JP4103936B2 - Antenna structure and wireless communication device including the same - Google Patents

Description

  The present invention relates to an antenna structure in which a substrate on which a radiation electrode is formed is mounted on a circuit board, and a radio communication apparatus including the antenna structure.

  As one of antennas provided in a wireless communication device, there is a surface mount antenna that is mounted on a circuit board of the wireless communication device and accommodated in a housing of the wireless communication device. This surface-mounted antenna has a configuration in which, for example, a radiation electrode for performing antenna operation is formed on a dielectric substrate.

Japanese Patent Laid-Open No. 10-209733 JP 2002-141739 A JP 2002-335117 A

  By the way, the frequency characteristics (return loss characteristics) of radio waves of a wireless communication device with a surface-mounted antenna mounted on a circuit board are not determined only by the radiation electrode of the surface-mounted antenna, but a surface-mounted antenna is mounted. Various elements such as ground electrodes and parts of the circuit board are determined. For this reason, the resonance frequency of the radio communication radio wave of the radio communication device is shifted from the resonance frequency of the radiation electrode of the surface mount antenna. As a result, even if the same surface mount antenna is mounted, for example, if the wireless communication device model is different, the resonance frequency of the radio communication radio wave of the wireless communication device (hereinafter referred to as the antenna resonance frequency) is different. A problem occurs.

  In other words, the size and shape of the ground electrode (ground) formed on the circuit board will differ, the types of parts installed around the surface mount antenna, The surrounding conditions of the surface-mounted antenna are different such that the distance between the mold antenna and its peripheral components is different or the material of the housing of the wireless communication device is different. Since the surrounding frequency of such a surface mount antenna is involved in a complicated manner and the resonance frequency of the antenna is determined, the type of radio communication device on which the surface mount antenna is mounted differs. If the state is different, the resonance frequency of the antenna is different even though the same surface-mounted antenna is provided.

  Even if the same surface mount antenna is provided in this way, the same antenna resonance frequency cannot be obtained if the models of the wireless communication devices are different. For this reason, even if the required resonance frequency of the antenna is the same, for example, if the model of the wireless communication device is different, the same surface-mounted antenna cannot be provided. It was necessary to customize the size of the radiation electrode, which was troublesome.

  Also, instead of surface mount antennas, for example, the circuit board circuit that is electrically connected to the surface mount antenna is changed for each wireless communication device model. A method of designing and adjusting the resonance frequency of the antenna to a set resonance frequency has been proposed (for example, see Patent Documents 1 to 3).

  However, the conventional methods of adjusting the resonance frequency of the antenna with the circuit on the circuit board have a problem that the current loss increases and the antenna gain decreases. In addition, when using a component having capacitance or inductance for adjusting the resonance frequency of the antenna, for example, if a general-purpose component is used due to cost problems, it has several predetermined capacitance or inductance values. Only parts (capacitor parts or inductor parts) can be prepared. For this reason, since it is often impossible to obtain capacitor components and inductor components having optimum numerical values, it is difficult to accurately adjust the resonance frequency of the antenna to the set resonance frequency.

The present invention has the following configuration as means for solving the above problems. That is, one of the configurations of the antenna structure according to the present invention is that a radiating electrode for performing antenna operation is provided on a base, the base is mounted on a circuit board, and the radiating electrode formed on the upper surface of the base is a circuit. in the antenna structure having a configuration that is kicked set so as to be opposed via a gap to the surface of the substrate,
The circuit board, between the ground of electrodes faces each other in the radiation electrode formed on the upper surface of the substrate on the lower side and a region of the bottom surface of the substrate to be mounted with a capacity between the opposed to the radiation electrode The capacitance loading electrode is formed in an electrically non-conducting connection state with the radiation electrode, and the circuit board has a space between the capacitance loading electrode and the grounding capacitance avoiding the formation area of the capacitance loading electrode between the grounding. A ground electrode that is electrically insulated from the electrode for loading capacitance between grounds is formed, and an element for adjusting the resonance frequency that connects between the electrode for loading capacitance between the ground and the ground electrode is provided. The resonance frequency adjusting element has a capacity or inductance for adjusting the resonance frequency of the antenna structure to a resonance frequency set in advance. In addition, the wireless communication device of the present invention is characterized in that an antenna structure having a configuration specific to the present invention is provided.

