Patent Description:
Recently, structures have been used in which a planar antenna and surface-mounted parts are mounted on a circuit board such as a multilayer circuit board. When a planar antenna is to be used, it is customary to employ a planar array in which an antenna element array is handled as one branch and a plurality of branches are combined. In this case, central power feeding by which electric power is supplied to the center of each branch is available as a method of supplying electric power to each branch. In central power feeding, a plurality of branches are placed on a multilayer circuit board. Therefore, it is necessary to use, for example, a waveguide tube to supply electric power to a power feed line from a wiring layer provided separately from a wiring layer in which branches are formed. However, the use of a waveguide tube increases the cost of a module in which the circuit board is mounted (see, for example, <CIT>).

<NPL>, related to a rat-race feeding circuit, wherein a power feed signal is provided to a ring-shaped feeding circuit from which two ports are connected to a patch antenna through a substrate such that a differential signal is applied to the antenna.

<NPL>, relates to a rat-race coupler acting as a filter.

One non-limiting and exemplary embodiment facilitates providing a circuit board that can perform central power feeding more inexpensively.

The present disclosure contributes to providing a circuit board by which central power feeding can be performed at a cost lower than before.

Additional benefits and advantages in one aspect of the present disclosure will become apparent from the specification and drawings. The benefits and/or advantages may be individually obtained by some embodiments and features described in the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages.

A circuit board according to the present disclosure will be described below with reference to the drawings.

First, terms will be defined in a first section.

In each drawing, the L axis, W axis, and T axis are mutually orthogonal and respectively indicate the length direction, width direction, and height direction of circuit boards <NUM> and <NUM>. Sometimes, the length direction, width direction, and height direction will be respectively referred to as the longitudinal direction, transverse direction, and vertical direction, as necessary. The length direction is an example of a first direction or a third direction, and the height direction is an example of a second direction.

<FIG> will be explained in a second section.

<FIG> is a top view illustrating a circuit board <NUM> according to a comparative example. <FIG> is a top view illustrating the central portion of one first power feed line <NUM> provided on the circuit board <NUM> illustrated in <FIG>, as well as the periphery of the central portion. <FIG> is an enlarged rear view of another end of one second power feed line <NUM> provided on the circuit board <NUM> illustrated in <FIG>, as well as the periphery of the other end. <FIG> is a cross-sectional view taken along line III-III in <FIG> as viewed from the direction indicated by an arrow B in the drawing. In <FIG>, <FIG>, and <FIG>, for convenience, the first connection conductor <NUM> is transparent and is thereby indicated by a dotted line.

<FIG> and <FIG> are also referenced in descriptions of a circuit board <NUM> according to the present disclosure. Therefore, the circuit board in these drawings is denoted by both of reference numerals <NUM> and <NUM>.

As illustrated in <FIG>, the circuit board <NUM> has a multilayer substrate <NUM>, a plurality of wiring layers <NUM>, a plurality of second connection conductors <NUM>, and at least one combination of the first power feed line <NUM>, a plurality of radiating elements <NUM>, the first connection conductor <NUM> and the second power feed line <NUM>.

The multilayer substrate <NUM> is a laminated structure formed by laminating a plurality of dielectric layers (insulating layers) in the T-axis direction in a rectangular parallelepiped form. The multilayer substrate <NUM> has a first main surface S1, which forms an upper surface, and a second main surface S3 opposite to the first main surface S1 in the height direction. The multilayer substrate <NUM> also has four side surfaces besides the first main surface S1 and second main surface S3.

<FIG> illustrates an example of four combinations, each of which includes the first power feed line <NUM>, a plurality of radiating elements <NUM>, the first connection conductor <NUM>, and the second power feed line <NUM>. These combinations have the same structure, so the description below will focus on one combination.

The first power feed line <NUM>, which is a strip line conductor extends in the L-axis direction on the first main surface S1. The central portion of the first power feed line <NUM> in the L-axis direction is defined a power feed point. The power feed point on the first power feed line <NUM> is joined to the first connection conductor <NUM>, which will be described later. Therefore, the power feed point forms a land L1.

The first power feed line <NUM> may be disposed between two dielectric layers that are adjacent in the T-axis direction (that is, the first power feed line <NUM> may be an interlayer power feed line).

