JP5292675B2 - Rubidium atomic oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubidium atomic oscillator which can suppress the deterioration of resonance characteristics which occurs when a microwave resonator is reduced in size by making appropriate the positional relationship between an antenna for radiation and a rubidium metal accumulating portion. <P>SOLUTION: The microwave resonator 3 comprises a cylindrical gas cell heat tube 30 which holds a rubidium gas inside and keeps it at a predetermined temperature; a ring 21 for adjusting tuning which adjusts the tuning frequency by adjusting the length inside the cylinder of the gas cell heat tube 30; a cylindrical Rb gas cell 6 which is filled with a rubidium gas and is equipped with the metal accumulating portion 23 for accumulating rubidium metal which cannot vaporize; an antenna 4 for radiation which radiates microwaves; an antenna 2 for reception which is installed to measure the intensity of the microwaves; a photo sensor 7 for detecting the intensity of light which penetrated the Rb gas cell 6; and a dielectric body 22 for shortening the resonant wavelength. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

The present invention relates to an improvement of a rubidium atomic oscillator, and more particularly to an appropriate positional relationship between a radiation antenna for radiating microwaves and a metal reservoir of a rubidium gas cell.

In recent years, digital networks such as communication networks and broadcasting networks have been developed, and accordingly, a highly accurate and highly stable oscillator is required as a clock source used for generating clock signals for transmission devices and reference frequencies for broadcasting stations. It has become indispensable. As an oscillator that meets such requirements,
Rubidium atomic oscillators with high oscillation frequency accuracy and stability are often used. In recent years, the demand for miniaturization of atomic oscillators has increased, and there is an urgent need to miniaturize the whole including the optical microwave unit (OMU unit). Along with this miniaturization, the microwave resonator has to be miniaturized. However, when the microwave resonator is downsized, the microwave radiation antenna and the metal reservoir of the rubidium gas cell are close to each other, which causes various problems. In other words, the microwave resonator has a resonance tube (cavity resonator) due to its characteristics.
If there is some foreign matter, especially metal, there is a problem that not only is loss very much for microwave resonance, but also the resonance frequency itself changes to deteriorate the resonance characteristics. In other words, the positional relationship between the metal reservoir and the radiating antenna greatly affects the resonance characteristics.

As a conventional technique for solving this problem, Patent Document 1 discloses that a resonance wavelength is shortened to reduce the resonance wavelength in addition to a tuning method for changing the length of the resonator so that the microwave resonator is tuned to a microwave having a desired wavelength. In order to reduce the size, a technique has been disclosed in which a notch is formed in a part of a cylindrical dielectric, and the tuning range can be expanded by changing the arrangement angle of the notch.
JP 2001-308416 A

However, the conventional technique disclosed in Patent Document 1 has a problem that the cost of dielectric parts increases because it is necessary to form a notch in the dielectric. Further, since Patent Document 1 does not consider the positional relationship between the metal reservoir and the antenna, there is a problem that the tuning range is significantly narrowed if the positional relationship is not appropriate.
However, no proposal has been made that focuses on the problems that have arisen due to the fact that the positional relationship between the metal reservoir and the antenna has not been set appropriately, and has taken improvement measures.

In view of the above problems, the present invention provides a rubidium atom that can suppress deterioration of resonance characteristics that occur when a microwave resonator is downsized by optimizing the positional relationship between a radiation antenna and a rubidium metal reservoir. An object is to provide an oscillator.
Another purpose is to optimize the positional relationship between the radiation antenna and the rubidium metal reservoir,
It is to determine the proper position of the receiving antenna for measuring the microwave intensity.