According to the present invention, the substrate on which the radiation electrode is provided is mounted on the circuit board, and the circuit board includes a grounded capacitive loading electrode that is disposed opposite the radiation electrode of the substrate and has a capacitance between the radiation electrode and the circuit board. Is formed. In addition, the circuit board is provided with a ground electrode via a gap between the electrodes for loading capacitance between grounds, and further provided with an element for adjusting a resonance frequency for connecting between the electrodes for loading capacitance between grounds and the ground electrode. Yes. The resonant frequency adjusting element has a capacity or inductance. In other words, in the present invention, the radiation electrode is connected to the ground electrode via a capacitance between the capacitance loading electrode and the capacitance or inductance of the resonance frequency adjusting element. The impedance of the circuit in which the capacitance between the radiation electrode and the electrode for loading the capacitance between the ground and the capacitance or inductance of the resonant frequency adjusting element is connected in series (hereinafter referred to as the resonant frequency adjusting circuit) is radiated. is that which is involved in decisions of the resonance frequency of the electrodes. Therefore, by the size or the inductance value of the capacitance of the resonance frequency adjusting element for variably adjusting impedance of the resonance frequency adjusting circuit is variable by this, the resonant frequency of the radiation electrode (i.e., the antenna structure (Resonance frequency) can be variably adjusted.

  As described above, the resonance frequency of the antenna structure can be variably adjusted without changing the design of the shape of the radiation electrode of the base body by merely changing the capacitance or inductance value of the resonance frequency adjusting element. As a result, a component (antenna component) in which the radiation electrode is formed on the base can be used in common for a plurality of types of wireless communication devices, and the component can be shared. This makes it easy to reduce the cost of antenna parts and wireless communication devices.

  Further, as the electrode area of the electrode for capacity loading between grounds is increased and the capacity between the electrode for capacity loading between grounds and the radiation electrode is increased, the capacitance size or inductance value of the resonance frequency adjusting element changes. The amount of change in the resonance frequency of the antenna structure with respect to the amount can be increased. In other words, the capacitance size or inductance value of the resonant frequency adjusting element is reduced as the electrode area of the capacitance loading electrode between grounds is reduced to reduce the capacitance between the capacitance loading electrode and the radiation electrode. The amount of change in the resonance frequency of the antenna structure with respect to the amount of change can be reduced.

  For this reason, for example, in order to reduce the cost, general-purpose capacitor parts or inductor parts are used as the resonance frequency adjustment element, and the capacitance size or inductance value of the resonance frequency adjustment element is only discontinuous. Even if variable adjustment is not possible, the resonant frequency of the antenna structure can be changed by changing the capacitance between the radiation electrode and the ground-capacity loading electrode by variably adjusting the electrode area of the ground-capacity loading electrode. The width can be reduced and the resonance frequency of the antenna structure can be finely adjusted. This makes it easy to obtain the resonance frequency of the radiation electrode that meets the requirements, and the reliability of the wireless communication device equipped with the antenna structure of the present invention for wireless communication can be improved.

  Furthermore, in the present invention, the electrode for loading the capacitance between the grounds is provided on the circuit board, and is not provided on the base on which the radiation electrode is formed. For this reason, when it is desired to change the capacitance between the radiation electrode and the electrode for capacitive loading between grounds due to a design change, etc., it is only necessary to change the electrode area of the electrode for loading capacitance between the grounds formed on the circuit board. It is not necessary to change the design of the part (antenna part) formed by forming the radiation electrode on the base. That is, it is possible to use the same antenna component after the design change as before the design change. As described above, the configuration in which the electrode for loading capacitance between the grounds is provided on the circuit board is also an important element that can promote the common use of the antenna components.

  Further, in the case where the radiation electrode is provided on the base so as to face the substrate surface of the circuit board with a gap, a ground-to-ground capacity loading electrode is temporarily provided on the side of the base. In this case, the virtual plane along the electrode surface of the radiation electrode and the virtual plane along the electrode surface of the electrode for loading capacitance between grounds have, for example, an orthogonal relationship or a substantially orthogonal relationship. The capacity between the loading electrodes is small. For this reason, when a large capacity is required between the radiation electrode and the electrode for capacity loading between the grounds, the electrode for capacity loading between the grounds must be formed enlarged, and the base (that is, the antenna component) is large. The problem of becoming a problem occurs.

