JPH07193404A - Band pass filter - Google Patents

Abstract

PURPOSE:To make a device where either a magnetic coupling or a capacity coupling can be realized in an interstage coupling, a coupling coefficient can be changed without changing the center space between resonators and productivity is excellent, by adding coupling capacitor to an interstage. CONSTITUTION:Variable capacitance elements 512 to 534 for interstage coupling are provided between resonators 21 to 24. When the opposing relation of elements 512 to 534 and element 21 to 24 are changed by rotating rotary spindles 612 to 634, the interstage coupling capacitance of the elements 21 to 24 changes and the impedance Z of the parallel resonance circuit PRC for each interstage coupling changes. The impedance Z of the PRC is inducive in an area where frequency is lower than a resonance frequency, an interstage coupling becomes a magnetic coupling and a magnetic coupling coefficient can be changed by changing the capacitance of the elements 512 to 534. The impedance Z of the PRC is capacitive in a frequency which is higher than the resonance frequency, the interstage coupling becomes capacitance coupling and a capacitance coupling coefficient can be changed by changing the capacitance of the elements 512 to 534.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bandpass filter which is incorporated in a radio communication device or a broadcasting device and is suitable for removing an interfering wave or noise.

[0002]

2. Description of the Related Art FIG. 19 (a) is a sectional view showing an essential part of an example of a conventional bandpass filter [sectional view taken along the line BB of FIG. 19 (b)], and FIG. in a-a sectional view of the 19 (a), 1 is - Rudoke - scan, 2 ₁ to 2 ₄ are resonance elements. FIG. 20 (a) is also a plan view showing a main part of an example of a conventional bandpass filter, and FIG. 20 (b) is a view of A in FIG. 20 (a).
In the cross-sectional view of -A, 2 ₁ to 2 ₄ are resonant elements, and 15 ₁ to 15 _{4 are}
In solid dielectric provided on the other around the resonant elements 2 ₁ to 2 _4, it is a metal layer provided on the side surface and bottom surface of each solid dielectric. 16 ₁ and 16 ₂ are input / output coupling capacitive elements, 17 ₁₂ , 17 ₂₁ and
17 ₂₂ , 17, ₃₁ , 17 ₃₂ and 17 ₄₁ are inter-stage coupling capacitance forming elements,
2 ₁ each resonator to is provided on each upper surface of the two _4.

[0003]

In the conventional band pass wave filter shown in FIG. 19 [0006], in order to obtain the necessary electrical properties, by varying appropriately the distance between the centers of 2 to ₄ resonant element 2 ₁ It is necessary to match the inter-stage magnetic coupling coefficient with the required value. Therefore, it is necessary to change the center interval of the resonant elements each time the required electrical characteristics are changed to design the bandpass filter. In the conventional band pass wave filter shown in FIG. 20, as well as equal to each other form the respective shape and size of the resonant elements 2 ₁ to 2 _4,
Solid dielectric provided on separately to each around the resonant element 2 ₁ to 2 ₄
15 ₁ to 15 ₄ of the shape, for it is formed dimensions and dielectric constant equal to each other, the coupling between adjacent resonant element is blocked by the metal layer provided on each side of the solid dielectric 15 ₁ to 15 _4, from 2 ₁ resonating element to obtain the required electrical characteristics
2 ₄ inter-stage coupling capacitance, that is, capacitance between the inter-stage coupling capacitance forming elements 17 ₁₂ and 17 ₂₁ , 17 ₂₂ and 17 ₃₁ , 17 ₃₂ and 17 ₄₁
It is necessary to match the capacitance between them with a required value, and therefore, the facing area, the facing distance, or both the facing area and the distance of the inter-stage coupling capacitance forming elements 17 ₁₂ to 17 ₄₁ are appropriately selected according to the required capacitance. Therefore, as in the conventional bandpass filter shown in FIG. 19, it is necessary to make the interstage coupling capacitance different for each different required electrical characteristic, and the interstage coupling capacitance forming element. 17 ₁₂ to 17 ₄₁ as a resonant element 2 ₁ to 2 ₄
Each element 17 ₁₂ or
17 It is necessary to solder every ₄₁ , so there is a drawback that the productivity is low.

