JPH05299903A - Polarized band pass filter - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a polarized band-pass filter having two attenuation poles having insertion loss characteristics on each side of the center frequency even if the resonator has four or five stages. [Structure] Four resonators 1 ₁ to 1 ₄ are arranged in a line and sequentially coupled. Input / output terminals 2 and 3 are provided at both ends of this resonator group, respectively. No resonator is provided at the same position as these input / output terminals 2 and 3. Of these resonators 1 ₁ to 1 ₄ , two resonators 1 ₁ and 1 ₄ on both outer sides of the _two resonators 1 ₂ and 1 ₃ adjacent to each other on the center side are interlaced by a negative admittance inverter 4. The input and output ends 2 and 3 at both ends of the resonator group are interlaced by a reactance 6. Between the input / output terminals 2 and 3 where the resonators are not provided at the same position and the resonators 1 ₁ and 1 ₄ adjacent to the input / output terminals 2 and 3, respectively, a transmission line 7 having a quarter wavelength is provided.
Connect at 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polar type bandpass filter used in a microwave band or the like.

[0002]

2. Description of the Related Art A conventional pole type bandpass filter having two attenuation poles on each side of the center frequency as shown in FIG. 7 has a minimum of 6 as shown in FIG. The first to sixth resonators 1 ₁ to ₁₆ are arranged in a line and sequentially coupled to each other, and input / output terminals 2 and 3 are provided at both ends of the resonator group. , The second and fifth resonators 1 _{2 on} both outer sides of the _fourth resonators 1 ₃ and 1 ₄ ,
1 ₆ is interlaced by a negative admittance inverter 4 composed of −J ₁ , and the input and output terminals 2 and 3 at both ends are interlaced by a positive admittance inverter 5 composed of + J ₂ .

[0003]

As described above, in the conventional polarized bandpass filter, two attenuation poles are provided on each side of the center frequency as shown in the insertion loss characteristic shown in FIG. In order to do so, it is necessary to set the number of resonators to a minimum of 6 as shown in FIG. 6, which makes it impossible to design efficiently, resulting in high cost and difficulty in securing an installation space. There was a problem.

An object of the present invention is to provide a polarized bandpass filter having two attenuation poles having insertion loss characteristics on both sides of the center frequency even if the resonator has four or five stages. It is in.

[0005]

The structure of the present invention for achieving the above object will be described. In the present invention, four or five resonators are sequentially coupled in a line, and both ends of this resonator group are connected. Input / output terminals are respectively provided, and resonators on both outer sides of two adjacent resonators of the resonators are interlaced by a negative admittance inverter, and the input / output terminals at both ends are interlaced by reactance. In a polarized band-pass filter, the distance between the input / output end where the resonator is not provided at the same position and the adjacent resonator is 1 /
It is characterized in that they are connected by a transmission line of four wavelengths.

[0006]

[Function] As described above, a quarter-wave transmission having a 90-degree phase difference is provided adjacent to the jump coupling point of the reactance and the jump coupling point of the negative admittance inverter and the jump coupling point of the reactance. If a path is provided, even if the resonator has four or five stages, at the jumping coupling point in the negative admittance inverter, the amplitude is equal at a certain frequency, the opposite phase is canceled, and the attenuation pole of the insertion loss characteristic is They appear symmetrically, and at the jumping coupling point in the reactance, the amplitudes are equal at other frequencies and the opposite phases cancel each other, so that the attenuation poles of the insertion loss characteristic appear symmetrically. Therefore, even if the resonator has four or five stages,
Attenuation poles of insertion loss characteristics are 2 on each side of the center frequency.
It is possible to obtain a polarized band-pass filter that exists one by one.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. The parts corresponding to those in FIG. 6 are given the same reference numerals.

FIG. 1 shows a first embodiment of the present invention. In the polarized bandpass filter of this embodiment, 4
It is successively coupled pieces of the resonator 1 ₁ to 1 ₄ in a row. At both ends of this resonator group, input / output terminals 2, 3 are respectively provided.
Is provided. In this embodiment, these input / output terminals 2,
No resonator is provided at the same position as 3. Of these resonators 1 ₁ to 1 ₄ , two resonators 1 ₁ and 1 _{4 on} both outer sides of the _two resonators 1 ₂ and 1 _{3 that} are adjacent on the center side are interlaced by a negative admittance inverter 4. . The input / output terminals 2 and 3 at both ends of the resonator group are interlaced by a reactance 6. The input / output terminals 2 and 3 in which the resonators are not provided at the same position and the adjacent resonators 1 ₁ and 1 ₄ are connected by transmission lines 7 and 8 of ¼ wavelength, respectively.