  In contrast, according to the present invention, the electrode for loading capacitance between grounds is formed on the surface of the circuit board facing the radiation electrode, so that the opposing area between the electrodes for loading capacitance between the ground and the radiation electrode can be increased and grounding is performed. It becomes easy to form a large capacitance between the inter-capacity loading electrode and the radiation electrode. In addition, since the electrode for loading capacitance between grounds is not provided on the base, the size of the base (antenna component) can be reduced as much as the electrode for loading capacitance between grounds is not provided on the base.

  Further, the capacitance loading electrode between the grounds is formed on the circuit board surface portion facing the radiation electrode, and a large capacitance can be formed between the capacitance loading electrode between the ground and the radiation electrode. The resonance frequency of the antenna structure can be variably adjusted while preventing the antenna gain from deteriorating.

FIG. 1 a is a schematic plan view for explaining the antenna structure of the first embodiment. FIG. 1b is a schematic perspective view of the antenna structure of FIG. 1a. FIG. 1c is a schematic plan view for explaining a configuration example of a circuit board constituting the antenna structure of FIG. 1a. FIG. 2 is a graph for explaining an example of a change in the return loss characteristic of the antenna structure due to a change in the capacitance of the resonance frequency adjusting element constituting the antenna structure of the first embodiment. FIG. 3 is a graph for explaining an example of a change in the return loss characteristic of the antenna structure due to a change in the inductance value of the resonant frequency adjusting element constituting the antenna structure of the first embodiment. FIG. 4 is a diagram for explaining a configuration example of a slit of the ground electrode constituting the antenna structure of the first embodiment. FIG. 5 is a graph for explaining an example of a change in the return loss characteristic of the antenna structure with respect to a change in the length of the resonance frequency adjusting slit provided in the ground electrode. FIG. 6a is a model diagram for explaining the effects obtained from the configuration of the first embodiment. FIG. 6B is a model diagram for explaining the problem of the conventional example. FIG. 6c is a model diagram for explaining the problem of the conventional example together with FIG. 6b. It is sectional drawing for demonstrating one of the other Examples with FIG. 7b. It is sectional drawing for demonstrating one of the other Examples with FIG. 7a.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Antenna structure 2 Dielectric base 3 Radiation electrode 5 Circuit board 6 Ground electrode 7 Electrode for capacity loading between grounds 8 Resonance frequency adjustment element 13 Slit

  Embodiments according to the present invention will be described below with reference to the drawings.

  FIG. 1a shows a schematic plan view of a first embodiment of an antenna structure according to the present invention, FIG. 1b shows a schematic perspective view of the antenna structure of FIG. 1a, and FIG. An example of a conductor pattern of a circuit board constituting the antenna structure is shown by a schematic plan view.

  The antenna structure 1 of the first embodiment includes a base 2 made of a dielectric, a radiation electrode 3 and a feed electrode 4 formed on the dielectric base 2, and a circuit board 5 on which the dielectric base 2 is surface-mounted. A grounding electrode 6 and an inter-ground capacitive loading electrode 7 formed on the circuit board 5, a resonant frequency adjusting element 8 connecting the ground electrode 6 and the inter-ground capacitive loading electrode 7, a circuit, The power supply line 9 is formed on the substrate 5 and electrically connected to the power supply electrode 4 of the dielectric substrate 2.

  That is, in the first embodiment, the dielectric substrate 2 has a rectangular parallelepiped shape. A schematic cross-sectional view of this dielectric substrate 2 is shown in FIG. 6a. The radiation electrode 3 is formed from the top surface of the dielectric substrate 2 so as to wrap around the edge of the bottom surface through, for example, the right end surface of FIG. In addition, the feeding electrode 4 is extended from the edge of the bottom surface of the dielectric substrate 2 to a position facing the radiation electrode 3 on the upper surface of the dielectric substrate 2 with a gap passing through the left end surface of FIG. .