[0004]

SUMMARY OF THE INVENTION The present invention overcomes the drawbacks of the prior art by providing a bandpass filter having interstage coupling capacitive elements interposed between resonant elements that are magnetically coupled to each other. It is something to remove.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 (a) is a plan view showing an essential part of one embodiment of the present invention, and FIG. 1 (b) is a sectional view taken along the line A--A in FIG. 1 (a).
FIG. 1C is a sectional view taken along the line BB of FIG.
Rudoke - scan, 2 ₁ to 2 ₄ resonant element, in 3 ₁ to 3 ₄ resonance frequency fine-tuning element, for example - Rudoke - screwed to the upper wall of the scan 1, the inner end face and the upper end surface of the resonator It is composed of metal screws facing each other and capable of changing the insertion length into the shield case 1. 4 ₁ to 4 ₄ are lock nuts, 5 ₁₂ , 5 ₂₃ and
5 ₃₄ is a variable capacitance element for interstage coupling, which is the gist of the present invention,
Appropriate width, for example, the resonant element 2 ₁ to consist of electrodes by bending a metal plate of substantially the same width as the 2 ₄ diameter U shape, between the resonance elements adjacent the pivot shaft 6 _12, 6 ₂₃ and 6 ₃₄ In, it is rotatably provided around the rotation spindle. The rotary support shafts 6 ₁₂ to 6 ₃₄ have metal screws or inner ends fixed to the variable capacitance elements 5 ₁₂ to 5 ₃₄ for inter-stage coupling via the insulating layer to the variable capacitance elements 5 ₁₂ to 5 ₃₄ . It consists of a round bar-shaped insulator that is fixed directly and has a screw cut on the outer circumference. In FIG. 1, an input / output coupling element (the present invention can be embodied in any element of a capacitive coupling element or a magnetic field coupling element) and an input / output terminal are not shown.

The variable capacitance element for interstage coupling 5 ₁₂ shown in FIG.
Through 5 ₃₄ and the rotary support shafts 6 ₁₂ through 6 ₃₄ are removed, the inter-stage coupling of the resonant elements 2 ₁ through 2 ₄ is magnetic coupling. Now, the basic equivalent circuit when attention is directed to the magnetic coupling coefficient M ₁₂ between the respective distributed inductance L ₁ and L ₂ of the resonant elements 2 ₁ and 2 ₂ resonant element 2 ₁ and 2 ₂ are shown in FIG. 2, FIG. 2 The equivalent circuit of is generally represented by the equivalent circuit shown in FIG. The equivalent circuit of FIG. 3 can be converted into the equivalent circuit shown in FIG. 4, which will be described with reference to FIGS. The circuit constants in FIG. 5 are Z ₁ , Z ₂ and Z ₃ , and the circuit constants in FIG. 6 are Z _A ,
Given Z _B and Z _C , the following equations hold between them due to the equivalent conversion formula.

[Equation 1] If the circuit constants in FIG. 4 are Z _AL , Z _BL, and Z _CL , then the circuit constants Z _AL , Z _BL, and Z _CL in FIG.
The relationship with each of the circuit constants L ₁ -M ₁₂ , L ₂ -M ₁₂ and M _{12 in} is expressed by the following equations from equations (1) to (3).

[Equation 2] The equivalent circuit of FIG. 3 is represented by the equivalent circuit of FIG. 4 by selecting each circuit constant in FIG. 4 so as to have the relationship shown by the expressions (4) to (6). still,
Since there is a relation of M ₁₂ << L ₁ ≈L ₂ ... (7) among L ₁ , L ₂ and M ₁₂ ,

[Equation 3] The value of is extremely large.