In order to solve this problem, the present invention includes a gas cell main body filled with rubidium gas, and a metal reservoir that protrudes to the outside from the appropriate position of the gas cell main body in order to store rubidium metal that cannot be vaporized in the gas cell main body. A rubidium atom comprising a microwave resonator having a cylindrical gas cell, a radiation antenna for radiating microwaves toward the gas cell, and a receiving antenna provided for measuring the intensity of the microwave An oscillator,
The relative positional relationship between the radiation antenna and the metal reservoir is set so that the microwave intensity in the microwave resonator is equal to or higher than a predetermined intensity.
If the microwave resonator is downsized, the resonance characteristics may be deteriorated depending on the positional relationship between the radiation antenna and the metal reservoir of the gas cell. However, no proposal has been made so far, focusing on such problems and taking measures to improve it. Therefore, in the present invention, in order to set an appropriate positional relationship that does not deteriorate the resonance characteristics, the relative positional relationship between the radiating antenna and the metal reservoir is set so that the microwave intensity in the microwave resonator is equal to or higher than a predetermined strength. In addition,
It is determined by measuring with a receiving antenna. As a result, it is possible to minimize the deterioration of the resonance characteristics accompanying the downsizing.

The rod-shaped radiation antenna is arranged in parallel to a cross section orthogonal to the axial direction of the gas cell, and a straight line connecting the center point of the cross section of the gas cell and the metal reservoir is orthogonal to the radiation antenna. The metal reservoir or / and the radiating antenna are arranged so that an angle formed with a line to be within a predetermined range.
In the present invention, a rod-shaped radiation antenna is arranged in parallel to a cross section orthogonal to the axial direction of the gas cell (the optical axis direction of incident light from the rubidium lamp), and the straight line connecting the center of the gas cell and the metal reservoir is radiated. The metal reservoir and the radiating antenna are relatively arranged so that the angle formed between the vertical line of the antenna and the antenna is a predetermined angle. Thereby, the other position can be uniquely determined by fixing either one.

Further, the angle is in a range of 120 ° ± 40 ° or −120 ° ± 40 °.
This angle is in the range of 80 degrees to 160 degrees in the positive direction and in the range of minus 80 degrees to minus 160 degrees in the negative direction. Since the range and direction of angles are set in this way,
The setting position has a degree of freedom, and the microwave resonator can be easily assembled.

Further, the receiving antenna is arranged as far as possible from both the radiating antenna and the metal reservoir.
Microwaves deteriorate the resonance characteristics when there are foreign objects such as metal around them. Therefore, the receiving antenna having a metal part may affect the resonance characteristics. Therefore, in the present invention, the receiving antenna is arranged as far as possible from both the radiating antenna and the metal reservoir. Thereby, the influence of the resonance characteristic by the receiving antenna can be reduced as much as possible.

Also, the rod-shaped receiving antenna is arranged in parallel to the cross section of the gas cell, the angle is in a range of 120 ° ± 40 °, and a line orthogonal to the radiation antenna passing through the center point of the gas cell. The receiving antenna is arranged within an arc range of 180 degrees to 270 degrees with respect to the angle, or the angle is set to a range of −120 degrees ± 40 degrees, and the radiation antenna passes through the center point of the gas cell. The angle with respect to the line orthogonal to the antenna is -180 degrees to -2
The reception antenna is arranged within a range of a 70-degree arc.
The specific position where the receiving antenna is disposed as far as possible from both the radiating antenna and the metal reservoir differs depending on the positions of both the radiating antenna and the metal reservoir. That is, when the angle of the radiating antenna and the metal reservoir is 120 ° ± 40 °, the receiving antenna is disposed within an arc range of 180 ° to 270 ° around the center point of the gas cell. In the case of −120 degrees ± 40 degrees, the angle around the center point of the gas cell is −180 degrees to −27.
A receiving antenna is arranged within a 0-degree arc. As a result, the receiving antenna can be arranged at an optimum position with respect to the positions of both the radiating antenna and the metal reservoir.