  The corner of the circuit board 5 forms an antenna component. On the board surface of the corner of the circuit board 5, a ground-loading electrode 7 and a power supply line 9 are formed. On the substrate surface of the circuit board 5, the ground electrode 6 is formed in almost the entire area avoiding the formation area of the inter-ground capacitance loading electrode 7 and the power supply line 9. The dielectric substrate 2 on which the radiation electrode 3 and the feeding electrode 4 are formed has a posture in which the bottom surface thereof is directed toward the circuit board 5 and the end on the right side of FIG. The circuit board 5 is mounted (surface mounted) on the antenna component part at the corner of the circuit board 5 in a state of being disposed on the ground electrode 6. As described above, when the dielectric substrate 2 is mounted on the circuit board 5, among the both end portions of the radiation electrode 3, the end portion far from the feeding electrode 4 (that is, the right end portion in FIG. 1 a, for example). The radiation electrode 3 that is directly bonded to the ground electrode 6 and provided on the upper surface of the dielectric substrate 2 is placed opposite to the substrate surface of the circuit board 5.

  One end side of the power supply line 9 is electrically connected to the power supply electrode 4. Further, the other end side of the power supply line 9 is electrically connected to, for example, a radio frequency circuit 10 for radio communication of a radio communication device. That is, the power supply line 9 electrically connects the radio communication high-frequency circuit 10 and the power supply electrode 4. The power supply line 9 is provided with a matching element 11 that constitutes a matching circuit for impedance matching between the power supply electrode 4 side and the high-frequency circuit 10 side.

  The power supply electrode 4 is formed with a space from the radiation electrode 3, and the power supply electrode 4 and the radiation electrode 3 are electromagnetically coupled through a capacitor. That is, for example, when a signal for wireless transmission is transmitted from the high frequency circuit 10 for wireless communication to the power supply electrode 4 through the power supply line 9, the power supply electrode 4 is connected by capacitive coupling between the power supply electrode 4 and the radiation electrode 3. A signal for wireless transmission is transmitted to the radiation electrode 3. That is, the radiation electrode 3 is a capacitive feed type radiation electrode.

  In the first embodiment, an inter-ground capacitive loading electrode 7 is formed on the circuit board 5 at a portion facing the radiation electrode 3 with a gap from the ground electrode 6 (see FIG. 1c). The grounded electrode for capacitive loading 7 has a lead-out portion 7a formed to be drawn out of the region where the dielectric substrate 2 is mounted. The resonance frequency adjusting element 8 is composed of a capacitor component or an inductor component, and is mounted on the circuit board 5 in such a manner that the lead portion 7a of the inter-ground capacitance loading electrode 7 and the ground electrode 6 are connected. . In this first embodiment, the dielectric substrate 2 provided with the radiation electrode 3 is of the ground mounting type, and originally, the ground electrode 6 is formed on the portion of the circuit board 5 on which the dielectric substrate 2 is mounted. However, in order to form the capacitance loading electrode 7 and the power supply line 9, the ground electrode 6 is not formed on the substrate surface in the region where the capacitance loading electrode 7 and the power supply line 9 are formed. It has become.

In this first embodiment, the capacitance loading electrode 7 is arranged opposite to the radiation electrode 3 so that a capacitance is formed between the radiation electrode 3 and the capacitance loading electrode 7 has a resonance frequency. It is connected to the ground electrode 6 through the adjustment element 8. In other words, the radiation electrode 3 is a circuit (resonance frequency adjustment circuit) in which the capacitance between the radiation electrode 3 and the ground-to-ground capacity loading electrode 7 and the capacitance or inductance of the resonance frequency adjustment element 8 are connected in series. Circuit) via the circuit). Impedance of the resonance frequency adjusting circuit is that which is involved in the resonant frequency. From this, the resonance frequency of the radiation electrode 3 (resonance of the antenna structure 1) can be adjusted by variably adjusting the magnitude or inductance value of the resonance frequency adjustment element 8 to variably adjust the impedance of the resonance frequency adjustment circuit. Frequency) can be variably adjusted.

  For example, when the resonant frequency adjusting element 8 is configured by a capacitor component, the resonant frequency of the antenna structure 1 can be made lower than when the resonant frequency adjusting element 8 is not provided. The amount of decrease in the resonance frequency increases as the capacitance of the resonance frequency adjusting element (capacitor component) 8 increases.

