JPH09326602A - High frequency filter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high frequency filter circuit having the pass characteristics of a narrower band in comparison with the conventional case. SOLUTION: In this high frequency filter circuit formed by electromagnetically coupling 1st and 2nd microstrip lines L1 and L2 through a slot line L3 consisting of a resonator, the 1st and 2nd microstrip lines L1 and L2 are electromagnetically coupled through another resonator Ls. Besides, concerning the high frequency filter circuit formed by electromagnetically coupling the 1st and 2nd microstrip lines L1 and L2 through the slot line L3 consisting of the resonator, another 1st resonator L4 is electromagnetically coupled to the 1st microstrip line L1, and another 2nd resonator L5 is electromagnetically coupled to the 2nd microstrip line L2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a high frequency filter circuit used in a frequency band such as the microwave, quasi-millimeter wave or millimeter wave.

[0002]

2. Description of the Related Art FIG. 3 shows a prior art reference 1, "Kikuo Tsunoda,
"Analysis of Antenna Feeding Hardware for Microwave Mobile Communications", ATR Technical Rep
ort, TR-0-0033, pp. 10-15, 19
FIG. 6 shows a conventional high-frequency filter circuit disclosed in "Issued in July 1990", and its equivalent circuit is shown in FIG.

In FIG. 3, after the microstrip conductor 1 is formed on the dielectric substrate 10, the dielectric layer 11 is formed on the dielectric substrate 10 and the microstrip conductor 1. Then, on the dielectric layer 11, a rectangular slot 3 that intersects the microstrip conductor 1 at a three-dimensionally right angle is formed.
After the flat plate-shaped ground conductor 12 having is formed, the dielectric layer 13 is formed on the ground conductor 12. further,
The microstrip conductors 2 are formed on the dielectric layer 13 so as to be parallel to the longitudinal direction of the microstrip conductors 1 and face each other and intersect the slots 3 at a right angle in three dimensions. Here, the transmission line L1 which is a microstrip line is constituted by the microstrip conductor 1 and the ground conductor 12 which sandwich the dielectric layer 11, and one end of the microstrip conductor 1 is used as the input terminal T1. The transmission line L2, which is a microstrip line, is formed by the microstrip conductor 2 and the ground conductor 12 that sandwich the dielectric layer 13, and one end of the microstrip conductor 2 is used as the output terminal T2.

The transmission line L1 and the transmission line L2 are electromagnetically coupled to each other via the slot line L3 formed by the slot 3 formed in the ground conductor 12. Here, the microstrip conductor 1 is formed so as to protrude from the center of the slot 3 by ¼ of the guide wavelength λm of the microstrip line L1, while the microstrip conductor 2 is formed from the center of the slot 3 to the microstrip line L2. It is formed so as to protrude by ¼ of the in-tube wavelength λm. The slot 3 has a length of ½ of the guide wavelength λs of the slot line L3 that the slot 3 forms, and projects from the intersection with the microstrip conductors 1 and 2 by λs / 4.

In the conventional high-frequency filter circuit configured as described above, the prior art document 2 “KC Gupta et.
al, “MICROSTRIP LINES and SLOTLINES”, ARTECH, pp.
234-239 ”, the high-frequency filter circuit is configured by vertically stacking microstrip-slot conversions using upper and lower layers of a multilayer structure. It is a filter circuit. That is, the resonator formed of the microstrip line L1 and the resonator formed of the microstrip line L2 are connected to the slot line L3.
Are coupled via a resonator constituted by to form a bandpass filter circuit.

In this type of high-frequency filter circuit, the maximally flat characteristic and Chebyshev characteristic are often used, and the element value at this time is g-value (hereinafter referred to as g-value) which represents the basic element value of the standardized low-pass filter. , G-value). Now, the transmission lines L1 and L
Let g1, g2, and g3 be g values of 2, L3, and external load be Z
r and the cutoff frequency is P ₀ , the characteristic impedances Zm1 and Zm of the transmission lines L1, L2 and L3, respectively.
2, Zs can be expressed by the following equation.

[0007]

[Formula 1] Zm1 = P ₀ · Zr · g1

(2) Zs = Zr / (P ₀ · g2)

[Formula 3] Zm2 = P ₀ · Zr · g3

The above-mentioned g value has a ripple of 0.01d, for example.
0.5 at Chebyshev characteristic of B to 1.0 dB
To about 2.0, and the characteristic impedance Zm1,
In view of the feasibility of Zs, it is easy to make the cutoff frequency P ₀ around 1. The cutoff frequency P ₀ = 1 corresponds to 100% in the actual frequency band.

