High-frequency circuit and radio device

A high-frequency circuit includes: a first ground layer having an electric conductor formed therein; a second ground layer having an electric conductor formed therein; and a conductive pattern layer having a first conductive pattern formed thereon. The first ground layer, the second ground layer, and the conductive pattern layer are laminated one on another. The conductive pattern layer includes a first area in which a distance to the electric conductor formed in the second ground layer is longer than a distance to the electric conductor formed in the first ground layer, in a lamination direction in which the first ground layer, the second ground layer, and the conductive pattern layer are laminated. At least a part of the first conductive pattern is disposed in the first area.

TECHNICAL FIELD

The present disclosure relates to a high-frequency circuit and a radio device. This application claims priority on Japanese Patent Application No. 2020-134329 filed on Aug. 7, 2020, the entire content of which is incorporated herein by reference.

BACKGROUND ART

Japanese Laid-Open Patent Publication No. 2010-87830 (PATENT LITERATURE 1) discloses a radio device in which SIRs are mounted on a multilayer board. In this radio device, two SIRs are formed in different layers of the multilayer board, respectively. The two SIRs are formed so as to overlap each other as viewed in a lamination direction of the multilayer board.

CITATION LIST

Patent Literature

SUMMARY OF THE INVENTION

A high-frequency circuit according to the present disclosure includes: a first ground layer having an electric conductor formed therein; a second ground layer having an electric conductor formed therein; and a conductive pattern layer having a first conductive pattern and a second conductive pattern formed thereon. The first ground layer, the second ground layer, and the conductive pattern layer are laminated on one another. An electrical distance from the conductive pattern layer to the second ground layer is longer than an electrical distance from the conductive pattern layer to the first ground layer. The conductive pattern layer includes a first area in which at least a part of the first conductive pattern is disposed and a second area in which at least a part of the first conductive pattern is disposed. A cavity is formed in a portion of the first ground layer opposing the first area in a lamination direction in which the first ground layer, the second ground layer and the conductive pattern layer are laminated, and the electric conductor is formed in a portion of the second ground layer opposing the second area in the lamination direction. Among an electrical distance from the first area to the electric conductor formed in the second ground layer and an electrical distance from the first area to the electric conductor formed in the first ground layer, the electrical distance from the first area to the electric conductor formed in the second ground layer is longer, in the lamination direction.

One aspect of the present disclosure can be realized as a semiconductor integrated circuit that realizes a part or the entirety of the high-frequency circuit, or can be realized as a communication system that includes the high-frequency circuit.

DETAILED DESCRIPTION

A radio device extracts a component in a specific frequency band from a received radio wave, for example, and performs various types of signal processing. As means for extracting a signal wave in a specific frequency band, filters have been known.

While there are various types of filters, a stepped impedance resonator (SIR) is sometimes used as a filter in terms of miniaturization of the radio device. The SIR is a type of pattern filter that is composed of a conductive pattern formed on a board. The SIR has a structure obtained by combining a low impedance part having a wide pattern width and a high impedance part having a narrow pattern width.

Problems to be Solved by the Present Disclosure

In a case where two SIRs are formed in the same layer of a multilayer board, the size of the multilayer board needs to be increased in order to secure a placement space for these SIRs. Meanwhile, in the radio device disclosed in PATENT LITERATURE 1, the two SIRs are formed in different layers. Therefore, the size of the multilayer board need not be increased, thereby miniaturizing the radio device.

However, the width of a conductive pattern that forms an SIR is deeply related to the frequency characteristics of the SIR. Therefore, even in the radio device described in PATENT LITERATURE 1, the width of the conductive pattern may become too wide depending on a cutoff frequency to be set, which may result in difficulty in placing the conductive pattern, or an increase in the size of the radio device.

In order to resolve the above problems, it is conceivable to narrow the width of the conductive pattern. In this case, however, it may become difficult to set a desired characteristic impedance in the SIR, or difficult to form the conductive pattern. Therefore, in the pattern filter, it is difficult to freely design a cutoff frequency, a passband width, etc., while maintaining a desired characteristic impedance.

The present disclosure has been made to solve the above problems, and an object of the present disclosure is to provide a high-frequency circuit and a radio device capable of increasing the degree of freedom in device design while realizing a desired characteristic impedance in a pattern filter.