FIG. 2 shows examples of return loss characteristics of five types of antenna structures 1 having the same configuration except for the configuration related to the resonance frequency adjusting element 8. That is, the dotted line A in the graph of FIG. 2 is an example of the return loss characteristic of the antenna structure 1 when the resonance frequency adjusting element 8 is not provided. Also, the solid lines B to E in the graph of FIG. 2 are examples of the return loss characteristics of the antenna structure 1 when a capacitor component is provided as the resonance frequency adjustment element 8, and the solid line B is the resonance frequency adjustment. The solid line C is an example when the capacitance of the resonance frequency adjustment element 8 is 1 pF, and the solid line D is an example when the capacitance of the resonance frequency adjustment element 8 is 3 pF. The solid line E is an example when the capacitance of the resonance frequency adjusting element 8 is 6 pF. As can be seen from the graph of FIG. 2, by providing the resonance frequency adjusting element (capacitor component) 8, the resonance frequency of the antenna structure 1 becomes lower than when the resonance frequency adjusting element 8 is not provided. Further, the amount of decrease Δf _B , Δf _C , Δf _D , Δf _E of the resonance frequency of the antenna structure 1 increases as the capacitance of the resonance frequency adjusting element 8 increases.

  Further, when the resonance frequency adjusting element 8 is formed of an inductor component, the resonance frequency of the antenna structure 1 can be increased as compared with the case where the resonance frequency adjusting element 8 is not provided. The amount of increase in the resonance frequency increases as the inductance value of the resonance frequency adjusting element (inductor component) 8 decreases, and the degree of influence of the resonance frequency adjusting element 8 increases and the resonance frequency of the antenna structure 1 increases. .

  FIG. 3 shows examples of return loss characteristics of the five types of antenna structures 1 having the same configuration except for the configuration related to the resonance frequency adjusting element 8. That is, the dotted line a in the graph of FIG. 3 is an example of the return loss characteristic of the antenna structure 1 when the resonance frequency adjusting element 8 is not provided. 3 are examples of the return loss characteristics of the antenna structure 1 when an inductor component is provided as the resonance frequency adjusting element 8, and the solid line b indicates the resonance frequency adjustment. The solid line c is an example when the inductance value of the resonance frequency adjusting element 8 is 4.7 nH, and the solid line d is an example when the inductance value of the resonance frequency adjusting element 8 is 6.8 nH. A solid line e is an example when the inductance value is 3.9 nH, and a solid line e is an example when the inductance value of the resonance frequency adjusting element 8 is 2.7 nH. As can be seen from the graph of FIG. 3, by providing the resonance frequency adjusting element (inductor component) 8, the resonance frequency of the antenna structure 1 becomes higher than when the resonance frequency adjusting element 8 is not provided. Further, the increase amounts Δfb, Δfc, Δfd, and Δfe of the resonance frequency of the antenna structure 1 increase as the inductance value of the resonance frequency adjusting element 8 decreases.

  Note that a resonance frequency adjusting circuit in which a capacitance between the radiation electrode 3 and the capacitance loading electrode 7 and the capacitance or inductance of the resonance frequency adjustment element 8 are connected in series is provided between the radiation electrode 3 and the ground. The amount of change in the impedance of the resonance frequency adjustment circuit with respect to the amount of change in the capacitance or the inductance value of the resonance frequency adjustment element 8 differs depending on the capacitance between the capacitor loading electrode 7 and the capacitor loading electrode 7. As a result, the capacitance of the resonance frequency adjusting element 8 can be adjusted by variably adjusting the capacitance between the radiation electrode 3 and the grounded capacitance loading electrode 7, that is, by adjusting the electrode area of the grounded capacitance loading electrode 7. It is possible to variably adjust the resonance frequency of the antenna structure 1 by adjusting the amount of change in impedance of the resonance frequency adjustment circuit with respect to the amount of change in size or inductance value.

  Specifically, the capacitance of the resonance frequency adjusting element 8 increases as the electrode area of the capacitance loading electrode 7 between the grounds is reduced to reduce the capacitance between the capacitance loading electrode 7 and the radiation electrode 3. In addition, the amount of change in the resonance frequency of the antenna structure 1 with respect to the amount of change in the inductance value is small. In other words, the capacity of the resonance frequency adjusting element 8 increases as the electrode area of the electrode for loading capacitance between grounds 7 increases to increase the capacitance between the electrode for loading capacitance between grounds 7 and the radiation electrode 3. Alternatively, the change amount of the resonance frequency of the antenna structure 1 with respect to the change amount of the inductance value becomes large. From this, for example, even if the capacitance size or inductance value of the resonance frequency adjusting element 8 is changed in the same manner, the fluctuation range of the resonance frequency of the antenna structure 1 varies depending on the electrode area of the electrode 7 for loading capacitance between grounds. To do. As a result, when fine adjustment of the resonance frequency of the antenna structure 1 is desired, the electrode area of the electrode 7 for loading the capacitance between the grounds is reduced, and conversely, when the resonance frequency of the antenna structure 1 is greatly changed. The electrode area of the electrode 7 for capacity loading between grounds is increased.

