Directional coupler, antenna device, and transceiver

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a directional coupler using a dielectric guide, and to an antenna device and a transceiver using the directional coupler.

2. Description of the Related Art

Conventionally, a dielectric guide, comprising a dielectric strip provided between two conductive plates, is used as a guide for transmission in the milliwave band and the like. When forming a milliwave circuit using such dielectric guides, a directional coupler is used in a portion where electrical power is split between two dielectric guides.

A conventional directional coupler using dielectric guides comprises two dielectric strips, having a linear portion and a curved portion, which are provided at a predetermined distance apart between two conductive plates. The dielectric strips are arranged close together and the dielectric guides are coupled at this closely arranged portion.

A milliwave radar is an example of the milliwave circuit using dielectric guides described above. An antenna device used in a milliwave radar comprises a dielectric lens and a primary emitter provided at the focal point of the dielectric lens.

However, since the direction of the antenna in the conventional milliwave radar is fixed, in certain conditions it is not possible to achieve the intended sensitivity and measurements, as will be explained below. For instance, as shown in

FIG. 22

, when a vehicle is traveling on a multi-lane road, it is not possible to determine immediately whether other vehicles in front of it are traveling in the same lane based only on waves reflected from the other vehicles. That is, in

FIG. 22

, when the vehicle Cm emits a beam B

2

, it picks up not only waves reflected from the vehicle Ca which is traveling in front, but also waves reflected from the vehicle Cb which is traveling in the opposite lane. Furthermore, as shown in the example of

FIG. 23

, when the vehicle Cm emits a beam B

1

in the forward direction, it is unable to detect the vehicle Ca which is traveling in front in the same lane. Moreover, as shown in

FIG. 24

, when traveling on an curving road, even though the vehicle Cm emits a beam B

1

in the forward direction, it cannot detect the vehicle Ca in front of it.

One conceivable solution is to provide an antenna device, combining a primary emitter and a dielectric lens, in which the direction of the beam is tilted by changing the position of the primary emitter. In order to change the position of the primary emitter, the configuration should be arranged so that the dielectric guide connecting to the primary emitter and the other dielectric guide connecting to the circuit can be relatively displaced while remaining coupled with low loss. To achieve this, the configuration of the directional coupler using dielectric guides described above need only be arranged so that two dielectric guides can be relatively displaced.

However, the separated positions (separated faces) of the two dielectric guides of the directional coupler are parallel to the two dielectric strips provided closely together. With this configuration, the end faces of the conductive plates on either side of the dielectric strips are provided parallel to the direction of propagation of the electromagnetic waves of the two dielectric guides, and consequently the path of the current flowing through the conductive plates is broken at the end face portions of the conductive plates, causing reflection. As a result, there are problems such as the creation of unwanted modes other than the propagation mode, increased loss, or an inability to obtain desired characteristics of the directional coupler, etc.

The above example describes case where the two dielectric guides of the directional coupler portion are relatively displaced, but the directional coupler can be used when forming a single device incorporating circuit modules using dielectric guides, to couple the dielectric guides between the circuit modules. In this case too, the path of the current flowing through the conductive plates is broken between the circuit modules, causing reflection. As a result, there are problems of increased loss and inability to obtain desired signal transmission characteristics between the circuit modules.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a directional coupler comprising two separated dielectric guides, wherein the above problems of reflection and loss are eliminated.

To provide dielectric strips of two dielectric guides of a directional coupler close together in a predetermined region only, a bend must be provided in dielectric guide portions joined to the directional coupler. However, to reduce loss due to conversion from the LSM mode to the LSE mode, for instance, the radius of curvature of the bend must be large. As a result, the overall size of the device is increased, and when it is used to form an antenna device, the moving portion cannot be made light, making it difficult to deflect the beam quickly. On the other hand, when the space between opposing faces of the two conductive plates clasping the dielectric strip is made narrow, although the radius of curvature of the bend can be set freely as long as dielectric guides transmitting only in the LSM01 mode as used, the coupling portion must be made long in order to obtain adequate coupling, inevitably increasing the overall size of the device and making it difficult to lighten the moving portion. If the space between the dielectric strips in the coupling portion is extremely narrow, strong coupling can be obtained, but the characteristics of the directional coupler will greatly depend on the precision of the positioning of the two separated dielectric guides.

It is another object of the present invention enable the directional coupler and a device using the directional coupler to be easily miniturized, to enable the mass of the moving portion to be reduced, and to enable the direction of the beam to be deflected quickly.

The directional coupler of the present invention comprises first and second dielectric guides, each comprising a dielectric strip provided between two conductive plates, arranged with the end faces of the conductive plates touching or not touching, and the dielectric strips of the first and second dielectric guides are provided substantially parallel to each other in the vicinity of the end faces of the conductive plates, so that the first and second dielectric guides are structurally separate. Furthermore, a groove is provided in an end face of the conductive plates of one of the first and second dielectric guide, the groove having a short-circuiting face in a position at a distance from the electrode faces of approximately an integral multiple of half the wavelength of a propagated wave.

