JP2017192006A - Propagation mode transducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a propagation mode transducer capable of reducing product cost.SOLUTION: In a transducer 20, a patch antenna 30 radiates microwaves, supplied from a connector 26, into a circular waveguide 40 in TMmode. Cutoff frequency of the circular waveguide 40, when the microwaves are propagated in TMmode, is lower than that when the microwaves are propagated in TEmode. Consequently, a relatively thinner waveguide can be employed in the TMmode than in the TE. Product cost can thereby be reduced.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a propagation mode transducer used by being connected to a waveguide.

  The technique disclosed in Patent Document 1 is an example of a propagation mode transducer that is used by being connected to a conductor wire instead of a waveguide, and measures the distance to the liquid surface that is the object to be measured by a pulse radar method. In the technique of Patent Document 1, a patch antenna as a transducer is mounted on a central conductor. And this center conductor has the short pin integrally couple | bonded with the housing | casing, The load of the conductor wire concerning a center conductor is added to a housing | casing via a short pin. As a result, no load is applied to the dielectric provided around the center conductor, so even if the load applied to the conductor conductor coupling portion of the center conductor fluctuates due to fluctuation of the conductor wire, etc. It enables measurement with stable accuracy without being affected.

JP 2014-134415 A

  However, in the technique disclosed in Patent Document 1, it is necessary that the center conductor has a plurality of short pins. Therefore, as shown in FIG. 3 of the document 1, the structure of the center conductor is complicated, which may lead to an increase in product cost. In addition, even if a part of the load applied to the conductor wire coupling portion of the central conductor due to the swing of the conductor wire can be released to the housing via the short pin, the sloshing load applied to the conductor wire coupling portion It is difficult to escape everything to the housing. Therefore, since it is necessary to considerably increase the mechanical strength of the conductor wire coupling portion, this can also contribute to an increase in product cost.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a propagation mode transducer that can reduce the product cost.

In order to achieve the above object, a propagation mode transducer according to claim 1 of the present invention is a propagation mode transducer used by being connected to a waveguide, comprising: a ground conductor plate; A circular patch antenna having a circular patch provided at a predetermined interval from the ground conductor plate, and the waveguide accommodates the patch in the tube so as to surround the patch on the connection end side. In addition, the circular patch antenna is electrically connected to the ground conductor plate and radiates microwaves or millimeter waves (hereinafter referred to as “microwaves”) fed from the outside in the TM ₀₁ mode into the tube. Technical features.

The circular patch antenna radiates microwaves fed from the outside into the tube in TM ₀₁ mode. The cutoff frequency of the waveguide when microwaves propagate in the TM ₀₁ mode is lower than the cutoff frequency when microwaves propagate in the TE ₀₁ mode. For example, in the FMCW radar system, it is desirable that the sweep frequency width is large in order to increase measurement accuracy. Further, as the cutoff frequency of the waveguide is lower, it is possible to pass a transmission wave that sweeps in a desired frequency width (particularly, a transmission wave having a lower limit frequency of sweeping). As a result, the TM ₀₁ mode can easily pass the lower limit side of the sweep frequency width than the TE ₀₁ mode, and a wide sweep frequency width can be secured. This means that the inner diameter (inner radius) of the waveguide can be relatively reduced. Therefore, when the waveguide is made of a metal (for example, stainless steel, aluminum, copper, brass, iron, etc.) whose unit price can be determined per weight, the product cost can be reduced. It becomes possible.

  The waveguide accommodates the patch in the tube so as to surround the periphery of the patch on the connection end side, and is electrically connected to the ground conductor plate. As a result, the waveguide is less likely to bend than a conductor wire such as a wire, and thus is less susceptible to sloshing. In addition, for example, both of them can be firmly connected by a relatively simple configuration such as mechanically connecting (for example, welding) the entire circumference on the connection end side of the waveguide to the ground conductor plate. Therefore, even when a sloshing load is applied to the waveguide, the load can be released to the ground conductor plate side through the entire circumference on the connection end side.

