90-degree hybrid circuit

A 90-degree hybrid circuit includes a dielectric substrate, a first conductor that includes a conductor pattern formed on the dielectric substrate and electrically conducts between a first port and a second port, a second conductor that includes a conductor pattern formed on the dielectric substrate and electrically conducts between a third port and a fourth port, and a coupled line comprising a portion of the first conductor and a portion of the second conductor that face each other on front and back sides of the dielectric substrate. A first coupled line portion as the portion of the first conductor includes a coplanar line with first ground patterns formed to sandwich the first coupled line portion from both sides. A second coupled line portion as the portion of the second conductor includes a coplanar line with second ground patterns formed to sandwich the second coupled line portion from both sides.

The present application is based on Japanese patent application No. 2017-005001 filed on Jan. 16, 2017, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a 90-degree hybrid circuit.

2. Description of the Related Art

A branch-line type 90-degree hybrid circuit is known which has four quarter-wave lines combined into a square shape (see, e.g., JP 2011/211299 A). In a 90-degree hybrid circuit in which the quarter-wave lines respectively connect, e.g., between a first port1and second/third ports and between the second/third ports and a fourth port, a signal input from the first port is output from the first and fourth ports and is not output from the third port. In addition, output power of the signal output from the second port is equal to that from the fourth port, and the phase of the signal output from the second port2has a phase advance of 90° relative to the phase of the signal output from the fourth port.

Also, JP 2009/225065 A may be a prior art document related to the invention.

SUMMARY OF THE INVENTION

The branch-line type 90-degree hybrid circuit needs to have a combination of plural tiers (preferably, not less than three tiers) of 90-degree hybrid circuits to achieve a wide bandwidth and, therefore, it may cause an increase in size.

Also, since the quarter-wave line is generally composed of a microstrip line, the effect of a dielectric constituting a substrate may intensify so as to increase the dielectric loss. For this reason, an expensive substrate with low dielectric loss tangent may be needed so as to increase the cost.

It is an object of the invention to provide a 90-degree hybrid circuit that is compact, wideband and low-loss.

According to an embodiment of the invention, a 90-degree hybrid circuit comprises:

a dielectric substrate;

a first conductor that comprises a conductor pattern formed on the dielectric substrate and electrically conducts between a first port and a second port;

a second conductor that comprises a conductor pattern formed on the dielectric substrate and electrically conducts between a third port and a fourth port; and

a coupled line comprising a portion of the first conductor and a portion of the second conductor that face each other on front and back sides of the dielectric substrate,

wherein a first coupled line portion as the portion of the first conductor constituting the coupled line comprises a coplanar line with first ground patterns formed to sandwich the first coupled line portion from both sides, and

wherein a second coupled line portion as the portion of the second conductor constituting the coupled line comprises a coplanar line with second ground patterns formed to sandwich the second coupled line portion from both sides.

Effects of the Invention

According to an embodiment of the invention, a 90-degree hybrid circuit can be provided that is compact, wideband and low-loss.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment

An embodiment of the invention will be described below in conjunction with the appended drawings.

FIG. 1Ais a perspective view showing a 90-degree hybrid circuit in the present embodiment andFIG. 1Bis a see-through perspective view when viewed through a dielectric substrate.FIG. 2Ais a plan view showing the 90-degree hybrid circuit ofFIG. 1Awhen viewed from the front surface side andFIG. 2Bis a see-through diagram illustrating the back surface when viewed from the front surface side.

As shown inFIGS. 1A to 2B, a 90-degree hybrid circuit1is provided with a dielectric substrate2, a first conductor3electrically conducting between a first port P1and a second port P2, and a second conductor4electrically conducting between a third port P3and a fourth port P4. The first conductor3and the second conductor4are constructed from conductor patterns formed on the dielectric substrate2.

In the present embodiment, the first port P1is an input port, and the second port P2and the third port P3are output ports. That is, a signal input from the first port P1is split and output from the second port P2and the third port P3. Power of the signal output from the second port P2is substantially equal to power of the signal output from the third port P3. In addition, a difference between the phase of the signal output from the second port P2and the phase of the signal output from the third port P3is 90°. The fourth port P4is an isolation port. Therefore, even when a signal is input from the first port P1, the signal is not output from the fourth port P4(or power of the signal output from the fourth port P4is very small).