Effects of the Present Disclosure

According to the present disclosure, it is possible to increase the degree of freedom in device design, while realizing a desired characteristic impedance in a pattern filter.

Description of Embodiment of the Present Disclosure

First, the contents of embodiments of the present disclosure are listed and described.(1) A high-frequency circuit according to an embodiment of the present disclosure includes: a first ground layer having an electric conductor formed therein; a second ground layer having an electric conductor formed therein; and a conductive pattern layer having a first conductive pattern and a second conductive pattern formed thereon. The first ground layer, the second ground layer, and the conductive pattern layer are laminated one on another. An electrical distance from the conductive pattern layer to the second ground layer is longer than an electrical distance from the conductive pattern layer to the first ground layer. The conductive pattern layer includes a first area in which at least a part of the first conductive pattern is disposed and a second area in which at least a part of the first conductive pattern is disposed. A cavity is formed in a portion of the first ground layer opposing the first area in a lamination direction in which the first ground layer, the second ground layer and the conductive pattern layer are laminated, and the electric conductor is formed in a portion of the second ground layer opposing the second area in the lamination direction. Among an electrical distance from the first area to the electric conductor formed in the second ground layer and an electrical distance from the first area to the electric conductor formed in the first ground layer, the electrical distance from the first area to the electric conductor formed in the second ground layer is longer, in the lamination direction.

In the case where a filter is formed of a conductive pattern, the characteristic impedance and the frequency characteristics of the filter are varied depending on the width of the conductive pattern, which may hinder desired characteristics from being achieved.

Meanwhile, in the above configuration, since at least a part of the first conductive pattern is disposed in the first area, the electrical distance from the first conductive pattern to the ground layer can be increased. When the electrical distance from the first conductive pattern to the ground layer is increased, the characteristic impedance of the first conductive pattern rises. Therefore, a reduction in the characteristic impedance of the first conductive pattern due to an increase in the width of the first conductive pattern can be offset by the increase in the electrical distance from the first conductive pattern to the ground layer. Thus, the width of the first conductive pattern can be increased while maintaining a desired characteristic impedance. Therefore, the degree of freedom in device design can be increased while realizing the desired impedance in the pattern filter.

In the case where an SIR having a coupled line is formed of a conductive pattern, a long coupled line is required in order to realize a large passband width, which may increase the size of the board. In order to reduce the length of the coupled line while maintaining the passband width, the degree of coupling of the coupled line needs to be increased. The degree of coupling can be increased by increasing the width of the conductive pattern. Thus, a desired passband width can be set while reducing the length of the coupled line. On the other hand, the increase in the width of the conductive pattern causes a reduction in the characteristic impedance of the SIR.

Meanwhile, in the above configuration, since at least a part of the first conductive pattern is disposed in the first area, a reduction in the characteristic impedance of the first conductive pattern due to an increase in the width of the first conductive pattern can be offset by an increase in the electrical distance from the first conductive pattern to the ground layer. Thus, the length of the coupled line can be reduced while maintaining a desired characteristic impedance. Therefore, the degree of freedom in device design can be increased while realizing the desired impedance in the pattern filter.(2) The electrical distance from the second area to the electric conductor formed in the second ground layer and an electrical distance from the second area to the electric conductor formed in the first ground layer may be equal.

In this configuration, by forming a conductor in the first ground layer, the electrical distance from the second area to the second ground layer is equal to the electrical distance from the second area to the first ground layer. Therefore, the characteristic impedance of the conductive pattern can be adjusted by forming a conductor or a cavity in the first ground layer, the degree of freedom in device design can be further increased.(3) The first conductive pattern may be disposed over the first area and the second area.

In this configuration, a filter with a high degree of freedom in which the first conductive pattern is disposed over the first area and the second area can be formed in the conductive pattern layer.(4) The first conductive pattern may form a part of a first filter, the second conductive pattern may form a part of a second filter, and the second filter may have a fractional bandwidth that is narrower than a fractional bandwidth of the first filter.

In a band-pass filter, a fractional bandwidth is represented by a value obtained by dividing a passband width with a center frequency. A band-pass filter having a wide fractional bandwidth requires a long coupled line, and a band-pass filter having a narrow fractional bandwidth requires a short coupled line. In the above configuration, since the fractional bandwidth of the second filter is narrower than the fractional bandwidth of the first filter, the first conductive pattern constituting the first filter having a wide fractional bandwidth is disposed in the first area in which the length of the coupled line can be increased, while the second conductive pattern constituting the second filter having a narrow fractional bandwidth is disposed in the second area in which the length of the coupled line can be reduced. Therefore, the degree of freedom in device design can be increased while realizing a desired fractional bandwidth in each filter.(5) The first area may be provided such that a characteristic impedance of the first conductive pattern becomes a constant value with respect to a frequency of a target signal.