The propagation mode transducer according to claim 2 of the present invention is the propagation mode transducer according to claim 1, wherein the waveguide is a circular waveguide and the patch is TM _01. Assuming that the patch of the annular patch antenna excited in the mode has a disk shape, when the inner radius r of the waveguide is smaller than r ₀ obtained from the following equation, r ₀ = (3.8137 × λ) / 2π (where λ is the wavelength of the microwave or millimeter wave), and the patch has a separation interval s between the outer peripheral edge of the patch and the inner peripheral wall of the circular waveguide is the predetermined interval Is technically characterized by a bottomed cylindrical shape in which a relationship of radius d = rs and height t≈r ₀ -d is established. The bottomed cylindrical shape includes a tea tube lid shape as an example. Further, t≈r ₀ -d includes t = r ₀ -d. d indicates the radius of the portion of the patch parallel to the ground conductor plate.

The patch of the circular patch antenna has a bottomed cylindrical shape in which a relationship of radius d = rs and height t≈r ₀ -d is established. The bottomed cylindrical patch is surrounded by a circular waveguide whose periphery is electrically connected to the ground conductor plate, and the separation between the outer peripheral edge of the patch and the inner peripheral wall of the circular waveguide. The interval s is equal to a predetermined interval between the ground conductor plate and the patch. As a result, a circular patch antenna whose patch is a disc shape mainly forms an electric field between the ground conductor plate and the patch, whereas a circular patch antenna whose bottom is a bottomed cylindrical shape (hereinafter referred to as “present”). In the case of a “bottom cylindrical patch antenna”), in addition to the space between the ground conductor plate and the patch, a circular waveguide (substantially the same potential as the ground conductor plate) is also provided in the height (thickness) direction of the patch. An electric field can be formed between the patches. As a result, the specific bandwidth of the antenna can be increased, and the sweep frequency width can be increased accordingly. Further, since the radius d of the bottomed cylindrical patch antenna can be made smaller than the radius r ₀ of the patch of the annular patch antenna excited in the TM ₀₁ mode, the circular waveguide is positively narrowed. You can also The “specific bandwidth” is the bandwidth obtained by subtracting the lower limit from the upper limit of the frequency at which the propagation mode transducer can radiate microwaves or the like in the TM ₀₁ mode in the waveguide, and the center frequency ( A value obtained by dividing by (center frequency) or a value obtained by multiplying the divided value by 100 (%).

Further, the propagation mode transducer according to claim 3 of the present invention is the propagation mode transducer according to claim 2 or 3, wherein the circular patch antenna has a feeding point such as the microwave as the feeding point. It is technically characterized by having a short-circuit point with respect to the ground conductor plate at a plurality of point-symmetrical positions with the feeding point as the center, as well as at the center of the patch. Power supply points such as microwaves are provided at the center of the patch, and short-circuit points with respect to the ground conductor plate are provided at a plurality of point symmetrical positions around the power supply point. Compared with the case where a point is provided, a circular patch antenna or a bottomed cylindrical patch antenna can be easily excited in the TM ₀₁ mode. Further, by having the short-circuit points at four places, it is possible to increase the specific bandwidth as compared with the case of having two short-circuit points.

In the propagation mode transducer of the present invention, the TM ₀₁ mode can realize a cut-off frequency lower than that of the TE ₀₁ mode. Therefore, for example, a relatively thin waveguide can be used in the FMCW radar system. Waveguides are often made of a metal (for example, stainless steel, aluminum, copper, brass, iron, etc.) whose unit price can be determined per weight. For this reason, positively narrowing the waveguide lowers the cost of the waveguide, thereby reducing the product cost. In addition, for example, the entire circumference of the connection end side of the waveguide is mechanically connected (for example, welded) to the ground conductor plate, and the both are strengthened by a configuration that is difficult to increase the product cost. It becomes possible to connect to. Therefore, even when a sloshing load is applied to the waveguide, the load can be released to the ground conductor plate side through the entire circumference on the connection end side. Therefore, the product cost can be reduced also by this.

In the propagation mode transducer of the present invention, the patch has a bottomed cylindrical patch antenna having a bottomed cylindrical shape, so that the patch radius d is greater than the patch radius r ₀ of the annular patch antenna excited in the TM ₀₁ mode. Therefore, the circular waveguide can be actively made thinner. Therefore, the cost of the waveguide can be further reduced, so that the product cost can be further reduced. In addition, when the patch is made of a metal whose unit price can be determined per weight (for example, stainless steel, aluminum, copper, brass, iron, etc.), the product cost can be further reduced along with the cost reduction of the patch. it can.

