JP2014134415A - Tm01 mode transducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a TM01 mode transducer of which the physical strength is sufficiently high when applied to a radar type measuring device.SOLUTION: The TM01 mode transducer comprises: a center conductor 50 to which a conductor line 70 suspended therefrom is coupled; a patch antenna 41 mounted in the center conductor 50; a power feeding part 36 capacitive-coupled with the patch antenna 41; a casing 24 covering the patch antenna 41 and the power feeding part 36; and a dielectric body 60 forming a cavity 80 together with the center conductor 50 and the casing 24. The patch antenna 41 is encapsulated in the cavity 80, the center conductor 50 includes a short-circuit pin 52 which is integrally coupled to the casing 24, and a load of the conductor line 70 applied to the center conductor 50 is applied to the casing 24 via the short-circuit pin 52. The power feeding part 36 is provided while penetrating the casing 24, and a high frequency signal supplied to the power feeding part 36 is converted into a TM01 mode electromagnetic wave by the patch antenna 41.

Description

  The present invention relates to a TM01 mode transducer used in a device that propagates a high-frequency signal using a single line as a transmission line. For example, it can be used as a transducer of a pulse radar type liquid level measuring device to which a time domain reflection coefficient measurement (Time Domain Reflectometry: TDR) technology is applied.

One of radar systems used for liquid level measurement is a pulse radar system. In the pulse radar system, as shown in FIG. 6, from the time (t0) when the pulse is irradiated from the reference point such as the ceiling of the tank toward the bottom of the tank, the time when the pulse reflected back from the liquid surface is received. From (t1), the distance from the reference position to the reflection point of the radio wave is obtained by measuring the time (t1-t0) required for propagation of the pulse. If the pulse propagation velocity is v, the distance L from the reference point to the reflecting surface is
L = v × (t1−t0) / 2
It can be calculated by the following formula.

  In the pulse radar type liquid level gauge, there is a case where a single line is stretched vertically in a tank and a pulse is propagated to the single line for measurement. At this time, a single-line transmission line transducer is used.

  FIG. 7 shows an outline of a pulse radar type liquid level gauge using a single line transmission line transducer. In FIG. 7, crude oil, liquefied gas, and other liquids 2 are accommodated in a tank 1 provided in a tanker or the like. A transducer 3 for a single-line transmission path is attached to the ceiling 11 of the tank 1. A wire 5 is stretched vertically from the liquid level gauge 3 toward the bottom 12 of the tank 1, and the lower end of the wire 5 is fixed to the bottom surface of the tank 1 in a stretched state. A part of the wire 5 is submerged in the liquid 2.

  A load due to the weight of the wire 5 is applied to the feeding point 4. Further, in the tanker, the liquid 2 in the tank moves due to the swing of the hull during navigation, and a sloshing load is applied to the wire 5 each time, so that a large load is concentrated on the feeding point 4. Therefore, it is necessary to ensure a sufficiently high load bearing performance with respect to the above load in the single-line transmission transducer.

  In this specification, “transducer” has the same meaning as an antenna. The transducer 3 is configured such that a power supply line from a high-frequency pulse signal source (not shown) is connected to the wire 5 at a power supply point 4 and a high-frequency pulse is supplied from the power supply point 4 to the wire 5. The transducer 3 has a structure for exciting the TM01 mode, and a high-frequency pulse excited from the transducer in the TM01 mode propagates through the wire 5.

  As a technique related to the present invention for exciting the TM01 mode, there is an annular antenna (for example, see page 176 of Non-Patent Document 1). A TM01 mode annular patch antenna using a short pin is also known (see, for example, page 228 of Non-Patent Document 2).

Published by Naohisa Goto, published by Ohm, "A book that understands antennas" "Introduction to Antenna Engineering" published by Naohisa Goto and Denpa Shimbun

  The present invention ensures a sufficiently high physical strength against the weight of the wire and the sloshing load in the tank, and improves the measurement accuracy when used as a transducer in a pulse radar type liquid level measuring device. It is an object to provide a TM01 mode transducer that can be used.

