WAVEGUIDE-MICROSTRIP LINE CONVERTER

A waveguide-microstrip line converter includes a waveguide having an open end, a dielectric substrate having a first surface facing the open end and a second surface facing the opposite direction to the first surface, a ground conductor provided on the first surface and connected to the open end, the ground conductor being provided with a slot in a region enclosed by the end face of the open end, and a line conductor provided on the second surface. The line conductor includes a conversion section that performs power conversion between the line conductor and the waveguide, a microstrip line-provided at a distance from the conversion section in a first direction, and an impedance transformer provided between the conversion section and the microstrip line, for performing impedance matching between the conversion section and the microstrip line. A hole is formed in the conversion section.

FIELD

The present disclosure relates to a waveguide-microstrip line converter capable of converting power propagating through a waveguide and power propagating through a microstrip line into each other.

BACKGROUND

Waveguide-microstrip line converters have been known which can convert power propagating through a waveguide and power propagating through a microstrip line into each other. Waveguide-microstrip line converters are widely used in antenna devices that transmit high-frequency signals in a microwave band or a millimeter-wave band.

Patent Literature 1 discloses a waveguide-microstrip line converter in which a ground conductor is provided on one surface of a dielectric substrate, and a line conductor is provided on a surface of the dielectric substrate facing the opposite direction to the surface on which the ground conductor is provided. An open end of a waveguide is connected to the ground conductor. A slot is provided in a region of the ground conductor enclosed by the end face of the open end. The line conductor includes a conversion section that performs power conversion between the line conductor and the waveguide, microstrip lines spaced apart from the conversion section, and impedance transformers that are provided between the conversion section and the microstrip lines to perform impedance matching between the conversion section and the microstrip lines.

CITATION LIST

Patent Literature

Patent Literature 1: WO 2019/138468 A

SUMMARY

Technical Problem

In the waveguide-microstrip line converter disclosed in Patent Literature 1, the wider the line width of the conversion section is made, the more unnecessary electromagnetic radiation from the slot can be reduced. On the other hand, the wider the line width of the conversion section is made, the larger the difference between the line width of the conversion section and the line width of the microstrip lines, and the larger the difference between the characteristic impedance of the conversion section and the characteristic impedance of the microstrip lines. As a result, the impedance transformers need to perform matching for sharp impedance changes, thus causing a problem of a narrowed usable frequency band of high-frequency signals.

The present disclosure has been made in view of the above, and an object thereof is to provide a waveguide-microstrip line converter capable of achieving both the reduction of unnecessary electromagnetic radiation from a slot and the widening of the band of the waveguide-microstrip line converter.

Solution to Problem

In order to solve the above-described problem and achieve the object, a waveguide-microstrip line converter according to the present disclosure includes: a waveguide having an open end; a dielectric substrate having a first surface facing the open end and a second surface facing the opposite direction to the first surface; a ground conductor provided on the first surface and connected to the open end, the ground conductor being provided with a slot in a region enclosed by the end face of the open end; and a line conductor provided on the second surface. The line conductor includes: a conversion section that performs power conversion between the line conductor and the waveguide; a microstrip line provided at a distance from the conversion section in a first direction; and an impedance transformer provided between the conversion section and the microstrip line, for performing impedance matching between the conversion section and the microstrip line. A hole is formed in the conversion section.

Advantageous Effects of Invention

The waveguide-microstrip line converter according to the present disclosure has the effect of being able to achieve both: the reduction of unnecessary electromagnetic radiation from the slot; and the widening of the band of the waveguide-microstrip line converter.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a waveguide-microstrip line converter according to embodiments will be described in detail with reference to the drawings.

First Embodiment

FIG.1is a plan view illustrating an external configuration of a waveguide-microstrip line converter10according to a first embodiment.FIG.1illustrates, by broken lines, elements of the waveguide-microstrip line converter10provided on the back side of the sheet surface behind elements indicated by solid lines.FIG.2is a cross-sectional view taken along line II-II illustrated inFIG.1. The X axis, the Y axis, and the Z axis illustrated in each drawing are three axes perpendicular to each other. A direction parallel to the X axis is referred to as an X-axis direction that is a first direction; a direction parallel to the Y axis is referred to as a Y-axis direction that is a second direction; and a direction parallel to the Z axis is referred to as a Z-axis direction that is a third direction.