With this configuration, the electrode faces in the portion where the end faces of the conductive plates of the first and second dielectric guides are aligned function as an equivalently continuous portion. Therefore, although the two dielectric guides are separated by the conductive plate portions, there is almost no loss in this space. Furthermore, since there is almost no reflection, no spurious modes are caused by reflection.

Furthermore, in the present invention, a position at a distance from the electrode face of approximately an integral multiple of half the wavelength of a plane wave, which travels in a direction such that it has a wave-number vector component equal to a phase constant of a transmitted wave propagating through the dielectric guides, in the direction of a transmitted wave propagating through the dielectric guides, is a short-circuiting face.

A plane wave, propagating through the aligned portion of the end faces of the conductive plates of the first and second dielectric guides, travels in a direction determined according to its size and the size of a transmission wave, propagating along the length of the dielectric guides. That is, the size of the plane wave (wave-number k) is predetermined, and when the plane wave is projected in the transmission direction of the dielectric guides, the plane wave proceeds in a direction (θ) which matches the phase constant of a transmission wave propagating through the dielectric guides. Therefore, when a groove is provided as a short-circuiting face at a distance from the electrode face of approximately an integral multiple of half the wavelength of a plane wave in that direction, the problem of reflection is avoided to an optimum degree.

Furthermore, the present invention further comprises a first type of nonradiative dielectric guide comprising the approximately parallel dielectric strip portions and the electrode faces, and a second type of nonradiative dielectric guide, wherein the space between the electrode faces other than those of the approximately parallel dielectric strip portions is narrower than the height of the approximately parallel dielectric strip portions, and comprising a dielectric strip portion other than the approximately parallel dielectric strip portions and the electrode faces, and transmitting in a single LSM01 mode. Then, a guide conversion portion is provided between the first and second types of nonradiative dielectric guide. Consequently, coupling can easily be achieved in the first type of nonradiative dielectric guide portion, without increasing the length of the parallel dielectric strip portions or greatly narrowing the space between them. In addition, in the second type of nonradiative dielectric guide portion, there is no conversion to the LSE mode even when a bend with a short radius of curvature is provided, thereby enabling the entire device to be miniturized without increasing transmission loss.

Furthermore, according to the present invention, a primary emitter is coupled to a first dielectric guide of the above directional coupler, and a dielectric lens is secured approximately at the focal point of the primary emitter. With this configuration, when the first dielectric guide is displaced in relation to a second dielectric guide, the primary emitter is displaced within the focal point inner face of the dielectric lens, tilting the direction of the beam. Moreover, there is little loss in the directional coupler portion, and the moving portion can be miniturized and of low mass by providing the first and second types of nonradiative dielectric guides on the side of the first dielectric guide. Further, by providing the first and second types of nonradiative dielectric guides to the second dielectric guide, a miniturized antenna device can be obtained.

When the directional coupler is arranged so that the amount of coupling between the first dielectric guide and the second dielectric guide of the directional coupler is approximately 0 dB, transmission signals and received signals can be transmitted most efficiently between the moving portion and the fixed portion, increasing the efficiency of the antenna.

Furthermore, in the present invention, a transmission signal is sent from a transmitter to the second dielectric guide, and input/output ports of a circulator for sending a received signal from the second dielectric guide to a receiver are connected to the second dielectric guide. With this configuration, it is possible to realize an antenna device for transmitting and receiving, in which the direction of the beam can be tilted using a single primary emitter and a single directional coupler.

Furthermore, the present invention comprises a transceiver wherein a transmitter is connected to an input port of the circulator, and a receiver is connected to an output port of the circulator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A

to

1

C show configurations of a directional coupler and an antenna device according to a first embodiment;

FIGS. 2A

to

2

C are diagrams showing the relation between relative positions of a dielectric lens and a primary emitter and the direction of a beam;

FIG. 3

is a cross-sectional view of a directional coupler portion;

FIGS. 4A

to

4

B are partial cross-sectional views of the configuration of end faces of conductive plates of a directional coupler;

FIGS. 5A

to

5

E are cross-sectional views of various example configurations of a directional coupler;

FIGS. 6A and 6B

are diagrams showing the relation between the configuration of a directional coupler and its characteristics;

FIGS. 7A

to

7

C are diagrams showing a cross-sectional configuration of two types of directional coupler;

FIG. 8

is a perspective view of a configuration of a guide converter portion;

FIGS. 9A and 9B

are a top view and a cross-sectional view, respectively, of the configuration of the same guide converter portion;

FIGS. 10A

to

10

D are diagrams showing example dimensions of each part of a directional coupler;

FIGS. 11A

to

11

C are diagrams showing characteristics of the same directional coupler;

FIGS. 12A

to

12

C are diagrams showing a configuration of a directional coupler according to a second embodiment;

FIGS. 13A

to

13

C are diagrams showing an example configuration of another directional coupler;

FIGS. 14A and 14B

are diagrams showing a configuration of another directional coupler having a differently configured moving portion side;

FIG. 15

is a cross-sectional view of the configuration of dielectric guides on a moving portion side;

FIG. 16

is a top view of an example configuration of another directional coupler;

FIG. 17

is a diagram showing a configuration of a transceiver;

FIG. 18

is an exploded perspective view of a configuration of an antenna device and a transceiver;

