JP2007074646A - Mode converter and microwave device equipped with this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microwave device whose size is small and the mode converter whose reflection characteristic is wideband. <P>SOLUTION: The mode converter which performs a mode-conversion between a waveguide mode and a coaxial mode comprises: a first cavity part 1a which consists of a cavity having an inlet 1d of an electromagnetic wave; a slot 1e which is provided on a wall surface of the first cavity part 1a in a direction of intersecting with a high frequency current flowing on the wall surface of the first cavity part 1a by an electromagnetic wave fed from the inlet 1d; a second cavity part 1b on which the slot 1e is continuously formed; a third cavity part 5 which communicates with the second cavity part 1b and whose cross sectional shape is the same as the inlet 1d; and a probe 2a projected in the third cavity part 5. A dielectric 4 is set at an inlet of the third cavity part 5. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a microwave device used in satellite communication or the like, and more particularly to a structure of a mode converter that picks up an input electromagnetic wave with a probe.

  Conventionally, as a microwave device, there is a frequency down converter for satellite communication, and the down converter is provided with a mode converter (waveguide-coaxial converter) that picks up an input electromagnetic wave with a probe. For example, as shown in the exploded perspective view of FIG. 7, this mode converter is composed of a casing 93 and a casing 91 formed by aluminum die casting, and a dielectric substrate 82 sandwiched between the upper and lower surfaces thereof. ing. Note that the housing 91 has a first cavity 92 having an introduction port through which a received signal is input.

  The dielectric substrate 82 removes the copper foils on the upper and lower surfaces of the substrate corresponding to the introduction port of the first cavity 92, and is connected to the probe 81a made of a conductor pattern of a predetermined length and the probe 81a as a transmission line. A microstrip line 81c that acts and a ground-side conductor pattern 81b provided on the upper and lower surfaces of the substrate are provided. The casing 93 has a second cavity portion 94 made of a quadrangular space and a third cavity portion 95 that constitutes a shield case for the microstrip line 81c. Accordingly, when viewed electrically, one waveguide is formed by the first cavity 92, the second cavity 94, and the dielectric substrate 82 from which the copper foils on both sides corresponding to the inlets of the first cavity 92 are removed. Can be considered a tube.

  The electromagnetic wave input from the inlet of the first cavity 92 of the housing 91 is guided to the second cavity 94 of the housing 93. Since the second cavity portion 94 has a reflecting surface at a depth corresponding to about ¼ wavelength of the wavelength of the input electromagnetic wave from the probe 81a, the input electromagnetic wave is most efficient in the probe 81a. It is often picked up, that is, mode-converted (see, for example, Patent Document 1).

  However, the mode converter has a unique reflection characteristic (return loss) determined by the size of the waveguide composed of each cavity, and the reflection characteristic is widened with the waveguide size being fixed. In addition, it is difficult to reduce the size of the mode converter itself.

JP 2004-320460 A (page 4-5, FIG. 2)

  An object of the present invention is to solve the above-described problems, to downsize the entire microwave device, and to widen the reflection characteristics of the mode converter.

  In order to solve the above-mentioned problems, the present invention provides a mode converter for mode-converting a waveguide mode and a coaxial mode, and a first cavity portion including a cavity having an electromagnetic wave entrance / exit, and the first cavity portion A slot provided in a direction crossing a high-frequency current flowing through the wall surface of the first cavity corresponding to an electromagnetic wave introduced or sent out from the inlet / outlet on the wall surface, and a second cavity part in which the slot is continuously formed A third cavity having the same cross-sectional shape as the inlet / outlet, and a conversion probe projecting into the third cavity, and a dielectric at the inlet of the third cavity Place.

  The dielectric is formed into a curved surface having a protruding cross section.

  On the other hand, a microwave device is configured using a mode converter having the structure of claim 1 or claim 2.

  By using the above means, according to the microwave device provided with the mode converter according to the present invention, the invention according to claim 1 increases the reflection loss over a wide band as compared with the case where no dielectric is used. be able to. Furthermore, since the dielectric is disposed in the cavity of the waveguide, the Q factor (Quality factor) in the waveguide is lowered, and as a result, the reflection characteristic can be widened. Therefore, by using a dielectric having a higher relative dielectric constant than air, and selecting and installing the cross-sectional shape and size as appropriate, the size of the cavity can be reduced, the mode converter can be downsized, and the reflection characteristics can be reduced. The bandwidth can be increased.