In the 90-degree hybrid circuit1of the embodiment, a coupled line (coupling line)5is composed of a portion of the first conductor3and a portion of the second conductor4which face each other from the front and back sides of the dielectric substrate2. Hereinafter, the portion of the first conductor3constituting the coupled line5is referred to as a first coupled line portion51, and the portion of the second conductor4constituting the coupled line5is referred to as a second coupled line portion52. The details of the coupled line5will be described later.

Firstly, specific shapes, etc., of the first conductor3and the second conductor4, except the portions constituting the coupled line5, will be described. In the following description, a vertical direction inFIG. 2Ais referred to as a width direction, a horizontal direction as a length direction, and a direction into the paper plane as a thickness direction, to simplify the description.

The first port P1and the fourth port P4are provided on the dielectric substrate2at one edge in the width direction. The second port P2and the third port P3are provided on the dielectric substrate2at the other edge in the width direction. The first port P1and the third port P3are positioned to face each other in the width direction, and the second port P2and the fourth port P4are positioned to face each other in the width direction. All ports P1to P4are provided on the same surface (the front surface) of the dielectric substrate2.

The entire first conductor3is formed on the front surface of the dielectric substrate2. The first conductor3integrally has the first coupled line portion51mentioned above, a first port connecting portion31having a linear shape and extending from the first port P1along the width direction, a first coupling portion32extending from a head end of the first port connecting portion31along the length direction and having a head end connected to one end of the first coupled line portion51, a second port connecting portion34having a linear shape and extending from the second port P2along the width direction, and a second coupling portion33extending from a head end of the second port connecting portion34along the length direction and having a head end connected to the other end of the first coupled line portion51. The first port P1is connected to the second port P2via the first port connecting portion31, the first coupling portion32, the first coupled line portion51, the second coupling portion33and the second port connecting portion34.

The lengths of the first port connecting portion31and the second port connecting portion34along the width direction are equal, and the lengths of the first coupling portion32and the second coupling portion33along the length direction are equal. The first coupled line portion51has a wider line width than the first and second port connecting portions31and34to adjust impedance. Each of the first and second coupling portions32and33has a constant width portion81and a wide width portion82. The constant width portions81extend from the head ends of the first and second port connecting portions31and34and have the same line width as the first and second port connecting portions31and34. Each wide width portion82connects a head end of the constant width portion81to the first coupled line portion51and is formed so that the line width gradually increases from the constant width portion81toward the first coupled line portion51. In the present embodiment, since through-holes93are formed on the second conductor4, each wide width portion82has a curved rim on the through-hole93side so as to keep an equal distance from the through-hole93. The details thereof will be described later. The entire shape of the first conductor3is 180-degree rotationally symmetric in a plan view.

The second conductor4is dividedly formed on the front and back surfaces of the dielectric substrate2. The second conductor4integrally has the second coupled line portion52mentioned above, a third port connecting portion41having a linear shape and extending from the third port P3along the width direction, a third coupling portion42coupling a head end of the third port connecting portion41to one end of the second coupled line portion52, a fourth port connecting portion44having a linear shape and extending from the fourth port P4along the width direction, and a fourth coupling portion43coupling a head end of the fourth port connecting portion44to the other end of the second coupled line portion52. The third port P3is connected to the fourth port P4via the third port connecting portion41, the third coupling portion42, the second coupled line portion52, the fourth coupling portion43and the fourth port connecting portion44.

The lengths of the third port connecting portion41and the fourth port connecting portion44along the width direction are equal to each other and are also equal to the lengths of the first port connecting portion31and the second port connecting portion34of the first conductor3along the width direction. Likewise, the lengths of the third coupling portion42and the fourth coupling portion43along the length direction are equal to each other and are also equal to the lengths of the first coupling portion32and the second coupling portion33of the first conductor3along the length direction.

The second coupled line portion52has a wider line width than the third and fourth port connecting portions41and44to adjust impedance. In addition, the second coupled line portion52is formed on the back surface of the dielectric substrate2. Each of the third and fourth coupling portions42and43is dividedly formed on the front and back surfaces of the dielectric substrate2.

Each of the third and fourth coupling portions42and43has a constant width portion91and a wide width portion92. The constant width portions91are formed on the front surface of the dielectric substrate2, extend from the head ends of the third and fourth port connecting portions41and44, and have a constant line width. Each wide width portion92is formed on the back surface of the dielectric substrate2, is connected to a head end of the constant width portion91via the through-hole93, and is formed so that the line width gradually increases from the through-hole93toward the second coupled line portion52. The entire shape of the second conductor4is 180-degree rotationally symmetric in a plan view.

