JPH0316301A - Band stop filter - Google Patents

Abstract

PURPOSE:To obtain a steep characteristic with a simple structure by coupling an active circuit to any resonator of a band pass filter. CONSTITUTION:With a signal inputted to an input terminal 14, an irreversible circuit element 18 supplies its signal to band pass filters 20, 22 and 24. The band pass filters 20, 22 and 24 pass a signal at an attenuation frequency, and reflects the signal at the outside of the attenuation frequency onto the irreversible circuit element 18. In such a case, when an active circuit 44 causing a negative resistance at the operating band of the band pass filters 20, 22 and 24 is coupled with any of the resonators, the Q is increased and a signal passes steeply the attenuation band, and reflects steeply on the band at the outside of the attenuation band. Then the irreversible circuit element 18 supplies the signal of the reflected band to an output terminal 58. Thus, a steep characteristic is obtained with simple structure.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a band-elimination filter, and more particularly to a band-elimination filter that uses a resonator and is used, for example, in cellular car telephones and other wireless devices. .

(Prior art) In recent years, in the United States, with the rapid spread of cellular car phones and the rapid increase in the number of cellular base stations, expansion of the frequency bandwidth used has been considered in order to increase the number of channels used. The allocation of frequency bands for use has been announced.In this case, the frequency used by one service system may be close to the frequency used by another service system, so in order to prevent mutual interference between those service systems, For example, there is a demand for a filter having a steep characteristic as shown in FIG. 8 or a filter having a steep characteristic as shown in FIG. 9. (Problems to be Solved by the Invention) In conventional band-stop filters, In order to obtain such steep characteristics, it is necessary to increase the Q value by coupling each active circuit to each resonator, which makes the structure complicated.

Furthermore, since a load is connected to the output end of the conventional band-pass filter, the Q0 value of the resonator must be made considerably large in consideration of the influence of the load. This requires the active circuit coupled to the resonator to operate in an unstable state, which is impractical.

Therefore, the main object of the present invention is to provide a band-elimination filter that can obtain steep characteristics with a simple structure.

(Means for Solving the Problems) The present invention provides a band rejection filter having a desired frequency band in its attenuation range, which includes an input terminal and a non-reciprocal circuit whose first terminal is connected to the input terminal. It has an element and a resonator, the input end of which is connected to the second terminal of the non-reciprocal circuit element which becomes the output side when the first terminal is the input side, and whose passband falls within the above-mentioned attenuation range. including a certain bandpass filter and an output terminal connected to a third terminal of a nonreciprocal circuit element that becomes an output side when the second terminal is the input side,
It is a band rejection type filter.

(Function) When a signal is input to the input terminal, the nonreciprocal circuit element provides the signal to the bandpass filter.

The bandpass filter passes signals in the attenuation range and reflects signals in bands other than the attenuation range to the irreciprocal circuit element. In this case, if a band-pass filter has an active circuit that is a negative resistance in the operating range of the band-pass filter coupled to one of its resonators, its Q value will increase and the attenuation range will increase. It passes through the band sharply and reflects bands other than the attenuation range sharply.

The non-reciprocal circuit element then provides the signal in the reflected band to the output terminal.

(Effects of the Invention) According to the present invention, a band-elimination filter can be obtained that can obtain steep characteristics with a simple structure in which an active circuit is coupled to one of the resonators of the band-pass filter. .

Moreover, since this band-stop filter does not require a load to be connected to the output end of the band-pass filter, the Q0 of the resonator in the band-pass filter does not have to be made very large, and coupling to the resonator of the band-pass filter is not necessary. It is possible to operate active circuits in a stable state, making it highly practical.

The above-mentioned objectives of this invention. Other purposes. Features and advantages will become more apparent from the following detailed description of the embodiments with reference to the drawings.

(Embodiment) FIG. 1 is an illustrative diagram showing an embodiment of the present invention. This band rejection filter 10 includes a box-shaped case l2 made of metal, for example. On one side wall of this case l2,
For example, a coaxial connector 14 is fixed as an input terminal through it. Furthermore, a first bandpass filter 16 made of a dielectric coaxial resonator is housed within the case 12. This first
The bandpass filter 16 is configured to pass through a desired frequency band (in this example, a band of 835 to 845 MHz and a band of 846.5 MHz).
It has a passband in a band (in this embodiment, a band of approximately 820 to 853 MHz) including a band of approximately 849 MHz. Therefore, the l-th bandpass filter 16 passes signals in a band including the desired frequency band. An input end 16a of the first bandpass filter 16 is connected to the input terminal 14 by, for example, a coaxial cable.

Furthermore, within case 12, the first bandpass filter 1
The output terminal 16b of 6 is connected to the first terminal 18a of a circulator l8 as a non-reciprocal circuit element.

