TWO-PORT TRIPLATE-LINE/WAVEGUIDE CONVERTER

TECHNICAL FIELD

The present invention relates to a two-port triplate-line/waveguide converter which has two ports coupled to an electromagnetic field in a rectangular waveguide and transfers the electromagnetic field to triplate lines connected to these ports.

Priority is claimed on Japanese Patent Application No. 2013-127069, filed Jun. 18, 2013, the content of which is incorporated herein by reference.

BACKGROUND ART

Satellite communication and fixed wireless access systems (FWA) in which wireless transmission is performed in a microwave band of 10 GHz or above or in a millimeter wave band mostly employ planar antennas consisting of an array of a large number of patch antennas. A feed line for these patch antennas has a simple structure, so that a parallel feed can be precisely realized at low cost. Moreover, the feed line is formed as a triplate line capable of ensuring high gain and high efficiency.

As shown in FIG. 6, a conventional triplate feed type planar antenna includes, for example, a ground plane 41, a foam sheet 42-1, a flexible substrate 43, a foam sheet 42-2, and a slot plate 44.

The elements stacked in this way are configured as follows.

(1) On an upper surface of the ground plane 41, a pattern corresponding to the plane Earth is formed.
(2) The foam sheets 42-1 and 42-2 are configured as a cushion material, a heat insulating material, and a dielectric with the flexible substrate 43 interposed between both surfaces thereof
(3) On the flexible substrate 43, an array of rectangular patch antennas 43A_1,1to 43A_m,narranged in a grid shape and a feed line 43F which realizes a tournament feed for these patch antennas are formed as a circuit pattern.
(4) Slot openings 44S_1,1to 44S_m,nin a grid shape are formed at positions individually corresponding to the patch antennas in a top surface of the slot plate 44, and a plane Earth pattern is formed all over the surface other than these positions.

A feed system of such a triplate feed type planar antenna is configured, for example, as shown in FIG. 7, as follows.

A waveguide-triplate line converter (simply referred to as “converter” below) 43C is disposed at a predetermined position surrounded by the patch antennas 43A_1,1to 43A_m,non the flexible substrate 43.

Also, on the flexible substrate 43, a main line 43B is formed to have one end extending to a probe 43CP inserted from a sidewall of a waveguide 43C_WCconstituting the converter 43C into the waveguide 43C_WCand the other end extending to a bus bar 43FM of the aforementioned feed line 43F realizing the tournament feed.

Among the components of the converter 43C, the waveguide 43C_WCincludes the following elements, as shown in FIG. 8.

(1) A waveguide flange 43CF that corresponds to (is connected to) one end of a rectangular waveguide connected to a wireless device not shown in the drawings, has a rectangular opening extending into the rectangular waveguide, and is disposed with the opening in contact with the corresponding position of the ground plane 41
(2) An annular member 43CR that is formed in the stacked foam sheet 42-1, flexible substrate 43, and foam sheet 42-2, inserted into a through-hole corresponding to an imaginary extended portion of the opening, and formed as a conductive cylinder having a through-hole penetrated by the aforementioned probe 43CP
(3) An annular member 43Cr that is stacked on the annular member 43CR with the slot plate 44 interposed therebetween, and extends from the inside of the waveguide flange 43CF to the outside of the slot plate 44 together with the annular member 43CR
(4) A short plate 43Cs that is laid on a top portion of the annular member 43Cr including an opening, and has a top portion in which holes (not shown) penetrated by screws 43S-1 to 43S-5 to be described below are formed
(5) The screws 43S-1 to 43S-5 that sandwich the ground plane 41, the annular member 43CR, the slot plate 44, and the annular member 43Cr between the waveguide flange 43CF and the short plate 43Cs by being screwed into screw holes which are formed in the waveguide flange 43CF to correspond to those holes

In the ground plane 41, the annular member 43CR, the slot plate 44, and the annular member 43Cr, holes (not shown) into which the screws 43S-1 to 43S-5 are inserted and which have inside walls having a size and a shape with which they stably come in contact with sidewalls of these screws 43 S-1 to 43 S-5 are formed in advance.