As described above, in the present embodiment, the second conductor4is configured that a portion including the second coupled line portion52(i.e., the second coupled line portion52and the wide width portions92) is formed on the back surface of the dielectric substrate2and is electrically connected, via the through-holes93, to other portions (the third and fourth port connecting portions41and44and the constant width portions91) which are formed on the front surface of the dielectric substrate2and extend from the third and fourth ports P3and P4.

A ground pattern7is formed on the substantially entire back surface of the dielectric substrate2. A rectangular region formed by removing the ground pattern7is provided at the center portion (the center in the width direction as well as the length direction) of the back surface of the dielectric substrate2, and the coupled line5is arranged in this region. The ground pattern7is formed to partially overlap the first to fourth port connecting portions31,34,41and44and the constant width portions81and91. In other words, the first to fourth port connecting portions31,34,41and44and the constant width portions81and91are partially configured as a microstrip line with the ground pattern7overlapping on the back side.

Description of the Coupled Line5

Next, the coupled line5will be described. The coupled line5is composed of the first coupled line portion51as a portion of the first conductor3and the second coupled line portion52as a portion of the second conductor4which are respectively formed on the front and back surfaces of the dielectric substrate2so as to face each other and are electromagnetically coupled to each other.

In the 90-degree hybrid circuit1of the present embodiment, the first coupled line portion51is configured as a coplanar line with first ground patterns61formed to sandwich the first coupled line portion51from both sides. Likewise, the second coupled line portion52is configured as a coplanar line with second ground patterns62formed to sandwich the second coupled line portion52from both sides. The coupled line5is formed to have a length of one quarter of the center wavelength of the signal to be transmitted.

The coplanar lines are less likely to be affected by dielectric constituting the dielectric substrate2and have a small dielectric loss due to strong electromagnetic fields generated between the first and second coupled line portions51,52and the ground patterns61,62. Therefore, it is possible to use a cheap dielectric substrate2with relatively high dielectric loss tangent. In other words, by configuring the first and second coupled line portions51,52as coplanar lines, it is possible to realize the 90-degree hybrid circuit1with low losses at low cost.

The second ground patterns62are formed on the back surface of the dielectric substrate2so as to protrude from the ground pattern7into the center region not having the ground pattern7. The first ground patterns61are formed in substantially the same shape as the second ground patterns62(a shape symmetric with respect to the center of the dielectric substrate2in the thickness direction) when viewed from a thickness direction of the dielectric substrate2. The first ground patterns61are electrically connected to the second ground patterns62via plural through-holes63.

Each first ground pattern61is formed to have a rim portion following a rim portion of the first coupled line portion51, and a width of a gap between the first ground pattern61and the first coupled line portion51is substantially constant (about 1 mm in this example). Likewise, each second ground pattern62is formed to have a rim portion following a rim portion of the second coupled line portion52, and a width of a gap between the second ground pattern62and the second coupled line portion52is substantially constant (about 1 mm in this example).

In the meantime, signal transmission from the first port P1to the second port P2is performed via the first coupled line portion51which is configured as a coplanar line. In the coplanar line, signal propagation speed is relatively high since it is less likely to be affected by dielectric constituting the dielectric substrate2and permittivity of the air is dominant.

Meanwhile, signal transmission from the first port P1to the third port P3is performed via the coupled line5. In the coupled line5, since electromagnetic coupling occurs while sandwiching the dielectric substrate2in-between, electromagnetic field distribution exhibits high values inside dielectric constituting the dielectric substrate2. Therefore, the coupled line5is likely to be affected by dielectric constituting the dielectric substrate2and signal propagation speed is relatively low.

For this reason, when the first and second coupled line portions51and52are simply formed in, e.g., a linear shape, the difference between the phase of the signal output from the second port P2and the phase of the signal output from the third port P3deviates from 900 due to a difference in signal propagation speed, which may cause a degradation of electrical characteristics.

Therefore, in the 90-degree hybrid circuit1of the present embodiment, the first coupled line portion51is bent several times so as to have a longer line length than a straight-line distance between the two ends thereof. The second coupled line portion52is formed to have the same shape as the first coupled line portion51(a shape symmetric with respect to the center of the dielectric substrate2in the thickness direction) when viewed from a thickness direction of the dielectric substrate2.