The TM01 mode transducer according to the present invention is
A central conductor for coupling the conductor wires in a suspended manner;
A patch antenna mounted on the center conductor;
A power feeding unit coupled with the patch antenna by a capacitance;
A casing covering the patch antenna and the power feeding unit;
A dielectric that forms a cavity with the central conductor and the housing, and
The patch antenna is enclosed in the cavity,
The center conductor has a structure in which the load of the conductor wire applied to the center conductor is applied to the housing via the short pin by having a short pin integrally coupled to the housing.
A feed line and a coaxial connector are provided to feed a high-frequency pulse to the feed unit through the housing,
The most important feature is that the high-frequency pulse signal supplied from the coaxial connector is converted from the patch antenna into a high-frequency pulse signal of TM01 mode.

  When the conductor wire is coupled to the center conductor and suspended, the load of the conductor wire is applied to the short pin and the casing of the center conductor, and no load is applied to the dielectric and the feeding portion. No pressure is applied to the dielectric even if the load applied to the conductor wire coupling portion of the central conductor fluctuates due to the fluctuation of the conductor wire. Therefore, when the TM01 mode transducer according to the present invention is used as a transducer of a pulse radar type measurement device using single line propagation, measurement can be performed with stable accuracy without being affected by a load.

It is a longitudinal cross-sectional view which shows the Example of the TM01 mode transducer based on this invention. It is sectional drawing which follows the AA line in FIG. It is a perspective view which shows the center conductor in the said Example. It is a cross-sectional enlarged view of the part of the short pin of the said center conductor. It is a longitudinal cross-sectional view which shows the usage condition of the said Example. It is a wave form diagram for demonstrating the measurement principle of a pulse radar type measuring device. It is a model figure which shows the usage example of the liquid level meter using the conventional TM01 mode transducer.

  Hereinafter, embodiments of the TM01 mode transducer according to the present invention will be described with reference to the drawings.

  1 and 2, the TM01 mode transducer 20 includes a casing 24, a patch antenna 41, a short pin 52, a central conductor 50, a dielectric 60, a power feeding portion 36, a coaxial connector 30, and a conductor wire 70 as main components. Have as.

  A flange 26 is formed at the open end of the housing 24, that is, the lower end in FIG. 1, and the flange 26 is fastened to the base plate 22, so that the flange 26 and the base plate 22 are joined together in close contact. .

  A step portion is formed on the inner peripheral side of the housing 24 by enlarging the diameter of the open end side of the housing 24, and a space generated between the step portion and the upper surface of the base plate 22 is formed. The outer peripheral edge of the dielectric 60 is sandwiched. The dielectric 60 is provided to prevent the liquid in the tank from penetrating into the cavity 80. The dielectric 60 is an annular member made of a material having dielectric properties, and has a thickness obtained by combining the space between the stepped portion and the upper surface of the base plate 22 and the thickness of the base plate 22. And the return loss to the coaxial connector 30 is set to be minimum. The outer peripheral edge of the dielectric 60 is formed in a step shape by a portion sandwiched between the spaces and a portion having a smaller diameter than this portion. By bringing the inner peripheral edge of the base plate 22 into the stepped portion of the dielectric 60, the adhesion between the dielectric 60 and the base plate 22 is increased.

  Further, a circumferential groove 62 opened on the lower surface side is formed on the outer peripheral edge of the dielectric 60, and a sealing material 66 made of an O-ring is fitted into the circumferential groove 62. The sealing material 66 is pressed by the base plate 22 and is elastically deformed so as to be in close contact with the base plate 22 and the dielectric 60. Thus, the hermeticity among the dielectric 60, the base plate 22, and the housing 24 is maintained.

  As shown in FIG. 3, the central conductor 50 is a member made of a conductive material shaped like a top as a whole. A flange 51 is formed on the upper portion of the main body portion of the center conductor 50, and four short pins 52 project upward from the upper surface of the flange 51 in parallel with the center axis of the center conductor 50. The four short pins 52 are formed at equal intervals in the circumferential direction of the central conductor 50.