A basic equivalent circuit diagram of the band pass filter of the present invention shown in FIG. 1 is shown in FIG. In FIG. 7, L ₁ through L ₄ are each distributed inductance of the resonant element 2 ₁ to 2 _4, C ₁
To C ₄ are the resonant elements 2 ₁ to 2 ₄ and the resonant elements
2 ₁ to 2 ₄ each upper end surface and resonance frequency fine adjustment element 3 ₁ to 3 ₄ combined capacity with each end surface, M ₁₂ is a resonance element
The magnetic coupling coefficient between 2 ₁ and 2 ₂ , M ₂₃ is the magnetic coupling coefficient between resonant elements 2 ₂ and 2 ₃ , M ₃₄ is the magnetic coupling coefficient between resonant elements 2 ₃ and 2 _4, and C
₀₁ and C ₄₅ are input / output coupling capacitances, C ₁₂ is a combined capacitance of the capacitance between the resonance element 2 ₁ and the interstage coupling variable capacitance element 5 ₁₂ and the capacitance between the element 5 ₁₂ and the resonance element 2 ₂ , and C ₂₃ is The combined capacitance of the capacitance between the resonant element 2 ₂ and the variable capacitance element for interstage coupling 5 ₂₃ and the capacitance between the element 5 ₂₃ and the resonant element 2 ₃ , C ₃₄ is the resonant element 2 ₃ and the variable capacitance element 5 for interstage coupling. capacitance between ₃₄ and element 5 ₃₄ and a combined capacitance of the capacitance between the resonant element 2 _4. 2 to 6
The equivalent circuit obtained by converting the basic equivalent circuit shown in FIG. 7 into a π-type circuit based on the equivalent conversion method described in FIG.
It is represented by. L ₁₂ in FIG. 8 is an inductance corresponding to Z _CL in FIG. 4, the resonant element 2 ₁ with capacitance C ₁₂
And forming a parallel resonant circuit coupled between the 2 _2. L ₂₃ is capacity
An inductance forming a coupling parallel resonant circuit between the resonance elements 2 ₂ and 2 ₃ together with C ₂₃ , and an L ₃₄ an inductance forming a coupling parallel resonance circuit between the resonance elements 2 ₃ and 2 ₄ together with the capacitance C ₃₄ . When the parallel resonant circuit for coupling between stages is generally expressed as shown in FIG. 9, its impedance Z is expressed by the following equation.