The waveguide-microstrip line converter10includes: a waveguide14; a dielectric substrate11; a ground conductor12; and a line conductor13including microstrip lines33. The waveguide-microstrip line converter10can convert power propagating through the waveguide14and power propagating through the microstrip lines33into each other. The waveguide14and the microstrip lines33are transmission paths that convey high-frequency signals.

FIG.3is a perspective view illustrating an external configuration of the waveguide14in the first embodiment. The waveguide14is a metal tube having a quadrangular tubular shape. The X-Y cross-sectional shape of the waveguide14is a rectangle having long sides parallel to the Y-axis direction and short sides parallel to the X-axis direction. In the waveguide14, an electromagnetic wave propagates through an internal space enclosed by metal tube walls19. The tube-axis direction of the waveguide14is parallel to the Z-axis direction. The tube axis is the center line of the waveguide14. The waveguide14has an open end16. The open end16is one end of the waveguide14in the tube-axis direction, and has an end face18of the same shape as the X-Y cross-sectional shape of the waveguide14. The end face18acts as a short-circuit surface connected to the ground conductor12illustrated inFIG.2. The other end of the waveguide14in the tube-axis direction acts as an input/output end17to which a high-frequency signal to be transmitted through the waveguide14is input or from which a high-frequency signal transmitted through the waveguide14is output. As illustrated inFIG.2, the end face18and the ground conductor12are connected in direct contact in the present embodiment, but may be connected in a noncontact manner. For example, a choke structure may be provided between the end face18and the ground conductor12so that the end face18and the ground conductor12are connected to each other in a noncontact manner.

The configuration of the waveguide14may be changed as appropriate. For example, the waveguide14may include a dielectric substrate through which a large number of through holes are formed, instead of the metal tube with the tubular tube walls19. Further, the waveguide14may be filled with a dielectric material in the internal space enclosed by the tube walls19. Furthermore, the waveguide14may be, for example, a waveguide of a shape with corners in an X-Y cross section having a curvature, or a ridge waveguide.

As illustrated inFIG.2, the dielectric substrate11is a flat-shaped member formed of a resin material. The dielectric substrate11has a first surface S1facing the open end16and a second surface S2facing the opposite direction to the first surface S1. The first surface S1and the second surface S2are both parallel to the X-axis direction and the Y-axis direction.

The ground conductor12is provided on the first surface S1of the dielectric substrate11. The ground conductor12is formed, for example, by attaching by pressure copper foil that is conductive metal foil to the first surface S1. The ground conductor12may be a metal plate that is formed in advance and then attached to the dielectric substrate11. The open end16is connected to the ground conductor12. A slot15is provided in a region of the ground conductor12enclosed by the end face18of the open end16. The slot15is formed by removing the conductor within an X-Y region of the ground conductor12enclosed by the end face18of the open end16. The slot15is an opening formed by removing a part of the ground conductor12. The slot15is formed, for example, by patterning the copper foil attached by pressure to the first surface S1.FIG.4is a plan view of the ground conductor12in the first embodiment. The shape of the slot15is a rectangle having long sides parallel to the Y axis and short sides parallel to the X axis.

The shape of the slot15is not particularly limited as long as it allows electromagnetic radiation.FIG.5is a plan view illustrating a modification of the slot15. The shape of the slot15may be, for example, an I shape with the width in the X-axis direction of both ends in the Y-axis direction is wider than the width in the X-axis direction of the center portion in the Y-axis direction. This shape strengthens an electric field in the center portion of the slot15, and strengthens electromagnetic coupling between the open end16of the waveguide14and the line conductor13illustrated inFIG.2. Consequently, power can be efficiently converted between the waveguide14and the line conductor13.

The line conductor13is provided on the second surface S2of the dielectric substrate11. The line conductor13on the second surface S2of the dielectric substrate11is provided to pass directly above the open end16of the waveguide14. The line conductor13is formed, for example, by patterning copper foil attached by pressure to the second surface S2. The line conductor13may be a metal plate that is formed in advance and then attached to the dielectric substrate11.

FIG.6is a plan view of the line conductor13in the first embodiment. InFIG.6, the slot15is illustrated by broken lines for reference. The line conductor13includes: a conversion section31that performs power conversion between the line conductor13and the waveguide14; the microstrip lines33provided at a distance in the X-axis direction from the conversion section31illustrated inFIG.6; and impedance transformers32that are provided between the conversion section31and the microstrip lines33to perform impedance matching between the conversion section31and the microstrip lines33. The conversion section31is located opposite the slot15across the dielectric substrate11illustrated inFIG.2. The conversion section31is provided in a position overlapping the slot15in the tube-axis direction of the waveguide14. In the present embodiment, the conversion section31is located immediately above the slot15. Hereinafter, a line length means the length of a transmission path along the propagation direction of an electromagnetic wave, and a line width means the width of a transmission path along a direction perpendicular to the line length.