  In addition, by widening the reflection characteristics in this way, a mode converter is prepared for each different frequency band as in the past, and a single unit can be covered without dividing and covering a wide frequency band with a plurality of units. It can be handled with a mode converter. Or, it is not necessary to have a complicated shape like a ridge waveguide in order to increase the bandwidth.

  In the invention according to the second aspect, the dielectric functions as a radio wave lens, and the electromagnetic wave can be concentrated on the conversion probe. Therefore, the reflection loss can be further improved as compared with the case where the structure of claim 1 is used.

  In the invention according to claim 3, since the mode converter is downsized by reducing the size of the cavity, or the mode converter having a wide reflection characteristic is used, the microwave device can be downsized, or the micro frequency band can be reduced. One wave device can be configured.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail as examples based on the attached drawings. The wavelength of the frequency handled by the mode converter according to the present invention is called λ. For example, the length of a quarter wavelength is described as λ / 4.

  FIG. 1 is an exploded perspective view in a see-through state showing a microwave device provided with a mode converter of K band (K band: 18 to 26 GHz) according to the present invention. 2 is a cross-sectional view of the microwave device of FIG. 1, FIG. 2 (A) is a side cross-sectional view, and FIG. 2 (B) is a front cross-sectional view. Hereinafter, the structure will be described with reference to FIGS.

  This microwave device is a frequency down-converter for satellite communications, and is connected to a lower housing 1 and an upper housing 3 formed by tetrahedral aluminum die casting, a probe 2a having a conductor pattern with an open tip, and the like. The dielectric substrate 2 is provided with a microstrip line 2e that functions as a transmission line. The dielectric substrate 2 is sandwiched between the lower housing 1 and the upper housing 3.

  The lower housing 1 includes a first cavity 1a having a rectangular inlet 1d through which a received signal is input, a second cavity 1b disposed above the terminal end of the first cavity 1a, and a second cavity 1b. And a third cavity A portion 1c disposed above the cavity portion 1b. The first cavity portion 1a and the third cavity A portion 1c communicate with each other through the second cavity portion 1b. In addition, since the introduction port 1d is used in the K band, it has a size of 4.32 mm × 10.67 mm. In this description, since the microwave device is described as a receiving device, the entrance of the electromagnetic wave is referred to as an introduction port. However, when the present invention is applied to a transmitter, it becomes an output port of the electromagnetic wave.

  The first cavity portion 1a is a bottomed rectangular tube shape in which only the introduction port 1d is opened, the third cavity A portion 1c is a rectangular tube shape in which the upper portion is opened, and the second cavity portion 1b is The upper and lower ends have an oval cylindrical shape with an oval slot 1e having an opening having a longitudinal direction of λ / 2. The slot 1e functions as a slot antenna, and the traveling direction of the electromagnetic wave incident from the introduction port 1d is bent upward by 90 degrees.

  Here, the slot 1e is provided in a direction intersecting with the high-frequency current flowing in the wall surface of the first cavity 1a by the reception signal input from the introduction port 1d. FIG. 5 shows the electromagnetic field distribution of the TE10 mode, which is the fundamental mode of the rectangular waveguide. In FIG. 5, the electric field E is represented by a solid line, the magnetic field H is represented by a dotted line, and the distribution of the high-frequency current I flowing through the wall surface is represented by a one-dot chain line.

  FIG. 6 shows an example in which a slot is provided on the wall surface of such a rectangular waveguide. The slot is provided in a direction intersecting with the high-frequency current other than the slot (a) parallel to the flow direction of the high-frequency current shown in FIG. Radio waves are emitted from the slot. Α represents an inclination angle with respect to the waveguide, d represents a distance indicating a deviation from the center position, l represents a length of the slot, and w represents a width of the slot. The slot corresponding to this embodiment is (f) in FIG.

  Further, the radiation efficiency of the slot 2e as an antenna is best when the length of the slot is λ / 2. However, the present embodiment is not limited to this, and the second cavity portion 1b or the third cavity portion is not limited thereto. The required length can be set so that optimum characteristics can be obtained in consideration of the mechanical dimensions of 5 and electrical characteristics such as reflection characteristics and transmission characteristics as a mode converter.