When the first terminal 18a of this circulator 18 is set as the input side, the second terminal 18b which becomes the output side is connected to the input terminal 2 of the three second band pass filters 20, 22 and 24.
0a, 22a and 24a are commonly connected.

These second bandpass filters 20.22 and 24
is the band to be attenuated among the bands to be passed by the first band-pass filter 16, for example, 845 to 846.5 MHz.
, a band of 849 MHz or higher, and a band of 835 MHz or lower, respectively. These second bandpass filters 20, 22 and 24 have similar structures, although the number of stages and passbands of the dielectric coaxial resonators used are different, so in particular, one second bandpass filter 20 will be described in detail. explain.

The second bandpass filter 20 includes a rectangular parallelepiped case 26 made of metal, for example, and the space inside this case 26 is divided into eight partitions by seven partition plates 28 made of metal, for example.
It is divided into storage compartments.

For example, λ/
Four dielectric coaxial resonators 30 and a substrate 32 made of an insulating material such as epoxy resin are housed. In this case, the outer conductor 30a as one end of those dielectric coaxial resonators 30 is grounded to the case 26. Further, the substrates 32 are arranged on the open end sides of the dielectric coaxial resonators 30, respectively.

As shown in FIG. 2A, an L-shaped conductor pattern 34 is formed on the substrate 32, and one end of the conductor pattern 34 serves as the other end of the dielectric coaxial resonator 30. Inner conductor 30b is connected by, for example, a conductor ribbon 36. Furthermore, a conductor pattern 34 is provided on the substrate 32.
Two electrodes 38a and 38b are formed near one end of the conductor pattern 34, and these electrodes 38a and 38b are coupled to the conductive pattern 34 through gap capacitances caused by gassops 40a and 40b, respectively. Further, an amplifier circuit 44 constituted of, for example, a Si bibolar transistor as an active circuit is connected to these electrodes 38a and 38b through phase adjustment lines 42a and 42b. Therefore, this amplifier circuit 44 will be coupled to the dielectric coaxial resonator 30. Further, this amplifier circuit 44 is designed to have a negative resistance in the operating range of the second bandpass filter 20. Therefore, the apparent Q value of the second band-pass filter 20 becomes large in the operating range of the second band-pass filter 20. Furthermore, a conductor pattern 46 for supplying power to the amplifier circuit 44 is formed on the substrate 32.

Further, the other end of the conductive pattern 34 on each substrate 32 is connected to a respective electrode 50 as a transmission line by a respective conductive ribbon 48. Further, these electrodes 50 are arranged in a row at intervals so that a gear capacitance is generated between them by a cap 52. therefore,
This dielectric coaxial resonator 30 and its peripheral equivalent circuit are shown in FIG. 2B.

Further, the electrodes 50 at both ends are connected to the input end 20a and the output end 20a through the gap capacitance caused by the gap 54, for example.
0b, respectively. Therefore, this second bandpass filter 20 becomes the equivalent circuit shown in FIG.

The output end 20b of the second bandpass filter 20 is in an unloaded state in this embodiment. Note that this second
For example, a load such as a resistor may be connected to the output end 20b of the bandpass filter 20.

In addition, the gap capacitance between the dielectric coaxial resonator 30 and the electrode 50 in the second bandpass filter 20 is set to 845 to 846.5 MH, which should attenuate their resonance frequency.
Those in the band z are selected. Therefore, this second
The bandpass filter 20 has a frequency characteristic of reflection on the input end 2Oa side as shown in FIG.

Although not shown, the conductor pattern 4 of each board 32
6 is connected to a power source end 20c that passes through the side wall of the case 26. A DC power supply 56 in the case 12 is connected to this power supply terminal 2oC, and power is supplied from the DC power supply 56.

The other second band-pass filter 22 has the same structure as the second band-pass filter 20 described above, except that it includes a dielectric coaxial resonator of 10 stages and has a pass band of 849 MH.
The difference is that the band is above z.

Still another second bandpass filter 24 is the second bandpass filter 24 described above.
This bandpass filter 20 is different from the bandpass filter 20 in that it includes an 18-stage dielectric coaxial resonator and has a passband of 835M}Iz or less.

And these second bandpass filters 22 and 2
4, their output terminals are placed in a no-load state, and power is supplied from the DC power supply 56 to the power supplies @22C and 24c. Note that a load such as a resistor may also be connected to the output terminals of these second bandpass filters 22 and 24, for example.

On the other hand, when the second terminal 18b of the circulator l8 is set as the input side, the third terminal 18C which becomes the output side is connected to the case 1.
Coaxial connector 58 as an output terminal passing through the side wall of 2
connected to.