The plurality of radiating elements <NUM> are brought close to the first power feed line <NUM> along it. The plurality of radiating elements <NUM> are disposed between one end and another end of the first power feed line <NUM>. Each two, adjacent in the L-axis direction, of the plurality of radiating elements <NUM> are placed with a predetermined spacing left between them. For convenience, the radiating elements <NUM> are illustrated only in <FIG>.

The plurality of radiating elements <NUM> are connected to the first power feed line <NUM> through, for example, conductors used for connection. Each radiating element <NUM> and the first power feed line <NUM> may be formed so that the radiating element <NUM> is joined to the first power feed line <NUM> through an electric field or capacitance.

Although there is no particular limitation on the shape of the radiating element <NUM>, it may have, for example, a rectangular, circular, C-like, or strip-line-like shape.

The first connection conductor <NUM> is, for example, a plated through-hole. It is formed so as to extend through the interior of the multilayer substrate <NUM> in the T-axis direction, from the first main surface S1 to the second main surface S3. More specifically, one end of the first connection conductor <NUM> abuts the land L1 (power feed point) on the first power feed line <NUM> and another end of the first connection conductor <NUM> abuts a land L3 (the other end of the second power feed line <NUM>) formed on the second power feed line <NUM>, which will be described later.

The second power feed line <NUM> is a strip line conductor. It is formed so as to, for example, extend in the L-axis direction on the second main surface S3. More specifically, as far as positions on an LW plane are concerned, one end of the second power feed line <NUM> is substantially identical to the one end of the first power feed line <NUM>, and the other end of the second power feed line <NUM> is substantially identical to the power feed point on the first power feed line <NUM>. The other end is joined to the first connection conductor <NUM> and thereby forms the land L3.

The second power feed line <NUM> may also be disposed between layers.

In this comparative example, the plurality of wiring layers <NUM> are disposed between layers in the multilayer substrate <NUM> as, for example, a ground layer. Each second connection conductors <NUM> is, for example, a via-hole conductor; it extends in the T-axis direction between two wiring layers (ground layers) <NUM> adjacent in the T-axis direction.

On the circuit board <NUM> structured as described above, a high-frequency signal (high-frequency current) in a millimeter wave band, for example, is supplied from a signal processing integrated circuit (IC), which is not illustrated, to the one end of the second power feed line <NUM>. This high-frequency signal is given from the other end of the second power feed line <NUM> through the first connection conductor <NUM> to the power feed point on the first power feed line <NUM>. At this power feed point, the high-frequency signal is essentially branched into two signals. One of the two signals is supplied to a backward half part 13b of the first power feed line <NUM>, the backward half part 13b being more backward than the power feed point on the first power feed line <NUM> in the L-axis direction. The other of the two signals is supplied to a forward half part 13a of the first power feed line <NUM>, the forward half part 13a being on the negative side in the L-axis direction. Each radiating element <NUM> receives electric power from the first power feed line <NUM> and emits an electric field. In central power feeding described above, it is prevented that a direction in which an electromagnetic wave is emitted is easily changed depending on the frequency in use, so a broad band can be used.

Each wiring layer (ground layer) <NUM> determines the characteristic impedance of a surrounding wire. The second connection conductors <NUM> have the effect of reducing the impedance of the first connection conductor <NUM>.

Conditions under which three-dimensional electromagnetic field analysis is performed for the circuit board <NUM> structured as described above are that, for example, the specific inductive capacity of the multilayer substrate <NUM> is <NUM> and the thickness of the multilayer substrate <NUM> is <NUM>.

<FIG> is a graph indicating, for each frequency, the magnitude of the electric power of a high-frequency signal supplied to the forward half part 13a and backward half part 13b of the first power feed line <NUM>, with frequency [GHz] on the horizontal axis and transmittance [dB] on the vertical axis. In <FIG>, electric power in the forward half part 13a is indicated by a solid line and electric power in the backward half part 13b is indicated by a broken line. It is found from <FIG> that electric power is not evenly distributed from the power feed point on the first power feed line <NUM> to the forward half part 13a and backward half part 13b. As described above, in central power feeding, it is prevented that a direction in which an electromagnetic wave is emitted is easily changed depending on the frequency in use, so a broad band can be used. However, if electric power is not evenly distributed to the forward half part 13a and backward half part 13b, the pattern of electromagnetic wave emission largely changes depending on the frequency in use. As a result, frequency bands available for the circuit board <NUM> may be narrowed.