  In the first embodiment, the ground electrode 6 is formed with a slit 13 extending from a portion joined to the radiation electrode 3. The slit 13 is for causing a part of the ground electrode 6 connected to the radiation electrode 3 to function as a part of the radiation electrode 3. The slit 13 is formed in a form that separates the portion of the ground electrode 6 that functions as a part of the radiation electrode 3 from the other portions of the ground electrode 6.

  By forming the slit 13, for example, a part of the ground electrode 6 surrounded by a chain line Z in FIG. 4 functions as a part of the radiation electrode 3. For this reason, changing the shape and length of the slit 13 to change the electrical length of the portion Z of the ground electrode 6 that functions as a part of the radiation electrode 3 means that the electrical length of the radiation electrode 3 is changed. It becomes an equivalent state to change the antenna frequency, and the resonance frequency of the antenna structure 1 can be changed. That is, for example, as the length of the slit 13 is extended as indicated by the dotted line from the length of the slit 13 as indicated by the solid line in FIG. In the graph of FIG. 5, the line changes as follows: solid line La → solid line Lb → solid line Lc → solid line Ld → solid line Le → solid line Lf. That is, the resonance frequency of the antenna structure 1 can be lowered as the length of the slit 13 increases and the equivalent electrical length of the radiation electrode 3 increases.

  Note that the resonance frequency of the antenna structure 1 can be set to, for example, a unit of about 10 MHz by adjusting the magnitude of the capacitance or the inductance value of the resonance frequency adjusting element 8 and adjusting the electrode area of the capacitance loading electrode 7 between grounds. Depending on the electrode area of the inter-capacity loading electrode 7, it can be variably adjusted in units of 1 MHz or several MHz. On the other hand, the resonance frequency of the antenna structure 1 can be variably adjusted by, for example, about 100 MHz by variable adjustment of the slit 13. As described above, in this first embodiment, the resonance frequency of the antenna structure 1 is roughly adjusted by the slits 13, and the antenna structure 1 is adjusted according to the electrode areas of the resonance frequency adjusting element 8 and the grounded capacitance loading electrode 7. By finely adjusting the resonance frequency, the resonance frequency of the antenna structure 1 can be adjusted with high accuracy.

  In the first embodiment, as described above, the capacitance size or inductance value of the resonant frequency adjusting element 8 and the electrode area of the grounding capacity loading electrode 7 (the grounding capacity loading electrode 7 and the radiation electrode 3 The resonance frequency of the antenna structure 1 can be variably adjusted by variably adjusting the length and shape of the slit 13. From this, the capacitance size or inductance value of the resonant frequency adjusting element 8 and the electrode area of the ground-to-ground capacitive loading electrode 7 are set so that the resonant frequency of the antenna structure 1 becomes a preset resonant frequency. The length and shape of the slit 13 are appropriately adjusted and set.

  By providing the configuration of the first embodiment, the capacitance or inductance value of the resonant frequency adjusting element 8 provided on the circuit board 5 or the capacitance for ground capacitance loading without changing the size or shape of the radiation electrode 3. 7, the resonance frequency of the antenna structure 1 can be adjusted to the set resonance frequency only by variably adjusting the electrode area 7 and the length and shape of the slit 13.