  A patch antenna 41 is formed on the upper surface of the main body portion of the center conductor 50. A conductor wire coupling portion 58 is provided at the lower end portion of the center conductor 50. Each short pin 52 and the patch antenna 41 are formed integrally with the main body portion of the central conductor 50.

  The center conductor 50 is fitted in a state where the main body portion is in close contact with the hole in the center portion of the dielectric 60. On the upper surface side of the inner peripheral portion of the dielectric 60, a step-like groove 64 is formed over the entire circumference in a cross section, and a second seal material 68 made of an O-ring is fitted in the groove 64. The sealing material 68 is in contact with the bottom surface and the peripheral wall of the groove 64, and is in contact with the peripheral wall of the dielectric 60 and the lower surface of the flange 51. Thus, the hermeticity between the center conductor 50 and the dielectric 60 is maintained.

  A sealed cavity 80 is formed by the inner peripheral wall surface of the housing 24, the upper surface of the dielectric 60, and a part of the center conductor 50. The patch antenna 41 is covered with the casing 24 through the cavity 80 and is enclosed in the cavity 80. The volume of the cavity 80 is determined mainly by the inner diameter of the casing 24 and the outer diameter of the central moving body 50.

  A coaxial connector 30 for connecting a cable connecting an external transmitter / receiver and the TM01 mode transducer 20 is fixed at the center of the upper surface of the housing 24. The conductor in the coaxial connector 30 is separated from the peripheral wall of the center hole 28 of the housing 24 as a power supply line 34, extends to the cavity 80, and is joined to the power supply unit 36. The power feeding unit 36 is a disk-shaped member smaller than the diameter of the patch antenna 41 and feeds power by capacitive coupling with a small gap with respect to the patch antenna 41. However, the feed line 34 and the patch antenna 41 may be directly connected depending on the location.

  A conductor wire coupling portion 58 is provided below the center conductor 50. One end of a conductor wire 70 is press-fitted into the conductor wire coupling portion 58. Since the conductor wire 70 extends to the bottom of the tank as will be described in detail later, a considerably large load is applied, and a lateral load is applied by the swell of the liquid in the tank. These loads are applied to the casing 24 via the main body portion of the central conductor 50 and the short pin 52, and are not applied to the dielectric 60 and the power feeding portion 36.

  The shape of the patch antenna 41 and each short pin 52 will be described in more detail with reference to FIG. As shown in FIG. 4, the cross-sectional shape of each short pin 52 arranged on the patch antenna 41 has two large and small arcs centered on the central axis of the patch antenna 41 and a predetermined opening centered on the central axis. A trapezoidal shape cut by two radial lines having an angle θ. Of the two arcs, the radius of the large arc is P, and the radius of the small arc is C. The outer surface and inner surface of each short pin 52 along these arcs are cylindrical surfaces, but since the opening angle θ is relatively small, the cross-sectional shape of each short pin 52 is trapezoidal.

  As described above, a wire for propagating a high-frequency pulse signal is coupled to the center conductor 50, and the wire is installed in a state of being vertically stretched in a tank that stores a liquid. Since the load of the wire is applied to the central conductor 50, the central conductor 50 must be firmly coupled to the casing 24. In order to firmly connect the center conductor 50 to the housing 24, for example, extensions extending upward from the upper ends of the four short pins 52 of the center conductor 50 are integrally provided, and these extensions are press-fitted into the holes of the housing 24. Then, it is good to make it the structure which adheres. Alternatively, the central conductor 50 and the casing 24 may be combined to form a single integrally molded part.

  FIG. 5 shows how the TM01 mode transducer described above is used. In FIG. 5, the TM01 mode transducer 20 according to the above embodiment is installed on the ceiling 86 of a tank 82 constructed in a tanker or the like. The tank 82 is constructed of a metal that is a conductor including the ceiling 86 and the bottom plate 84, and the casing 24 of the transducer 20 is coupled to the ceiling 86 with the base plate 22 interposed therebetween, so that the casing 24 is grounded. linked. In addition, the central conductor 50 is connected to the ground together with the casing 24. In the tank 82, crude oil or other liquid 88 as a cargo is stored.