The conversion section31, the impedance transformers32, and the microstrip lines33illustrated inFIG.6are integrally formed by one metal member, which is formed of metal foil or a metal sheet. The conversion section31and the adjacent impedance transformers32are formed to have different line widths. The impedance transformers32and the adjacent microstrip lines33are formed to have different line widths from each other.

The number of the microstrip lines33provided is two in total, one on each side of the conversion section31in the X-axis direction. The microstrip lines33are quadrilateral portions having a constant line width W0in the X-axis direction. The microstrip lines33are located in end portions of the line conductor13in the X-axis direction. The line length of the microstrip lines33is not limited to the illustrated example, and may be appropriately changed.

The conversion section31is a quadrilateral portion having a constant line width W1in the X-axis direction. The conversion section31is located in the center of the line conductor13in the X-axis direction. The line width W1of the conversion section31is wider than the line width W0of the microstrip lines33. That is, the relationship W1>W0holds. The line length of the conversion section31is a length corresponding to λ/2, where λ is the wavelength of a high-frequency signal transmitted through the line conductor13.

A hole31ais formed in the conversion section31. The position of the hole31ais not particularly limited, but is the center of the conversion section31in the present embodiment. The shape of the hole31ais not particularly limited, but is a quadrilateral in the present embodiment. The conversion section31and the hole31aare formed such that the relationships L2<λ/2 and W2<W1hold, where L2is the length of the hole31ain the X-axis direction, and W2is the length in the Y-axis direction. The conversion section31is provided with two wide portions31band two narrow portions31caround the hole31a. One wide portion31bis provided on each side of the hole31ain the X-axis direction, extending in the Y-axis direction. One narrow portion31cis provided on each side of the hole31ain the Y-axis direction, extending in the X-axis direction. The wide portions31bare quadrilateral portions having a constant line width W3in the X-axis direction. The line width W3is equal to the line width Wi.

That is, the relationship W3=W1holds. The narrow portions31care quadrilateral portions having a constant line width W4in the X-axis direction. The line width W4is narrower than the line width W1. In the present embodiment, the conversion section31and the hole31aare formed such that the relationship W4=(W1−W2)/2 holds.

The impedance transformers32are quadrilateral portions having a constant line width W5in the X-axis direction. One impedance transformer32is provided on each side of the conversion section31in the X-axis direction. The line width W5of the impedance transformers32is wider than the line width W0of the microstrip lines33. That is, the relationship W1>W0holds. The relationship between the line width W1of the conversion section31and the line width W5of the impedance transformers32is W1>W5inFIG.6, but is not particularly limited, and may be appropriately changed. The line length of the impedance transformers32is a length corresponding to λ/4.

Next, the operation of the waveguide-microstrip line converter10according to the present embodiment will be described with reference toFIGS.2and6. Here, a case where a high-frequency signal is transmitted from the waveguide14to the microstrip lines33will be described as an example.

As illustrated inFIG.2, an electromagnetic wave that has propagated inside the waveguide14reaches the ground conductor12. The electromagnetic wave that has reached the ground conductor12propagates to the conversion section31through the slot15. The propagation of the electromagnetic wave to the conversion section31includes generation of energy of the electromagnetic wave between the ground conductor12and the conversion section31. As illustrated inFIG.6, the electromagnetic wave that has propagated to the conversion section31propagates toward the two microstrip lines33. The waveguide-microstrip line converter10outputs high-frequency signals transmitted from the two microstrip lines33in the X-axis direction. The high-frequency signals output from both sides have opposite phases.

Next, effects of the waveguide-microstrip line converter10according to the present embodiment will be described.