In this configuration, in a transmission path, for a target signal, including a filter, the degree of freedom in device design can be increased while realizing a desired impedance.

A radio device according to the embodiment of the present disclosure includes the high-frequency circuit described above.

In this configuration, in the radio device, the degree of freedom in device design can be increased while realizing a desired characteristic impedance in the pattern filter.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference signs, and descriptions thereof are not repeated. At least some parts of the embodiments described below can be combined together as desired.

First, how the ideas for the high-frequency circuit and the radio device of the present disclosure have been conceived, will be described.

FIG.1is a cross-sectional view schematically showing a filter formed of a conductive pattern. With reference toFIG.1, a filter100includes a linear conductive pattern1002formed at a front surface of a plate-shaped dielectric layer1001, and a ground layer1003formed at a rear surface of the dielectric layer1001. The filter100is a pattern filter having a microstrip line structure. In the filter100, a constant of an LC circuit constituting a filter is replaced with a conductive pattern. Specifically, L (coil) is replaced with a high-impedance conductive pattern, and C (capacitor) is replaced with a low-impedance conductive pattern.

Here, the characteristic impedance of the conductive pattern1002is mainly affected by a width W of the conductive pattern1002, and a distance (a spatial distance) H from the conductive pattern1002to the ground layer1003. Assuming that the distance H is constant, the wider the width W is, the lower the characteristic impedance is, and the narrower the width W is, the higher the characteristic impedance is.

Meanwhile, assuming that the width W is constant, the longer the distance H is, the higher the characteristic impedance is, and the shorter the distance H is, the lower the characteristic impedance is. Therefore, in designing the filter100, the width W and the distance H of the conductive pattern1002are adjusted to set a desired characteristic impedance.

However, if the width W of the conductive pattern1002is too wide, it is difficult, in terms of space, to dispose the conductive pattern1002on the board, and the size of the filter100is increased. On the other hand, if the width W of the conductive pattern1002is too narrow, it is difficult to manufacture the conductive pattern1002. Therefore, depending on the characteristic impedance, of the conductive pattern1002, to be set in the filter100, it is sometimes difficult to realize a desired width W of the conductive pattern1002.

FIG.2is a plan view schematically showing an example of a band-pass filter formed of a conductive pattern. With reference toFIG.2, a band-pass filter200is, for example, a stepped impedance resonator (SIR) that is formed by combining: low impedance parts2001A,2001B each being formed of a conductive pattern having a width W1; and high impedance parts2002A,2002B each being formed of a conductive pattern having a width W2narrower than the width W1. The high impedance part2002A and the high impedance part2002B form a coupled line2003by being disposed with a slight gap between them. Each of the low impedance parts2001A,2001B and the high impedance parts2002A,2002B is formed of the conductive pattern1002as shown inFIG.1.

The low impedance parts2001A,2001B are different in characteristic impedance from the high impedance parts2002A,2002B. In the SIR, a resonance condition, i.e., a cutoff frequency, is set by adjusting the width and the length of the low impedance parts2001A,2001B and the width and the length of the high impedance parts2002A,2002B.

Generally, coupling of a coupled line of a band-pass filter is performed through an electromagnetic field. In the band-pass filter200shown inFIG.2, the coupled line2003is connected to the ground layer1003shown inFIG.1such that the coupling through a magnetic field is strengthened by causing a current to flow.

The length of the coupled line2003affects the passband width in the band-pass filter. The shorter the coupled line2003is, the narrower the passband width is. The longer the coupled line2003is, the wider the passband width is. Therefore, in designing the band-pass filter200using the SIR having the coupled line2003, the length of the coupled line2003is adjusted to set a desired passband width.

Meanwhile, when the coupled line2003is too short, it is difficult, in terms of manufacture, to form the coupled line2003on the board. In this case, it is conceivable to reduce the degree of coupling of the coupled line2003by increasing the length of the coupled line2003. In order to reduce the degree of coupling of the coupled line2003, the width of the conductive pattern needs to be narrowed. However, if the width of the conductive pattern is narrowed, the characteristic impedance changes, and the cutoff frequency of the band-pass filter deviates from a set value.