[0009]

FIG. 9 shows the characteristic impedance Zm1 of the microstrip line L1 = the characteristic impedance Zm2 of the microstrip line L2 = 60.
Ω, characteristic impedance of slot line L3 Zs = 4
1.7Ω, center frequency of pass band f ₀ = 20.0 GHz
The simulation result of the high frequency filter circuit of the said prior art example calculated by FIG. As is clear from FIG. 9, in the conventional example, the 3 dB bandwidth is 15 GHz or more, and a very wide band pass characteristic is obtained. Therefore, the high frequency filter circuit is basically suitable for a wide band circuit, but on the contrary, there is a problem that it is difficult to narrow the band.

An object of the present invention is to solve the above problems and to provide a high frequency filter circuit having a narrow band pass characteristic as compared with the conventional example.

[0011]

According to a first aspect of the present invention, there is provided a high frequency filter circuit, wherein a first microstrip line and a second microstrip line are electromagnetically coupled via a slot line which constitutes a resonator. In a high-frequency filter circuit that is mechanically coupled, the first microstrip line and the second microstrip line are electromagnetically coupled via another resonator.

A high frequency filter circuit according to a second aspect of the present invention is the high frequency filter circuit according to the first aspect, wherein the other resonator is formed by a slot line.

A high frequency filter circuit according to a third aspect of the present invention is formed by electromagnetically coupling a first microstrip line and a second microstrip line through a slot line forming a resonator. In the high frequency filter circuit, another first resonator is electromagnetically coupled to the first microstrip line, and another second resonator is electromagnetically coupled to the second microstrip line. It is characterized by having done.

A high frequency filter circuit according to a fourth aspect is the high frequency filter circuit according to the third aspect, wherein each of the first and second resonators is formed of a microstrip line. To do.

[0015]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment> FIG. 1 is a perspective view of a high-frequency filter circuit according to a first embodiment of the present invention, and its equivalent circuit is shown in FIG. As shown in FIG. 1, the high-frequency filter circuit of the first embodiment is different from the conventional high-frequency filter circuit of FIG. 3 in that the microstrip conductor 1 of the microstrip line L1 and the microstrip conductor 2 of the microstrip line L2. By forming the rectangular electromagnetic coupling slot 6 in the grounding conductor 12 located between the microstrip line L1 and the microstrip line L2 via the resonator constituted by the slot 6, the electromagnetic coupling is performed electromagnetically. It is characterized by being combined.

In FIG. 1, after the microstrip conductor 1 is formed on the dielectric substrate 10, the dielectric layer 11 is formed on the dielectric substrate 10 and the microstrip conductor 1. Then, on the dielectric layer 11, a rectangular slot 3 that intersects the microstrip conductor 1 at a three-dimensionally right angle is formed.
And a flat plate-shaped grounding conductor 12 having a rectangular electromagnetic coupling slot 6 having a longitudinal direction parallel to the longitudinal direction of the microstrip conductor 1 and located at a position different from the slot 3 is formed. A dielectric layer 13 is formed on the ground conductor 12. Further, the microstrip conductor 2 is formed on the dielectric layer 13 so as to be parallel to the longitudinal direction of the microstrip conductor 1 and face each other and intersect the slot 3 at a right angle in three dimensions. Here, the dielectric layer 1
Microstrip conductor 1 and ground conductor 12 sandwiching 1
By the transmission line L1 which is a microstrip line
After passing through the slot 3, the microstrip conductor 1 is bent at a right angle and extends to an end of one side of the dielectric substrate 10, and the end serves as an input terminal T1. In addition, the microstrip conductor 2 that sandwiches the dielectric layer 13
A transmission line L2, which is a microstrip line, is constituted by the ground conductor 12 and the ground conductor 12, and one end of the microstrip conductor 2 serves as an output terminal T2.