The wider the line width W1of the conversion section31illustrated inFIG.6is made, the more unnecessary electromagnetic radiation from the slot15can be reduced. By adjusting the line width W1of the conversion section31, unnecessary electromagnetic radiation from discontinuous portions between the conversion section31and the impedance transformers32can be adjusted. Consequently, unnecessary electromagnetic radiation in the entire waveguide-microstrip line converter10can be controlled. On the other hand, the conversion section31, the impedance transformers32, and the microstrip lines33have characteristic impedances corresponding to their respective line widths. The wider the line width W1of the conversion section31is made, the larger the difference between the line width W1of the conversion section31and the line width W0of the microstrip lines33, that is, the difference between the characteristic impedance of the conversion section31and the characteristic impedance of the microstrip lines33. This requires matching for sharp impedance changes at the impedance transformers32, thus resulting in a narrowed usable frequency range of high-frequency signals. In the present embodiment, by forming the hole31ain the conversion section31, the wide portions31bhaving the line width W3and the narrow portions31chaving the line width W4are formed in the conversion section31. Here, in the conversion section31, the characteristic impedance corresponding to the line width W4is referred to as Z4. The two narrow portions31chaving the line width W4are present in parallel in regions of the conversion section31located immediately above the slot15. Thus, the characteristic impedance of the conversion section31immediately above the slot15is Z4/2. By contrast, if the conversion section31does not have the hole31a, the characteristic impedance of the conversion section31immediately above the slot15is Z1corresponding to the line width W1. Since the characteristic impedance Z4/2 is smaller than the characteristic impedance Z1, the relationship Z4/2<Z1holds. Thus, even when the line width W1of the conversion section31is increased, the difference in characteristic impedance between the conversion section31and the microstrip lines33can be reduced by the narrow portions31c. This eliminates the need for matching for sharp impedance changes at the impedance transformers32, widening the usable frequency band of high-frequency signals. That is, the present embodiment can achieve both the reduction of unnecessary electromagnetic radiation from the slot15and the widening of the band of the waveguide-microstrip line converter10. Since the size of the hole31ais smaller than λ, the hole31ahas little effect on the reduction of unnecessary electromagnetic radiation from the slot15.

The line width W1of the conversion section31illustrated inFIG.6is smaller than the long sides of the waveguide14and is smaller than the length of the slot15in the Y-axis direction. The conversion of power from the waveguide14to the conversion section31is not necessarily controlled by physical dimensions, and sufficient electromagnetic coupling between the waveguide14and the conversion section31allows efficient conversion.

In the microstrip lines33illustrated inFIG.6, the characteristic impedance corresponding to the line width W0is referred to as Z0. The difference in line width between the conversion section31and the microstrip lines33is relatively large. Thus, if the microstrip lines33directly adjoin the conversion section31, power loss increases due to the mismatch between the characteristic impedance Z1of the conversion section31and the characteristic impedance Z0of the microstrip lines33. In this regard, in the present embodiment, the impedance transformers32having a line width wider than that of the microstrip lines33and narrower than that of the conversion section31are provided between the conversion section31and the microstrip lines33, so that impedance matching between the conversion section31and the microstrip lines33can be performed, and thus power loss can be reduced. Consequently, high electrical performance can be obtained without a through hole being provided in the dielectric substrate11illustrated inFIG.2.

The present embodiment eliminates the need for a through hole in the dielectric substrate11illustrated inFIG.2, and thus allows the simplification of a manufacturing process and the reduction of manufacturing costs by the omission of through hole processing. In addition, the present embodiment can avoid a situation where electrical performance is degraded by the breakage of a through hole, and thus can improve reliability and obtain stable electrical performance. When the waveguide-microstrip line converter10is used in a feed circuit of an antenna device (not illustrated), the antenna device can obtain stable transmission power and reception power.

There is a conventionally known configuration in which a fine gap is provided in a conductor of a portion corresponding to the conversion section31illustrated inFIG.6to divide a line, and a high-frequency signal is transmitted by electromagnetic coupling. If a defect occurs in the processing of the gap, an error can occur in the line length. By contrast, the line conductor13of the present embodiment is one metal member with portions from the conversion section31to the microstrip lines33continuously formed without divisions. The present embodiment eliminates the need to form a gap in the line conductor13, and thus can avoid the problem of a gap processing defect, and can facilitate the processing of the line conductor13.

In the waveguide-microstrip line converter10illustrated inFIG.1, unnecessary electromagnetic radiation can occur from the slot15or from portions of the line conductor13where the line width is discontinuous. By adjusting the dimensions of the slot15and the portions of the line conductor13, the amplitude and phase of a radiated electromagnetic wave can be adjusted. By adjusting the amplitude and phase of a radiated electromagnetic wave, unnecessary electromagnetic radiation in a specific direction such as toward the +side of the Z axis from the waveguide-microstrip line converter10may be reduced, or unnecessary electromagnetic radiation may be evenly diffused in all directions so that large power is not radiated in any direction. Even with this, the waveguide-microstrip line converter10can obtain high electrical performance.