In the triplate feed type planar antenna having such a configuration, the waveguide 43C_WCis sandwiched by the screws 43S-1 to 43S-5 between the aforementioned waveguide flange 43CF and the short plate 43Cs, and formed by inside walls of the ground plane 41, the annular member 43CR, the slot plate 44, and the annular member 43Cr electrically connected by these screws 43 S-1 to 43S-5.

In FIG. 7, the probe 43CP converts transmission waves which are output by a transmitter not shown in the drawings and transferred as an electromagnetic field of the fundamental mode propagating in the waveguide 43C_WCinto an “electromagnetic field of a triplate line.”

On the flexible substrate 43, this “electromagnetic field of a triplate line” is guided to a point which is deviated from the center of the bus bar 43FM by a distance corresponding to a quarter of a wavelength, and is fed to half of the patch antennas 43A_1,1to 43A_m,nand the other half thereof with a phase difference of 180 degrees through the bus bar 43FM in a tournament manner.

Also, in such a triplate feed type planar antenna, cross-polarization components become two components having opposite phases and cancel each other out due to the half of the patch antennas 43A_1,1to 43A_m,nand the other half, and thus cross-polarization discrimination is improved.

As prior art relevant to the present invention, there are Patent Literature 1 to Patent Literature 3 listed below.

Patent Literature 1 discloses a polarized wave shared planar antenna “obtained by sequentially stacking a ground conductor 11, a dielectric 10, a feed substrate 9 having a plurality of radiation elements 7 and a feed line 8 formed therein, a dielectric 6, a ground conductor 1 having a plurality of slots 12 installed so that the respective slots 12 are disposed right above the radiation elements 7, a dielectric 2, a feed substrate 5 having a plurality of radiation elements 3 and a feed line 4 formed therein, a dielectric 13, and a ground conductor 15 having a plurality of slots 14 installed so that the respective slots 14 are disposed right above the radiation elements 3, and configured by electromagnetically coupling the radiation elements 3 and the radiation elements 7 together so that the excitation direction of the radiation elements 3 in accordance with the feed line 4 and the excitation direction of the radiation elements 7 in accordance with the feed line 8 cross at right angles, in which radiation elements corresponding to about half the number of array elements of the feed substrate 5 and the feed substrate 9 and a feed line or elements corresponding to about half the number of array elements of any one feed substrate and a feed line are spatially rotated 180 degrees with respect to a reference excitation direction and disposed, and which electrically changes a feeding phase by 180 degrees to be excited,” thus having a characteristic such that “load on a signal-processing circuit is reduced in a planar antenna side as much as possible, and thus a cross-polarization characteristic and a wide band characteristic of isolation are obtained.”

Patent Literature 2 discloses a waveguide/microstrip line converter “in which a substrate providing a microstrip line so that an antenna probe is disposed toward an opening of a waveguide is sandwiched between a cap corresponding to the opening of the waveguide and a base member, and the microstrip line is connected to both ends of the antenna probe installed on the substrate” thus having a characteristic such that “it also has a function of distributing a feed from the antenna probe in order to reduce removal of antenna elements on the substrate as much as possible.”

Patent Literature 3 discloses a planar antenna “that has a triplate configuration in which strip lines formed on a substrate are inserted into a ground substrate with gaps left on both sides, has radiation elements formed on one side of the ground substrate, and supplies power to the respective radiation elements in parallel by a feed line of the strip lines, in which strip line-waveguide converters having strip lines of a final feed point inserted from both side surfaces of a waveguide and having a phase difference of 180 degrees between powers input from both strip lines to the waveguide are formed in spaces between radiation elements horizontally and vertically formed at regular spatial intervals,” thus having a characteristic such that “it enables a feed by a waveguide capable of achieving favorable power combining (branching).”

CITATION LIST
Patent Literature
Patent Literature 1

Japanese Unexamined Patent Application, First Publication No. Hei 09-312515

Patent Literature 2

Japanese Unexamined Patent Application, First Publication No. Hei 11-312909

Patent Literature 3

Japanese Patent No. 2595339

SUMMARY OF INVENTION
Technical Problem

In the conventional example described above, the main line 43B is connected to the point deviated from the center of the bus bar 43FM by a quarter of a wavelength, so that the aforementioned phase difference of 180 degrees is ensured.