  Moreover, since the electrode 7 for capacitive loading between grounds is formed in the board | substrate surface part of the circuit board 5 which opposes the radiation electrode 3, the effect that the enlargement of the dielectric substrate 2 can be suppressed is acquired. Can do. That is, for example, as shown in the schematic cross-sectional view of FIG. 6 b, when the electrode 14 for forming a capacitance between the radiation electrode 3 and the ground electrode 6 is formed on the end face of the dielectric substrate 2. For example, as shown in FIG. 6 c, which is a view of the end face configuration of the dielectric base 2 from the left side of FIG. 6 b, the electrode 14 is formed on the end face of the dielectric base 2 in addition to the feeding electrode 4. Become. For this reason, the dielectric substrate 2 must be enlarged, and the antenna structure 1 is enlarged. In addition, since the electrode 14 and the radiation electrode 3 are not arranged to face each other, the capacitance between the electrode 14 and the radiation electrode 3 is small. Therefore, when the capacitance between the electrode 14 and the radiation electrode 3 is increased, for example, the electrode 14 is formed to extend toward the radiation electrode 3 so that the gap (gap) between the electrode 14 and the radiation electrode 3 is reduced. It is conceivable to increase the capacity between the electrode 14 and the radiation electrode 3. However, as the distance between the electrode 14 and the radiation electrode 3 becomes narrower, the variation in the capacitance between the electrode 14 and the radiation electrode 3 due to the variation in the distance increases, which is not preferable. Therefore, in order to increase the electrode area of the electrode 14 in order to increase the capacitance between the electrode 14 and the radiation electrode 3, the dielectric substrate 2 must be enlarged, and the antenna structure 1 is increased in size. The problem of incurring.

On the other hand, in the first embodiment, as shown in the schematic cross-sectional view of FIG. 6A, the inter-ground capacitance loading electrode 7 is formed on the substrate surface of the circuit board 5 facing the radiation electrode 3. The configuration. For this reason, since the capacitance loading electrode 7 is disposed opposite to the radiation electrode 3, it is easy to obtain a large capacity between the radiation electrode 3. In addition, the capacitance loading electrode 7 between the grounds is formed on the substrate surface of the circuit board 5 and is not provided on the dielectric substrate 2, but the circuit board surface portion on which the capacitance loading electrode 7 is formed. is a dead de space in which the dielectric substrate 2 has not been used until now been installed. For these reasons, in order to increase the capacitance between the grounding capacity loading electrode 7 and the radiation electrode 3, the size of the dielectric substrate 2 (that is, the antenna) The increase in size of the structure 1 can be suppressed.

  Further, even if the resonance frequency adjusting element 8 is provided as shown in the first embodiment, the fluctuation of the antenna gain can be suppressed to a small value. This has been confirmed by the inventors' experiments. In the experiment, three types of antenna structures 1 (samples α, β, and γ) having the same conditions except for the configuration related to the resonance frequency adjusting element 8 were prepared. That is, the sample α is not provided with the resonance frequency adjusting element 8. In the sample β, a capacitor component having a capacitance of 6 pF, for example, is provided as the resonance frequency adjusting element 8. The sample γ is provided with an inductor component having an inductance value of 3.9 nH, for example, as the resonance frequency adjusting element 8. The linearly polarized antenna gain was determined for each of these samples α, β, and γ. The experimental results are shown in Tables 1 to 3. Table 1 relates to sample α, Table 2 relates to sample β, and Table 3 relates to sample γ.

  Table 1 showing the antenna gain of the sample α (without the resonance frequency adjusting element 8) and the antenna gain of the samples β and γ (with the resonance frequency adjusting element 8) As can be seen from the comparison with Tables 2 and 3, it can be confirmed that the antenna gain similar to that obtained when the resonant frequency adjusting element 8 is not provided can be obtained even if the resonant frequency adjusting element 8 is provided.

  The second embodiment will be described below. The second embodiment relates to a wireless communication device. The wireless communication device of the second embodiment is provided with the antenna structure 1 shown in the first embodiment. There are various configurations of the radio communication device, and any configuration of the radio communication device other than the antenna structure 1 may be adopted, and the description thereof is omitted here. Further, since the configuration of the antenna structure 1 has been described in the first embodiment, a duplicate description thereof will be omitted.

  In addition, this invention is not limited to the form of each 1st and 2nd Example, Various embodiment can be taken. For example, in the antenna structure 1 of each of the first and second embodiments, the slit 13 for causing one part of the ground electrode 6 to function as a part of the radiation electrode 3 is provided. For example, the slit 13 is provided. If the resonance frequency of the antenna structure 1 can be adjusted to the set resonance frequency, the slit 13 may be omitted.