FIG. 19

is a perspective view of an example configuration of a forward-screw system;

FIGS. 20A and 20B

are diagrams showing an example configuration of a voice-coil motor

FIG. 21

is a block diagram showing a configuration of a milliwave radar for a vehicle;

FIG. 22

is a diagram showing the state when the emitted beam of the milliwave radar for a vehicle is tilted horizontally;

FIG. 23

is a diagram showing the state when the emitted beam of the milliwave radar for a vehicle is tilted horizontally;

FIG. 24

is a diagram showing the state when the emitted beam of a milliwave radar for a vehicle is tilted vertically;

FIG. 25

is a partial perspective view of a configuration of an aligned portion of two upper conductive plates;

FIG. 26

is a cross-sectional view of a configuration of an aligned portion of the conductive plates;

FIG. 27

is a diagram defining ports of a directional coupler;

FIG. 28

is a diagram showing measurements of transparency characteristics of a directional coupler; and

FIGS. 29A and 29B

are diagrams showing measurements of transparency characteristics of a directional coupler as a comparative example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The configurations of a directional coupler and an antenna device according to a first embodiment of the present invention will be explained with reference to

FIGS. 1A

to

11

.

FIGS. 1A and 1B

show the relation between the configuration of a directional coupler and a primary emitter and a dielectric lens. In

FIG. 1A

is a top view of the state when the upper conductive plate is removed, and

FIG. 1B

is a cross-sectional view through the primary emitter portion. In

FIG. 1A

, a moving portion

31

can be displaced with respect to a fixed portion

32

in the direction indicated by the arrows. In the moving portion

31

, numeral

14

represents a lower conductive plate and numeral

11

represent a dielectric strip. The dielectric strip

11

is provided between an upper conductive plate and the lower conductive plate

14

, thereby forming a first nonradiative dielectric guide (hereinafter “NRD guide”). In the fixed portion

32

, numeral

16

represents a lower conductive plate and

12

is a dielectric strip. The dielectric strip

12

is provided between an upper conductive plate and the lower conductive plate

16

, thereby forming a second NRD guide.

The end faces of the conductive plates of the first and second NRD guides are provided with a predetermined gap in between so that they do not contact each other. The dielectric strips

11

and

12

of the first and second NRD guides are provided close together in parallel near the end faces of the conductive plates

14

and

16

. Thus a directional coupler is formed, comprising the first and second NRD guides.

Dielectric strip portions, shown in

FIG. 1

by the portions

11

′ and

12

′, and the upper and lower conductive plates clasping them, form NRD guides (hereinafter “hyper NRD guides”) which transmit in a single mode, LSM01 mode.

A primary emitter

13

, comprising a cylindrical rod-like dielectric resonator, is provided at an end of the dielectric strip

11

′ of the moving portion

31

. As shown in

FIG. 1B

, an opening, having a horn-like taper, is provided in the upper conductive plate

15

and is coaxial to the primary emitter

13

. As shown in the diagram, a slit plate, comprising a conductive plate with a slit in it, is inserted between the primary emitter

13

and the opening. As a consequence, electromagnetic waves are propagated in the dielectric strip

11

′ in an LSM mode carrying electrical field components at a right angle to the length of the dielectric strip

11

′ and parallel to the conductive plates

14

and

15

, and carrying magnetic field components in a direction perpendicular to the conductive plates

14

and

15

. The dielectric strip

11

′ and the primary emitter

13

are electromagnetically coupled, generating an HE111 mode carrying electrical field components inside the primary emitter

13

in the same direction as the electrical field of the dielectric strip

11

′. Then, vertically polarized electromagnetic waves are emitted through the opening in a direction perpendicular to the conductive plate

14

. The dielectric lens

18

converges these waves into a predetermined beam. Conversely, when electromagnetic waves are emitted through a dielectric lens into the opening, the primary emitter

13

is excited in the HE111 mode, and electromagnetic waves are propagated in the LSM mode to the dielectric strip

11

′ coupled to it.

A terminator

20

is provided at one end of the dielectric strip

12

′ on the fixed portion

32

side. With this configuration, transmission signals are input to the hyper NRD guide comprising the other dielectric strip

12

′, which outputs received signals.

FIG. 2

shows changes in direction of the beam due to displacement of the primary emitter. The primary emitter

13

is positioned approximately at the focal point of the dielectric lens

18

, and the transmitted/received beam B is deflected to the left and right as shown in

FIG. 2

by displacing the focal point of the inner face (by displacing the moving portion

31

in relation to the fixed portion

32

shown in

FIG. 1A

)

FIG. 3

is a cross-sectional view taken along the line A—A of FIG.

1

A. The first NRD guide on the moving portion side comprises the upper and lower conductive plates

14

and

15

, and the dielectric strip

11

provided between them. The second NRD guide on the moving portion side comprises the upper and lower conductive plates

16

and

17

, and the dielectric strip

12

provided between them. The end faces of the conductive plates of the first and second NRD guides are arranged opposite each other with a predetermined gap between them, and predetermined grooves running parallel to the conductive plates

16

and

17

are provided in the end faces of the conductive plates

16

and

17

.