The transmission line L1 and the transmission line L2 are electromagnetically coupled to each other via the slot line L3 formed by the slot 3 formed in the ground conductor 12. Here, the microstrip conductor 1 is formed so as to protrude from the center of the slot 3 by ¼ of the guide wavelength λm of the microstrip line L1, thereby forming a resonator. 1/1 of the guide wavelength λm of the microstrip line L2 from the center
It is formed so as to protrude by 4 and thus constitutes a resonator. Here, the slot 3 has a length of ½ of the in-tube wavelength λs of the slot line L3 that constitutes the slot 3 to form a resonator, and λs / 4 from the intersection with the microstrip conductors 1 and 2. Only each is protruding. On the other hand, the electromagnetic coupling slot 6 formed in the microstrip conductor 2 is formed to face the microstrip conductors 1 and 2 and to have a longitudinal direction parallel to the longitudinal directions of the microstrip conductors 1 and 2. And formed so as to be separated from the slot 3 by a predetermined distance. Here, the rectangular slot 6 formed in the ground conductor 12
Constitutes the slot line Ls, and has a width w1 narrower than the width of the microstrip conductors 1 and 2, and a length l1 in the longitudinal direction shorter than the length λm / 4.

The equivalent circuit of the high-frequency filter circuit configured as described above is shown in FIG. 4, and as is clear from this, it is composed of the resonator constituted by the microstrip line L1 and the microstrip line L2. A resonator formed by the slot line L3, and further connected to the microstrip line L1.
Of the slot line Ls of the slot 6 and the resonator of the microstrip line L2.
A band pass filter circuit is configured between the terminal T1 and the terminal T2 by electromagnetically coupling via the.

The frequency characteristics which are the simulation results of the high frequency filter circuit are shown in FIGS. Here, the set values of the respective parameters in the first embodiment of FIG. 7 are as follows. (A) Center frequency f ₀ of pass band = 20.0 GHz; (b) Characteristic impedance Zme = 120Ω of even mode in slot line Ls of electromagnetic coupling slot 6; (c) Slot line Ls of electromagnetic coupling slot 6 (D) Characteristic impedance Zs = 4 of the slot line L3
1.7Ω; and (e) at the center frequency f ₀ , the electromagnetic coupling slot 6
Electrical length θm = electrical length θs of slot line L3 =
π / 2.

The set values of the respective parameters in the second embodiment shown in FIG. 8 are as follows. (A) Center frequency f ₀ of pass band = 20.0 GHz; (b) Characteristic impedance Zme = 240Ω of even mode in slot line Ls of slot 6 for electromagnetic coupling; (c) Slot line Ls of slot 6 for electromagnetic coupling. (D) Characteristic impedance Zs = 4 of the slot line L3
1.7Ω; and (e) at the center frequency f ₀ , the electromagnetic coupling slot 6
Electrical length θm = electrical length θs of slot line L3 =
π / 2.

As is apparent by comparing FIGS. 7 and 8 with FIG. 9 of the conventional example, two microstrip lines L1 and L are provided via a slot line Ls which is another resonator.
By electromagnetically coupling the two and utilizing the frequency dependence of the coupler configured by the slot line Ls, the pass band width in the high frequency filter circuit can be narrowed, in other words, the frequency selectivity as a filter. Can be improved.

Further, when two high frequency filter circuits of the second embodiment having different center frequencies f ₀ (f ₀₁ = 20 GHz, f ₀₂ = 14 GHz) are prepared and are cascaded to form a high frequency filter circuit. The simulation results of are shown in FIGS. 10 and 11. Here, FIG. 11 corresponds to FIG.
It is an enlarged view of 0. As is clear from FIGS. 10 and 11, the pass band width can be significantly narrowed compared with the case of one high frequency filter circuit in the second embodiment, in other words, the frequency selectivity as a filter. Can be improved.

<Second Embodiment> FIG. 2 is a perspective view of a high frequency filter circuit according to a second embodiment of the present invention, and its equivalent circuit is shown in FIG. In the second embodiment, as compared with the conventional example of FIG. 3, a microstrip line L1 that constitutes another first resonator is electromagnetically coupled to the microstrip line L1, and the microstrip line L2 is used. In addition, the microstrip line L5 forming another second resonator is electromagnetically coupled. Hereinafter, the difference from the conventional example will be described in detail.

In FIG. 2, in the vicinity of the end portion of the microstrip conductor 1 on the dielectric substrate 10, it is parallel to the longitudinal direction of the microstrip conductor 1 and in the vicinity thereof so as to be electromagnetically coupled to the microstrip conductor 1. , The microstrip conductor 4 having the same width w2 and the electrical length 12 as the microstrip conductor 1 is formed.
In addition, in the vicinity of the end portion of the microstrip conductor 2 on the dielectric layer 13, the microstrip conductor 2 is parallel to the longitudinal direction of the microstrip conductor 2 and is electromagnetically coupled to the microstrip conductor 2 in the vicinity thereof. A microstrip conductor 5 having the same width w2 and electrical length 12 is formed. Therefore, the microstrip conductor 4 constitutes a resonator constituted by the microstrip line L4, while the microstrip conductor 5 constitutes a resonator constituted by the microstrip line L5.

