JPH0122241Y2 - - Google Patents

Description

[Detailed explanation of the idea] [Purpose of invention] (Industrial application field) The present invention relates to improvements in waveguide filter circuits.

(Prior Art) In the microwave band, a filter circuit is required in which a predetermined frequency band _A is a pass band and another frequency band _B is a stop band.

For example, in a radar device, the receiving frequency _A is passed through, and the frequency of the spurious signal generated by the transmitter etc.
It is used to prevent frequency _B from entering the receiver, and in the communication device, it passes the receiving frequency _A and transmits the transmitting frequency _B.
A filter circuit is used to prevent the transmitting and receiving antennas from entering the receiver due to coupling between the transmitting and receiving antennas.

Since these filter circuits are connected to the input side of a microwave receiver and are required to have low loss, waveguide filter circuits are often used.

An example of this will be explained with reference to FIGS. 3 and 4.

This filter circuit is commonly called a dumbbell-shaped filter circuit 4, and consists of a metal plate pattern 1 with a thickness of 0.3 to 1 mm, with side parts 3 serving as inductors in the width direction.
A post-shaped metal piece 2a, 2b with a width d and a length l is placed at the center of the rectangular resonance window 2 having a predetermined width and a predetermined height in the center, leaving the metal pieces 2a and 3b. The dumbbell-shaped filter circuit 4 is inserted into the waveguide 5 so as to be perpendicular to the direction of propagation of the microwave. Since it operates as a tube filter circuit, it has the advantage that the size of the filter section can be reduced.

Next, the equivalent circuit of this waveguide filter circuit is
To explain with a diagram, the dumbbell-shaped filter circuit 4 can be represented by a portion surrounded by a broken line 13.

That is, between the waveguide main line 7, the metal pieces 2a, 2
b is the inductor Lp/2, 8a, 8b, and its value (Lp/2) is determined by the width d and length l of the metal pieces 2a, 2b. Further, the gap g between the metal pieces 2a and 2b constitutes a capacitor C10. Furthermore, since the side parts 3a and 3b change the lateral direction of the waveguide 5, they become inductors 2L, 9a and 9b, and the value 2L is the gap between 3a and 3b, that is, the width W of the resonance window 2.
determined by.

Therefore, the impedance Z of the dumbbell-shaped filter circuit 4 in FIG. 3 is as follows: Z=L/C(1-W ² LpC·) 1/j{W(L+Lp)-1/WC} (1). Therefore, the frequency at which Z=∞ is _A , Z=0
Let _B be the frequency where , _A and _B are where _A is the center of the passband and _B is the center of the stopband. Therefore, the dumbbell-shaped filter circuit 4 has the dimensions (d, l, g, w, t) of the metal plate pattern 1.
By appropriately selecting , the desired passband and stopband can be determined.

In the filter circuit with the structure shown in Figure 3, the desired _A and _B
If it becomes necessary to reduce the width _d1 of the post-shaped metal pieces 12a and 12b as shown in FIG. 6a, processing becomes difficult, and the For example, if the metal piece 12b is bent like the metal piece _12b1 shown by the broken line, _A and _B will deviate from the desired frequencies. Further, when the desired capacitance value of the capacitor C10 is large, the gap g becomes small, so the processing accuracy becomes strict, and even a small dimensional error causes a large change in the capacitance value, so that _A and _B may deviate.

Therefore, as shown in the side view in FIG. 6c, the filter circuit is formed by forming a metal film pattern 1 having the same shape as the metal plate pattern 1 by photolithography or the like on the dielectric substrate 20.
2, the metal pieces 12a, 12b
deformation can be prevented, and the dimensional accuracy of the gap g can also be maintained.

However, in the equivalent circuit shown in Figure 5,
If you want to increase Lp/2 and C, make the post-shaped metal pieces 12a and 12b thinner, and at the same time,
Although it is necessary to make the gap g narrower, the metal pattern shown in FIG.

(Problems to be Solved by the Invention) In the conventional waveguide filter circuit, it has been difficult to increase the values of the inductor and capacitor in the post-shaped metal piece due to the configuration of the metal film pattern of the resonant circuit.

Therefore, an object of the present invention is to provide a waveguide filter circuit in which the number of inductors and capacitors in a post-shaped metal piece can be easily increased and the frequency setting range of the filter can be expanded.

[Structure of the idea]

(Means for solving the problem) This idea is to install a dielectric substrate formed by depositing a metal film pattern of a resonant circuit inside or at the end of a waveguide, which is perpendicular to the direction of propagation of microwaves. In the waveguide filter circuit provided with at least one waveguide filter circuit, the resonant circuit is formed by a metal film pattern formed on both sides of the dielectric substrate, and the metal film pattern is placed on the dielectric substrate at the center of the resonant window. It is characterized in that the tip portions are sandwiched and disposed opposite each other, and are connected to the resonant window frame through the respective post portions.