FIG. 4

shows two examples of the configuration of the above grooves. In example

FIG. 4A

, a groove of depth d

0

and thickness g

0

is provided at a distance of h

0

from the electrode face (the opposing faces of the upper and lower conductive plates). Here, g

0

is equal to the gap g between the conductive plates

15

and

17

. Further, h

0

=d

0

, these lengths being an odd multiple of a quarter of the wavelength of the electromagnetic waves propagating through the gap. Since the end P

3

of the groove is a short-circuiting terminal, a point P

2

, which is a distance d

0

from the end P

3

, is an equivalently open point, and a point P

1

, which is a distance h

0

from the point P

2

, is an equivalently short-circuiting point (short-circuiting face). Therefore, the electrode faces of conductive plates

15

and

17

are equivalently continuous.

As shown in the example of

FIG. 4B

, the width g

1

of the groove is wider than the gap g of the conductive plates

15

and

17

. In such a configuration, the position, depth, and width of the groove should be set so that the position of P

1

, as viewed from the short-circuited face P

3

, is an equivalently short-circuited face. Normally, the greater the width g

1

of the groove, the shorter the distance h

1

from the electrode face to the groove, and consequently it is possible to make the point P

2

portion between the two conductive plates an equivalently open point. When the portion between the two conductive plates is made an open terminal in this manner, no current flows to the conductive plates, thereby reducing conductive loss.

Although the two NRD guides, comprising a moving portion and a fixed portion, are separated at the conductive plate portion, their electrode faces are equivalently continuous, and so almost no loss is caused by the presence of the gap. Furthermore, since there is almost no reflection in the space, no spurious mode is caused by reflection.

FIGS. 5A

to

5

E show cross-sectional views of other configurations of a coupling portion between two NRD guides. In the example shown in

FIG. 3

, grooves were provided in the end faces of both the upper and lower conductive plates; however, as shown in

FIG. 5A

, grooves can be provided not only in the fixed portion side but also in the moving portion side. Furthermore, as shown in example

FIG. 5B

, grooves can be provided in opposite parts of the upper and lower conductive plates of the fixed portion and the moving portion. Alternatively, as in example

FIG. 5C

, the grooves can be provided facing each other on both sides. The thicknesses of the conductive plates of the fixed portion and the moving portion do not necessarily have to be the same, but when they differ, the opposing end faces of the conductive plates should have the same thickness, as in FIG.

5

D. When the conductive plates

14

and

15

on the moving portion side are made thin overall, the overall size and weight of the moving portion can be made small, enabling it to be displaced easily using even a low-torque motor. Furthermore, as shown in FIG.

5

E, a groove may be provided in just one of the conductive plates, to achieve a desired effect.

In the example shown in

FIG. 4

, in a 60 GHz band, g=g

0

=0.2 mm, h

0

=d

0

=1.2 mm. In

FIG. 4B

, g=0.2 mm, g

1

=1.0 mm, h

1

=0.96 mm and d

1

=1.5 mm. In this example, the distance from the end P

3

of the groove to the electrode face P

1

was half the wavelength of the propagated waves, but this distance need only be nλ/2, where n is a whole number greater than 1, and λ is the wavelength. Furthermore, the distance from the electrode face P

1

and the groove end P

3

to the midpoint P

2

should be (2 m−1) λ/4 (where m is an integer greater than 1). The longer the distance from point P

1

to point P

3

, the narrower the width of the frequency band in which the point P

1

can function equivalently as a short-circuited face, and for this reason, the distance from point P

1

and point P

3

to the midpoint P

2

should be approximately λ/4 to obtain the above effect over a wide band.

FIG. 6

shows the relation between the directional coupler described above and the power splitting ratio. Now, if the phase constant of the even modes of the coupled guides, comprising the dielectric strips

11

and

12

, is expressed as βe, the phase constant of the odd modes as βo, and Δβ=|βe−βo|, and the power ratio between an electromagnetic wave input from port #

1

and an electromagnetic wave output to port #

2

is expressed by P

2

/P

1

=1−sin

2

(Δβz/2), and the power ratio between an electromagnetic wave input from port #

1

and an electromagnetic wave output to port #

4

is expressed by P

4

/P

1

=1−sin

2

(Δβz/2). Therefore, with a constant of (Δβz/2)=nπ+π/2(n: 0, 1, 2 . . . ), the entire input from the port #

1

is output to the port #

4

, forming an 0 dB directional coupler.

FIGS. 7A and 7B

show the cross-sectional configurations of the hyper NRD guide and the normal NRD guide portion in the directional coupler shown in FIG.

1

.

FIG. 7A

is a cross-sectional view of the NRD guide

12

taken along the line A—A of

FIG. 1

, and

FIG. 7B

is a cross-sectional view taken along the line B—B in FIG.