If the coupled line2003is too long, the size of the board is increased to secure a space for placing the coupled line2003. In this case, it is conceivable to increase the degree of coupling of the coupled line2003by reducing the length of the coupled line2003. In order to increase the degree of coupling of the coupled line2003, the width of the conductive pattern needs to be increased. However, if the width of the conductive pattern is increased, the characteristic impedance changes, and the cutoff frequency of the band-pass filter deviates from the set value.

Therefore, depending on the passband width to be set, it is sometimes difficult to ensure a desired length of the coupled line2003.

As described above, in the conventional art, when the filter is formed of the conductive pattern, a restriction imposed on the width of the conductive pattern or the length of the coupled line makes it difficult to realize a desired cutoff frequency or passband width. Because of the background as described above, the radio device of the present disclosure has been conceived.

Hereinafter, the high-frequency circuit and the radio device according to the embodiment of the present disclosure will be described.

FIG.3is a plan view showing a configuration of a radio device according to the embodiment of the present disclosure.FIG.3shows a radio device1mounted on a vehicle, for example.

With reference toFIG.3, the radio device1includes a high-frequency circuit2, an input/output terminal1A, a television input/output terminal1B, a GPS (Global Positioning System) input/output terminal1C, and a radio input/output terminal1D.

The input/output terminal1A is connected to an antenna (not shown) through a high-frequency cable1E. For example, the antenna is mounted on a front windshield, a rear windshield, a roof panel, or the like of a vehicle, and receives an RF signal (Radio Frequency Signal).

Each of the television input/output terminal1B, the GPS input/output terminal1C, and the radio input/output terminal1D is connected to an in-vehicle apparatus (not shown) capable of providing a service using a radio signal in a corresponding frequency band. For example, the television input/output terminal1B is connected to an in-vehicle apparatus corresponding to a television, such as a television tuner. The GPS input/output terminal1C is connected to an in-vehicle apparatus corresponding to a GPS, such as a car navigation system. The radio input/output terminal1D is connected to an in-vehicle apparatus corresponding to an AM/FM radio, such as a radio tuner.

The high-frequency circuit2separates a radio wave received at the input/output terminal1A into a radio wave for the in-vehicle apparatus corresponding to the television, a radio wave for the in-vehicle apparatus corresponding to the GPS, and a radio wave for the in-vehicle apparatus corresponding to the radio. The high-frequency circuit2may be configured to combine RF signals transmitted from the in-vehicle apparatus corresponding to the television and the in-vehicle apparatus corresponding to the GPS, and output the combined signal from the input/output terminal1A.

FIG.4is a cross-sectional view taken along a line IV-IV inFIG.3. For facilitating the understanding, inFIG.4, the plan view shown inFIG.3is represented by broken lines except for the filters.

With reference toFIG.4, the high-frequency circuit2is composed of a multilayer board10.

Multilayer Board

The multilayer board10is a printed circuit board, for example. The multilayer board10, from a main surface side in a lamination direction, includes a layer L1having a conductive pattern201formed thereon, a dielectric layer101A, a first ground layer102, a dielectric layer101B, an intermediate ground layer103, a dielectric layer101C, and a second ground layer104in this order.

The layer L1having the conductive pattern201formed thereon forms a main surface of the multilayer board10, and includes the conductive pattern and the like. Hereinafter, a layer having the conductive pattern201formed thereon is referred to as a conductive pattern layer. The conductive pattern201is an example of a first conductive pattern.

The dielectric layer101A is disposed between the conductive pattern layer L1and the first ground layer102, and insulates the conductive pattern layer L1and the first ground layer102from each other. The material of the dielectric layer101A is glass epoxy resin, for example. The same applies to the dielectric layers101B,101C described later.

The first ground layer102is a layer different from the conductive pattern layer L1, and is located at a position lower than the conductive pattern layer L1. In the multilayer board10, the first ground layer102is disposed between the dielectric layer101A and the dielectric layer101B. The first ground layer102is a layer having a thin electric conductor, such as a copper foil, formed therein. The same applies to the intermediate ground layer103and the second ground layer104described later. The first ground layer102has a shape in which the electric conductor is partially removed. A portion where the electric conductor is removed becomes a cavity.

