JP2594584B2 - Cavity resonator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a cavity resonator in which a temperature change of a resonance frequency is suppressed to zero or a small value.

[Conventional technology]

In the conventional cavity resonator, as shown in the conceptual structure of FIG. 3, the resonator rod 13 is attached to an inner wall of a cavity defined by a housing 11 made of a conductor so as to protrude inward. Had a structure. In this cavity resonator, the resonance frequency is determined by the length of the resonance rod in the cavity, that is, L 'in FIG.

[Problems to be solved by the invention]

In the above-described conventional cavity resonator, when the length L 'of the resonance rod 13 changes due to thermal expansion due to a temperature change, the resonance frequency also changes accordingly, and as a result, the temperature changes. It has a problem of exhibiting dependent and unstable frequency characteristics.

SUMMARY OF THE INVENTION An object of the present invention is to provide a cavity resonator in which a change in frequency characteristic with respect to a temperature change is zero or a very small value.

[Means for solving the problem]

The cavity resonator of the present invention is a cavity resonator that changes the length of a resonance rod protruding into a cavity of a housing made of a dielectric to change its resonance frequency.
The resonance rod and the housing are brought into contact with a metal, and the outer end of the resonance rod is fixed by a resonance rod fixing part made of a polymer-based insulating material. The resonance rod is fixed by bonding to the resonance rod at any position, and the coefficients of thermal expansion of the resonance rod and the fixed part of the resonance rod are set to α ₁ and α ₂ respectively. The distance from the junction between the resonance rod and the tip of the resonance rod, and the distance between the junction between the resonance rod fixing part and the housing and the inner wall surface of the housing are defined as l ₁ and d, respectively. city distance to the junction of the fixed portion, the thermal expansion coefficient of the housing when the α _3, α ₁ l ₁
= Is configured so as to satisfy the relation _{α 2 l 2 + α 3 d} .

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a first embodiment of the present invention. In the figure, a hole is formed in a part of a housing 1 made of a conductor, and a resonance rod fixing part 2 formed separately from the housing 1 is attached here. The resonance rod 3 protruding into the cavity of the housing 1 is joined at its outer end A by a resonance rod fixing portion 2. The resonance rod 3 is in electrical contact with the inner edge B of the hole of the housing 1.

In this configuration, the effective length of the resonance rod 3 (the distance from the inner wall of the housing 1 to the tip of the resonance rod 3) is L. Also,
The distance from the junction between the resonance rod 3 and the resonance rod fixing part 2 to the tip of the resonance rod 3 is l ₁ , and the distance from the junction to the inner wall of the housing 1 is l ₂ . Further, the coefficients of thermal expansion of the resonance rod 3 and the resonance rod fixing portion 2 are denoted by α ₁ and α ₂ , respectively. α ₁ and α ₂ are given by the following equations.

α ₁ = (1 / l ₁ ) × (dl ₁ / dT) α ₂ = (1 / l ₂ ) × (dl ₂ / dT) (1) (T: absolute temperature) Also, the effective length L of the resonance rod Is given by the following equation.

L = l ₁ −l ₂ (2) Assuming that the temperature coefficient of the effective length L is α _L , α _L = (1 / L) × (dL / dT) = [1 / (l ₁ −l ₂ )] × (Dl ₁ / dT−dl ₂ / dT) = (α ₁ l ₁ −α ₂ l ₂ ) / (l ₁ −l ₂ ) (3) Therefore, α ₁ : α ₂ = 1 / l ₁ : 1 / When l ₂ (4) holds, α _L = 0. At this time, the resonance frequency of the cavity resonator can be kept constant regardless of the temperature.

For example, it is assumed that platinum is used for the resonance rod 3 and zinc is used for the resonance rod fixing part 2, and the required effective length L of the resonance rod is 21 mm. platinum,
The thermal expansion coefficients of zinc at room temperature are 9 [K ^-1 ] and 30
Since [K ^-1 ], l ₁ is 30 m from formulas (2) and (4).
m and l ₂ may be set to 9 mm.

(Second Embodiment) FIG. 2 is a view showing a second embodiment of the present invention, and the same or equivalent parts as in FIG. 1 are denoted by the same reference numerals.

In this embodiment, a high molecular compound such as polyethylene or nylon, that is, an insulator is used for the resonance rod fixing portion 2, and the coefficient of thermal expansion is increased to several tens of times that of metal.