1

. As shown in

FIG. 7A

, in the normal NRD guide, the space Dh between the electrode faces of the conductive plates

16

and

17

is equal to the height of the dielectric strip

12

. As shown in

FIG. 7B

, in the hyper NRD guide, grooves of depth Gh are provided in the conductive plates

16

and

17

, so that the space Eh between the electrode faces of the conductive plates

16

and

17

is narrower than the height Dh of the dielectric strip

12

′. In addition to providing these grooves, the space between the propagation region of the dielectric strips and the conductive break plate in the nonpropagation region where there are no dielectric strips is determined, the dielectric constants of the dielectric strips are determined, and the cut-off frequency of the LSM01 mode is set lower than the cut-off frequency of the LSE01 mode, and the cut-off frequency of the LSE01 mode is set higher than the frequency used. With this configuration, waves can always be transmitted in a single mode, the LSM01 mode, irrespective of the radius of curvature and the like of the bends of the dielectric strips. Consequently, the overall directional coupler can be made small with reduced loss.

When signals are transmitted at a single frequency, the width DHw of the dielectric strip

12

′ of the hyper NRD guide is smaller than the width DNw of the dielectric strip

12

of the normal NRD guide. For instance, in a band of 60 GHz, if the specific dielectric constant ∈r of the dielectric strips is 2.04, then Dh=2.2 mm, DNw=3.0 mm, Gh=0.5 mm, Eh=1.2 mm and DHw=1.8 mm.

FIG. 8

is a perspective view of the configuration of a normal NRD guide, a hyper NRD guide, and a guide converter.

FIG. 9

shows a top view and a cross-sectional view of the same. FIG.

8

and

FIG. 9

show states when the upper conductive plate has been removed. As shown in these diagrams, the converter portion of the hyper NRD guide and the normal NRD guide is tapered so as to gradually eliminate the dimensional difference in the widths of the dielectric strips of the NRD guides. Furthermore, the space between the electrode faces of the conductive plates

16

and

17

changes in stages. That is, the space between the electrode faces of the hyper NRD guide does not change from the position of the interface between the hyper NRD guide and the converter to w

1

. Similarly, the space between the electrode faces of the normal NRD guide does not change from the position of the interface between the normal NRD guide and the converter to w

2

. However, in the portion between w

1

and w

2

, the spaces between the electrode faces of the normal NRD guide and the hyper NRD guide have an intermediate value. For instance, w

1

=w

2

=0.75 mm, w

0

=3.0 mm, gh

1

=0.13 mm, gh

2

=0.37 mm. Here, w

3

corresponds to approximately one-quarter of the wavelength of the propagated waves. Consequently, a reflected wave

1

and a reflected wave

2

are coupled in reverse phase in the step portion of the space between the electrode faces, thereby cancelling the emitted waves. As a result, the hyper NRD guide and the normal NRD guide can be converted with no problem of reflection.

The above example described the configurations and conversion portion of the hyper NRD guide and the normal NRD guide on the fixed portion side, but the moving side is the same.

FIGS. 10A

to

10

D show sizes of all the portions when the directional coupler described above is configured as an 0 dB directional coupler, and

FIG. 11

shows its characteristics.

FIGS. 10A

to

10

D show the dimensions of all the portions in millimeters.

FIG. 10A

is a top view when the upper conductive plate is removed,

FIG. 10B

is a cross-sectional view taken along the line A—A of

FIG. 10B

, and

FIG. 10C

is a top view of the guide converter portion of the normal NRD guide and the hyper NRD guide and a cross-sectional view of the area near it. Finally,

FIG. 10D

is a diagram showing the original position of the moving portion.

FIG. 11

is a diagram showing transparency characteristics of the directional coupler when the moving portion has been displaced by −8 mm, 0 mm and +8 mm to three different positions,

FIG. 11A

showing the transparency characteristics at each frequency,

FIG. 11B

being an enlarged view of the transparency characteristics to the primary emitter, and

FIG. 11C

showing changes in the transparency characteristics in relation to the position of the moving portion at 59.5 GHz. Even when the moving portion is moved across such a comparatively wide range of frequencies, power can be split at approximately 0 dB. 0 dB is not achieved since, in addition to deviation in the power split, there are also guide loss and transmission loss.

Next, other examples of configurations of a directional coupler will be explained with reference to

FIG. 12A

to FIG.

14

B.

FIG. 12A

is a top view of the state when the upper conductive plate is removed, and

FIG. 12B

is a cross-sectional view taken along the line A—A in FIG.

12

A.

FIG. 12C

is a cross-sectional view as a comparative example. In contrast to the case shown in

FIG. 1

, in this example, one portion

11

′ of the dielectric strip

11

of the NRD guide on the moving portion side is a hyper NRD guide, and the other end portion

11

″ is also a hyper NRD guide. With this configuration, since the horizontal widths of both ends of the dielectric strip

11

are small, the dielectric strip

11

can be exactly positioned in its axial direction. Moreover, when this directional coupler is a 0 dB directional coupler, almost no transmission signals are output from the port #

1

to the hyper NRD guide using the dielectric strip

11

″ on the opposite side of the primary emitter

13

, and consequently, since there is no need for resistance-termination, it can be used as an open terminal or as a short-circuiting terminal.