It is explanatory drawing which shows the structural example of the liquid level measuring apparatus which concerns on one Embodiment of this invention. It is typical sectional drawing which shows the structural example of the transducer which comprises the liquid level measuring apparatus of this embodiment. It is typical sectional drawing which shows the III-III line | wire cross section represented by FIG. FIG. 4A is an explanatory diagram showing a feed circuit of a radial line for a concentric array antenna. FIG. 4B is an explanatory diagram showing an example in which the resonator represented by the thick line in FIG. 4A is modified to a TM ₀₁ mode annular patch antenna. 4 (C) and 4 (D) are explanatory views for comparing the configurations of the transducers of this embodiment having a bottomed cylindrical patch antenna. It is a typical sectional view showing other examples of composition of a transducer of this embodiment.

  Hereinafter, an embodiment in which a propagation mode transducer of the present invention is applied to a liquid level measuring device will be described with reference to the drawings. First, an outline of the configuration of the liquid level measuring device 10 of the present embodiment will be described based on FIG. FIG. 1 is an explanatory diagram illustrating a configuration example of the liquid level measuring device 10.

  As shown in FIG. 1, the liquid level measuring device 10 is provided in a cargo tank 91 of a ship that transports a liquid 100 such as a tanker, and mainly includes a transducer 20, a pipe 13, a radar transceiver, a controller, and the like. It is configured. The liquid 100 is, for example, water, petroleum, liquefied natural gas, or the like. In FIG. 1, the illustration of the radar transceiver and the controller is omitted.

The transducer 20 is an antenna device that can transmit and receive microwaves or millimeter waves, and is attached to the ceiling 93 of the cargo tank 91. A mounting hole 94 for mounting the transducer 20 is formed in the ceiling 93. The transducer 20 is fixed to the ceiling 93 such that a patch antenna 30 described later is exposed in the cargo tank 91 from the mounting hole 94. The transducer 20 is connected to the radar transceiver via a coaxial cable. The transducer 20 of this embodiment transmits a radar wave output from a radar transceiver in the TM ₀₁ mode, or receives a TM ₀₁ mode radar wave reflected back to the object to be measured and receives the radar transceiver. Or output to

  The pipe 13 is a metal cylindrical tube extending from the ceiling 93 of the cargo tank 91 toward the bottom plate 95. In the present embodiment, the pipe 13 functions as a circular waveguide as will be described later. The metal is, for example, stainless steel, aluminum, copper, brass, iron or the like, and the unit price can be determined per weight. In FIG. 1, the length of the pipe 13 is expressed to be relatively short for convenience of drawing, but the pipe 13 is set to a length of 50 m (meters), for example. Further, the end of the pipe 13 may be electrically connected to the bottom plate 95 or may not be electrically connected to the bottom plate 95. The inside of the pipe 13 is filled with the liquid 100 having the same liquid level as that of the liquid 100 stored in the cargo tank 91.

  In the present embodiment, the radar transceiver is a wireless device capable of transmitting and receiving at a frequency of an SHF (Super High Frequency) band, for example. In this embodiment, the distance to the object to be measured is measured by an FMCW (Frequency Modulated Continuous Wave) radar system. Therefore, the radar transceiver generates, for example, a transmission wave by applying triangular wave FM modulation to a voltage controlled oscillator (VCO) and outputs the transmission wave to the transducer 20. As a result, the transmission wave is emitted from the transducer 20 toward the object to be measured. In the radar transceiver, a part of the transmission wave is distributed and used as a local wave of the receiving mixer. The reflected wave reflected by the object to be measured is received by the transducer 20 and output to the radar transceiver. The reception wave input to the radar transceiver is input to the reception mixer and mixed with the local wave (distributed transmission wave), thereby generating a beat signal. By analyzing this beat signal, the distance to the object to be measured can be calculated.

  The controller is connected to the radar transceiver via a plurality of signal lines and the like. The controller is, for example, a microcomputer and includes a CPU, a memory, a DSP, and the like. For example, the controller outputs a voltage signal for controlling the voltage-controlled oscillator to the radar transceiver and analyzes the waveform of the beat signal input from the radar transceiver. For details, for example, refer to JP2013-253936A. In the present embodiment, the radar transceiver and the controller are configured separately from the transducer 20, but may be configured in the transducer 20.

  Next, a configuration example of the transducer 20 will be described with reference to FIGS. 2 and 3. FIG. 2 is a schematic cross-sectional view showing a configuration example of the transducer 20. FIG. 3 is a schematic cross-sectional view showing a cross section taken along line III-III shown in FIG.