  The upper housing 3 has an opening corresponding to the opening of the third cavity A portion 1c, and has a rectangular hollow third cavity B portion 3a having a depth of λ / 4 from the probe 2a, and a dielectric substrate. And an L-shaped fourth cavity 3b that shields the two probes 2a, and a square cylindrical fifth cavity 3c that shields the converter circuit 2d disposed on the dielectric substrate 2. The third cavity B part 3a, the fourth cavity part 3b, and the fifth cavity part 3c communicate with each other in a part of the upper housing 3.

  On the other hand, the dielectric substrate 2 includes a probe 2a, a ground conductor pattern 2b provided on the upper and lower surfaces of the substrate, and a copper foil pattern (upper and lower surfaces) of the wiring pattern of the converter circuit 2d. The copper foil of the ground-side conductor pattern 2b on the upper and lower surfaces at the position corresponding to the opening of the third cavity A part 1c and the third cavity B part 3a is cut off to form a rectangular third cavity C part 2c. ing. The cross sections of the third cavity A portion 1c, the third cavity B portion 3a, and the third cavity C portion 2c are 4.32 mm × 10.67 mm and are formed in the same size. It is the same size as the cross section. That is, the first cavity 1a is bent 90 degrees upward via the second cavity 1b, and the third cavity A 1c, the third cavity C 2c, and the third cavity B 3a are sequentially connected. The configuration communicates with the third cavity 5.

  Here, for convenience of explanation, the third cavity A portion 1c, the third cavity C portion 2c, and the third cavity B portion 3a are individually described. It can be regarded as a waveguide composed of the cavity 5.

  A dielectric 4 having a curved cross-section is disposed at the bottom of the third cavity A portion 1c of the lower housing 1 so as to cover the slot 1e. Therefore, for example, when an electromagnetic wave of 20 GHz (gigahertz) is input from the introduction port 1d, it is reflected by the reflection surface at the back of the first cavity 1a and is guided to the third cavity A 1c via the second cavity 1b. It is burned.

  At this time, if the dielectric 4 is not present, the input electromagnetic wave passes upward through the third cavity A portion 1c, is reflected by the third cavity B portion 3a, and reaches the probe 2a. However, in this case, since all wavefronts of the electromagnetic waves radiated to the second cavity portion 1b and the third cavity A portion 1c are not parallel to the probe 2a, only the electromagnetic waves near the center of the probe 2a are picked up. That is, other electromagnetic waves return to the introduction port 1d as reflected waves, resulting in a small return loss (poor reflection characteristics).

  In the present embodiment, as described above, the dielectric 4 having a curved cross section is provided at the bottom of the third cavity A portion 1c. Therefore, the dielectric 4 is a radio wave lens for electromagnetic waves that have traveled straight upward in the second cavity 1b. As a result, the wavefront is regulated to be parallel to the probe 2a. Accordingly, if the shape of the dielectric 4 and the dielectric constant are determined to be required values, the electromagnetic wave that has traveled straight upward in the second cavity 1b can be efficiently picked up by the probe 2a.

  In addition, as an apparatus using a dielectric lens, JP-A-10-126109 and JP-A-2002-9542, and as for a dielectric lens, “Richard C. Johnson,” ANTENNA ENGINEERING HANDBOOK THIRD EDITION ”p16-2˜ Refer to documents such as “p16-11,1993”.

  Thus, according to the present invention, the reflection characteristics of the mode converter can be improved, and the conversion efficiency between the waveguide mode and the coaxial mode can be improved. Although this effect has different characteristics depending on the shape of the dielectric 4, the effect can be obtained only by inserting the dielectric 4. Below, the effect by the difference in the shape of the dielectric 4 is demonstrated.

  FIG. 3 is a perspective view showing three different shapes of the dielectric 4. 3A shows a bar shape, FIG. 3B shows a plate shape, and FIG. 3C shows a cross-sectional curved shape. FIG. 4 shows the result of measuring the reflection characteristics of the mode converter according to the present invention while exchanging them. In the graph of FIG. 4, the vertical axis represents reflection loss (dB), and the horizontal axis represents the RF frequency (GHz) input to the mode converter. The relative dielectric constant of the mounted dielectric is 2.3 fluororesin (tetrafluoroethylene resin).

  In FIG. 4, when there is no dielectric, the reflection loss in the measurement frequency band is about −10 dB to −13 dB, but the loss can be improved by 2 to 5 dB just by arranging the rod-shaped dielectric. Furthermore, in the case of a plate-like dielectric material, it can be improved by about 8 to 15 dB compared with the case where there is no dielectric material. Furthermore, it can be read that the use of a dielectric having a curved cross section can improve 9 dB to 18 dB compared to the case where there is no dielectric.