Unevenness in electric power distribution as described above will be described. <FIG> illustrates the distribution of electric field intensity at a cross-section of a circuit board 5a, the cross-section being along a plane parallel to a TL plane, at a certain timing. In <FIG>, the closer to black the color of a portion is, the higher the electric field in the portion is; the closer to white the color of a portion is, the lower the electric field in the portion is.

The main structure of the circuit board 5a in <FIG> is similar to the main structure of the circuit board <NUM> in <FIG>. In <FIG>, therefore, elements equivalent to corresponding elements in <FIG> will be denoted by like reference characters and detailed descriptions of these equivalent elements will be omitted.

In the i distribution of electric field intensity around the first connection conductor <NUM> in <FIG>, the forward portion and backward portion are asymmetric with respect to the first connection conductor <NUM>. Therefore, it is also found that high-frequency signals are transferred to the interior of the circuit board 5a in a state in which the asymmetric distribution in electric field intensity is maintained between the forward portion and the backward portion.

A possible reason for the asymmetric distribution in electric field intensity will be described below. The second power feed line <NUM> extends from the other end (power feed point) only in one direction (in the example in <FIG>, the forward direction) and a high-frequency signal is transmitted through the second power feed line <NUM>. In the opposite direction (in the example in <FIG>, the backward direction), however, the other end is open. A parasitic capacitive component at this open portion causes the asymmetric distribution in electric field intensity. In the first power feed line <NUM>, therefore, high-frequency signals having different signal intensities and the like propagate from the power feed point to different portions, one of which is in one direction and the other of which is in the opposite direction. As a result, asymmetricity occurs in electric power as illustrated in <FIG>. As described above, it was found from three-dimensional electromagnetic field analysis that the asymmetric structure causes asymmetricity in electric power.

In a third section in which the circuit board <NUM> as illustrated in <FIG>, <FIG>, and <FIG> can be considered according to the above description, the circuit board <NUM> according to the present disclosure will be described with reference to <FIG> besides <FIG>, <FIG>, and <FIG>.

<FIG> is a top view illustrating the circuit board <NUM> according to the present disclosure. <FIG> is a top view illustrating the power feed point on the first power feed line <NUM> in illustrated in <FIG> as well as the periphery of the power feed point. <FIG> is an enlarged rear view of another end of a second power feed line <NUM> illustrated in <FIG>, as well as the periphery of the other end.

As illustrated in <FIG>, <FIG>, and <FIG>, the circuit board <NUM> differs from the circuit board <NUM> in that the circuit board <NUM> has the second power feed line <NUM> instead of the second power feed line <NUM>. Elements, included in the circuit board <NUM>, equivalent to corresponding elements included in the circuit board <NUM> will be denoted by like reference characters and descriptions of these equivalent elements will be omitted. For convenience, the ground layer <NUM> on the second main surface S3 is not illustrated in <FIG>.

Results in three-dimensional electromagnetic field analysis showed that when the thickness of the multilayer substrate <NUM> is sufficiently small, influence of asymmetricity as described above is small. More specifically, it was found that if λe designates the effective wavelength of a high-frequency signal, when the thickness of the multilayer substrate <NUM> is about smaller than λe/<NUM>, influence of asymmetricity can be reduced. However, when the thickness of the multilayer substrate <NUM> is to be determined, not only influence of asymmetricity but also other factors such as the number of wiring layers <NUM> and the impedances of wires need to be considered. Therefore, the thickness of the multilayer substrate <NUM> may not be smaller than λe/<NUM>. If, for example, a millimeter wave band is used, λe/<NUM> may become <NUM> or smaller. To assure high reliability, however, the thickness of the multilayer substrate <NUM> is, for example, λe/<NUM> or larger (more specifically, about <NUM> to about <NUM>). According to the present disclosure as well, the thickness of the multilayer substrate <NUM> is exemplarily λe/<NUM> or larger. In this case, influence of asymmetricity needs to be reduced by a method other than thinning the multilayer substrate <NUM>.