The present embodiment has illustrated the case where a high-frequency signal is transmitted from the waveguide14to the microstrip lines33, but high-frequency signals may be transmitted from the microstrip lines33to the waveguide14. In this case, high-frequency signals having opposite phases are input to the two microstrip lines33. Even with this, power loss in the waveguide-microstrip line converter10can be reduced. The shape of the hole31ais a quadrilateral in the present embodiment, but may be a shape other than a quadrilateral such as a circle, a trapezoid, or a triangle. The center of the hole31acoincides with the center of the conversion section31in the present embodiment, but may be shifted from the center of the conversion section31in at least one of the X-axis direction and the Y-axis direction. The conversion section31is located immediately above the slot15in the present embodiment, which is not intended to limit the positional relationship between the conversion section31and the slot15. That is, the waveguide-microstrip line converter10can be arranged with the tube-axis direction of the waveguide14directed not only in the vertical direction but also in any direction. It is only required that the conversion section31and the slot15are in positions overlapping each other in the tube-axis direction of the waveguide14.

Second Embodiment

FIG.7is a plan view illustrating an external configuration of a waveguide-microstrip line converter51according to a second embodiment.FIG.8is a plan view of a line conductor52in the second embodiment. InFIG.8, the slot15is indicated by broken lines for reference. The same portions as those in the first embodiment described above are denoted by the same reference numerals without duplicate explanations. In the second embodiment, the line conductor52is provided instead of the line conductor13of the first embodiment.

As illustrated inFIG.7, the line conductor52includes: the conversion section31that is located opposite the slot15across the dielectric substrate11to perform power conversion between the line conductor52and the waveguide14; the microstrip lines33provided at a distance from the conversion section31in the X-axis direction; and the impedance transformers32that are provided between the conversion section31and the microstrip lines33to perform impedance matching between the conversion section31and the microstrip lines33.

Each impedance transformer32includes: a first impedance transformation section32a; a second impedance transformation section32bprovided at a distance from the first impedance transformation section32ain the X-axis direction; and a third impedance transformation section32cprovided between the first impedance transformation section32aand the second impedance transformation section32band having a line width smaller than both the line width of the first impedance transformation section32aand the line width of the second impedance transformation section32b.

The first impedance transformation section32a, the third impedance transformation section32c, and the second impedance transformation section32bare arranged in this order from the conversion section31toward the microstrip line33. As illustrated inFIG.8, the first impedance transformation section32ahas a constant line width W6in the X-axis direction. The second impedance transformation section32bhas a constant line width W7in the X-axis direction. The third impedance transformation section32chas a constant line width W8in the X-axis direction. The line width W8of the third impedance transformation section32cis narrower than the line width W6of the first impedance transformation section32a. That is, the relationship W8<W6holds.

The second impedance transformation section32bis located between the third impedance transformation section32cand the microstrip line33. The line width W7of the second impedance transformation section32bis wider than both the line width W8of the third impedance transformation section32cand the line width W0of the microstrip line33. That is, the relationships W7>W8and W7>W0hold. The line lengths of the second impedance transformation section32band the third impedance transformation section32care each a length corresponding to λ/4.

The first impedance transformation section32a, the second impedance transformation section32b, and the third impedance transformation section32chave characteristic impedances corresponding to their respective line widths. Here, the characteristic impedance of the first impedance transformation section32ais referred to as Z6corresponding to the line width W6. The characteristic impedance of the second impedance transformation section32bis referred to as Z7corresponding to the line width W7. The characteristic impedance of the third impedance transformation section32cis referred to as Z8corresponding to the line width W8. The characteristic impedance Z8is larger than the characteristic impedance Z6. That is, the relationship Z8>Z6holds. The characteristic impedance Z7is smaller than both the characteristic impedance Z8and the characteristic impedance Z0. That is, the relationships Z7<Z8and Z7<Z0hold.

In the present embodiment, as illustrated inFIG.7, the waveguide-microstrip line converter51is provided with the first impedance transformation sections32aand the second impedance transformation sections32bhaving a line width wider than that of the microstrip lines33, so that impedance matching between the conversion section31and the microstrip lines33can be performed. Consequently, power loss can be reduced.

In the present embodiment, as illustrated inFIG.8, the third impedance transformation sections32cand the second impedance transformation sections32bfunction to reduce an impedance mismatch due to the difference in line width between the first impedance transformation sections32aand the microstrip lines33. The line conductor52includes the first impedance transformation sections32a, the second impedance transformation sections32b, and the third impedance transformation sections32c, which are portions with the line widths varied stepwise, so that sharp changes in impedance in the propagation of an electromagnetic wave can be mitigated. Consequently, power loss can be effectively reduced. Note that a high-frequency signal may be input from the waveguide14and output from each microstrip line33, or may be input from each microstrip line33and output from the waveguide14.