  As shown in FIGS. 2 and 3, the transducer 20 mainly includes a base plate 21, a cover 24, a patch antenna 30, a circular waveguide 40, and the like. The base plate 21 is a circular metal plate. In the present embodiment, the base plate 21 functions as a mounting plate for attaching the transducer 20 to the cargo tank 91 and electrically functions as a ground conductor plate constituting the patch antenna 30. To do. Therefore, the base plate 21 is connected to the ceiling 93 of the cargo tank 91 through an unillustrated bolt or nut so as to be electrically conductive.

  A plurality of holes are formed in the base plate 21. The through holes 22 formed at four locations at 90 ° intervals in the circumferential direction in the vicinity of the peripheral edge portion are for inserting bolts for fixing the base plate 21 (transducer 20) to the ceiling 93 of the cargo tank 91 (see FIG. 3). ). In the present embodiment, the base plate 21 is fastened together with the cover 24. On the other hand, the feed hole 23 formed in the substantially central portion of the base plate 21 is for inserting the feed line 27 for feeding the patch antenna 30 with the high frequency power of the radar wave. Although not shown in FIG. 2 and the like, the base plate 21 is also formed with a connector mounting hole for mounting a connector 26 (for example, an SMA type coaxial connector).

  The cover 24 is a lid for protecting the surface of the base plate 21 from the seawater, wind and rain, and the like, which are attached to the base plate 21. Sometimes called a cap. In this embodiment, the cover 24 is formed in a bottomed cylindrical shape, and includes a flange that protrudes outward in the radial direction around the cover 24. Similar to the through holes 22 of the base plate 21, the through holes 25 are formed in the flange at four locations at intervals of 90 degrees in the circumferential direction. Thereby, the cover 24 can be fastened together with the base plate 21 to the ceiling 93. Although not shown, an O-ring or the like for sealing the gap between the base plate 21 and the flange of the cover 24 in a liquid-tight manner is interposed. A similar O-ring or the like is interposed between the ceiling 93 of the cargo tank 91 and the base plate 21.

  The patch antenna 30 includes the base plate 21 (ground conductor plate) and the patch 31 described above. The patch 31 is made of metal, and is formed in a bottomed cylindrical shape such as a lid portion of a tea tube, for example. The metal is, for example, stainless steel, aluminum, copper, brass, iron or the like, and the unit price can be determined per weight. The inside of the patch 31 is a cavity. The internal space of the patch 31 is surrounded by the upper surface 32 and the inner peripheral surface 36. The side (lower surface) facing the upper surface 32 is an opening surface 33 that opens into the space inside the circular waveguide 40.

  The patch 31 has an outer diameter that is smaller than the inner diameter of the circular waveguide 40. Therefore, a gap (interval) s is formed between the outer peripheral surface 35 of the patch 31 and the inner peripheral wall 45 a of the circular waveguide 40. The patch 31 faces the back surface of the base plate 21 with a gap (interval) h. That is, a gap (interval) h is formed between the upper surface 32 of the patch 31 and the base plate 21.

  In the present embodiment, as will be described later with reference to FIG. 4, the outer diameter or axial length of the patch 31 or the circular waveguide 40 is set so that these gaps (intervals) s and h have the same value. Each inner diameter is set. Therefore, the short pin 28 that electrically connects the patch 31 and the base plate 21 has an axial length so that the back surface of the base plate 21 and the upper surface 32 of the patch 31 have a gap (interval) h. At the center of the patch 31, the core wire of the power supply line 27 connected to the connector 26 is electrically connected (power supply point 37 shown in FIG. 3). In addition, short pins 28 are electrically connected to four locations at intervals of 90 degrees in the circumferential direction on a circle that is radially separated from the feeding point 37 by a predetermined distance. That is, the short pins 28 are connected at equal intervals in the circumferential direction of a circle that is separated from the cylindrical shaft center of the patch 31 by a predetermined distance in the radial direction. In FIG. 2, it should be noted that the illustration of the short pin 28 that overlaps with the power supply line 27 is omitted for convenience of drawing representation.