[Equation 4] In the band-pass filter of the present invention, the rotary support shaft 6 ₁₂ is rotated to rotate the interstage coupling variable capacitance element 5 ₁₂ , and the mechanical opposing relationship between the resonant elements 2 ₁ and 2 ₂ and the element 5 ₁₂ is established. changing the resonance element 2 ₁ interstage coupling capacitor C ₁₂ is changed between the 2 _2, Inpi in equation (8) - Dance Z changes. Rotating spindle
Variable capacitors for interstage coupling 5 ₂₃ by rotating 6 ₂₃ and 6 ₃₄
And 5 ₃₄ are also rotated, the interstage coupling capacitances C _{2 3} and C ₃₄ between the resonant elements 2 ₂ and 2 _{3 and} between the resonant elements 2 ₃ and 2 ₄ change, and The impedance of the resonant circuit changes. Resonant element 2 ₁ to the frequency region lower than the resonance frequency of the parallel resonant circuit coupled between the respective stages of the 2 _4, Inpi parallel resonant circuit coupled between the respective stages - dance becomes inductive, parallel resonant coupling between the respective stages In a frequency range higher than the resonance frequency of the circuit, the impedance of the parallel resonance circuit for inter-stage coupling becomes capacitive. Therefore, in the bandpass filter of the present invention, the resonance frequency of each parallel resonant circuit for coupling between stages is selected to be higher than the center frequency in the pass band required for the bandpass filter of the present invention, and Inpi of the parallel resonant circuit during binding - by setting a range of the inductive dance, no magnetic coupling the coupling between the respective stages of the resonant element 2 ₁ to 2 ₄ to indicate the equivalent circuit in FIG. 10 and FIG. 11 , The variable capacitance element for interstage coupling within the range in which the impedance of each parallel resonant circuit for interstage coupling is kept inductive.
By rotating ₁₂ to ₅₄ , the magnetic coupling coefficient between each stage can be changed. Further, the resonance frequency of the parallel resonant circuit for interstage coupling is selected to be lower than the center frequency in the pass band required for the bandpass filter of the present invention, and the impedance of the parallel resonant circuit for interstage coupling is selected. the by setting the range of the capacitive, no capacitive coupling of the coupling between the respective stages of the resonant element 2 ₁ to 2 ₄ to an equivalent circuit in FIG. 12, Inpi parallel resonant circuit coupled between the respective stages -
By rotating the variable capacitance elements 5 ₁₂ to 5 ₃₄ for interstage coupling within the range where the dance is kept capacitive,
The capacitive coupling coefficient between each stage can be changed. As described above, in the band-pass filter of the present invention, each inter-stage coupling can be realized in any coupling mode of magnetic coupling or capacitive coupling, and each inter-stage coupling is either magnetic coupling or capacitive coupling. Even when a coupling mode is selected, it is possible to make the coupling coefficients between the stages different from each other.
Even when all the center intervals of 2 ₁ to 2 ₄ are formed to be constant, the required electric characteristics can be provided.
As described in the formulas (6) and (7), the value of Z _CL , that is, the values of L ₁₂ , L _23, and L ₃₄ are extremely large, and therefore, together with L ₁₂ , L _23, and L ₃₄ , Even when the values of C ₁₂ , C ₂₃ and C ₃₄ forming the parallel resonant circuit for interstage coupling are small, the interstage coupling coefficient can be freely adjusted.

[0008] without intervention of a solid dielectric around the coaxial resonator element 2 ₁ to 2 ₄ in FIG. 1, a case has been exemplified where is interposed only air, sectional view of a main portion in FIG. 13 [Figure 1 ( b)
As shown the cross-section view] corresponding to the common dielectric block 7 around the coaxial resonator element 2 ₁ to 2 ₄ is provided, to the electrode ₈₁ is not in the upper end portion of the coaxial resonator 2 ₁ to 2 ₄ 8 ₄ It mounting, variable capacitance element 5 _{from 12} for interstage coupling between the electrodes 5
_The present invention can be implemented even when ₃₄ is provided. FIG. 13 shows variable capacitance elements 5 ₁₂ to 5 ₃₄ for interstage coupling.
Although the above is an example of a case where it is formed by a small variable capacitor such as a butterfly capacitor, it may be formed by a rotary U-shaped electrode similar to that shown in FIG. Figure 1
Other symbols and configurations in 3 are the same as those in FIG. Although FIG. 1 and FIG. 13 illustrates a case where from 2 ₁ coaxial resonator to form a 2 ₄ a conductor of round bar may be formed with square bar conductor or plate-like conductor. FIG. 14A is a cross-sectional view showing a main part of another embodiment of the present invention [C-C cross-sectional view of FIG. 14C], and FIG. 14B is an A- of FIG. 14A. A sectional view,
FIG. 14 (c), at B-B sectional view of FIG 14 (a), 12 ₁
To 12 ₄ in the ring resonant elements, as shown, one end of the metal plate of appropriate width - Rudoke - fixed to the bottom wall of the scan 1,
Bend over halfway to form an almost U-shape,
A gap is provided between the other end and the bottom wall of the shield case 1. In the thus-formed resonance element, an inductance component is formed by the metal plate portion, and a capacitance component is formed by the void portion between the other end of the metal plate and the bottom wall of the shield case 1. Although not shown in FIG. 14, a variable capacitor for inter-stage coupling, which is composed of a rotary U-shaped electrode similar to that shown in FIG. 1 and a rotary support shaft thereof, is provided between adjacent ring resonant elements. Although an element is provided, as described in the equations (6) and (7), the inductance component forming the parallel resonant circuit for interstage coupling is extremely large, and thus the interstage coupling is performed even when the capacitance is small. It is sufficiently possible to exhibit the function of, and therefore, the place for providing the variable capacitance element for interstage coupling is
The present invention can be carried out by selecting any appropriate place except the place where the electric field is extremely weak. As the variable capacitance element for inter-stage coupling, a variable capacitance element for inter-stage coupling formed of a small variable capacitor similar to that shown in FIG. 13 may be used.
In FIG. 14, as in FIG. 1, the illustration of the input / output coupling element and the input / output terminal is omitted.