  The effect of the present invention lies in that such reflection characteristics can be improved not only in a specific narrow frequency band but also in a wide frequency band as shown in FIG. 4 simply by adding a dielectric having a simple shape. For this reason, a mode converter is prepared for each different frequency band as in the past, and a single mode converter can be used without dividing and covering a wide frequency band with a plurality of units.

  In addition, in order to increase the bandwidth as in the past, a waveguide having a complicated shape such as a ridge waveguide is used, or a matching state is adjusted by projecting a conductive rod into the waveguide. Improves reflection characteristics over a wide band with an inexpensive and simple configuration without causing structural deterioration, increased manufacturing costs, or loss of characteristics such as signal loss that may occur due to the conductor rod. it can.

  In addition, since the dielectric (dielectric constant 2.3) is disposed instead of the air (dielectric constant 1.0) in the third cavity A portion 1c, the Q value (Quality factor) in the waveguide is lowered. As a result, the reflection characteristic can be widened. Therefore, by using a dielectric having a higher relative dielectric constant than air, and selecting and installing the cross-sectional shape and size as appropriate, the size of the cavity can be reduced, the mode converter can be downsized, and the reflection characteristics can be reduced. The bandwidth can be increased.

  In this embodiment, the protruding direction of the dielectric 4 is arranged in the direction toward the probe 2a. However, the present invention is not limited to this, and the same is true even if the protruding direction of the dielectric 4 is arranged in the direction toward the slot 1e. The effect of can be obtained.

  In this embodiment, a rectangular waveguide is used for explanation. However, the present application is not limited to this, and a similar effect can be obtained by using a circular waveguide. Furthermore, although the present embodiment has been described as a frequency downconverter that is a receiving device, the present invention is not limited to this, and the same effect can be obtained even when used in a transmitter for satellite communication.

In this embodiment, fluororesin (tetrafluoroethylene resin) is used as the dielectric material. However, the present invention is not limited to this, and a material having good high frequency characteristics such as low loss in the frequency band to be used is appropriately selected. be able to.
In this embodiment, the probe is formed in a conductor pattern on the dielectric substrate. However, the present invention is not limited to this. The conductor rod may be connected to the conductor pattern on the dielectric substrate and protruded into the third cavity. Good.
The reflection characteristic can be measured using a measuring instrument for measuring normal reflection characteristics such as a network analyzer.

It is a disassembled perspective view in the see-through state which shows the Example of the microwave apparatus provided with the mode converter by this invention. The Example of the microwave apparatus provided with the mode converter by this invention is shown, (A) is sectional drawing of a side surface, (B) is sectional drawing of a front. It is a perspective view which shows the example of a shape of a dielectric material, (A) is rod shape, (B) is plate shape, (C) is a cross-sectional curve shape. It is a graph of the reflection characteristic by the shape of a different dielectric material. It is an electromagnetic field distribution map in the fundamental mode of a rectangular waveguide. It is a perspective view which shows the example of a slot of a waveguide. It is a disassembled perspective view which shows the conventional mode converter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lower housing | casing 1a 1st cavity part 1b 2nd cavity part 1c 3rd cavity A part 1d Inlet 1e Slot 2 Dielectric board 2a Probe 2b Ground side conductor pattern 2c 3rd cavity C part 2d Converter circuit 3 Upper housing 3a Third cavity part B 3b Fourth cavity part 3c Fifth cavity part 4 Dielectric 5 Third cavity part

Claims (3)

In a mode converter for mode conversion between a waveguide mode and a coaxial mode,
A high-frequency current flowing through the wall surface of the first cavity portion corresponding to the electromagnetic wave introduced or sent out from the entrance / exit to the wall surface of the first cavity portion, the first cavity portion comprising a cavity having an electromagnetic wave entrance / exit A slot provided in a direction intersecting with the second cavity, a second cavity formed continuously with the slot, a third cavity communicating with the second cavity and having the same cross-sectional shape as the inlet / outlet, and the third cavity A conversion probe protruding into the cavity,
A mode converter comprising a dielectric disposed at the entrance of the third cavity.   2. The mode converter according to claim 1, wherein the dielectric is formed into a curved surface having a projecting cross section.   A microwave device comprising the mode converter according to claim 1.

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