(Function) In the present invention, a metal film pattern is formed with a dielectric substrate sandwiched between them, and the tips are placed opposite each other across the dielectric substrate in the center of the resonant window, so that the area of both tips can be increased. A large inductor can be obtained by making the capacitor large and making the post part as thin as necessary.

(Embodiments) Hereinafter, embodiments of the waveguide filter circuit according to the present invention will be described in detail with reference to the drawings.

FIG. 1a shows an embodiment of the waveguide filter circuit according to the present invention, in particular, the metal film pattern 2
1 is a plan view taken out and shown.

That is, as shown in the side view of FIG. 1b, a metal film pattern 21 having a shape almost similar to that of a dumbbell-shaped filter is formed on both sides of the dielectric substrate 20, and the metal film pattern 21 on one side is coated. A post-shaped metal film piece 42a shown by a solid line in FIG _.
By making 42b ₁ thin and providing the tip portions 42a ₂ and 42b ₂ facing each other with the dielectric substrate interposed therebetween,
Lp/2 and C can be increased.

This filter circuit is similar to the conventional dumbbell-shaped filter circuit 4, so the details will be omitted.
In this filter circuit, metal is deposited in the form of a film on both sides of the dielectric substrate 20, and then a predetermined metal film pattern 21 can be formed on each side by photolithography, etc., so it is excellent in mass production, and each part dimensional accuracy can be improved.

Figures 2a, b, and c each show an example in which the filter circuit shown in Figure 1 is actually attached to a waveguide. It is a front view.

That is, in FIG. 2a, a counterbore is formed on the end face of the input or output part of the waveguide 25, and the dielectric substrate 20 is inserted into the counterbore.
By soldering the periphery of the metal film pattern 21 formed on both sides of the waveguide 25,
It forms a waveguide filter circuit.

In FIG. 2b, a dielectric substrate 20 having metal film patterns 21 deposited on both sides is inserted into flanges 36 ₁ and 36 ₂ provided on the end faces of two waveguides 35 ₁ and 35 ₂ , respectively. This is a waveguide filter circuit in which a dielectric substrate 20 is fastened between flanges 36 ₁ and 36 ₂ with screws 37 ₁ and 37 ₂ .

FIG. 2c shows L-shaped spring members 38 ₁ and 38 ₂ soldered to the periphery of the metal film pattern 21 formed on both sides of the dielectric substrate 20 and inserted into the waveguide 45. , is a waveguide filter circuit fixed inside the waveguide 45 by the elasticity of spring members 38 ₁ and 38 ₂ .

Although the embodiment shown in FIG. 2 shows a case in which one dielectric substrate formed with a metal film pattern of a resonant circuit is incorporated into the waveguide, the number of dielectric substrates is not limited to one. It goes without saying that by using a plurality of them at predetermined intervals, although the insertion loss increases slightly, it is possible to significantly improve the insertion loss in the stop band.

[Effect of idea]

According to the present invention, a dielectric substrate having a metal film pattern of a dumbbell-shaped resonant circuit adhered on both sides is placed inside or at the end of the waveguide at least once perpendicularly to the direction of propagation of the microwave. By providing a waveguide filter circuit that passes the desired frequency and acts as a stopband for other frequencies, the capacity of the inductor and capacitor can be increased, especially in the post section of the resonant circuit. The present invention provides a waveguide filter circuit that can expand the frequency range.

[Brief explanation of the drawing]

Fig. 1a is a plan view showing a resonant circuit in a waveguide filter circuit according to the present invention, and Fig. 1b is a plan view of the resonant circuit in the waveguide filter circuit according to the present invention.
_{Figures 2a} , b and c are respectively cross-sectional views showing an embodiment of a waveguide filter circuit to which the resonant circuit of Figure 1 is applied; Figure a is a plan view showing a metal pattern of a resonant circuit in a conventional waveguide filter circuit, figure b is a cross-sectional view taken along the line ₁ - _X1 in figure a, and viewed in the direction of the arrow. A cross-sectional view showing a conventional waveguide filter circuit, FIG. 5 is an equivalent circuit diagram of FIG. 4, and FIG. 6 is a diagram showing problems with metal patterns. ₂ − ₂ in a
A cross-sectional view taken from the line in the direction of the arrow, and FIG. 3C is a cross-sectional view showing the metal pattern of FIG. 20...Dielectric substrate, 21...Metal film pattern, 22...Resonance window, _42a1 , _42b1 ...Post portion, _42a2 , _42b2 ...Tip portion.

Claims (1)

[Scope of utility model registration request] A waveguide filter in which at least one dielectric substrate on which a metal film pattern of a resonant circuit is adhered is provided inside or at the end of a waveguide so as to be perpendicular to the direction of propagation of microwaves. In the circuit, the resonant circuit is formed by metal film patterns formed on both sides of the dielectric substrate, and the metal film patterns are arranged with their tips facing each other across the dielectric substrate in the center of the resonant window, and are respectively attached to posts. 1. A waveguide filter circuit characterized in that the waveguide filter circuit is configured to be connected to a resonant window frame through a section.