The dielectric layer101B is disposed between the first ground layer102and the intermediate ground layer103, and insulates the first ground layer102and the intermediate ground layer103from each other.

The intermediate ground layer103is disposed between the dielectric layer101B and the dielectric layer101C. The intermediate ground layer103has a shape in which the electric conductor is partially removed. A portion where the electric conductor is removed becomes a cavity.

The dielectric layer101C is disposed between the intermediate ground layer103and the second ground layer104, and insulates the intermediate ground layer103and the second ground layer104from each other.

The second ground layer104is a layer different from the conductive pattern layer L1and the first ground layer102, and is located at a position lower than the first ground layer102. In the multilayer board10, the second ground layer104is disposed below the dielectric layer101C, and forms a rear surface of the multilayer board10. Therefore, in the lamination direction, the spatial distance from the conductive pattern layer L1to the second ground layer104is longer than the spatial distance from the conductive pattern layer L1to the first ground layer102. “Spatial distance” means a distance in a metric space (three-dimensional space), and a specific example is an Euclidean distance. The second ground layer104is disposed substantially over the entire area of the multilayer board10in a plan view. The second ground layer104is electrically connected to the first ground layer102and the intermediate ground layer103through vias.

With reference toFIG.3andFIG.4, the conductive pattern layer L1includes a first area105in which an electrical distance to the electric conductor formed in the second ground layer104is longer than an electrical distance to the electric conductor formed in the first ground layer102, in the lamination direction of the first ground layer102, the second ground layer104, and the conductive pattern layer L1. That is, among the electrical distance from the first area105to the electric conductor formed in the second ground layer104and the electrical distance from the first area105to the electric conductor formed in the first ground layer102, the electrical distance from the first area105to the electric conductor formed in the second ground layer104is longer, in a lamination direction in which the first ground layer102, the second ground layer104, and the conductive pattern layer L1are laminated. “Electrical distance” is an index indicating a positional relationship between two conductors, and is one of factors that determine characteristic impedances of the conductors. The longer the electrical distance is, the higher the characteristic impedances of the conductors are, and the smaller the electrical distance is, the lower the characteristic impedances of the conductors are. When a uniform dielectric exists between two conductors, the larger the spatial distance between the two conductors is, the higher the characteristic impedances are, and the smaller the spatial distance between the two conductors is, the lower the characteristic impedances are. That is, in this case, the electrical distance between the two conductors corresponds to the spatial distance between the two conductors. Such an “electrical distance” is different from an “electrical length” that defines a propagation speed of an electromagnetic wave. For example, the first area105is an area that opposes the second ground layer104in the lamination direction of the respective layers in the multilayer board10. Specifically, the first area105has a rectangular shape in a plan view, is provided at the conductive pattern layer L1, and has an arbitrary size. As shown inFIG.4, no electric conductor is disposed in areas, opposing the first area105, of the first ground layer102and the intermediate ground layer103, and cavities are formed in these areas. Below the first area105in the lamination direction, the dielectric layers101A,101B,101C, and the second ground layer104are disposed.

The conductive pattern layer L1includes a second area107in which a spatial distance to the electric conductor formed in the first ground layer102is longer than a spatial distance to the electric conductor formed in the second ground layer104, in the lamination direction of the first ground layer102, the second ground layer104, and the conductive pattern layer L1. The electrical distance from the second area107to the electric conductor formed in the first ground layer102and the electrical distance from the second area107to the electric conductor formed in the second ground layer104are equal, in a lamination direction in which the first ground layer102, the second ground layer104, and the conductive pattern layer L1are laminated. For example, the second area107is an area that opposes the first ground layer102in the lamination direction of the respective layers in the multilayer board10. Specifically, the second area107is an area other than the first area105in the conductive pattern layer L1. The second area107does not overlap the first area105in the conductive pattern layer L1, and is separated from the first area105. As shown inFIG.4, the electric conductor is disposed in an area, opposing the second area107, of the first ground layer102. Below the second area107in the lamination direction, the dielectric layer101A and the first ground layer102are disposed.

Filter

Referring back toFIG.3, a conductive pattern formed on the conductive pattern layer L1of the multilayer board10forms a part of a filter. In the multilayer board10, the conductive pattern201forms a part of a television filter. Specifically, the television filter is composed of the conductive pattern201and the second ground layer104. The television filter is an example of a first filter. The television filter is set to have a passband of 470 MHz to 710 MHz, for example. In this case, the television filter has a passband width of 240 MHz, a center frequency of 590 MHz, and a fractional bandwidth of 0.41.