Third Embodiment

FIG.9is a plan view illustrating an external configuration of a waveguide-microstrip line converter53according to a third embodiment.FIG.10is a plan view of a line conductor54in the third embodiment. InFIG.10, the slot15is indicated by broken lines for reference. The same portions as those in the second embodiment described above are denoted by the same reference numerals without duplicate explanations. In the present embodiment, the line conductor54is provided instead of the line conductor52of the second embodiment. The present embodiment is different from the second embodiment in the extending direction of the microstrip lines33.

In the present embodiment, as illustrated inFIG.9, the microstrip lines33extend from the second impedance transformation sections32bin the Y-axis direction perpendicular to the X-axis direction. That is, the extending direction of the microstrip lines33is parallel to the Y-axis direction. In the microstrip lines33, high-frequency signals are propagated in the Y-axis direction. As illustrated inFIG.10, the second impedance transformation sections32band the microstrip lines33are arranged such that an edge36of the second impedance transformation sections32bin the X-axis direction and an edge37of the microstrip lines33in the X-axis direction form one straight line along the Y-axis direction. This configuration allows the microstrip lines33to be extended in the Y-axis direction while suppressing unnecessary electromagnetic radiation at bends between the second impedance transformation sections32band the microstrip lines33.

Between the second impedance transformation sections32band the microstrip lines33, a portion where the line width between the second impedance transformation sections32band the microstrip lines33is discontinuous and a bend in the transmission path are in one body. If the microstrip lines33of the constant line width include a bend between a portion extended in the X-axis direction and a portion extended in the Y-axis direction, unnecessary electromagnetic radiation can occur at two portions, the portion where the line width between the second impedance transformation sections32band the microstrip lines33is discontinuous and the bend in the microstrip lines33. In the present embodiment, since the portion where the line width is discontinuous and the bend in the transmission path are formed in one body, unnecessary electromagnetic radiation can occur at one place. This allows the waveguide-microstrip line converter53that transmits high-frequency signals between portions extending in directions perpendicular to each other to reduce power loss due to unnecessary electromagnetic radiation. Note that a high-frequency signal may be input from the waveguide14and output from each microstrip line33, or may be input from each microstrip line33and output from the waveguide14.

Next, a modification of the waveguide-microstrip line converter53according to the third embodiment will be described.FIG.11is a plan view of a line conductor55in the modification of the third embodiment. InFIG.11, the slot15is indicated by broken lines for reference. The line conductor55in the present modification is different from the line conductor54described above in that the extending directions of the second impedance transformation sections32band the third impedance transformation sections32care oblique directions, and stubs34are added.

The first impedance transformation sections32aextend in the X-axis direction. The second impedance transformation sections32band the third impedance transformation sections32cextend in directions oblique to the X-axis direction and the Y-axis direction. The second impedance transformation sections32band the third impedance transformation sections32care inclined toward the +side of the Y axis from the first impedance transformation sections32atoward the microstrip lines33. Thus, the line length of the microstrip lines33can be shortened. The loss of power due to the properties of the material of the dielectric substrate11and the loss of power due to the conductivity of the line conductor55are substantially proportional to the line length of the entire line conductor55. Therefore, since the length of the microstrip lines33can be shortened, power loss due to the transmission of high-frequency signals can be reduced.

The positions of the second impedance transformation sections32band the third impedance transformation sections32cmay be adjusted to bring the extending directions of the second impedance transformation sections32band the third impedance transformation sections32ccloser to the X-axis direction or the Y-axis direction. By thus adjusting the positions of the second impedance transformation sections32band the third impedance transformation sections32c, the positions of discontinuous portions of the line conductor55and the amplitude and phase of electromagnetic waves radiated from the discontinuous portions can be adjusted, so that unnecessary electromagnetic waves radiated from the line conductor55can be reduced.

The line conductor55includes the two stubs34that are branch portions branching off from the conversion section31. The two stubs34are provided in the center position of the conversion section31in the X-axis direction. One stub34extends from an edge of the conversion section31on the +side of the Y axis toward the +side of the Y axis. The other stub34extends from an edge of the conversion section31on the −side of the Y axis toward the −side of the Y axis. An end35of each stub34facing the opposite direction to the conversion section31is an open end.