That is, the coefficients of thermal expansion of the metals are the same except for alkali metals such as sodium and potassium. Therefore, in order to increase the effect as described in the first embodiment, it is necessary to increase the l _2. On the other hand, if the above-described polymer compound is used for the resonance rod fixing device 2, the coefficient of thermal expansion is several tens of times that of metal, so that l ₂ can be reduced.

However, in this case, in order to ensure electrical conduction between the resonance rod 3 and the housing 1, a contact 4 made of a metal material having a spring property such as phosphor bronze as shown in FIG. It is provided facing the hole of the housing 1 and is in contact with the peripheral surface of the resonance rod 3.

In the embodiment shown in FIG. 2, since the junction between the resonance rod fixing portion 2 and the outer metal portion of the housing 1 does not coincide with the inner wall surface of the housing 1, it is necessary to consider the distance d.

The effective length L of the resonance rod 3 is expressed as follows in FIG.

L = l ₁ −l ₂ −d (5) Assuming that the coefficient of thermal expansion of the outer metal part of the housing 1 is α ₃ , the temperature coefficient α _L of the effective length _L is as follows.

α _L = α ₁ l ₁ −α ₂ l ₂ −α ₃ d) / (l ₁ −l ₂ −d) (6) Therefore, the condition for α _{L to} be zero is α ₁ l ₁ = α ₂ l ₂ + α ₃ d (7)

For example, the resonance rod 3 is made of copper, the resonance rod fixing part 2 is made of Teflon,
It is assumed that aluminum is used for the outer metal part of the housing 1 and the required effective length L of the resonance rod is 21 mm and α is 2 mm. The thermal expansion coefficients of copper, Teflon and aluminum are 16.7K ^-1 and 110, respectively.
Since K ⁻¹ and 23K ⁻¹ , l ₁ is calculated as 2 from the equations (5) and (7).
6.6 mm and l ₂ may be set to 3.6 mm.

In consideration of the thickness of the housing as in the second embodiment, since the joint between the resonance rod fixing portion and the housing coincides with the inner surface of the housing in the first embodiment, resonance occurs. It can be considered that the distance d from the joint between the rod and the resonance rod fixing part to the inner surface of the housing is set to zero.

[Effects of the Invention] As described above, the present invention provides a joint between a resonance rod and a housing in a resonance rod fixing portion for fixing a resonance rod, and a thermal expansion coefficient of each of the joints so as to satisfy a predetermined relational expression. The effective length of the resonance rod is affected by the temperature change, including the case where the thickness of the housing is changed by the temperature change and the position of the joint between the resonance rod fixing part and the housing is changed. And the fluctuation of the resonance frequency of the cavity resonator can be reduced to zero or a very small value.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a first embodiment of a cavity resonator according to the present invention, FIG. 2 is a cross-sectional view of a second embodiment using a polymer insulating material for a resonance rod fixing portion, and FIG. It is a conceptual sectional view of a cavity resonator. DESCRIPTION OF SYMBOLS 1 ... housing | casing (cavity part), 2 ... resonance rod fixed part, 3 ... resonance rod, 11 ... housing | casing (cavity part), 13 ... resonance rod.

Claims (1)

(57) [Claims] 1. A cavity resonator that changes the length of a resonance rod protruding into a cavity of a housing made of a dielectric to change its resonance frequency, wherein the resonance rod and the housing are made of metal. And the outer end of the resonance rod is fixed by a resonance rod fixing portion made of a polymer-based insulating material, and the resonance rod fixing portion is joined to the housing and the resonance rod at arbitrary positions. And the thermal expansion coefficients of the resonance rod and the fixed part of the resonance rod are set to α ₁ and α ₂ , respectively, and the distance from the junction between the resonance rod and the fixed part of the resonance rod to the tip of the resonance rod is set. The distance and the distance from the junction between the resonance rod fixing part and the housing to the inner wall surface of the housing are respectively l ₁ and d, and the distance from the junction to the junction between the housing and the resonance rod fixing part is also and then, the thermal expansion coefficient of the housing when the alpha _3, so as to satisfy the relation _{α 1 l 1 = α 2 l} 2 + α 3 d A cavity resonator comprising: a cavity resonator;