In the present embodiment, the first coupled line portion51has a zigzag shape (triangle wave shape) as a whole and integrally has plural first inclined portions51a, which are linearly formed with an inclination of a predetermined angle with respect to a virtual reference line C along the length direction and are arranged in parallel to each other, and plural second inclined portions51b, which are linearly formed with an inclination in an opposite direction to the first inclined portions51aat the predetermined angle with respect to the reference line C and are arranged in parallel to each other so as to couple end portions of the adjacent first inclined portions51a.

Downwardly convex vertex portions a of the upper rim inFIG. 2Aand upwardly convex vertex portions b of the lower rim inFIG. 2Aare both located at the same position in the width direction (the positions at the center of the first coupled line portion51in the width direction, the positions on the reference line C shown in the drawing). In other words, a portion of the first coupled line portion51on one side of the reference line C in the width direction has a shape formed by arranging isosceles triangular conductors with no space in-between in the length direction so that the vertices face outward in the width direction and the bases are positioned along the length direction, and a portion of the first coupled line portion51on the other side in the width direction has a shape formed by arranging the same isosceles triangular conductors with no space in-between in the length direction so as to have a shift of a half cycle and so that the vertices face the opposite direction.

The second coupled line portion52is formed to have the same shape as the first coupled line portion51when viewed from a thickness direction of the dielectric substrate2. In the other words, the second coupled line portion52has a zigzag shape (triangle wave shape) as a whole and integrally has plural third inclined portions52a, which are linearly formed with an inclination of a predetermined angle with respect to the virtual reference line C and are arranged in parallel to each other, and plural fourth inclined portions52b, which are linearly formed with an inclination in an opposite direction to the first inclined portions52aat the predetermined angle with respect to the reference line C and are arranged in parallel to each other so as to couple end portions of the adjacent third inclined portions52a. The third inclined portions52aface the first inclined portions51awith the dielectric substrate2sandwiched therebetween, and the fourth inclined portions52bface the second inclined portions51bwith the dielectric substrate2sandwiched therebetween.

In the coplanar line transmitting a signal between the first port P1and the second port P2, the electromagnetic field is concentrated between the first coupled line portion51and the first ground pattern61and the electrical length of the coplanar line thus substantially coincides with the length of the rim of the first coupled line portion51, as indicated by a dashed line A inFIG. 3A.

On the other hand, in the coupled line5transmitting a signal between the first port P1and the third port P3, the electromagnetic field is concentrated between the first coupled line portion51and the second coupled line portion52and the electrical length of the coupled line5is thus substantially equal to a path roughly tracing the center of the conductor and is shorter than the length of the rim of the first coupled line portion51, as indicated by a dashed line B inFIG. 3B.

As such, by forming the first and second coupled line portions51and52into a zigzag shape, it is possible to increase the electrical length of the coplanar line with relatively high propagation speed and to reduce the electrical length of the coupled line with relatively low propagation speed, and it is thereby possible to match signal propagation time from the first port P1to the second and third ports P2and P3. As a result, the output phase difference between the second and third ports P2and P3can be accurately maintained at 90°.

The shape of the first and second coupled line portions51and52is not limited to a zigzag shape (triangle wave shape) and may be, e.g., a sine wave shape.

In addition, each corner portion connecting the first inclined portion51ato the second inclined portion51b(or the third inclined portion52ato the fourth inclined portion52b) has a pointed shape in the present embodiment, but may have a chamfered shape as does a corner portion53shown inFIG. 4. In this case, it is easy to form the first conductor3and the second conductor4by patterning and it is also possible to reduce the manufacturing cost.

Functions and Effects of the Embodiment

As described above, in the 90-degree hybrid circuit1of the present embodiment, the coupled line5is composed of a portion of the first conductor3electrically conducting between the first port P1and the second port P2and a portion of the second conductor4electrically conducting between the third port P3and the fourth port P4and is formed so that the portion of the first conductor3and the portion of the second conductor4face each other from the front and back sides of the dielectric substrate2, and the first coupled line portion51as the portion of the first conductor3constituting the coupled line5and the second coupled line portion52as the portion of the second conductor4constituting the coupled line5are configured as the coplanar lines.

Use of the coupled line5allows the 90-degree hybrid circuit1to have a smaller size than a conventional branch-line 90-degree hybrid circuit with a combination of four quarter-wave lines.