Therefore, when a frequency of a wireless signal to be transmitted or received has a wide-ranging value or a band occupied by the wireless signal is wide (for example, 2 GHz in a 12 GHz band), it is difficult to set the phase difference with sufficient precision.

Moreover, an error of such a phase difference in accordance with a frequency is a primary factor that causes degradation of cross-polarization discrimination to shift the direction of a main lobe, and puts a limitation on application of the triplate feed type planar antenna.

The error of such a phase difference can be reduced by configuring the triplate feed type planar antenna, for example, as shown in FIG. 9, as follows.

(1) A probe 43CP′ is disposed at a portion on the flexible substrate 43CP corresponding to a central portion in the waveguide 43C_WCinstead of the probe 43CP.
(2) The probe 43CP′ is installed in the central portion of the main line 43B.
(3) Such a main line 43B passes through slits (through-holes) formed in opposite sidewalls of the waveguide 43C_WC, and is guided to the outside of the waveguide 43C_WC.

Also, the error of a phase difference can be reduced by configuring the triplate feed type planar antenna, for example, as shown in FIG. 10, as follows.

(1) The probe 43CP′ is not provided.
(2) The main line 43B is divided into two parts at its central portion, and tips are formed opposite to each other by a predetermined distance around the central portion in the waveguide 43C_WCand facing the gap.

However, in these configurations shown in FIG. 9 and FIG. 10, impedance matching is not easily achieved in practice, and it is not possible to ensure a sufficient return loss bandwidth.

(1) Since there is air around the probe 43CP′, it is difficult to effectively reduce a wavelength based on a relative permittivity.
(2) In general, a distance b between inside walls of the waveguide 43C_WCopposite to each other is much smaller than a resonant length (=λ/2).

Therefore, in practice, the configurations shown in FIG. 9 and FIG. 10 are obstructed by limitations, such as a frequency, and physical sizes, shapes, dispositions, and the like of components other than the waveguide 43C_WC, and are not applied frequently.

An object of the present invention is to provide a two-port triplate-line/waveguide converter in which coupling of triplate lines is realized over a wide band in opposite phases, at low cost without drastically complicating the configuration.

Solution to Problem

In accordance with a first aspect of the present invention, a two-port triplate-line/waveguide converter includes a rectangular waveguide, and two probes which connect to central conductors of separate triplate lines through slits separately formed in two opposite inside walls of the rectangular waveguide and having openings on an imaginary straight line crossing the two inside walls at right angles. Tips of the two probes are bent inside the rectangular waveguide, and the two probes constitute monopole antennas with the inside walls functioning as ground planes.

In other words, the two probes are bent in the rectangular waveguide, so that unnecessary coupling between the two probes is reduced or suppressed. Moreover, the two probes function as the monopole antennas, so that two ports of opposite phases coupled to an electromagnetic field in the waveguide over a wide band are formed between the two probes and the separate triplate lines.

In accordance with a second aspect of the present invention, a two-port triplate-line/waveguide converter includes a rectangular waveguide, and two probes which connect to central conductors of separate triplate lines through slits separately formed in two opposite inside walls of the rectangular waveguide and having openings on an imaginary straight line crossing the two inside walls at right angles. Tips of the two probes branch in a plurality of directions inside the rectangular waveguide, and the two probes constitute monopole antennas with the inside walls functioning as ground planes.

In other words, the two probes branch in a plurality of directions in the rectangular waveguide, so that unnecessary coupling between the two probes is reduced or suppressed. Moreover, the two probes function as the monopole antennas, so that two ports of opposite phases coupled to an electromagnetic field in the waveguide over a wide band are formed between the two probes and the separate triplate lines.

In accordance with a third aspect of the present invention, a two-port triplate-line/waveguide converter includes two probes which connect to central conductors of separate triplate lines through slits separately formed in two opposite inside walls of the rectangular waveguide and having openings on an imaginary straight line crossing the two inside walls at right angles. Tips of the two probes are bent in directions not opposite to each other inside the rectangular waveguide, and the two probes constitute monopole antennas with the inside walls functioning as ground planes.