However, when the hyper NRD guide is provided close to the dielectric strip

12

of the normal NRD guide on the fixed portion side in this way, a wall (electrical wall) is created close to the dielectric strip

12

as indicated by the symbol O in

FIG. 12C

, causing coupling from the LSM01 mode to the LSE mode. Therefore, as shown in

FIG. 12B

, the space between the conductive plates

14

and

15

in the portion which faces the conductive plates

16

and

17

on the fixed portion side is made equal to the space between the electrode faces of the conductive plates

16

and

17

. Similarly, the hyper NRD guide portion comprising the dielectric strip

11

′ which is coupled to the primary emitter

13

is provided close to the normal NRD guide of the fixed portion side, creating an electrical wall, but when the directional coupler is a 0 dB directional coupler, almost no electromagnetic waves propagate through this portion and so there is no problem of coupling to the LSE mode.

When the hyper NRD guide is parallel to the normal NRD guide, with both left and right sides symmetrically arranged as shown in

FIG. 12C

, an LSE mode suppresser should be provided inside the dielectric strip

12

of the normal NRD guide which is comparatively close to the hyper NRD guide, as shown in FIG.

13

.

FIG. 13B

is a partially cross-sectional view in the vertical direction through the center of the dielectric strip

12

, and

FIG. 13C

is a cross-sectional view taken along the line A—A of FIG.

13

A. An LSE mode suppresser is basically a conductive member provided perpendicular to the electrode faces and parallel to the direction of wave propagation, for preventing LSE mode in this portion. Furthermore, the height of this conductive member is alternately changed to form a filter circuit, thereby ensuring that there is no coupling with the TEM mode. The diagram shows an example at the 60 GHz band, and dimensions are shown in millimeters.

In the example shown in

FIG. 13

, a terminator

20

is provided to the dielectric strip

11

′ portion of the hyper NRD guide on the moving portion side. When the terminator

20

is provided to the hyper NRD guide, even when the coupling balance of the directional coupler is slightly inexact, resulting in reflection of waves from the port #

3

, the effects of such reflection can be reduced.

Furthermore, as shown in

FIG. 13

, when the terminator

20

is provided to the hyper NRD guide, the terminator portion is a considerable distance away from the dielectric strip

12

of the normal NRD guide on the fixed portion side, ensuring that there is no coupling between them. Consequently, it is not necessary to provide a bend to keep the terminator portion away from the normal NRD guide on the fixed portion side.

In

FIGS. 12A

to

12

C and

FIG. 13

, the port of the NRD guide comprising the dielectric strip

11

′ can be used for other purposes. For instance, output terminals may be provided at port #

2

and port #

3

, and transmission signal power and frequency and the like can be monitored from port #

2

, and the reflection at the antenna terminal can be monitored from port #

3

.

In

FIGS. 14A

to

14

B are diagrams showing other examples of configurations of a directional coupler. In the several examples above, a bend was provided in the hyper NRD guide coupled to the primary emitter on the moving portion side, but as shown in

FIG. 14A

, the primary emitter can be arranged without a bend. In this case, the polarized wave face of the primary emitter

13

is parallel to the direction in which the moving portion

31

moves. If a bend is provided and the primary emitter

13

is coupled at an angle of 45 degrees as in the previous examples, the electromagnetic wave polarized wave face tilts by 45 degrees. Therefore, the bend portion can be provided to suit the intended purpose.

Furthermore, as shown in

FIG. 14B

, the entire NRD guide of the moving portion

31

can be a normal NRD guide. This will usually increase the size of the moving portion

31

, so the radius of curvature of the bend should be set to minimize transmission loss when switching between modes.

FIG. 15

is a cross-sectional view of another example configuration of the moving portion side of a directional coupler. In this example, the upper and lower conductive plates

14

and

15

are formed by plating the outer faces of synthetic resin plates with a metal film. When forming the grooves in the moving portion, the base material of the resin should be shaped in advance and the metal plating is applied to all the outer faces thereof, including the inner faces of the grooves. Since the electrode film acting as the NRD guide is on the faces clasping the dielectric strip

11

on either side, it is not essential to provide an electrode film on the outer faces.

FIG. 16

is another example of a configuration of the moving portion, and shows a top view when the upper conductive plate is removed. In this example, the range (area) of the conductive plates has been reduced as far as possible in regions other than the positions of the primary emitter

13

and the dielectric strips

11

and

11

′ provided to the moving portion

31

. To achieve this, notches are provided as shown at A and B, and a hole is provided as shown at C. These should be limited within a range which does not affect the NRD guide characteristics and the primary emitter characteristics. For instance, in the hyper NRD guide portion, the notches and the hole are provided at least 2 mm in the width direction from the dielectric strip

11

′, and at least 8 mm from the primary emitter

13

. In

FIG. 16

, the secure range is represented by a broken line.

Next, examples of configurations of an antenna device and a transceiver will be explained with reference to

FIG. 17

to FIG.

21

.

FIG. 17

is a top view when the upper conductive plate portion is removed. The configuration of the directional coupler in the moving portion

31

and the fixed portion

32

is the same as FIG.