The four short pins 28 are short-circuit members for enabling the patch antenna 30 to be excited in the TM ₀₁ mode. As described above, in the patch antenna 30 of the present embodiment, a plurality of point symmetrical positions with the feeding point 37 as the center are set as the short-circuit points 39. In the present embodiment, a short pin 28 that is electrically connected to the base plate 21 (ground conductor plate) is disposed at the short-circuit point 39. Thereby, the patch antenna 30 can be excited in the TM ₀₁ mode. In contrast to this, even when a configuration is adopted in which the center of the patch 31 is the short-circuit point 39 and a plurality of point-symmetrical positions around the short-circuit point 39 is the feed point 37, the patch antenna 30 is also TM _01. Can be excited in mode.

  The circular waveguide 40 is a metal cylindrical tube, and is configured in substantially the same manner as the pipe 13 described above. In the present embodiment, the circular waveguide 40 and the pipe 13 are separated in order to facilitate understanding of the configuration of the transducer 20. However, a configuration in which both are electrically and mechanically joined may be employed, or a configuration in which the circular waveguide 40 is extended to correspond to the length of the pipe 13 may be employed. The upper end portion of the pipe 13 may also function as the circular waveguide 40.

  Further, in the present embodiment, the base end portion 41 of the circular waveguide 40 is electrically connected to the back surface of the base plate 21 over the entire circumference. The electrical connection is performed by, for example, welding or soldering. That is, the circular waveguide 40 accommodates the patch 31 in the circular waveguide 40 so as to surround the periphery of the patch 31 at the base end portion 41 and is electrically and mechanically connected to the base plate 21. The circular waveguide 40 is generally less likely to bend than a conductor wire such as a wire. Therefore, for example, it becomes difficult to be affected by sloshing that may occur during navigation of a tanker. Further, even if a sloshing load is applied to the circular waveguide 40, the load can be released to the base plate 21 side (the ceiling 93 of the cargo tank 91) through almost the entire circumference of the base end portion 41. Become.

Here, the configuration of the patch antenna 30 will be described in more detail with reference to FIG. FIG. 4A shows a feed circuit for a radial line for a concentric array antenna. FIG. 4B is an explanatory diagram showing an example in which the resonator represented by the thick line in FIG. 4A is modified to a TM ₀₁ mode annular patch antenna. FIG. 4C is a perspective view schematically showing the configuration of the transducer 20, and FIG. 4D is a cross-sectional view schematically showing the configuration of the transducer 20. . 4A and 4B corresponds to the central axis of the cavity resonator or the annular patch antenna.

As shown in FIG. 4 (A), in the radial line feed circuit for the concentric array antenna, the cavity resonator (thick line portion shown in FIG. 4 (A)) of the wavelength λ determined by the radio frequency to be fed is shown. At the radius r ₀ , the resonance condition of the TM ₀₁ mode is derived from the following equation.

r ₀ = (3.8137 × λ) /2π=0.60983×λ

  Here, it is shown in Fig. 9 Radial line feed circuit for concentric array antenna published in "Concentric Array Antenna Using Radial Line" (Naohisa Goto, IEICE Technical Report, Dec. 2015). The slot width w (corresponding to the symbol “s” shown in FIG. 2) and h (corresponding to the symbol “h” shown in FIG. 2) are sufficiently small with respect to λ. The constant 3.8137 is a value at which the first-order Bessel function becomes zero following the origin.

Further, in the cavity resonator indicated by a bold line in FIG. 4A, the radius a ′ is brought closer to the slot position a, and w ′ = h ′ is brought closer to w = h, thereby the TM shown in FIG. It is transformed into a ₀₁ mode annular patch antenna. The TM ₀₁ mode of the annular patch antenna can be excited by supplying a common pin from four locations on a concentric circle with a short pin at the center point. However, on the contrary, it is also known that it can be excited by supplying power to the central point and providing short pins at four concentric circles ("Introduction to Antenna Engineering" (written by Naohisa Goto, published by Denpa Shimbun) 2008, p.230). Note that in FIG. 4 (a), the equal to the radius a 'is the r ₀ from the z-axis. in FIG. 4 (B), the radius a of the z-axis in the r ₀ equal.