In other words, the tips of the two probes are bent in directions not opposite to each other in the rectangular waveguide, so that unnecessary coupling between the two probes is reduced or suppressed. Moreover, the two probes function as the monopole antennas, so that two ports of opposite phases coupled to an electromagnetic field in the waveguide over a wide band are formed between the two probes and the separate triplate lines.

Advantageous Effects of Invention

According to the present invention, transfer of signals having phases opposite to each other is realized in parallel between a rectangular waveguide and two triplate lines without involving a drastic change of the configuration and a heavy dependence on a frequency compared to the conventional example.

An apparatus or a system to which the present invention is applied does not place serious obstructions or limitations on cost, installation, temperature, power consumption, or the like, and prevents the occurrence of technical problems resulting from a lack of precision in the opposite phases or a change of performance with high precision.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a return loss achieved by the present embodiment.

FIG. 3 is a diagram (1/2) showing another aspect of a configuration of the present embodiment.

FIG. 4 is a diagram (2/2) showing another aspect of a configuration of the present embodiment.

FIG. 5 is a diagram showing a configuration of a polarized wave shared triplate feed type planar antenna to which the present invention can be applied.

FIG. 6 is a diagram showing an example of a configuration of a conventional triplate feed type planar antenna.

FIG. 7 is a diagram (1/2) showing a configuration of a feed system of a conventional triplate feed type planar antenna.

FIG. 8 is a diagram (2/2) showing a configuration of a feed system of a conventional triplate feed type planar antenna.

FIG. 9 is a diagram (1/2) showing a solution to a conventional example.

FIG. 10 is a diagram (2/2) showing a solution to a conventional example.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described in detail based on the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention.

In FIG. 1, the same elements as those shown in FIG. 6 to FIG. 8 are given like signs, and descriptions thereof will be omitted here.

The present embodiment and the conventional example shown in FIG. 7 have the following differences in configuration

(1) The main line 43B is not provided.
(2) Instead of the waveguide 43C_WC, a waveguide 11 is provided, and separate through-holes are formed at positions corresponding to one side surface of the flexible substrate 43 in two opposite sidewalls of the waveguide 11.
(3) The bus bar 43FM is divided into two parts at a central portion in the longitudinal direction, and tips of the parts are guided into the waveguide 11 through the respective through-holes. The two parts divided from the bus bar 43FM in this way are denoted by “43FM-1” and “43FM-2” below.
(4) Two probes 12-1 and 12-2 configured as will be described below are provided instead of the probe 43CP.
(4-1) The two probes 12-1 and 12-2 are formed on the flexible substrate 43 as circuit patterns, and as shown in FIG. 1, connect to the bus bars 43FM-1 and 43FM-2, respectively.
(4-2) The tips are bent in L shapes in directions so that areas of the tips opposite to each other in the waveguide 11 are minimized.
(4-3) The disposition of each of these tips in an inside wall of the waveguide 11 and the size are set as follows.
(4-3-1) In relation to a length L1 from an inside wall of the waveguide 11 to a bent portion and a length L2 from the bent portion to a tip, a length L in the waveguide 11 is given by the following equation.

L=L1+L2

(4-3-2) In relation to a wavelength X of a center frequency fin a band of a signal to be transferred from the inside of the waveguide 11 to the bus bars 43FM-1 and 43FM-2, the length L is given by the following equation.

L=λ/4

(4-3-3) The length L1 is set based on a balance between the degree of coupling between an electromagnetic field in the waveguide 11 and the probe 12-1 (12-2) and isolation to be ensured between the probes 12-1 and 12-2.

In the present embodiment configured in this way, both of the probes 12-1 and 12-2 function as monopole antennas which use a sidewall of the waveguide 11 as a ground plane.

Here, both of the probes 12-1 and 12-2 are bent in L shapes, and thus are sufficiently isolated from each other. Also, since both the probes 12-1 and 12-2 resonate with L=(1/4)λ, the current distribution of each of the probes 12-1 and 12-2 becomes even, and thus a band is widened.