In such a polarized band-pass filter, the interlaced coupling point in the negative admittance inverter 4 and the interlaced coupling point in the reactance 5 are provided and adjacent to the interlaced coupling point in the reactance 5. 1/4 wavelength transmission line 7, 8 with a phase difference of 90 degrees
Even if the resonator has four or five stages, the frequency at the interlaced coupling point in the negative admittance inverter 4 (approximately 100 MHz, approximately -100 MHz in this embodiment).
), The amplitudes are equal and the opposite phases are canceled, the attenuation poles of the insertion loss characteristic appear symmetrically, and at the jump coupling point of the reactance 6, another frequency (in the present embodiment,
At approximately 250 MHz and approximately –250 MHz), the amplitudes are equal and the opposite phases are canceled out, and the attenuation poles of the insertion loss characteristic appear symmetrically. Therefore, even if the resonator has four or five stages, it is possible to obtain a polarized band-pass filter having two attenuation poles having insertion loss characteristics on both sides of the center frequency.

That is, at the interlaced connection point in the negative admittance inverter 4 in this embodiment, a signal of a certain frequency from the resonator 1 ₁ to the resonator 1 ₄ through the main line undergoes three-stage 90 ° phase shift. Since it goes through, it has a phase difference of 90 ° × 3 = 270 °, and the signal passing through the negative admittance inverter 4 is 90 °.
The phase difference between the two is 270 ° −90 °.
= 180 °, that is, the phases are opposite to each other. When the value of the negative admittance inverter 4 is appropriately selected, the amplitudes become equal, the amplitudes become equal at a certain frequency, and the opposite phases cancel each other out, so that the attenuation poles of the insertion loss characteristic appear symmetrically.
Similarly, at the jump-coupling point of the reactance 6 in this embodiment, a signal of another frequency from the input / output terminal 2 to the input / output terminal 3 through the main line undergoes a 90 ° phase shift of 5 stages. Since the signal passing through the reactance 6 has a phase difference of 270 ° with a phase difference of 90 ° × 5 = 450 °, the difference between the two is 450 ° −270 ° = 180 °, that is, the opposite phase. Become. If the value of the reactance 6 is appropriately selected, the amplitudes become equal, the amplitudes become equal at some other frequency, and the opposite phases cancel each other out, so that the attenuation poles of the insertion loss characteristic appear symmetrically.

As an example of the insertion loss characteristic of the polar type bandpass filter of the first embodiment, Fo = 10,000 MH
z, pass band width Fb = 50MHz (return attenuation of pass band 26
When the insertion loss characteristic was calculated for the first pole frequency Fc1 = 100 MHz, the results shown in FIG. 2 were obtained. In this case, the value of the negative admittance inverter 4 is -0.0451 and the value of the reactance 6 is +0.001. Also, the insertion loss when XL = 0 of the reactance 6 (conventional bandpass filter with one attenuation pole) is also shown.
Within the range of three times the pole frequency, the two pairs of attenuation poles according to the present invention show a better value of about 6 dB.

FIG. 3 shows a second embodiment of the present invention. In the polarized bandpass filter of this embodiment, 5
The individual resonators 1 ₁ to ₁₅ are arranged in a line and sequentially coupled. At both ends of this resonator group, input / output terminals 2 and 3 are respectively provided.
Is provided. In this embodiment, the resonator ₁₁ is provided at the same position as the one input / output terminal 2, and the resonator is not provided at the same position as the other input / output terminal 3. These resonators 1
Of the ₁ to ₁₅ two adjacent resonators 1 ₃ on the center side,
The resonators 1 ₂ and 1 _{5 on} both outer sides of 1 ₄ are interlaced by a negative admittance inverter 4. The input and output ends 2 and 3 at both ends of the resonator group are interlaced by a reactance 6. During the resonator input and output terminal 3 that is not provided at the same position as the resonator 1 ₅ of the adjacent are connected by a transmission line 8 of 1/4 wavelength.