The second power feed line <NUM> is, for example, a strip line conductor formed from a plated pattern. The second power feed line <NUM> includes a first line part <NUM>, a second line part <NUM>, and a stub <NUM>.

The first line part <NUM> extends in the forward direction of the L axis on the second main surface S3. As far as positions on an LW plane are concerned, for example, one end of the first line part <NUM> is essentially identical to the one of the first power feed line <NUM>, and another end of the first line part <NUM> is substantially identical to the power feed point on the first power feed line <NUM>. The other end is joined to the first connection conductor <NUM> and thereby forms a land L5.

To reduce asymmetricity in the distribution of electric field intensity, according to the present disclosure, the first line part <NUM> and first power feed line <NUM> will be described, assuming that they extend in the same direction. However, this is not a limitation; the first line part <NUM> and first power feed line <NUM> may extend in different directions.

The second line part <NUM> branches from the first line part <NUM> at one end of the second line part <NUM>, and joints to the other end of the first line part <NUM> at another end of the second line part <NUM> from an L-axis direction side. More specifically, at a node N1 set on the first line part <NUM>, the second line part <NUM> branches at its one end from the first line part <NUM>, after which the second line part <NUM> is curved toward the L-axis direction side of the other end (land L5) of the first line part <NUM> so as to bypass the land L5, extends toward the negative side in the L-axis direction, and joints to the other end of the first line part <NUM> (that is, the land L5) from its backward side (that is, from the positive side in the L-axis direction).

Now, the length of the second line part <NUM> from the one end to the other end will be defined <NUM>.

First, φ will be defined as described below. The symbol φ is an amount by which the phase of a high-frequency signal is shifted in a portion P1 from the node N1 on the first line part <NUM> to its other end. In this case, the second line part <NUM> is designed to a length that is enough to shift the phase of a high-frequency signal by φ+2nπ (n is an arbitrary natural number). To reduce asymmetricity in the distribution of electric field intensity as much as possible, n is set to, for example, <NUM>.

In other words, the line length l1 is represented as in equation (<NUM>) below. <MAT> where λe is a know value representing the effective wavelength of the high-frequency signal.

There is no particular limitation on the shape of the second line part <NUM>. To reduce capacitive coupling with the land L5 as much as possible, for example, the second line part <NUM> is formed in a portion in which any point is equally distant from the land L5. That is, the second line part <NUM> is formed in an arc shape in a plan view viewed from above.

A transmission loss difference is caused by a line length difference Δ1 between the second line part <NUM> and the portion P1 in the first line part <NUM>. Specifically, the line length l1 of the second line part <NUM> is n×λe longer than the length of the portion P1. To reduce the transfer loss difference, therefore, the line width of the second line part <NUM>, for example, is larger than the line width of the portion P1. It suffices to design specific line widths of the portion P1 and second line part <NUM>, as necessary.

A distribution ratio of signal electric power at the node N1 depends on a ration between the characteristic impedance of the portion P1 and the characteristic impedance of the second line part <NUM>. The characteristic impedances of the portion P1 and second line part <NUM> can be changed by changing their line widths. More specifically, among lines made of materials having the same electric resistivity, the wider the line is, the lower the characteristic impedance is, so much electric power tends to be distributed to the line. Therefore, when the line width of the second line part <NUM> is made wider than the line width of the portion P1 as described above, it is possible to reduce a difference in electric power distributed to the forward half part 13a and backward half part 13b of the first power feed line <NUM>.

The stub <NUM> is provided to reduce the reflection of a high-frequency signal (that is, to match impedances) due to the branch of the line at the node N1 (that is, due to the node N1). On the first line part <NUM>, the stub <NUM> is positioned within a distance of λe/<NUM> from the node N1 toward the negative side in the L-axis direction.

Conditions under which three-dimensional electromagnetic field analysis is performed for the circuit board <NUM> structured as described above are the same as in the second section.