The conductive pattern201includes low impedance parts2011,2012and high impedance parts2013,2014.

The low impedance parts2011,2012each have a substantially rectangular shape in a plan view, and are disposed side by side at an interval.

The radio device1further includes capacitors1F1,1F2. The low impedance part2011is connected to the input/output terminal1A via the capacitor1F1. The low impedance part2012is connected to the television input/output terminal1B via the capacitor1F2.

The width of the conductive pattern in the high impedance parts2013,2014is narrower than that in the low impedance parts2011,2012. The width and the length of the conductive pattern in the high impedance parts2013,2014and the width and the length of the conductive pattern in the low impedance parts2011,2012are appropriately set in accordance with a desired cutoff frequency.

The high impedance parts2013,2014each have a substantially L shape in a plan view, and are disposed side by side between the low impedance parts2011,2012. Portions of the high impedance parts2013,2014are disposed in parallel with a slight gap between them, thereby forming a coupled line2016. In the coupled line2016, the high impedance parts2013,2014are electromagnetically coupled to each other.

The length of a resonator composed of the low impedance parts2011,2012and the high impedance parts2013,2014is set to be ¼ of the wavelength at the center frequency of the passband. However, the length of the resonator may be ½ of the wavelength at the center frequency of the passband.

At least a part of the conductive pattern201is disposed in the first area105, and is electrically connected to the second ground layer104. For example, the conductive pattern201is disposed within the first area105, and is not disposed outside the first area105. The coupled line2016in the conductive pattern201is connected to a ground pattern106formed on the conductive pattern layer L1. The ground pattern106has one or a plurality of vias2017formed therein. The vias2017electrically connect the ground pattern106to the second ground layer104. InFIG.3, “L4GND” means that the conductive pattern201uses, as a reference ground, the second ground layer104corresponding to the fourth layer as a wiring layer.

As shown inFIG.3andFIG.4, on the conductive pattern layer L1, a conductive pattern202different from the conductive pattern201is further formed. The conductive pattern202is an example of a second conductive pattern. In the multilayer board10, the conductive pattern202forms a part of a GPS filter. Specifically, the GPS filter is composed of the conductive pattern202and the first ground layer102. The GPS filter is an example of a second filter.

The conductive pattern202is disposed in the second area107, and is electrically connected to the first ground layer102. For example, the conductive pattern202is disposed within the second area107, and is not disposed outside the second area107. The GPS filter is set to have a passband of 1525 MHz to 1625 MHz, for example. In this case, the GPS filter has a passband width of 100 MHz, a center frequency of 1575 MHz, and a fractional bandwidth of 0.06. That is, the fractional bandwidth of the GPS filter is narrower than the fractional bandwidth of the television filter.

The low impedance parts2021,2022each have a substantially rectangular shape in a plan view, and are disposed in a straight line at an interval.

The radio device1further includes capacitors1F3,1F4. The low impedance part2021is connected to the input/output terminal1A via the capacitor1F3. The low impedance part2022is connected to the GPS input/output terminal1C via the capacitor1F4.

The width of the conductive pattern in the high impedance parts2023,2024is narrower than that in the low impedance parts2021,2022. The width and the length of the conductive pattern in the high impedance parts2023,2024and the width and the length of the conductive pattern in the low impedance parts2021,2022are appropriately set in accordance with a desired cutoff frequency.

The high impedance parts2023,2024each have a substantially L shape in a plan view, and are disposed side by side between the low impedance parts2021,2022. Portions of the high impedance parts2023,2024are disposed in parallel with a slight gap between them, thereby forming a coupled line2026. In the coupled line2026, the high impedance parts2023,2024are electromagnetically connected to each other.

The length of a resonator composed of the low impedance parts2021,2022and the high impedance parts2023,2024is set to be ¼ of the wavelength at the center frequency of the passband. However, the length of the resonator may be ½ of the wavelength at the center frequency of the passband.

The coupled line2026is connected to a ground pattern108formed on the conductive pattern layer L1. The ground pattern108has one or a plurality of vias2027formed therein. The vias2027electrically connect the ground pattern108to the first ground layer102. InFIG.3, “L2GND” means that the conductive pattern202uses, as a reference ground, the first ground layer102corresponding to the second layer as a wiring layer.