  The upper end portion of the conductor wire 70 is coupled to the conductor wire coupling portion 58 of the center conductor 50, and the lower end of the conductor wire 70 is coupled to the bottom plate 84 of the tank 82. When a high-frequency pulse signal is input from the transmitter of the pulse radar to the TM01 mode transducer 20 via the coaxial connector 30, the high-frequency pulse signal is transmitted to the patch antenna 41 in which the power feeding units 36 facing each other are capacitively coupled. By inputting a high-frequency pulse signal from the power feeding unit 36 to the patch antenna 41, a circular magnetic field is generated around the center conductor 50 in a concentric manner around the central axis, and the Fleming's right-hand rule is generated by the circular magnetic field. As a result, a current is generated in the conductor wire 70, and this current propagates downward through the conductor wire 70.

  When the high-frequency pulse signal propagating through the conductor wire 70 reaches the upper surface of the liquid 88, it is reflected on the liquid surface due to a difference in impedance due to a difference in relative dielectric constant between the gas above the tank 82 and the liquid 88. The reflected high-frequency pulse signal propagates upward through the conductor line 70, returns to the TM01 mode transducer 20, and is received by a pulse radar receiver.

  In this type of pulse radar, the pulse width of the pulse signal is extremely small in order to increase measurement accuracy. For this reason, the transducer 20 is required to have a high carrier frequency of, for example, about 10 GHz and a wide frequency bandwidth of, for example, about 1 GHz. In addition to this, the load of the conductor wire 70 depending from the transducer 20 and the load due to the conductor wire 70 being shaken with the undulation of the liquid 88 are applied to the transducer 20. The transducer 20 needs to have a structure capable of withstanding the load, and a device for avoiding a decrease in measurement accuracy of the pulse radar due to the load is required.

  In that respect, according to the illustrated embodiment, the load of the conductor wire 70 and the load of the center conductor 50 are applied to the casing 24 via the short pin 52 as described above. Since the casing 24 is supported by the ceiling 86 of the tank 82, the load applied to the casing 24 is applied to the ceiling 86 and does not apply to the dielectric 60 or the power feeding unit 36. Therefore, even if the load applied to the conductor wire coupling portion 58 of the center conductor 50 fluctuates due to the swing of the conductor wire 70, the pressure applied to the dielectric 60 or the power feeding portion 36 does not change, and the electrical impedance may fluctuate. Absent. Therefore, when the TM01 mode transducer according to the present invention is used as a transducer of a radar type measurement apparatus that propagates electromagnetic waves to a single line such as the conductor line 70, the measurement accuracy can be improved.

  Since a tank for storing a liquid such as crude oil or liquefied gas needs to be maintained in an airtight state, the installation portion of the transducer 20 on the tank needs to be maintained in an airtight state. In the illustrated structure of the transducer 20, the gap between the dielectric 60 and the housing 24 is sealed with a sealing material 66, and the gap between the dielectric 60 and the central conductor 50 is sealed with a sealing material 68. It is kept. Since the casing 24 is installed on the ceiling of the tank 82 (see FIG. 5) with an appropriate sealing material interposed therebetween, the airtightness of the tank 82 is also maintained.

  The dielectric 60 also functions as a sealing material for the tank 82. As a material for the dielectric 60, for example, a fluororesin may be used.

  The TM01 mode transducer is required to optimize the resonance frequency and bandwidth. According to the embodiment of the TM01 mode transducer of the present invention, the shape of the short pin 52 is unique and the patch antenna 41 is used, so that the resonance frequency and bandwidth can be optimized. . As described with reference to FIG. 4, the short pin 52 has a trapezoidal cross-sectional shape. The height of the trapezoidal short pin 52, that is, the difference between the radius P and the radius C affects the impedance of the transducer 20. The length of the bottom side of the trapezoidal short pin 52, that is, the circumferential length L of the outer surface of the short pin 52 in FIG. 4 affects the resonance frequency of the transducer 20.