With the polar bandpass filter having such a structure, the same effect as that of the first embodiment can be obtained.

As an example of the insertion loss characteristic of the polarized bandpass filter of the second embodiment, the insertion loss characteristic was calculated under the same conditions as in the case of the four stages described above except Fc1 = 89 MHz. The results shown in 4 were obtained. In this case, the value of the negative admittance inverter 4 is −
The value of 0.0394 and reactance 6 is +0.0068. Also,
The insertion loss of the reactance 6 when XL = 0 (conventional bandpass filter with one attenuation pole) is also shown. However, two attenuation poles according to the present invention have about two values within a range of twice the pole frequency.
It shows a good value of 10 dB.

FIG. 5 shows a third embodiment of the present invention. In the polarized bandpass filter of the present embodiment, five resonators 1 ₁ to ₁₅ are arranged in a line and sequentially coupled, as in the second embodiment. Input and output terminals 2 and 3 are provided at both ends of this resonator group, respectively. Also in this embodiment, the resonator ₁₁ is provided at the same position as the one input / output terminal 2, and the resonator is not provided at the same position as the other input / output terminal 3. Of these resonators 1 ₁ to ₁₅ , _two resonators 1 ₁ and 1 _{4 on} both outer sides of the _two resonators 1 ₂ and 1 _{3 that} are adjacent to each other on the inner side.
Are interlaced with the negative admittance inverter 4. The input and output ends 2 and 3 at both ends of the resonator group are interlaced by a reactance 6. During the resonator input and output terminal 3 that is not provided at the same position as the resonator 1 ₅ of the adjacent are connected by a transmission line 8 of 1/4 wavelength.

The same effect as in the second embodiment can be obtained with the polar bandpass filter having such a structure.

[0017]

As described above, in the polarized band-pass filter according to the present invention, the interlaced coupling point in the negative admittance inverter and the interlaced coupling point in the reactance are provided, and the interlaced coupling point in the reactance is provided. Since a 1/4 wavelength transmission line with a phase difference of 90 degrees is provided adjacent to, even if the resonator has 4 or 5 stages,
At the jump-coupling point in the negative admittance inverter, the amplitude is equal at a certain frequency and the opposite phase is canceled, the attenuation pole of the insertion loss characteristic appears symmetrically. Are equal to each other and the opposite phases cancel each other out, so that the attenuation poles of the insertion loss characteristic appear symmetrically. Therefore, the resonator has four stages or five stages.
Even with a stage, it is possible to obtain a polar bandpass filter in which two attenuation poles having insertion loss characteristics are present on each side of the center frequency.

Therefore, according to the present invention, it is possible to obtain the same insertion loss characteristic as the conventional one with a smaller number of resonator stages. Therefore, in the bandpass filter using the expensive dielectric resonator, the cost can be reduced and the size can be reduced by the reduction in the number of resonators used.

[Brief description of drawings]

FIG. 1 is a first polar bandpass filter according to the present invention.
It is a circuit diagram of an example.

FIG. 2 is an insertion loss characteristic diagram of the polar bandpass filter shown in FIG.

FIG. 3 is a second polar bandpass filter according to the present invention.
It is a circuit diagram of an example.

FIG. 4 is an insertion loss characteristic diagram of the polarized bandpass filter shown in FIG.

FIG. 5 shows a third polar type bandpass filter according to the present invention.
It is a circuit diagram of an example.

FIG. 6 is a circuit diagram of a conventional polarized bandpass filter.

FIG. 7 is an insertion loss characteristic diagram of a conventional polarized bandpass filter.

[Explanation of symbols]

1 ₁ to ₁₆ ... Resonator, 2, 3 ... Input / output terminal, 4 ... Negative admittance inverter, 5 ... Positive admittance inverter, 6 ... Reactance, 7, 8 ... Quarter wavelength transmission line.

Claims (1)

[Claims] 1. Four or five resonators are arranged in a line and are sequentially coupled to each other, and input / output terminals are provided at both ends of the resonator group. In a polarized bandpass filter in which the resonators on both outsides are interlaced by a negative admittance inverter and the input and output ends at both ends are interlaced by reactance, the resonators not provided at the same position A polarized band-pass filter characterized in that the output end and the resonator adjacent to the output end are connected by a ¼ wavelength transmission line.