The high-frequency circuit2further includes a radio filter that is disposed in an area, in the second area107, different from the area where the conductive pattern202is disposed. Generally, a radio filter is a low-pass filter (LPF) composed of an inductor and a capacitor. In a radio filter203shown inFIG.3, an inductor is composed of a coil and a pattern. The radio filter203is connected to the radio input/output terminal1D. The configuration of an electric circuit of the radio filter203is well known and therefore will not be described in detail.

As described above, in the high-frequency circuit2and the radio device1according to the present embodiment, since the conductive pattern201is disposed in the first area105, the distance from the conductive pattern201to the electric conductor formed in the second ground layer104can be increased. When the distance from the conductive pattern201to the electric conductor formed in the second ground layer104is increased, the characteristic impedance of the conductive pattern201rises. Therefore, a reduction in the characteristic impedance of the conductive pattern201due to an increase in the width of the conductive pattern201can be offset by the increase in the distance from the conductive pattern201to the electric conductor formed in the second ground layer104. Thus, the width of the conductive pattern201can be increased while maintaining a desired characteristic impedance. Therefore, the degree of freedom in device design can be increased while realizing a desired impedance in the pattern filter.

Moreover, in a case where an SIR having a coupled line is formed by using a conductive pattern, when the conductive pattern201is disposed in the first area105, a reduction in the characteristic impedance of the conductive pattern201due to an increase in the width of the conductive pattern201can be offset by an increase in the electrical distance from the conductive pattern201to the electric conductor formed in the second ground layer104. Thus, the coupled line2016can be shortened while maintaining a desired characteristic impedance. Therefore, the degree of freedom in device design can be increased while realizing a desired impedance in the pattern filter.

Modifications

FIG.5is a plan view showing a configuration of a radio device according to a modification of the embodiment of the present disclosure. In the radio device shown inFIG.5, the low impedance parts2011,2012and the first area105in the conductive pattern201are smaller than those in the radio device shown inFIG.3.

FIG.6is a cross-sectional view taken along a VI-VI line inFIG.5. For facilitating the understanding, inFIG.6, the plan view shown inFIG.5is represented by broken lines except for the conductive patterns.

With reference toFIG.5andFIG.6, in the radio device1according to the modification, the conductive pattern201is disposed over the first area105and the second area107. Specifically, in the conductive pattern201, the high impedance parts2013,2014are disposed in the first area105and the low impedance parts2011,2012are disposed in the second area107.

Even in this case, a part of the conductive pattern201opposes the second ground layer104in the lamination direction. Therefore, the electrical distance from the conductive pattern201to the reference ground can be increased, whereby the degree of freedom in device design can be further increased while realizing a desired characteristic impedance.

The embodiments disclosed herein are merely illustrative in all aspects and should not be recognized as being restrictive. The scope of the present disclosure is defined not by the above description but by the scope of the claims, and is intended to include meaning equivalent to the scope of the claims and all modifications within the scope.

In the conductive pattern layer L1, the position of the first area105is not particularly limited. The first area105only needs to be provided such that the characteristic impedance of the conductive pattern201becomes a constant value with respect to the frequency of a target signal, i.e., an RF signal received at the antenna connected to the input/output terminal1A. For example, it is preferable that the first area105is provided such that a variation width of the characteristic impedance of the conductive pattern201with respect to a variation in the frequency of the RF signal received at the antenna connected to the input/output terminal1A, is less than 5%. More preferably, the first area105is provided such that the variation width is less than 3%, and further preferably, the first area105is provided such that the variation width is less than 1%.

In the above description, the high-frequency circuit2includes the radio filter203. However, the high-frequency circuit2may not necessarily include the radio filter203.

In the above description, each of the television filter including the conductive pattern201and the GPS filter including the conductive pattern202is an SIR having a coupled line. However, in the high-frequency circuit2, the filter is not limited to an SIR having a coupled line. The filter may be an SIR composed of a single line, or a pattern filter composed of a conductor pattern having a constant width. This filter is formed of a conductor pattern having a constant width in the conductive pattern layer L1of the multilayer board10, and is disposed in the first area105that opposes the second ground layer104in the lamination direction.