In addition, at least the radiation antenna and the reception antenna are formed on a printed circuit board.
The radiating antenna and the receiving antenna may have any form as long as they are arranged at appropriate angles. However, in order to fix the antenna without using a separate fixing metal member, the antenna pattern is formed on the printed circuit board. Is preferably formed directly. As a result, mass production becomes possible, and component costs can be reduced.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the components, types, combinations, shapes, relative arrangements, and the like described in this embodiment are merely illustrative examples and not intended to limit the scope of the present invention only unless otherwise specified. .
FIG. 1 is a block diagram showing a schematic configuration of a rubidium atomic oscillator of the present invention. The rubidium atomic oscillator 100 includes a lamp excitation unit 1 for lighting a rubidium lamp (hereinafter referred to as Rb lamp) 5, an Rb lamp 5 for exciting rubidium gas in a rubidium gas cell (hereinafter referred to as Rb gas cell) 6, Rb gas cell 6 in which rubidium atoms are sealed, microwave resonator 3 that resonates in the vicinity of the resonance frequency of the rubidium atom in Rb gas cell 6, radiation antenna 4 that radiates microwaves to microwave resonator 3, and microwave A receiving antenna 2 for measuring the microwave intensity in the resonator 3, a photosensor 7 for detecting the intensity of light transmitted through the Rb gas cell 6, and a phase discriminator for discriminating the phase of the low frequency amplitude modulation signal appearing at Amp 9. 10
And a low frequency phase signal generator 11 that modulates the phase of the microwave with a low frequency, a frequency multiplication and synthesis modulator 12 that multiplies the oscillation signal of the voltage controlled crystal oscillator 13 into a microwave, and the voltage of the phase discriminator 10. And a voltage controlled crystal oscillator 13 that oscillates at a predetermined frequency. A unit composed of the Rb lamp 5, the microwave resonator 3, and the photosensor 7 is referred to as an optical microwave unit 8. The output of the frequency multiplication / synthesis modulator 12 is connected to the radiation antenna 4.

Next, since the operation of the rubidium atomic oscillator of the present invention is known, the description thereof is omitted here, but the outline of the microwave resonator 3 which is the main component of the present invention will be described.
In the operation process of the rubidium atomic oscillator, the energy level in a steady state (F = 1
) The presence of a microwave for dropping electrons in a higher level (F = 2) to the level of F = 1 is very important in operating as an atomic oscillator, and in order to sufficiently increase the intensity of the microwave. A microwave resonator is used. The microwave resonator is designed so as to transmit 6.83468 ·· GHz from the radiating antenna 4 attached in the microwave resonator 3 and to resonate at this frequency. In practice, the receiving antenna 2 is arranged separately from the radiating antenna 4 in order to measure the microwave intensity in the microwave resonator 3.

FIG. 2 is a configuration diagram of a microwave resonator according to an embodiment of the present invention. 2 (a) is a side view, FIG. 2 (b) is a view of the substrate viewed from the antenna mounting surface, and FIG. 2 (A) is a side view of the substrate removed.
FIG. 2B is a front view when the substrate is removed. In the present embodiment, the internal arrangement is indicated by a broken line.
This microwave resonator 3 holds the Rb gas cell 6 inside, and adjusts the cylindrical gas cell heat cylinder 30 for maintaining the internal temperature at a predetermined temperature, and the length of the gas cell heat cylinder 30 in the cylinder. A tuning adjustment ring 21 for adjusting the resonance frequency, a gas cell main body 6b filled with rubidium gas, and a metal reservoir protruding outside from a proper position of the gas cell main body 6b for storing rubidium atoms that cannot be vaporized in the gas cell main body 6b. Cylindrical Rb gas cell 6 with 23
A radiation antenna 4 that radiates microwaves to the Rb gas cell 6, a reception antenna 2 provided for measuring the intensity of the microwave, and a photosensor 7 that detects the intensity of light transmitted through the Rb gas cell 6. And a dielectric 22 that shortens the resonance wavelength (see FIG. 2A). Further, the radiation antenna 4 and the reception antenna 2 may have any form as long as they are arranged at appropriate angles. However, in order to fix the antenna without using a separate metal member for fixing, the substrate 25 is used. It is preferable to directly form the antenna pattern. This
Mass production is possible, and component costs can be reduced. That is, the receiving antenna 2,
The radiation antenna 4 and the photosensor 7 are provided on a substrate 25, and the substrate 25 is fixed to the gas cell thermal cylinder 30 with screws 26 (see FIG. 2B). Further, since the Rb gas cell 6 is fitted into the dielectric 22 and can be rotated around the central axis of the cylinder of the gas cell thermal cylinder 30, the Rb gas cell 6 can be fixed at an arbitrary rotational position. it can. Therefore, the metal reservoir 23 can be moved in a circular shape by rotating the Rb gas cell 6 (FIG. 2).
(See (A) and (B)).