The present invention can be implemented by using a helical resonance element or a resonance element formed by a printing method as the resonance element, in addition to the above-exemplified ones. FIG. 15A is a cross-sectional view showing a main part of an embodiment using a resonance element formed by a printing method as the resonance element [FIG.
5 (b) is a cross-sectional view taken along the line BB], and FIG.
In the A-A sectional view of (a), reference numeral 9 is a dielectric plate made of alumina or the like, the peripheral edges of which are fixed to the top wall, bottom wall and both end walls of the shield case 1. Reference numerals 22 ₁ to 22 ₄ denote resonance elements composed of thin metal layers attached to the dielectric plate 9. The lower end portions of the respective thin metal layers are electrically connected to the bottom wall of the shield case 1 and the upper end portions thereof are connected to each other. Is formed so as not to be electrically connected to the upper wall of the shield case 1 and to function as an element similar to the coaxial resonance element. 10 ₁₂ , 10 ₂₃ and 10 ₃₄ are rotary electrode plates for forming a capacitance, 11 ₁₂ , 11 ₂₃ and 11 ₃₄ are rotary shafts, and like the rotary shafts 6 ₁₂ to 6 ₃₄ shown in FIG. end secured directly to the capacitance forming rotating electrode plate 10 ₁₂ to 10 ₃₄ to the rotating electrode plate 10 ₁₂ no capacitance forming a metal screw or inner end fixed to 10 ₃₄ in Te, round bar insulator chopped screw on the outer periphery Consists of The inter-stage coupling capacitance is changed by operating the rotary support shafts 11 ₁₂ , 11 ₂₃ and 11 ₃₄ to rotate the capacity forming rotary electrode plates 10 ₁₂ , 10 ₂₃ and 10 ₃₄ and changing the facing relationship with the resonance element. be able to.