InFIG.11, the center positions of the stubs34in the X-axis direction coincide with the center position of the slot15in the X-axis direction. In this case, the line conductor55has symmetry with respect to the center of the slot15, so that propagation of power to the two stubs34does not occur. However, an error in the manufacturing of the line conductor55or the like can cause a misalignment between the center position of the line conductor55in the X-axis direction and the center position of the slot15in the X-axis direction, causing misalignments between the center positions of the stubs34in the X-axis direction and the center position of the slot15in the X-axis direction.

Electric fields are produced in the stubs34with the misalignment between the center position of the line conductor55and the center position of the slot15. Since the ends35of the stubs34are open ends, boundary conditions for the electric fields to become zero at connections between the stubs34and the conversion section31are satisfied. This ensures electrical symmetry in the line conductor55, so that the phases of high-frequency signals output from the two microstrip lines33become opposite to each other. The provision of the stubs34in this manner can reduce the effect of a misalignment between the center position of the line conductor55and the center position of the slot15on high-frequency signals. That is, by ensuring the electrical symmetry using the two stubs34, variations in the phases of high-frequency signals in the microstrip lines33can be reduced. Note that only one stub34may be provided to the line conductor55. When only one stub34is provided, the stub34may be provided at either the edge of the conversion section31on the +side of the Y axis or the edge on the −side of the Y axis.

The present modification adopts both making the extending directions of the second impedance transformation sections32band the third impedance transformation sections32coblique directions and adding the stubs34, but may adopt only one of them. That is, the line conductor54of the third embodiment illustrated inFIG.10may have a configuration in which the extending directions of the second impedance transformation sections32band the third impedance transformation sections32care made oblique directions illustrated inFIG.11, and the stubs34illustrated inFIG.11are not added. Alternatively, in the line conductor54of the third embodiment illustrated inFIG.10, the stubs34illustrated inFIG.11may be added without changing the extending directions of the second impedance transformation sections32band the third impedance transformation sections32c.

Fourth Embodiment

FIG.12is a plan view illustrating an external configuration of a waveguide-microstrip line converter56according to a fourth embodiment.FIG.13is a plan view of a line conductor57in the fourth embodiment. InFIG.13, the slot15is indicated by broken lines for reference. The same portions as those in the third embodiment described above are denoted by the same reference numerals without duplicate explanations. In the present embodiment, the line conductor57is provided instead of the line conductor55in the modification of the third embodiment. The present embodiment is different from the modification of the third embodiment described above in including two first microstrip lines33a, a second microstrip line71, a third microstrip line81, a fourth microstrip line83, and a fourth impedance transformation section82illustrated inFIG.13. In the following, when the two first microstrip lines33aare distinguished, one located on the +side of the X axis is referred to as a first microstrip line33b, and the other located on the −side of the X axis as a first microstrip line33c. The configuration of the first microstrip lines33band33cis similar to the configuration of the microstrip lines33in the first to third embodiments described above.

As illustrated inFIG.13, the second microstrip line71is connected to the first microstrip line33c. The second microstrip line71includes: a first area72extending from the end of the first microstrip line33con the +side of the Y axis toward the +side of the Y axis; a second area73extending in an oblique direction from the end of the first area72on the +side of the Y axis toward the +side of the X axis so as to be located on the +side of the Y axis; and a third area74extending from the end of the second area73facing the opposite direction to the first area72toward the +side of the X axis.

A first bend75is provided between the first area72and the second area73. A second bend76forming an obtuse angle is provided between the second area73and the third area74. The line width W9of the second microstrip line71is equal to the line width W0of the first microstrip lines33a. That is, the relationship W9=W0holds.

The third microstrip line81extends from the end of the first microstrip line33bon the +side of the Y axis toward the +side of the Y axis. The line width W10of the third microstrip line81is equal to the line width W0of the first microstrip lines33a. That is, the relationship W10=W0holds.

The fourth impedance transformation section82is located between the third area74of the second microstrip line71and the third microstrip line81, and the fourth microstrip line83. The fourth impedance transformation section82performs impedance matching between the second microstrip line71and the third microstrip line81, and the fourth microstrip line83. The line length of the fourth impedance transformation section82is a length corresponding to λ/4.

The fourth microstrip line83extends from the end of the fourth impedance transformation section82on the +side of the X axis toward the +side of the X axis. The fourth microstrip line83is located in an end portion of the line conductor57in the X-axis direction. The line width and the line length of the fourth microstrip line83are not particularly limited, and may be appropriately changed.