If the microwave resonator 3 is downsized, the resonance characteristics may be deteriorated depending on the positional relationship between the radiation antenna 4 and the metal reservoir 23 of the Rb gas cell 6. Therefore, in the present embodiment, in order to set an appropriate positional relationship that does not deteriorate the resonance characteristics, the relative positional relationship between the radiating antenna 4 and the metal reservoir 23 is set so that the microwave intensity in the microwave resonator 3 is a predetermined strength. As described above, it is determined by measuring with the receiving antenna 2. As a result, it is possible to minimize the deterioration of the resonance characteristics accompanying the downsizing. The receiving antenna 2 is also used when adjusting the tuning adjustment ring 21.

FIG. 3 is a diagram for explaining the positional relationship between the radiating antenna and the metal reservoir. FIG. 3A is a front view, and FIG. 3B is a perspective view showing a relative positional relationship between the substrate and the Rb gas cell. As described above, it is necessary to make the positional relationship between the radiation antenna 4 and the metal reservoir 23 appropriate in order to reduce the size of the microwave resonator. Therefore, in the present invention, the relative positional relationship between the radiation antenna 4 and the metal reservoir 23 is defined by the angle α when the metal reservoir 23 provided on the circumference of the Rb gas cell 6 rotates. That is, the relative positional relationship between the radiating antenna 4 and the metal reservoir 23 must be determined so that the microwave intensity in the microwave resonator 3 is equal to or higher than a predetermined intensity. In other words, when the radiation antenna 4 is arranged in parallel to the cylindrical cross section 6a of the Rb gas cell 6, the radiation antenna 4 is lowered to the straight line PC connecting the center P of the cylindrical cross section 6a of the Rb gas cell 6 and the metal reservoir 23. The angle α (
The metal reservoir 23 and / or the radiating antenna 4 so that the angle APC is within a predetermined range.
Is to arrange. The angle α is an angle when the radiating antenna 4 and the metal reservoir 23 are relatively disposed. For example, the radiating antenna 4 is first fixed and the metal reservoir 23 is fixed.
May be rotated on the circumference of the Rb gas cell 6. Alternatively, the metal reservoir 23 may be fixed first, and the radiation antenna 4 may be moved by rotating the substrate 25.

FIG. 4 is a diagram for explaining an appropriate positional relationship between the radiation antenna and the metal reservoir.
In the present invention, in order to determine an appropriate value of the angle α, the angle α is variously changed according to an example described later, and the microwave intensity is received and measured by the receiving antenna 2 (
Details will be described later). As a result, it was found that α = 120 ° ± 40 ° is optimal.
FIG. 4A shows the positional relationship between the radiation antenna 4 and the metal reservoir 23 when α = 120 ° −40 ° = 80 °, and the radiation antenna 4 and the metal reservoir 23 are closest to each other. It is in the state. At this time, both the radiating antenna 4 and the metal reservoir 23 are in the state farthest from the receiving antenna 2. FIG. 4B shows the radiation antenna 4 when α = 120 °.
The metal reservoir 23 is shown in a state in which the metal reservoir 23 is positioned approximately in the middle between the radiation antenna 4 and the reception antenna 2. FIG. 4C shows α = 120 ° + 40.
The positional relationship between the radiating antenna 4 and the metal reservoir 23 when ° = 160 ° is shown, and the radiating antenna 4 and the metal reservoir 23 are in the most distant state. At this time, the metal reservoir 23 is closest to the receiving antenna 2. The angle α may be rotated in the opposite direction so that α = −120 ° ± 40 °.