In the high-frequency filter circuit configured as described above, as shown in FIG. 5, another microstrip line L4 is electromagnetically coupled to the microstrip line L1 and the microstrip line L2 is used.
In addition, another microstrip line L5 is electromagnetically coupled. By electromagnetically coupling the resonators in this way, the frequency selectivity of the coupler can be utilized to improve the frequency selectivity of the filter.

[0027]

As described above in detail, in the high frequency filter circuit according to the first aspect of the present invention, the first microstrip line and the second microstrip line are connected to the slot line which constitutes the resonator. In the high-frequency filter circuit electromagnetically coupled via the above, the first microstrip line and the second microstrip line are electromagnetically coupled via another resonator. Therefore, the passband width of the high-frequency filter characteristic can be made narrower than that of the conventional example by utilizing the frequency selection characteristic of another resonator, in other words, the frequency selectivity of the filter can be improved. . Here, the another resonator is preferably composed of a slot line.

In a high frequency filter circuit according to a third aspect of the present invention, the first microstrip line and the second microstrip line are electromagnetically coupled to each other through a slot line that constitutes a resonator. In the high-frequency filter circuit according to the above, another first resonator is electromagnetically coupled to the first microstrip line, and
Another second resonator was electromagnetically coupled to the second microstrip line. Therefore, the passband width of the high-frequency filter characteristic can be made narrower than that of the conventional example by utilizing the frequency selection characteristic of another resonator, in other words, the frequency selectivity of the filter can be improved. . Here, each of the other first and second resonators is preferably constituted by a microstrip line.

[Brief description of drawings]

FIG. 1 is a perspective view of a high frequency filter circuit according to a first embodiment of the present invention.

FIG. 2 is a perspective view of a high frequency filter circuit according to a second embodiment of the present invention.

FIG. 3 is a perspective view of a conventional high frequency filter circuit.

FIG. 4 is a circuit diagram showing an equivalent circuit of the high frequency filter circuit according to the first embodiment of FIG.

FIG. 5 is a circuit diagram showing an equivalent circuit of a high frequency filter circuit according to a second embodiment of FIG.

FIG. 6 is a circuit diagram showing an equivalent circuit of a conventional high frequency filter circuit.

FIG. 7 is a graph showing the frequency characteristic of the attenuation amount of the high frequency filter circuit of the first example of the first embodiment of FIG.

FIG. 8 is a graph showing the frequency characteristic of the attenuation amount of the high frequency filter circuit of the second example of the first embodiment of FIG. 1.

FIG. 9 is a graph showing frequency characteristics of attenuation amount of the conventional high frequency filter circuit of FIG.

FIG. 10 is a case where two high frequency filter circuits of the second example of the first embodiment of FIG. 1 are cascaded (third example).
5 is a graph showing frequency characteristics of attenuation amount of.

11 is an enlarged view of the frequency characteristic of the attenuation amount of FIG.

[Explanation of symbols]

 1, 2 ... Microstrip conductor, 3 ... Slot, 4, 5 ... Microstrip conductor for coupling, 6 ... Slot, 10 ... Dielectric substrate, 11, 13 ... Dielectric layer, 12 ... Ground conductor, T1 ... Input terminal, T2 ... Output terminals L1, L2, L4, L5 ... Microstrip line, L3, Ls ... Slot line.

Claims (4)

[Claims] 1. A high-frequency filter circuit in which a first microstrip line and a second microstrip line are electromagnetically coupled via a slot line that constitutes a resonator, wherein the first microstrip line is provided. And a second microstrip line electromagnetically coupled to each other via another resonator. 2. The high frequency filter circuit according to claim 1, wherein the another resonator is formed by a slot line. 3. A high-frequency filter circuit in which a first microstrip line and a second microstrip line are electromagnetically coupled via a slot line forming a resonator, wherein the first microstrip line is provided. In addition to electromagnetically coupling another first resonator, another high frequency filter circuit is electromagnetically coupled to the second microstrip line. 4. The high frequency filter circuit according to claim 3, wherein each of the other first and second resonators is constituted by a microstrip line.