Moreover, phases of an electromagnetic field coupled to the probes 12-1 and 12-2 in the waveguide 11 become opposite to each other, that is, 180 degrees.

In other words, half of the patch antennas 43A_1,1to 43A_m,nand the other half thereof are fed in parallel with power in opposite phases by the two-port waveguide-triplate line converter which includes the waveguide 11 and the probes 12-1 and 12-2 as described above.

Therefore, in the triplate feed type planar antenna to which the present embodiment is applied, slight changes are made as will be described below, and each half of the provided patch antennas is stably fed in an opposite phase.

(1) A configuration of the waveguide 11
(2) A specific circuit pattern associated with coupling with the waveguide 11 among circuit patterns formed on the flexible substrate 43

As shown in FIG. 2, such a feed is efficiently performed over a wide band compared to the conventional example.

In the present embodiment, a feed by opposite phases is stably realized over a wide band as described above, and thus a shift of a main lobe which is about 0.3 degrees in the conventional example is suppressed to be within 0.1 degrees.

In the present embodiment, when isolation between the probes 12-1 and 12-2 and overall feed efficiency are achieved in a desired range, the probes 12-1 and 12-2 are not limited to the aspect shown in FIG. 1 and may be configured in any of the forms listed below.

(1) As shown in FIG. 3, the tips are disposed to be opposite to each other within a range allowed by a reduction in isolation between the probes 12-1 and 12-2.
(2) As shown in FIG. 4, the tips branch not in L shapes but in T shapes so that the probes 12-1 and 12-2 function as T-shaped monopole antennas.
(3) The tips branch into three or more parts.
(4) A direction in which the tips branch is not limited to the pattern surface of the flexible substrate 43 and is set to cross the pattern surface of the flexible substrate 43 within the limitation of cost or the range of technical feasibility.
(5) The probes 12-1 and 12-2 are formed on a different surface of the flexible substrate 43 than the bus bars 43FM-1 and 43FM-2 in a form in which they are connected to the bus bars 43FM-1 and 43FM-2, which are central conductors of the triplate lines, outside the waveguide 11.
(6) The probes 12-1 and 12-2 are different in both or either one of shape and size.

In the present embodiment, through-holes into which the probes 12-1 and 12-2 are inserted are formed in a linear shape in two sidewalls of the waveguide 11 opposite to each other.

However, such a shape of the through-holes may be a shape which is bent in a desired shape and size as long as there is no problem in overall characteristics.

These through-holes may not necessarily have the same shape or size.

In the present embodiment, the number of patch antennas to be fed in phases opposite to each other may be any value.

In addition, the present invention can be applied not only to a triplate feed type planar antenna but also to any apparatus or system in which coupling between a waveguide and two triplate lines should be stably realized over a wide band with high precision in opposite phases.

Also, the present invention can be applied not only to a polarized wave-dedicated planar antenna that forms a wireless transmission path with polarized waves common in an uplink and a downlink, but also to, for example, a polarized wave shared planar antenna that forms these links with polarized waves orthogonal to each other as shown in FIG. 5.

The present invention is not limited to the embodiment described above. Various embodiments can be made within the scope of the present invention, and any modifications may be made to all or some of the components.

Industrial Applicability

The present invention can be widely applied to two-port triplate-line/waveguide converters that have two ports coupled to an electromagnetic field in a rectangular waveguide, and transfer the electromagnetic field to triplate lines connecting to these ports.

An apparatus or a system to which the present invention is applied does not put serious obstructions or limitations on cost, installation, temperature, power consumption, or the like, and prevents the occurrence of technical problems resulting from a lack of precision in the opposite phases or a change of performance with high precision.

REFERENCE SIGNS LIST

11, 43C_WCWaveguide

12, 43CP Probe

41 Ground plane

42 Foam sheet

43 Flexible substrate

43A Patch antenna

43B Main line

43C Waveguide-triplate line converter

43CF Waveguide flange

43CR Annular member

43Cr Annular member

43Cs Short plate

43F Feed line

43FM Bus bar

44 Slot plate

44S Slot opening

TWO-PORT TRIPLATE-LINE/WAVEGUIDE CONVERTER

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