In contrast, as shown in FIGS. 4C and 4D, when the TM ₀₁ mode is excited in a circular waveguide 40 having an inner radius r smaller than r ₀ , the patch end ( The distance s between the outer peripheral edge of the patch antenna 30 and the inner peripheral wall 45a of the circular waveguide 40 is equal to the distance h between the patch surface (upper surface 32 of the patch 31) and the ground conductor plate (base plate 21). The patch end is bent along the inner peripheral wall 45 a of the circular waveguide 40 toward the opening side (upward) of the circular waveguide 40. Here, h is a value sufficiently smaller than λ. Thereby, the patch radius d (= rs) of the patch antenna 30 having a bottomed cylindrical shape is determined. Further, the length t of bending (folding up) along the inner wall surface of the pipe is determined based on the results of experiments and computer simulations using the value derived from d + t≈r ₀ as a guide. As a result, a magnetic field similar to that of the conventional annular patch antenna is generated from the upper end of the patch, and TM ₀₁ mode microwaves or the like can be radiated into the pipe.

The “specific bandwidth” is the bandwidth obtained by subtracting the lower limit from the upper limit of the frequency at which the transducer 20 can radiate microwaves or the like into the circular waveguide 40 in the TM ₀₁ mode. A value (%) obtained by dividing by the frequency (center frequency) and multiplying by 100. According to the confirmation test by the inventors of the present application, when the return loss due to the reflection coefficient S11 was measured, it was confirmed that the transducer 20 of this embodiment was able to secure a specific bandwidth exceeding 10%.

In the transducer 20 described so far, a bottomed cylindrical patch 31 is illustrated as the patch antenna 30. As shown in FIG. 5, a patch antenna 50 corresponding to a TM ₀₁ mode annular patch antenna may be accommodated in a circular waveguide 140. FIG. 5 is a schematic cross-sectional view showing a transducer 120 as another configuration example of the transducer. In the figure, components substantially the same as those of the transducer 20 are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 5, the transducer 120 includes a patch antenna 50 having a patch 51 formed in a disk shape. The upper surface 52 of the patch 51 is opposed to the back surface of the base plate 121 with a gap (interval) h, and is electrically connected to the base plate 121 via four short pins 28. The outer peripheral edge 55 of the patch 51 is opposed to the inner peripheral wall 145a of the circular waveguide 140 with a gap (interval) s. The lower surface 53 of the patch 51 faces the opening side of the circular waveguide 140. In FIG. 5, it should be noted that the illustration of the short pin 28 that overlaps with the power supply line 27 is omitted for convenience of drawing representation.

The patch 51 of the patch antenna 50 corresponds to an annular patch antenna of TM ₀₁ mode. Therefore, as compared with the patch 31 of the patch antenna 30, the radius d is larger as described with reference to FIG. The inner radius r ₀ of the circular waveguide 140 is also larger than the inner radius r of the circular waveguide 40 described above. Similar to the base end portion 41 of the circular waveguide 40, the base end portion 141 of the circular waveguide 140 is electrically connected to the back surface of the base plate 121 over substantially the entire circumference of the base end portion 141. Further, a pipe 13 having the same size as that of the circular waveguide 140 is connected to the distal end portion 143 of the circular waveguide 140. The base plate 121 and the cover 124 are set to have outer diameter dimensions that match the size of the patch antenna 50. Therefore, the outer diameter is larger than the base plate 21 and the cover 24 described above.

As described above, in the transducers 20 and 120 of the present embodiment, the patch antennas 30 and 50 radiate the microwaves fed from the connector 26 into the circular waveguides 40 and 140 in the TM ₀₁ mode. The cut-off frequency of the circular waveguides 40 and 140 when the microwave or the like propagates in the TM ₀₁ mode is lower than the cut-off frequency when the microwave or the like propagates in the TE ₀₁ mode. As a result, the TM ₀₁ mode can adopt a waveguide that is relatively thinner than the TE ₀₁ mode. Therefore, the product cost can be reduced.

  In the transducers 20 and 120 of the present embodiment, the circular waveguides 40 and 140 are placed in the circular waveguides 40 and 140 so that the proximal ends 41 surround the patches 31 and 51. It is accommodated and electrically connected to the base plates 21 and 121. Thereby, since the circular waveguides 40 and 140 are hard to bend compared with conductor wires, such as a wire, they are hard to receive the influence of sloshing. Further, for example, the base end portions 41 and 141 of the circular waveguides 40 and 140 are connected by a relatively simple configuration such that the entire circumference thereof is mechanically connected (for example, welding) to the base plates 21 and 121. . Therefore, since it becomes possible to connect the base plates 21 and 121 and the circular waveguides 40 and 140 firmly, even if a sloshing load is applied to the circular waveguides 40 and 140, the load is applied to the base end. It is possible to escape toward the base plates 21 and 121 through the entire circumference of the portions 41 and 141. Therefore, since a countermeasure against sloshing can be taken with a simple configuration without adopting a complicated configuration, the product cost of the transducers 20 and 120 can be reduced.