1

. Here, the port #

1

is the signal input/output portion of the directional coupler and connects to a circulator

19

. A hyper NRD guide comprising a dielectric strip

21

connects to the input port of the circulator

19

, and a hyper NRD guide comprising a dielectric strip

23

connects to the output port of the circulator

19

. An oscillator is connected to the hyper NRD guide comprising the dielectric strip

21

, and a mixer is connected to the hyper NRD guide comprising the dielectric strip

23

. A dielectric strip

22

is provided between the dielectric strips

21

and

23

and is coupled to the hyper NRD guides, comprising the dielectric strips

21

and

23

respectively, thereby forming a directional coupler. Terminators

20

are provided at both ends of the dielectric strip

22

. Here, the mixer and the oscillator comprising a hyper NRD guide with a substrate in between to provide a circuit for applying bias voltage to these diodes comprises a varactor diode and a Gunn diode.

With the above configuration, the oscillating signal of the oscillator is sent from the dielectric strip

21

→the circulator

19

→the dielectric strip

12

→the dielectric strip

11

→the primary emitter

13

. Conversely, electromagnetic waves received at the primary emitter

13

are sent from the dielectric strip

11

→the dielectric strip

12

→the circulator

19

→the dielectric strip

23

, and are finally input to the mixer. Furthermore, part of the oscillating signal is sent as a local signal to the mixer together with the received signal, via the two directional couplers comprising the dielectric strips

21

,

22

and

23

. Consequently, the mixer outputs the frequency components of the difference between the transmitted signal and the received signal as an intermediate-frequency signal.

FIG. 18

is an exploded perspective view of an overall configuration of a transceiver. In the diagram, a moving portion drive unit

42

for displacing the moving portion

31

will be explained below. A horn

43

has an opening, comprising a long hole extending in the direction which the moving portion

31

is displaced in. The moving portion

31

and a “0 dB coupler” form a directional coupler. A circuit portion RF comprises the above mixer, and a circuit portion VCO comprises the above oscillator. Furthermore, a controller controls the moving portion drive unit

42

, extracts information based on the intermediate-frequency signal including the distance, angle and relative speed of the moving portion drive unit

42

, and sends these data to an external device. To assemble these portions, all the units are placed in a case

41

, the horn

43

is attached, the dielectric lens

18

is placed over this with an O-ring

44

in between, and the entire device is screwed together by four screws which enter from the bottom face of the case

41

.

FIG. 19

is a perspective view of the configuration of the moving portion drive unit. In the diagram, one end of a forward screw

54

is attached via a bearing to a frame so that the forward screw

54

can rotate freely. The other end of the forward screw

54

connects to the axis of a pulse motor

55

which is securely screwed to the frame. The frame has a forward guide

51

which is parallel to the forward screw

54

, and the forward screw

54

screws into a nut portion which can slide along the forward guide

51

. The moving portion

31

has a primary emitter and is securely screwed to the nut portion. Further, an interceptor plate

52

is attached to the nut portion. The frame has a photointerrupter

53

, and the interceptor plate

52

passes through the optical axis of the photointerrupter

53

.

This forward screw system is basically open-loop controlled, since the moving portion

31

is displaced to a predetermined position by applying a predetermined number of pulses to the pulse motor

55

. That is, a CPU controls the pulse of the pulse motor by applying a predetermined number of pulses to the pulse motor, thereby controlling the position of the moving portion. Simultaneously, a memory or register counts the pulse number representing the present position of the moving portion, thereby indirectly detecting the position of the moving portion. Since the position of the moving portion

31

cannot be detected immediately after power injection or when the pulse motor has malfunctioned, in such cases its position is detected using the interceptor plate

52

and the photointerrupter

53

.

In the above example, the moving portion was displaced using a rotating motor, but the moving portion can alternatively be displaced using a linear motor.

FIGS. 20A and 20B

show the configuration of the moving portion drive unit in such a case.

FIG. 20A

is a perspective view, and

FIG. 20B

is a cross-sectional view through the face perpendicular to the displacement direction of the moving portion. In

FIGS. 20A and 20B

, a magnetic circuit comprises external yokes

46

and

47

, an internal yoke

45

, and magnets

48

and

49

, attached to the inner faces of the external yokes

46

and

47

. Two guide pins

51

and

51

are secured to the external yoke

47

and are parallel to the internal yoke

45

. A moving coil

50

is provided in a single body with a moving push portion, which slides along the guide pins

51

and

51

. Simultaneously, the internal yoke

45

passes through the moving coil

50

while maintaining a fixed distance thereto. On the other hand, the moving portion

31

comprising a primary emitter is securely screwed to the moving push portion. An interceptor plate

52

is attached to the moving push portion and has a rhombic window. Two photointerrupters

53

a

and

53

b

are attached to the external yoke

47

, so that their optical axes pass through the rhombic window.

In the above voice-coil motor system, the position of the moving portion

31

is detected in accordance with the difference in the amounts of light received by the two photointerrupters

53

a

and

53

b

, and the motor is driven to move the moving portion

31

to a predetermined position.

FIG. 21

is a block diagram showing an overall configuration of a milliwave radar comprising the antenna device and the transceiver described above. In the diagram, a signal processing portion in a signal processor uses a transceiver to detect numerical data such as, for instance, the relative speed and distance to a vehicle traveling in front. Then, based on the relation between the traveling speed of the main vehicle and the distance between the main vehicle and the vehicle in front, a control/warning portion issues a warning when, for instance, predetermined conditions are satisfied, or issues a warning when the speed relative to the vehicle in front has exceeded a predetermined threshold value.