In addition, by using the coplanar lines in the coupled line5, an effect of dielectric loss tangent of dielectric constituting the dielectric substrate2and dielectric loss are reduced as compared to a conventional 90-degree hybrid circuit using quarter-wave lines having a microstrip structure. In addition, since it is less affected by the dielectric constituting the dielectric substrate2, it is possible to use a cheap dielectric substrate2with high dielectric loss tangent, hence, contributing to cost reduction.

When the 90-degree hybrid circuit1in the present embodiment was manufactured by way of trial, good characteristics were obtained in a bandwidth of 1.6 GHz to 2.2 GHz, and the wideband 90-degree hybrid circuit1with a fractional bandwidth of not less than 30% was obtained. In other words, in the present embodiment, it is possible to realize the compact and wideband 90-degree hybrid circuit1with low losses.

In addition, the 90-degree hybrid circuit1can be formed by patterning conductor patterns on the dielectric substrate2and is thus easily manufactured. In addition, since the coupled line5is configured to include coplanar lines, adjustment of characteristic impedance and designing of the coupling line are easier than, e.g., when conductors are simply arranged to face each other.

The 90-degree hybrid circuit1in the present embodiment can be used as, e.g., a frequency synthesizer or two-way splitter of an antenna device.

SUMMARY OF THE EMBODIMENTS

Technical ideas understood from the embodiment will be described below citing the reference numerals, etc., used for the embodiment. However, each reference numeral, etc., described below is not intended to limit the constituent elements in the claims to the members, etc., specifically described in the embodiment.

[1] A 90-degree hybrid circuit (1), comprising: a dielectric substrate (2); a first conductor (3) that comprises a conductor pattern formed on the dielectric substrate (2) and electrically conducts between a first port (P1) and a second port (P2); a second conductor (4) that comprises a conductor pattern formed on the dielectric substrate (2) and electrically conducts a third port (P3) and a fourth port (P4); and a coupled line (5) comprising a portion of the first conductor (3) and a portion of the second conductor (4) that face each other on front and back sides of the dielectric substrate (2), a first coupled line portion (51) as the portion of the first conductor (3) constituting the coupled line (5) comprises a coplanar line with first ground patterns (61) formed to sandwich the first coupled line portion (51) from both sides, and a second coupled line portion (52) as the portion of the second conductor (4) constituting the coupled line (5) comprises a coplanar line with second ground patterns (62) formed to sandwich the second coupled line portion (62) from both sides.

[2] The 90-degree hybrid circuit (1) defined by [1], wherein the first coupled line portion (51) is bent a plurality of times so as to have a longer line length than a straight-line distance between the two ends thereof, and the second coupled line portion (52) is formed to have the same shape as the first coupled line portion (51) when viewed in a thickness direction of the dielectric substrate (2).

[3] The 90-degree hybrid circuit (1) defined by [1] or [2], wherein the first to fourth ports (P1to P4) are provided on the front surface of the dielectric substrate (2), the first conductor (3) is formed on the front surface of the dielectric substrate (2), and the second conductor (4) is configured that a portion including the second coupled line portion is formed on the back surface of the dielectric substrate (2) and is electrically connected, via through-holes (93), to other portions formed on the front surface of dielectric substrate (2) and extending from the third and fourth ports (P3, P4).

[4] The 90-degree hybrid circuit (1) defined by any one of [1] to [3], wherein the first ground patterns (61) are electrically connected to the second ground patterns (62) via through-holes (63).

[5] The 90-degree hybrid circuit (1) defined by any one of [1] to [4], wherein the first coupled line portion (51) integrally comprises a plurality of first inclined portions (51a) and a plurality of second inclined portions (51b), the first inclined portions (51a) being linearly formed with an inclination of a predetermined angle with respect to a virtual reference line (C) and arranged in parallel to each other, and the second inclined portions (51b) being linearly formed with an inclination in an opposite direction to the first inclined portions (51a) at the predetermined angle with respect to the reference line (C) and arranged in parallel to each other so as to couple end portions of the adjacent first inclined portions (51a), and the second coupled line portion (52) is formed to have the same shape as the first coupled line portion (51) when viewed in a thickness direction of the dielectric substrate (2).

[6] The 90-degree hybrid circuit (1) defined by [5], wherein each corner portion connecting the first inclined portion (51a) to the second inclined portion (51b) has a chamfered shape.

Although the embodiment of the invention has been described, the invention according to claims is not to be limited to the embodiment. Further, please note that all combinations of the features described in the embodiment are not necessary to solve the problem of the invention.

The invention can be appropriately modified and implemented without departing from the gist thereof.