Furthermore, in the transducer 20 of the present embodiment, the patch 31 of the patch antenna 30 has a bottomed cylindrical shape in which a relationship of radius d = rs and height t≈r ₀ -d is established. This makes it possible to employ a thinner circular waveguide. Therefore, when the circular waveguide 40 or the pipe 13 is manufactured from a metal (for example, stainless steel, aluminum, copper, brass, iron, etc.) whose unit price can be determined per weight, the circular waveguide 40 or the pipe 13 is manufactured. With the cost reduction of 13, the product cost can be reduced.

  In this embodiment, the circular waveguides 40 and 140 and the pipe 13 are formed in a cylindrical shape. However, if the metal tube functions as a waveguide such as a microwave, the opening shape (radial cross-sectional shape) may be a waveguide having a rectangular shape, a polygonal shape, an elliptical shape, an oval shape, or the like. good.

  In the present embodiment, the liquid level measuring device 10 to which the transducers 20 and 120 are applied has been described by way of example of the FMCW method. However, the propagation mode transducer of the present invention can be applied to, for example, a liquid level measuring device of another method such as a pulse method or a Doppler method, as long as the frequency of the microwave used is affected by the cutoff frequency of the waveguide. Can also be applied.

  Furthermore, in this embodiment, the case where the transducers 20 and 120 are applied to the liquid level measuring device 10 has been described as an example. However, if the propagation mode transducer of the present invention adopts a configuration in which a waveguide (circular waveguides 40, 140) is connected to a ground conductor plate (base plates 21, 121), for example, an in-vehicle millimeter wave The present invention can also be applied to obstacle detection devices such as radar.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications or changes of the specific examples described above. In addition, the technical elements described in the present specification or drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technique illustrated in this specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of these objects. Note that the description in parentheses in the [Explanation of Symbols] section can clearly indicate the correspondence between the terms used in the above-described embodiments and the terms described in the claims.

10 ... Liquid level measuring device 13 ... Pipe (circular waveguide)
20, 120 ... Transducer (propagation mode transducer)
21, 121 ... Base plate (ground conductor plate)
24, 124 ... Cover 26 ... Connector 27 ... Feed line 28 ... Short pin 30, 50 ... Patch antenna (circular patch antenna)
31, 51 ... Patch 32,52 ... Upper surface 35 ... Outer peripheral surface (outer periphery)
37 ... Feeding point 39 ... Short-circuiting point 40,140 ... Circular waveguide 41,141 ... Base end (connection end side)
45, 145 ... peripheral wall portion 45a, 145a ... inner peripheral wall 55 ... outer peripheral edge 91 ... cargo tank 93 ... ceiling 95 ... bottom plate 100 ... liquid (measurement object)

Claims (3)

A propagation mode transducer used in connection with a waveguide,
A circular patch antenna having a ground conductor plate and a circular patch provided with a predetermined interval from the ground conductor plate;
The waveguide is electrically connected to the ground conductor plate while accommodating the patch in the tube so as to surround the periphery of the patch on the connection end side,
The circular patch antenna radiates microwaves or millimeter waves fed from outside into the tube in TM ₀₁ mode. When it is assumed that the waveguide is a circular waveguide and the patch is a disk shape of a patch of an annular patch antenna excited in the TM ₀₁ mode, the wave guide is more than r ₀ obtained from the following equation. When the inner radius r of the tube is small,
r ₀ = (3.8137 × λ) / 2π
(Where λ is the wavelength of the microwave or millimeter wave)
The patch is
A bottomed cylinder in which a relationship of radius d = rs−height and height t≈r ₀ −d is established when the spacing s between the outer peripheral edge of the patch and the inner peripheral wall of the circular waveguide is equal to the predetermined distance. The propagation mode transducer according to claim 1, which has a shape.   The circular patch antenna has a feeding point of the microwave or millimeter wave at a central portion of the patch, and has a short-circuit point with respect to the ground conductor plate at a plurality of point symmetrical positions with the feeding point as a center. The propagation mode transducer according to claim 2 or 3, characterized by the above.