<FIG> illustrates the distribution of electric field intensity at a cross-section of a circuit board 1a at a certain timing, the cross-section being cut along a plane parallel to a TL plane. In <FIG> as well, the closer to black the color of a portion is, the higher the electric field in the portion is, as in <FIG>.

The circuit board 1a in <FIG> is substantially similar to the circuit board <NUM> in <FIG>. In <FIG>, therefore, elements equivalent to corresponding elements in <FIG> will be denoted by like reference characters and detailed descriptions of these equivalent elements will be omitted.

In <FIG>, symmetricity in the distribution of electric field intensity around the first connection conductor <NUM> is largely improved in the forward potion and the backward portion with respect to the first connection conductor <NUM> when compared with <FIG>. This symmetricity in the distribution of electric field intensity is achieved by the second power feed line <NUM> according to the present disclosure. Since the second power feed line <NUM> is provided, high-frequency signals that have substantially the same intensity and are substantially in phase are supplied to the first connection conductor <NUM> from the negative side and positive side in the L-axis direction, improving symmetricity in the distribution of electric field intensity.

In particular, since high-frequency signals that are substantially in phase are supplied to the first connection conductor <NUM> from both side in the L-axis direction as described above, the line length difference Δ1 between the second line part <NUM> and the portion P1 of the first line part <NUM> is n×λe (n is an arbitrary natural number).

<FIG> illustrates relationships of the phases of high-frequency signals entered into the first connection conductor <NUM> according to the present disclosure. In the example in <FIG>, these high-frequency signals are each a sine wave and n is <NUM>. In particular, the upper graph in <FIG> indicates a time waveform f1 of a high-frequency signal that passes through only the first line part <NUM> and reaches the land L5 (this high-frequency signal will be referred to below as the first high-frequency signal f1), and the lower graph in <FIG> indicates a time waveform f2 of a high-frequency signal that passes through the second line part <NUM> and reaches the land L5 (this high-frequency signal will be referred to below as the second high-frequency signal f2).

As illustrated in <FIG>, if the line length difference Δ1 is 2nπ, a phase delay of 2π occurs in the second high-frequency signal f2 with respect to the first high-frequency signal f1. However, the first high-frequency signal f1 and second high-frequency signal f2 have substantially the same intensity at the land L5. Therefore, symmetricity in the distribution of electric field intensity is improved as described above. In particular, when n is <NUM>, the transfer loss in the second line part <NUM> can be minimized, so symmetricity in the distribution of electric field intensity is further improved.

<FIG> is a graph indicating, for each frequency, the magnitude of the electric power of a high-frequency signal supplied to the forward half part 13a and backward half part 13b of the first power feed line <NUM> on the circuit board <NUM> that is designed so that the line length difference is about <NUM>, with frequency [GHz] on the horizontal axis and transmittance [dB] on the vertical axis. In <FIG>, electric power in the forward half part 13a is indicated by a solid line and electric power in the backward half part 13b is indicated by a broken line. <FIG> indicates that electric power is more evenly distributed from the power feed point on the first power feed line <NUM> to the forward half part 13a and backward half part 13b over a wide band (for example, from about <NUM> to about <NUM>) around the frequency band in use (<NUM>-GHz band).

First of all, the circuit board <NUM> according to the present disclosure has the first power feed line <NUM> disposed so as to be close to a plurality of radiating elements <NUM> and to extend in the L-axis direction, as described above. in addition, the circuit board <NUM> has the land L1 disposed so as to extend in the T-axis direction and to be placed at the central portion of the first power feed line <NUM> in the L-axis direction, and also has the first connection conductor <NUM> connected to one end of the circuit board <NUM>. The circuit board <NUM> further has the second power feed line <NUM> including the first line part <NUM>, which extends in the L-axis direction and joins to the other end (land L5) of the first connection conductor <NUM>, and the second line part <NUM>, which branches from the first line part <NUM> and joins to the other end (land L5) from an L-axis direction side. In this structure, it is possible to reduce a difference in power distributed to the forward half part 13a and backward half part 13b of the first power feed line <NUM> over a wide band around the frequency band in use. Furthermore, since the need to use a waveguide tube is eliminated, it is possible to provide the circuit board <NUM> that can be structured at a low cost.