In the first to third embodiments described above, the two microstrip lines33act as independent input/output ends, and the number of the microstrip lines33acting as the input/output ends is two. On the other hand, in the present embodiment, the two first microstrip lines33band33care connected to the single fourth microstrip line83via the second microstrip line71, the third microstrip line81, and the fourth impedance transformation section82. The number of the fourth microstrip line83, acting as an input/output end, is one. Antennas (not illustrated) may be connected to the ends of the microstrip lines33and the fourth microstrip line83, which act as the input/output ends. In this case, in the above-described first to third embodiments, since the number of the microstrip lines33acting as the input/output ends is two, two antennas are connected to each of the waveguide-microstrip line converters10,51, and53. On the other hand, in the present embodiment, since the single fourth microstrip line83acts as the input/output end, one antenna is connected to the waveguide-microstrip line converter56. Thus, the present embodiment is effective when one antenna is connected.

Next, the operation of the waveguide-microstrip line converter56will be described with reference toFIGS.12and13. Here, a case where a high-frequency signal is transmitted from the waveguide14to the fourth microstrip line83will be described as an example.

An electromagnetic wave that has propagated inside the waveguide14illustrated inFIG.12propagates to each of the two first microstrip lines33band33cvia the conversion section31and others. As illustrated inFIG.13, the phase of the high-frequency signal at the boundary77between the first microstrip line33cand the second microstrip line71is opposite to the phase of the high-frequency signal at the boundary78between the first microstrip line33band the third microstrip line81.

The high-frequency signal that has passed through the boundary77propagates to the fourth microstrip line83via the second microstrip line71and the fourth impedance transformation section82. The high-frequency signal that has passed through the boundary78propagates to the fourth microstrip line83via the third microstrip line81and the fourth impedance transformation section82. The waveguide-microstrip line converter56illustrated inFIG.12outputs the high-frequency signal transmitted from the fourth microstrip line83toward the +side of the X axis. In the present embodiment, the line length of the second microstrip line71is set such that the phase of the high-frequency signal that has passed through the second microstrip line71becomes the same as the phase of the high-frequency signal that has passed through the third microstrip line81in the fourth impedance transformation section82to which the second microstrip line71and the third microstrip line81are connected.

Here, a line length L0is the sum of the line length of the first microstrip line33cand the line length of the first area72of the second microstrip line71illustrated inFIG.13. The line length L0is preferably as short as possible. The line length L0is preferably, for example, a length of λ/4 or less, and is more preferably shorter than λ/4 . The shorter the line length L0is made, the closer the first bend75is to the second impedance transformation section32b. This brings together the bends formed between the second impedance transformation section32blocated on the −side of the X axis and the first microstrip line33cand between the first microstrip line33cand the second microstrip line71in a loop-shaped transmission path. As a result of bringing together the bents in the transmission path, the number of places where unnecessary electromagnetic radiation can occur can be reduced. Consequently, the line conductor57including the loop-shaped transmission path can reduce power loss due to unnecessary electromagnetic radiation.

The degree of the angle of the second bend76is smaller than the degree of the angle of the first bend75, and thus unnecessary electromagnetic radiation due to the provision of the second bend76can be suppressed. Note that the second bend76may be omitted from the second microstrip line71. That is, the second area73of the second microstrip line71may be extended in the X-axis direction from the first bend75and connected to the fourth impedance transformation section82, or may be extended in an oblique direction from the first bend75to the fourth impedance transformation section82.

The present embodiment can have the same effects as those of the first to third embodiments. Further, the present embodiment can reduce power loss due to unnecessary electromagnetic radiation in the loop-shaped transmission path by setting the line length L0to a length of λ/4 or less. This can provide stable and high electrical performance and can improve reliability.

Note that a high-frequency signal may be input from the waveguide14and output from the fourth microstrip line83, or a high-frequency signal may be input from the fourth microstrip line83and output from the waveguide14. Further, the fourth impedance transformation section82may be omitted, the second microstrip line71and the third microstrip line81may each be directly connected to the fourth microstrip line83, and an impedance transformation section (not illustrated) may be provided in the middle of each of the second microstrip line71and the third microstrip line81. Furthermore, the extending direction of each of the fourth impedance transformation section82and the fourth microstrip line83may be a direction other than the X-axis direction.

The configurations described in the above embodiments illustrate an example and can be combined with another known art. The embodiments can be combined with each other. The configurations can be partly omitted or changed without departing from the gist.

REFERENCE SIGNS LIST