 11. FIG. It is explanatory drawing of the surface of the antenna board | substrate 1 in an Example. It is explanatory drawing of the coordinate system in an Example. It is the whole model block diagram in an Example. It is a graph which shows the gain result of Co-Poralization. It is explanatory drawing of the antenna board | substrate 1 in an Example. It is a graph which shows the gain in +/- 90 degrees when b / a shown in FIG. 10 is changed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Antenna substrate 11 ... Insulating substrate 12 ... Patch conductor 13 ... Microstrip line 14 ... Slot 2 ... Module substrate 3 ... Solder ball 4... Semiconductor element 5... Sealing cap 6.

Claims (2)

A radiation board is provided on the surface of or inside the insulating substrate, and an antenna substrate in which the surface of the peripheral portion of the insulating substrate is inclined toward the back surface toward the end portion is mounted on the module substrate. Antenna module. The antenna module according to claim 1, wherein a semiconductor element is mounted on a back surface of the insulating substrate, and the semiconductor element and the radiating element are connected.

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