In this embodiment, the rod-shaped radiation antenna 4 is arranged in parallel to the cross section perpendicular to the axial direction of the Rb gas cell 6, and the straight line connecting the center P of the Rb gas cell 6 and the metal reservoir 23 is connected to the radiation antenna 4. The metal reservoir 23 and the radiating antenna 4 are relatively arranged so that the angle α formed with the lowered perpendicular is a predetermined angle. Thereby, the other position can be uniquely determined by fixing either one of the metal reservoir 23 or the radiation antenna 4 first.
Further, the angle α is in the range of 80 ° to 160 ° in the positive direction, and −80 ° in the negative direction.
Within the range of -160 °. Thus, since the range and direction of the angle are set, a degree of freedom is generated at the set position, and the microwave resonator can be easily assembled.

As described above, the positional relationship between the radiation antenna 4 and the metal reservoir 23 is determined, but at the same time, the position of the reception antenna 2 needs to be appropriately arranged. In other words, the microwave deteriorates the resonance characteristics when foreign objects such as metal are present around the microwave. Therefore, the receiving antenna 2 having a metal member may also affect the resonance characteristics. Therefore, in the present embodiment, consideration is given to disposing the receiving antenna 2 as far as possible from both the radiating antenna 4 and the metal reservoir 23. Thereby, the influence of the resonance characteristic by the receiving antenna 2 can be reduced as much as possible.
Further, as shown in FIG. 5, the receiving antenna 2 is arranged in parallel to the cylindrical cross section 6a of the Rb gas cell 6 so that the angle α is in the range of 120 ° ± 40 °, and the cylindrical cross section of the Rb gas cell 6 is used. It is preferable to arrange the receiving antenna 2 within the range of the arc S in which the arc angle β of 6a is 180 ° to 270 °. Alternatively, it is preferable that α = −120 ° ± 40 ° and that the receiving antenna 2 be arranged in a circular arc range where the circular arc angle β of the cylindrical cross section of the Rb gas cell 6 is −180 ° to −270 °. As a result, the receiving antenna 2 can be arranged at an optimum position with respect to both the radiation antenna 4 and the metal reservoir 23.

FIG. 6 shows the positional relationship (angle α) between the radiation antenna of the microwave resonator of the present invention and the metal reservoir.
) And the microwave intensity. In addition, each microwave intensity plots the maximum value of the value measured by FIGS. 9-17 mentioned later. The vertical axis represents the microwave intensity (dBm), and the horizontal axis represents the angle θ (α) (°). Note that the reference point for the angle θ when measuring the data (FIGS. 9 to 17) is different from the reference point for the angle α described with reference to FIG. That is, as shown in FIG. 7, when the straight line 33 and the circle 34 are drawn in contact with each other at the end D of the radiating antenna 4 and a perpendicular 32 perpendicular to the straight line 33 is drawn from the end D, the midpoint P of the circle 34 is The angle formed by the perpendicular line 32 passing through and the straight line PQ connecting the midpoint P and the metal reservoir 23 is defined as θ.
As shown in FIG. 6, the angle indicating the strongest intensity (−22.01 dBm) is θ = 45 ° (α
= 90 °), and the angle indicating the weakest intensity (−37.4 dBm) is θ = 270 °.
It can be seen that (α = 315 °). That is, α = 80 ° to 160 determined in FIG.
° corresponds to the range A in FIG. 6, and it was proved from the experiment that the microwave intensity was strong.

FIG. 8 is an exploded configuration diagram of the microwave resonator according to the embodiment of the present invention. The same components will be described with the same reference numerals as in FIG. The mold block 34 is configured to include the tuning adjustment ring 21, and this is set in the gas cell heat cylinder 30. The Rb gas cell 6 is inserted into the center hole 22 a which is a hollow portion of the dielectric 22 and is held in the gas cell heat cylinder 30. In addition, the radiation antenna 4 and the reception antenna 2 are mounted on the substrate 25 in advance so as to have the above-described positional relationship with the metal reservoir 23. Then, by assembling them so that the axis XY is the central axis, one microwave resonator 3 is completed.