In all of the above, the case where the variable capacitance element is used as the capacitance element for coupling between stages is shown, but a fixed capacitance element may be used as in the embodiment shown in FIG. FIG.
16A is a sectional view showing a main part of another embodiment of the present invention [a sectional view taken along the line CC in FIG. 16B], and FIG.
16A is a sectional view taken along line AA of FIG. 16A, and FIG.
In the sectional view taken along line B-B, 1 sheet - Rudoke - scan, 2 ₁ to 2 ₄ are coaxial resonator element, 7 is a common dielectric block, 13 is a dielectric plate, each of the resonant elements 2 ₁ to 2 ₄ It is mechanically fixed to the upper end surface. Note that whether to protrude by appropriate height of each upper end portion of the resonant element 2 ₁ to 2 ₄ from the top surface of a common dielectric block 7,
From 2 ₁ resonance element as shown in FIG. 13 is attached to electrodes on the upper end of the 2 _4, provided with a suitable spacing between the lower edge of the upper surface and the dielectric plate 13 of the common dielectric block 7 is there. 1
4 ₁₂ , 14 ₂₁ , 14 ₂₂ , 14 ₃₁ , 14 ₃₂ and 14 ₄₁ are thin metal layers for forming inter-stage coupling capacitance, for example, the thin metal layers 14 ₁₂ , 14 ₃₁ and 14 ₃₂ are attached to the back surface of the dielectric plate 13. together, the thin metal layer 14 ₁₂ is electrically connected to the upper end surface of the resonator element 2 _1, the metal thin layer 14 ₃₁ and 14 ₃₂ is electrically connected to the upper end surface of the resonator element 2 _3, the metal thin layer 14 ₂₁ , 14 ₂₂ and 14 ₄₁ with adhering to the surface of the dielectric plate 13, the thin metal layer 14 ₂₁ and 14 ₂₂ is electrically connected to the upper end surface of the resonator element 2 _2, the metal thin layer 14 ₄₁ resonant element 2 _It is electrically connected to the upper end surface of ₄ . The facing area between the metal thin layers 14 ₁₂ and 14 ₂₁ and the facing area between the metal thin layers 14 ₂₂ and 14 ₃₁ and the metal thin layer 14 ₃₂
By appropriately selecting the facing area with 14 ₄₁ ,
It can have the required electrical characteristics. In each of the above embodiments, the case where the number of resonant elements is four (4th order) has been illustrated, but the present invention can be implemented by appropriately increasing or decreasing the order. In FIGS. 1 and 13 to 15, an element including a rotary electrode formed by bending a metal plate in a U shape, a small variable capacitor, or a plate-shaped rotary electrode is used as the variable capacitance element for interstage coupling. As an example, a strip-shaped metal plate is provided between adjacent resonant elements so that the longitudinal direction thereof is parallel to the axial direction of the resonant element, and is formed so as to rotate around the longitudinal axis. An electrode and a strip-shaped metal plate are interposed between adjacent resonance elements, and the plate surface is supported so as to form a right angle to the direction in which the resonance elements are connected so that the insertion length into the shield case can be changed. You may make it use the variable capacitance element for interstage couplings which consists of electrodes etc. which were formed in. Also in the embodiment shown in FIGS. 1 and 13 to 15, instead of the variable capacitance element for interstage coupling, a fixed capacitance element similar to that shown in FIG. 16 or a small fixed capacitance capacitor is provided. Good. In the embodiment shown in FIGS. 15 and 16, the description of the fine tuning element of the resonance frequency is omitted, but the fine tuning element can be omitted by performing the designing and manufacturing accurately so that the fine tuning element is matched with the required resonance frequency. It is possible.

When the pass band in the band pass filter of the present invention is formed to have a Chebyshev characteristic, its transmission characteristic can be obtained by the following equation.

[Equation 5] L: Transmission loss T _n (x): Chebyshev polynomial, in the case of x <1, T _n (x) = cos (n cos ⁻¹ x) In the case of x> 1, T _n (x) = cosh (n cosh ^-1 x) x: normalized reactance,

[Equation 6] f ₀ : Center frequency in the pass band of the band pass filter f: Arbitrary transmission frequency B _Wr : Allowable pass frequency bandwidth of the band pass filter S: Allowable voltage standing wave ratio (VSWR) in the pass band

FIG. 17 shows a band-pass filter of the present invention in which the impedance of the parallel resonant circuit for interstage coupling is inductive and the equivalent circuit of the main part is constructed as shown in FIGS. In the curve diagram showing the transmission characteristics, the horizontal axis is frequency and the vertical axis is attenuation amount, and the slope of the attenuation curve is steep in the frequency region higher than the center frequency of the pass band. FIG. 18 (the horizontal axis and the vertical axis are the same as those in FIG. 17) shows that the impedance of the parallel resonant circuit for interstage coupling is capacitive, and the equivalent circuit of the main part is configured as shown in FIG. In the curve diagram showing the transmission characteristics of the band pass filter, the slope of the attenuation curve is steep in the frequency region lower than the center frequency of the pass band.

[0013]

As described above, according to the present invention, in a band-pass filter in which resonant elements, which are originally magnetically coupled, are connected in series, the coupling capacitance is added between the stages so as to realize the coupling between the stages. It can be either magnetically coupled or capacitively coupled, and it is possible to have the required electrical characteristics by changing the magnetic coupling coefficient or the capacitive coupling coefficient while keeping the center distance of the resonance element constant. Therefore, the band pass filter having various electric characteristics can be realized by using the common parts and the mold, and the productivity can be remarkably enhanced.