Since the line length l1 of the second line part <NUM> is determined according to an integer multiple of the effective wavelength of a high-frequency signal, it is possible to make an approximate match between the phase of the first high-frequency signal f1 and the phase of the second high-frequency signal f2 (see <FIG>). Therefore, symmetricity in the distribution of electric field intensity can be improved in the forward half part 13a and backward half part 13b, so it is possible to reduce a difference in power distributed to the forward half part 13a and backward half part 13b of the first power feed line <NUM> over a wide band around the frequency band in use.

On the first line part <NUM> of the second power feed line <NUM>, the stub <NUM> is positioned within a distance equal to a half of the effective wavelength from the node N1 located between the first line part <NUM> and the second line part <NUM>, it is possible to reduce the reflection of a high-frequency signal at the node N1.

Since the wiring layers <NUM> are provided in the multilayer substrate <NUM>, the characteristic impedances of surrounding wires can be made adequate.

Both the first power feed line <NUM> and the second power feed line <NUM> extend in the L-axis direction, so it is possible to reduce a difference in power distributed to the forward half part 13a and backward half part 13b.

Since the line width of the second line part <NUM> is larger than the line width of the first line part <NUM>, transmission loss in the second line part <NUM> can be relatively reduced. As a result, it becomes easy to reduce a difference in power distributed to the forward half part 13a and backward half part 13b.

As illustrated in <FIG> and other drawings, the circuit board <NUM> includes a plurality of wiring layers <NUM> and a plurality of second connection conductors <NUM>, which are substantially symmetric with respect to a plane perpendicular to both the first power feed line <NUM> and the second power feed line <NUM>, which are linked together by the first connection conductor <NUM>. This can improve symmetricity in the distribution of electric field intensity in the forward half part 13a and backward half part 13b, so it is possible to reduce a difference in power distributed to the forward half part 13a and backward half part 13b of the first power feed line <NUM>.

The present disclosure can be realized by software, hardware, or software in cooperation with hardware.

Each functional block used in the description of the embodiment described above can be partly or entirely realized by an LSI such as an integrated circuit, and each process described in the embodiment may be controlled partly or entirely by the same LSI or a combination of LSIs. The LSI may be individually formed as chips, or one chip may be formed so as to include part or all of the functional blocks. The LSI may include a data input and output coupled thereto. The LSI here may be referred to as an IC, a system LSI, a super LSI, or an ultra LSI depending on a difference in the degree of integration.

However, the technique of implementing an integrated circuit is not limited to the LSI and may be realized by using a dedicated circuit, a general-purpose processor, or a special-purpose processor. In addition, a field programmable gate array (FPGA) that can be programmed after the manufacture of the LSI or a reconfigurable processor in which the connections and the settings of circuit cells disposed inside the LSI can be reconfigured may be used. The present disclosure can be realized as digital processing or analogue processing.

If future integrated circuit technology replaces LSIs as a result of the advancement of semiconductor technology or other derivative technology, the functional blocks could be integrated using the future integrated circuit technology. Biotechnology can also be applied.

Claim 1:
A circuit board comprising:
a substrate (<NUM>);
a first power feed line (<NUM>) provided on a surface (S1) of the substrate (<NUM>) and to extend in a first direction;
a first connection conductor (<NUM>) extending in a second direction orthogonal to the first direction, one end of the first connection conductor (<NUM>) being connected to the first power feed line (<NUM>) substantially at a central portion of the first power feed line (<NUM>) in the first direction; and
a second power feed line (<NUM>) that has a first line part (<NUM>), the first line part (<NUM>) joining to another end of the first connection conductor (<NUM>), and also has a second line part (<NUM>) branching from the first line part;
characterized in that
the first power feed line (<NUM>) is disposed so as to be close to a plurality of radiating elements (<NUM>);
the first line part (<NUM>) extends in a third direction orthogonal to the second direction, the second line part (<NUM>) joins to the another end from a third direction side;
a line length of the second line part (<NUM>) is determined according to an integer multiple of an effective wavelength of an alternate current to be supplied to the first line part (<NUM>); and
a thickness of the substrate (<NUM>) in the second direction is at least a half of the effective wavelength of the alternate current to be supplied to the first line part (<NUM>).