In the above description, as shown inFIG.3, the conductive patterns201,202are formed on the main surface of the multilayer board10(on the layer L1on which the filters are formed). However, the layer at which the conductive patterns201,202are formed is not limited thereto. The conductive patterns201,202may be formed at a layer lower than the main surface, i.e., a layer inside the multilayer board10. For example, in the multilayer board10shown inFIG.3, the conductive pattern layer L1may be disposed at a position one layer below the main surface (inFIG.4, at a position where the first ground layer102is present). In this case, the first ground layer may be disposed at a position two layers below the main surface (inFIG.4, at a position where the intermediate ground layer103is present), or may be disposed at the main surface. In the case where the first ground layer is disposed at the main surface, the second ground layer may be disposed at a position two layers below the main surface (inFIG.4, at a position where the intermediate ground layer103is present). Both the first ground layer102and the second ground layer104may be disposed at positions higher than or lower than the conductive pattern layer L1. One of the first ground layer102and the second ground layer104may be disposed at a position higher than the conductive pattern layer L1while the other layer may be disposed at a position lower than the conductive pattern layer L1. That is, placement of the conductive pattern layer L1, the first ground layer102, and the second ground layer104is not limited to the example shown inFIG.3, and these layers may be disposed anywhere as long as the electrical distance from the conductive pattern layer L1to the first ground layer102is different from the electrical distance from the conductive pattern layer L1to the second ground layer104.

In the above description, as shown inFIG.3, the first ground layer102has a shape in which the electric conductor is partially removed. However, the first ground layer102and the intermediate ground layer103are not limited thereto. For example, in the case where one of the first ground layer102and the second ground layer104is disposed at a position higher than the conductive pattern layer L1while the other layer is disposed at a position lower than the conductive pattern layer L1and the electrical distance from the conductive pattern layer L1to the second ground layer104is longer than the electrical distance from the conductive pattern layer L1to the first ground layer102, the first ground layer102may have a shape in which the electric conductor is formed over the entire surface thereof. In this case, the entirety of the conductive pattern layer L1is the first area105, and does not include the second area107. That is, it is only necessary for the conductive pattern layer L1to include the first area105in which the electrical distance to the electric conductor formed in the second ground layer104is longer than the electrical distance to the electric conductor formed in the first ground layer102, and for at least a part of the conductive pattern201to be formed in the first area105.

In the above description, the multilayer board10includes the intermediate ground layer103. However, the multilayer board10only needs to include the first ground layer102and the second ground layer104, and may not necessarily include the intermediate ground layer103. In the case where the multilayer board10includes the intermediate ground layer103, the multilayer board10may include a plurality of intermediate ground layers103.

In the above description, the first ground layer102is disposed between the dielectric layers101A,101B, and the second ground layer104is disposed at the rear surface of the multilayer board10. However, placement of the first ground layer102and the second ground layer104is not limited thereto. The second ground layer104only needs to be disposed at a position lower than the first ground layer102.

In the above description, the radio device1is mounted on a vehicle. However, the radio device1is not limited thereto. The radio device1may be mounted on transport equipment other than vehicles, may be installed in buildings, or may be portable wireless equipment. That is, the radio device1may be any equipment that performs radio communication.

The above description includes the features in the additional notes below.

Additional Note 1

A radio device comprising:a multilayer board;a filter formed of a conductive pattern in the multilayer board; anda stepped impedance resonator having a coupled line, and formed of a conductive pattern in a layer, in the multilayer board, at which the filter is formed, whereinthe multilayer board includesa first ground layer disposed at a layer different from the filter, anda second ground layer disposed at a layer different from the filter and the first ground layer,an electrical distance from the layer at which the filter is formed to the second ground layer is longer than an electrical distance from the layer at which the filter is formed to the first ground layer,the layer at which the filter is formed includes a first area that opposes the second ground layer in a lamination direction, andthe stepped impedance resonator is disposed in the first area.

Additional Note 2

A radio device comprising:a multilayer board including a first ground layer, and a second ground layer that is disposed at a layer different from the first ground layer; anda filter formed of a conductive pattern, and disposed at a layer different from the first ground layer and the second ground layer in the multilayer board, whereinan electrical distance from a layer at which the filter is formed to the second ground layer is longer than an electrical distance from the layer at which the filter is formed to the first ground layer,the layer at which the filter is formed includes a first area that opposes the second ground layer in a lamination direction, andthe filter is disposed in the first area.

REFERENCE SIGNS LIST