9 to 17, the angle θ in FIG. 7 is set to 0 °, 45 °, 90 °, 135 °, 180 °, and 225.
It shows the frequency characteristics of the microwave intensity when set to °, 270 °, 315 °, and 360 °, respectively. The vertical axis represents the microwave intensity (dBm), and the horizontal axis represents the frequency (frequency width: 200 MHz). Here, A indicates a point where the microwave intensity is maximized. For example, in the case of the angle θ = 0 ° in FIG. 9, the microwave frequency is 6.88.
When the frequency is 05 GHz, the maximum intensity of the microwave is −25.32 dBm.

It is a block diagram which shows schematic structure of the rubidium atomic oscillator of this invention. It is a block diagram of the microwave resonator which concerns on one Embodiment of this invention. It is a figure explaining the positional relationship of a radiation antenna and a metal pool part. It is a figure explaining the appropriate positional relationship of a radiation antenna and a metal reservoir part. It is a figure explaining the appropriate positional relationship of a receiving antenna. It is a figure which shows the positional relationship (angle (alpha)) of the radiation antenna and metal reservoir part of a microwave resonator, and the relationship of microwave intensity | strength. It is a figure which defines angle (theta). 1 is an exploded configuration diagram of a microwave resonator according to an embodiment of the present invention. FIG. 8 is a frequency characteristic diagram of microwave intensity when the angle θ of FIG. 7 is 0 °. FIG. 8 is a frequency characteristic diagram of microwave intensity when the angle θ in FIG. 7 is 45 °. FIG. 8 is a frequency characteristic diagram of microwave intensity when the angle θ of FIG. 7 is 90 °. FIG. 8 is a frequency characteristic diagram of microwave intensity when the angle θ of FIG. 7 is 135 °. FIG. 8 is a frequency characteristic diagram of microwave intensity when the angle θ of FIG. 7 is 180 °. FIG. 8 is a frequency characteristic diagram of microwave intensity when the angle θ in FIG. 7 is 225 °. FIG. 8 is a frequency characteristic diagram of microwave intensity when the angle θ of FIG. 7 is 270 °. FIG. 8 is a frequency characteristic diagram of microwave intensity when the angle θ of FIG. 7 is 315 °. FIG. 8 is a frequency characteristic diagram of microwave intensity when the angle θ of FIG. 7 is 360 °.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lamp excitation part, 2 Reception antenna, 3 Microwave resonator, 4 Radiation antenna, 5 Rb lamp, 6 Rb gas cell, 7 Photo sensor, 8 Optical microwave unit,
9 Amp, 10 Phase discriminator, 11 Low frequency phase signal generator, 12 Frequency multiplication / synthesis modulator, 13 Voltage controlled crystal oscillator, 21 Tuning adjustment ring, 22 Dielectric, 23 Metal reservoir, 25 Substrate, 30 Gas cell heat Tube, 100 rubidium atomic oscillator

Claims (1)

A rubidium atom,
  A gas cell body containing the rubidium atoms;
  Metal reservoir for storing rubidium metal that protrudes outward from the gas cell body
A gas cell comprising a section;
  A radiation antenna for radiating microwaves toward the gas cell;
  A receiving antenna for receiving the microwave;
A microwave resonator having
  The metal reservoir has the radiation antenna and the reception antenna of the gas cell.
Close to the edge
  The rod-shaped radiation antenna is arranged in parallel to the cross section perpendicular to the axial direction of the gas cell.
And
  A straight line connecting the center point of the cross section and the metal reservoir in a plan view from the axial direction;
The angle formed between the radiating antenna and the line perpendicular to the radiating antenna is 80 degrees or more.
It is in the range of 160 degrees or less above, passes through the center point of the cross section and is orthogonal to the radiation antenna
The receiving antenna is arranged in an angle range of 180 degrees or more and 270 degrees or less with respect to the line to be
Being
A rubidium atomic oscillator characterized by that.

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