In this band-elimination filter 10, a first band-pass filter 16 passes a signal in a band including a desired frequency band to a first terminal 18a of a circulator 18. Then, this circulator 18 transfers the signal to three second
The input ends 20 of the bandpass filters 20, 22 and 24 of
a, 22a and 24a. One second bandpass filter 20 has a passband in the band to be attenuated, 845 to 846.5MHz, so
Signals in other bands are steeply reflected and applied to the second terminal 18b of the circulator 18. Similarly, another second band-pass filter 22 steeply reflects signals in bands other than the band of 849 MHz or higher, and applies the reflected signals to the second terminal 18b of the circulator l8. steeply reflects signals in bands other than the band below 835 MHz and connects them to the second terminal 18 of the circulator l8.
give to b. Therefore, the second terminal 18b of the circulator 18 is given a signal in a desired frequency band. Therefore, a signal in a desired frequency band is output from the third terminal 18c of the circuit 18, and the signal is applied to the coaxial connector 58. Therefore, this band-elimination filter 10 has the frequency characteristics shown in FIG. 5.

In addition, in the above-mentioned embodiment, the first band pass filter 16 is provided before the circulator l8, but in the present invention, the filter does not need to be provided before the circulator l8. In this case, the first terminal 18a of the circulator l8 is connected directly to the input terminal 14.

Furthermore, although a λ/4 dielectric coaxial resonator is used in the second bandpass filter, λ/2 is used instead of λ/4.
A dielectric coaxial resonator may be used. In this case, as shown in FIGS. 6 and 7, one end of the inner conductor 30b of the λ/2 dielectric coaxial resonator 30 is coupled to an amplifier circuit 44 as an active circuit, and the other end is connected to a transmission line. What is necessary is to connect it to the electrode 50 as shown in FIG. Alternatively, the resonator used in the second band-pass filter is not limited to a dielectric coaxial resonator, but a resonator with another structure such as a strip line resonator may be used, and its resonance mode is also TE mode. or TM mode.

Further, although the above-described embodiment has the characteristic of attenuating a plurality of bands, the present invention is also applied to a band-elimination filter having the characteristic of attenuating i bands. in this case,
For example, in the embodiment shown in FIG. 1, the second terminal 18b of the circulator 18 only needs to be connected to the input end of one second band-pass filter having a passband in the band to be attenuated.

Furthermore, in one second band-pass filter, an active circuit may be coupled to only one of the resonators. In this case, it is preferable that the active circuit be coupled only to the front-stage or rear-stage resonator, and in consideration of the noise generated from the second bandpass filter to the circulator side, it is most preferable to couple the active circuit to the rear-stage resonator. .

[Brief explanation of drawings]

FIG. 1 is an illustrative view showing an embodiment of the present invention. FIG. 2A is an illustrative diagram showing the main parts of the bandpass filter used in the embodiment shown in FIG. 1, and FIG. 2B is an equivalent circuit diagram of the main parts. FIG. 3 is an equivalent circuit diagram of the bandpass filter used in the embodiment of FIG. 1. FIG. 4 is a graph showing the frequency characteristics of reflection at the input end side of the bandpass filter shown in FIG. 3. FIG. FIG. 5 is a graph showing the frequency characteristics of the embodiment shown in FIG. FIG. 6 is an illustrative diagram showing the main parts of another example of the bandpass filter used in the embodiment of FIG. FIG. 7 is an equivalent circuit diagram of the bandpass filter shown in FIG. 6. FIGS. 8 and 9 are graphs that form the background of the present invention and show required frequency characteristics, respectively. In the figure, IO is a band-stop filter, 14 is a coaxial connector as an input terminal, 18 is a circulator as a non-reciprocal circuit element, 20, 22 and 24 are band-pass filters, 30 is a dielectric coaxial resonator, and 44 is an active An amplifier circuit is used as a circuit, and 58 indicates a coaxial connector as an output terminal.

Claims (1)

[Claims] 1. A band-elimination filter whose attenuation range includes a desired frequency band, and includes: an input terminal, a non-reciprocal circuit element whose first terminal is connected to the input terminal, and a resonator. and a bandpass filter whose input terminal is connected to a second terminal of the non-reciprocal circuit element which becomes an output side when the first terminal is an input side, and whose passband is in the attenuation band; A band rejection filter including an output terminal connected to a third terminal of the non-reciprocal circuit element which becomes an output side when the second terminal is an input side. 2. The band rejection filter according to claim 1, wherein the output end of the band pass filter is in a no-load state. 3. The band-stop filter according to claim 1 or 2, comprising a plurality of the band-pass filters. 4. The bandpass according to any one of claims 1 to 3, including an active circuit coupled to the resonator of the bandpass filter and serving as a negative resistance in the operating range of the bandpass filter. Blocking filter. 5. the active circuit is coupled to the final stage resonator;
A band rejection filter according to claim 4.