  The radius of the patch antenna 41 also affects the resonance frequency of the transducer 20. The distance between the power feeding unit 36 and the patch antenna 41 affects the frequency bandwidth and impedance of the transducer 20. The feeding unit 36 and the patch antenna 41 facing each other constitute a capacitor, and a high-frequency signal is supplied from the feeding line 34 to the patch antenna 41 through the capacitor in series. The capacitance of the capacitor constituting the series power feeding circuit affects the impedance of the transducer 20.

  According to the TM01 mode transducer according to the above embodiment, the resonance frequency and the impedance are adjusted to the optimum design values suitable for the purpose of use by adjusting the height of the trapezoid of the trapezoidal short pin 52 and the length of the base. It becomes possible to set. Further, the frequency bandwidth and impedance of the transducer 20 can be set to optimum values by adjusting the radius of the patch antenna 41, the distance between the power feeding unit 36 and the patch antenna 41, and the capacitance of the series capacitor. become.

  When the resonance frequency and impedance are set to the optimum values as described above, and the structural parameters of the cavity 80 are adjusted so that the resonance frequency of the cavity 80 becomes the optimum value, the frequency bandwidth of the transducer 20 can be expanded and optimized. Can be planned. In particular, it is not known to combine the adjustment of the frequency bandwidth and impedance by the patch antenna 41 using the trapezoidal parameters. In addition, the effect of increasing the frequency bandwidth of the transducer 20 is not known. Thus, according to the embodiment of the present invention, the application range of the TM01 mode transducer can be expanded.

The relationship between the structural parameters of the cavity 80 and the characteristic items that can be optimized is as follows.
Inner diameter of cavity 80: resonance frequency Outer diameter of center conductor 50: frequency bandwidth, impedance

  The TM01 mode transducer according to the present invention is mainly assumed to be a pulse radar type distance measuring device such as a level gauge transducer, but can also be used as a transducer of other devices.

20 TM01 mode transducer 22 Base plate 24 Case 26 Flange 28 Center hole (Coaxial line outer conductor)
30 Coaxial connector 32 Dielectric 34 Feed line (Inner conductor of coaxial line)
36 Feeding part 41 Patch antenna 50 Center conductor 52 Short pin 66 O-ring 68 O-ring 70 Conductor wire 80 Cavity

Claims (8)

A central conductor for coupling the conductor wires in a suspended manner;
A patch antenna mounted on the center conductor;
A power feeding unit coupled with the patch antenna by a capacitance;
A casing covering the patch antenna and the power feeding unit;
A dielectric that forms a cavity with the central conductor and the housing, and
The patch antenna is enclosed in the cavity,
The center conductor has a structure in which the load of the conductor wire applied to the center conductor is applied to the housing via the short pin by having a short pin integrally coupled to the housing.
A feed line and a coaxial connector are provided to feed a high-frequency pulse to the feed unit through the housing,
A TM01 mode transducer for converting a high frequency pulse signal supplied from the coaxial connector into a TM01 mode high frequency pulse signal from the patch antenna.   2. The TM01 mode transducer according to claim 1, wherein there are a plurality of short pins of the center conductor, and the plurality of short pins are press-fitted into the housing so that the center conductor and the housing are integrally coupled.   The TM01 mode transducer according to claim 1 or 2, wherein the dielectric is sandwiched between the base plate and the casing.   4. The TM01 mode transducer according to claim 3, wherein a sealing material for sealing the inside of the cavity is interposed between the base plate and the dielectric.   The TM01 mode transducer according to any one of claims 1 to 4, wherein a second sealing material that seals the inside of the cavity is interposed between the central conductor and the dielectric.   The TM01 mode transducer according to any one of claims 1 to 5, wherein the casing is connected to ground.   The TM01 mode transducer according to any one of claims 1 to 6, wherein the central conductor and the casing are concentric circles, and the conductor wire coupling portion of the central conductor is at the center of the concentric circle. The cross-sectional shape of the short pin of the center conductor was cut by two large and small arcs centered on the center axis of the center conductor and two radial lines centered on the center axis and having a predetermined opening angle. The TM01 mode transducer according to any one of claims 1 to 7, which has a trapezoidal shape.

Images