  In addition to the configurations of the first and second embodiments, the schematic cross-sectional view of FIG. 7a and its decomposition are also applied to the bottom surface portion of the dielectric substrate facing the capacitance loading electrode 7 of the circuit board 5. As shown in FIG. 7b, an electrode for loading capacitance between grounds 7 'may be provided. The grounding capacity loading electrode 7 ′ on the dielectric substrate 2 side is joined to the grounding capacity loading electrode 7 on the circuit board 5 side by a conductive joining material such as solder. With this configuration, the following effects can be obtained. That is, the dielectric substrate 2 is mounted on the circuit board 5 with a conductive bonding material such as solder. A part of the conductive bonding material is interposed between the dielectric substrate 2 and the circuit board 5. The amount of the intervening varies depending on various conditions such as a heating state and a molten state of the conductive bonding material when the dielectric substrate 2 is mounted on the circuit board 5 with the conductive bonding material, and varies. For this reason, the distance between the dielectric substrate 2 and the circuit board 5 varies. As a result, the distance between the radiation electrode 3 of the dielectric substrate 2 and the grounded capacitance loading electrode 7 of the circuit board 5 varies. For example, in the case of the configuration shown in FIG. The capacitance between the second radiation electrode 3 and the grounded capacitance loading electrode 7 of the circuit board 5 also varies. On the other hand, by providing the electrode for loading capacitance between grounds 7 ′ on the bottom surface of the dielectric substrate 2, the distance between the radiation electrode 3 and the electrode for loading capacitance between the grounds 7 ′ is made almost exactly as designed. be able to. For this reason, the gap between the dielectric substrate 2 and the circuit board 5 is bonded to the capacitance loading electrode 7 'of the circuit board 5 via the conductive bonding material. Even if there is a variation, it is possible to suppress the variation in capacitance between the radiation electrode 3 and the grounded capacitance loading electrodes 7 and 7 '. Thereby, the antenna performance can be further improved.

  Furthermore, in each of the first and second embodiments, the dielectric substrate 2 has a rectangular parallelepiped shape, but may have another shape such as a columnar shape or a polygonal column shape. Furthermore, the radiation electrode 3 may have a shape other than the shape illustrated in FIG. 1, for example, as long as it is a capacitive power supply type radiation electrode. Further, in each of the first and second embodiments, the ground electrode 6 is not formed in the circuit board region where the inter-ground capacitance loading electrode 7 is formed. A configuration may be employed in which the grounding electrode 7 is formed, and the ground electrode 6 is formed on the back surface or the inner layer of the portion of the circuit board 5 on which the grounding electrode 7 is formed. Further, the dielectric substrate 2 provided with the radiation electrode 3 is mounted on the ground region, but the present invention is also applied to a configuration in which the dielectric substrate provided with the radiation electrode is mounted on the non-ground region. It can be applied.

The present invention can easily adjust the resonance frequency of the antenna structure to the set resonance frequency with high accuracy while suppressing the increase in the size of the antenna structure and the deterioration of the antenna gain. It is effective for application to a wireless communication device.

Claims (3)

Radiation electrode for performing an antenna operation is provided on the substrate, the substrate is mounted on the circuit board, set such that the radiation electrode formed on the upper surface of the substrate to face each other with a distance to the substrate surface of the circuit board In the antenna structure with the configuration
The circuit board, between the ground of electrodes faces each other in the radiation electrode formed on the upper surface of the substrate on the lower side and a region of the bottom surface of the substrate to be mounted with a capacity between the opposed to the radiation electrode The capacitance loading electrode is formed in an electrically non-conducting connection state with the radiation electrode, and the circuit board has a space between the capacitance loading electrode and the grounding capacitance avoiding the formation area of the capacitance loading electrode between the grounding. A ground electrode that is electrically insulated from the electrode for loading capacitance between grounds is formed, and an element for adjusting the resonance frequency that connects between the electrode for loading capacitance between the ground and the ground electrode is provided. The resonance frequency adjusting element has a capacitance or inductance for adjusting the resonance frequency of the antenna structure to a resonance frequency set in advance.   The substrate is mounted on the circuit board with a part of the substrate disposed on the ground electrode, and the radiation electrode extends to the ground electrode through the substrate portion disposed on the ground electrode. The ground electrode is configured such that a part of the ground electrode is continuously extended from the portion where the radiation electrode is joined to the radiation electrode to radiate the ground electrode portion. The slit for functioning as a part of an electrode is formed in a form in which a ground electrode part functioning as one part of a radiation electrode is separated from other remaining ground electrode parts. Antenna structure.   A wireless communication device provided with the antenna structure according to claim 1.

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