Next, there will be described an example of optimizing the transparency and reflection characteristics in the portion of the end faces of the conductive plates of the first and second dielectric guides.

FIG. 25

is a partial perspective view of a configuration of the aligned portion of two upper conductive plates. In the diagram, plane waves propagating through the space are considered to include not only waves transmitted perpendicular to the electrode faces (direction x) but also waves propagating parallel to the length of the dielectric guide (the z direction) in the LSM mode, which is a main mode of the NRD guide. That is, plane waves are deemed to propagate in a direction θ (=cos

−1

(β/k), determined based on the phase constant β of the LSM mode propagating parallel to the length of the dielectric guide and the number k of plane waves propagating through the space, and a groove, which is parallel to the direction of plane waves having this propagation vector, is provided at a distance from the electrode face of approximately an integral multiple of a half wavelength.

In

FIG. 25

, plane waves propagating from point p

1

shift to the y direction of the groove at point p

2

, and are then reflected from point p

3

to point p

4

. After that, they are reflected yet again until they reach point p

5

. Here, the points p

1

and p

5

of

FIG. 25

correspond to the points P

1

and P

2

of

FIG. 4

, point p

2

and p

4

correspond to point P

2

, and point p

3

corresponds to point P

3

of FIG.

4

.

The number of waves k is determined by k=ω{square root over ((∈μ))}. Here, ω is the frequency, ∈ is the dielectric constant of the groove, and μ is the permeability of the groove. Particularly, in air, k=ω{square root over ((∈oμo))}. When the dimensions and position of the dielectric strip at the aligned portion of the conductive plates are as shown in

FIG. 26

, the dimensions of the portions of

FIG. 25

in a 76 GHz band are g=0.2 mm, g

2

=1.0 mm, h

2

=1.07 mm, d

2

=1.6 mm.

FIG. 28

shows measurements of the characteristics of the directional coupler at this time. Here, the ports of the directional coupler are defined as in FIG.

27

. Fluorine resin with a specific dielectric constant of 2.04 was used as the dielectric material.

Thus, stable transparency characteristics can be obtained with low loss over a wide band of frequencies centering around 76 GHz. By way of comparison,

FIG. 29A

shows the transparency characteristic when no groove is provided. When no groove is provided, the transparency characteristic is extremely poor. Furthermore,

FIG. 29B

shows the transparency characteristic only for waves which are propagating in the direction perpendicular to the electrode face (x direction), in a case where the dimensions of the groove are g=0.2 mm, g

2

=1.0 mm, h

2

=0.7 mm and d

2

=1.22 mm. When the groove does not have appropriate dimensions, the LSM mode converts to the LSE mode at certain frequencies (in the example shown, approximately 73 GHz, 75 GHz, 77 GHz, 79 GHz, 81 GHz), resulting in severe loss.

According to the present invention, although the aligned portions of end faces of conductive plates of first and second dielectric guides are separated, the device functions with the electrode faces of both conductive plates being equivalently continuous, and so there is almost no loss in the space between the conductive plates. Furthermore, since there is almost no reflection in the space, there are no spurious modes caused by reflection.

A short-circuiting face is provided in an optimum position in correspondence with the direction of plane waves propagating through the portion where the end faces of the conductive plates of the first and second dielectric guides are aligned, whereby reflection in the aligned portion of the conductive plates can be most effectively reduced.

Furthermore, according to a first type of nonradiative dielectric guide portion, coupling is possible without making the space between dielectric strips extremely narrow. In addition, according to a second type of nonradiative dielectric guide portion, even though a bend of small radius of curvature is provided, there is no conversion from LSM mode to LSE, whereby the entire device can easily be made small without increasing transmission loss.

The present invention provides an antenna device wherein the direction of the beam is tilted by relatively displacing a first dielectric guide with respect to a second dielectric guide, so that there is low loss in the directional coupler portion. Moreover, by providing first and second types of nonradiative dielectric guide portions on the dielectric guide side, the moving portion can be made small and of low mass, so that the beam can be tilted quickly even when a low-torque motor is used. Furthermore, by providing first and second types of nonradiative dielectric guide portions on the second dielectric guide side, an antenna device which is miniturized overall can be obtained.

According to the present invention, transmission signals and received signals can be electrically transmitted with maximum efficiency between a moving portion and a fixed portion, increasing the efficiency of the antenna.

The present invention also provides a miniturized antenna for transmitting and receiving, wherein the direction of the beam can be tilted using a single primary emitter and a single directional coupler.

Furthermore, the present invention provides a transceiver which is miniturized and has low loss.

Number	Date	Country	Kind
10-189508	Jul 1998	JP
10-373808	Dec 1998	JP

Number	Name	Date
5030962	Rees	Jul 1991
5770989	Ishikawa et al.	Jun 1998
5917232	Tanizaki et al.	Jun 1999
5920245	Ishikawa et al.	Jun 1999
5933120	Manasson et al.	Aug 1999

Directional coupler, antenna device, and transceiver

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

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US

International Classifications

Abstract

Description

Claims

Priority Claims (2)

US Referenced Citations (5)