[Brief description of drawings]

FIG. 1 is a diagram showing a main part of an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram for explaining a configuration principle of the present invention.

FIG. 3 is an equivalent circuit diagram for explaining a configuration principle of the present invention.

FIG. 4 is an equivalent circuit diagram for explaining a configuration principle of the present invention.

FIG. 5 is a circuit diagram for explaining a configuration principle of the present invention.

FIG. 6 is a circuit diagram for explaining a configuration principle of the present invention.

FIG. 7 is an equivalent circuit diagram of the bandpass filter of the present invention.

FIG. 8 is an equivalent circuit diagram of the bandpass filter of the present invention.

FIG. 9 is an equivalent circuit diagram for explaining the operation of the bandpass filter of the present invention.

FIG. 10 is an equivalent circuit diagram for explaining the operation of the bandpass filter of the present invention.

FIG. 11 is an equivalent circuit diagram for explaining the operation of the bandpass filter of the present invention.

FIG. 12 is an equivalent circuit diagram for explaining the operation of the bandpass filter of the present invention.

FIG. 13 is a cross-sectional view showing the main parts of another embodiment of the present invention.

FIG. 14 is a cross-sectional view showing the main parts of another embodiment of the present invention.

FIG. 15 is a cross-sectional view showing the main parts of another embodiment of the present invention.

FIG. 16 is a cross-sectional view showing the main parts of another embodiment of the present invention.

FIG. 17 is a curve diagram showing the transmission characteristics of the bandpass filter of the present invention.

FIG. 18 is a curve diagram showing the transmission characteristics of the bandpass filter of the present invention.

FIG. 19 is a diagram showing a main part of a conventional bandpass filter.

FIG. 20 is a diagram showing a main part of a conventional bandpass filter.

[Explanation of symbols]

1 Shield case 2 ₁ to 2 ₄ Resonance element 3 ₁ to 3 ₄ Resonance frequency fine adjustment element 4 ₁ to 4 ₄ Lock nut 5 ₁₂ to 5 ₃₄ Variable capacitance element for coupling between stages 6 ₁₂ to 6 ₃₄ Rotating spindle 7 Solid Dielectric 8 ₁ to 8 ₄ Electrode 12 ₁ to 12 ₄ Resonant Element 9 Dielectric Plate 22 ₁ to 22 ₄ Thin Metal Layer 10 ₁₂ to 10 ₃₄ Rotating Electrode Plate 11 ₁₂ to 11 ₃₄ Rotating Spindle 13 Dielectric Plate 14 ₁₂ to 14 ₄₁ Thin metal layer 15 ₁ to 15 ₄ Solid dielectric 16 ₁ and 16 ₂ Input / output coupling capacitance element 17 ₁₂ to 17 ₄₁ Interstage coupling capacitance forming element

Claims (7)

[Claims] 1. A band pass filter comprising an inter-stage coupling capacitive element interposed between resonant elements magnetically coupled to each other. 2. The band pass filter according to claim 1, wherein the inter-stage coupling capacitive element is a variable capacitive element. 3. The bandpass filter according to claim 1, wherein the interstage coupling capacitive element is a fixed capacitive element. 4. The bandpass filter according to claim 1, wherein the resonant element is a coaxial resonant element. 5. The bandpass filter according to claim 1, wherein the resonant element is a coaxial resonant element forming a coaxial dielectric resonator. 6. A resonator element has a metal plate, one end of which is fixed to a bottom wall of a shield case, is bent into a substantially U-shape, and an air gap is provided between the other end and the bottom wall of the shield case. The band pass filter according to claim 1, which is a ring resonant element provided. 7. The bandpass filter according to claim 1, wherein the resonant element is a helical resonant element.