JPH0314310A - Multiband filter - Google Patents

Abstract

PURPOSE:To obtain a miniaturized multiband filter having sharp characteristics by forming a band pass filter(BPF) for passing a band including the passing area of a required frequency band and plural band stop filters for attenuating an attenuation area. CONSTITUTION:An amplifier circuit 40 constituted of a Si bipolar transistor(TR) as an active circuit is connected to a dielectric coaxial resonator 28 and constituted so as to be a negative resistor in the operation area of a band-stop filter 18. The BPF 16 passes a signal in a band including a required frequency band. Plural band stop filters 18, 20, 22 are used for attenuating signals in unrequired frequency bands. Since the active circuit 40 connected to the resonator 28 acts as a negative resistor in this case, the Q value of the band-stop filter is increased. Thereby, the plural band stop filters 18, 20, 22 are used for sharply attenuating signals in unrequired frequency bands. Consequently, the miniaturized multi-band filter having sharp characteristics can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a multiband filter, and more particularly to a multiband filter used in, for example, 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 is being considered in order to increase the number of channels used. The allocation of frequency bands to be used has been announced. In this case, since the frequency used in one service system and the frequency used in another service system may be close to each other, in order to prevent mutual interference between these service systems, for example, the steep characteristic shown in FIG. There is a demand for a multi-band filter having the following characteristics and a multi-band filter having the steep characteristics shown in FIG.

(Problem to be solved by the invention) In order to obtain such a steep characteristic, it is possible to construct a multiband filter using a cavity resonator, but the shape becomes large and it is difficult to miniaturize. Conflicting demands.

Therefore, the main object of the present invention is to provide a multiband filter that is compact and has steep characteristics.

(Means for Solving the Problems) A first multi-band filter according to the present invention is a multi-band filter in which a desired frequency band is in its pass band and an undesired frequency band is in its attenuation band. an input terminal, the input end of which is connected to the input terminal, a band-pass filter for passing a band including the above-mentioned pass band, and a band-pass filter that is connected in series at a subsequent stage of the band-pass filter;
The band-stop filter includes a plurality of band-stop filters for attenuating the above-mentioned attenuation range, and an output terminal connected to the latter stage of the band-stop filters, and the band-stop filter includes a dielectric coaxial resonator and the dielectric coaxial resonance. This is a multi-band filter including an active circuit coupled to the band-elimination filter and having a negative resistance in the operating range of the band-elimination filter.

A second multi-band filter according to the present invention is a multi-band filter in which a desired frequency band is in its pass band and an undesired frequency band is in its attenuation band, and includes an input terminal and an input terminal thereof. is connected to the input terminal and passes through a band including the above-mentioned passband, and a nonreciprocal circuit element whose first terminal is connected to the output terminal of the first bandpass filter. and whose input terminals are commonly connected to the second terminal of the irreversible circuit element which becomes the output side when the first terminal is the input side, and whose passband is in the above attenuation range. The second band-pass filter includes a second band-pass 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 an input side. , a multi-band filter including a dielectric coaxial resonator and an active circuit coupled to the dielectric coaxial resonator and having a negative resistance in the operating range of the second bandpass filter.

(Operation) In the first multiband filter, the bandpass filter passes signals in a band including a desired frequency band. The plurality of band-elimination filters then attenuate signals in undesired frequency bands. In this case, the active circuit coupled to the dielectric coaxial resonator in the band-elimination filter becomes a corrosive resistance, so the Q value of the band-elimination filter becomes large. Therefore, the plurality of band rejection filters sharply attenuate signals in undesired frequency bands.

Further, in the second multi-band filter, the first band-pass filter passes a signal in a band including a desired frequency band, and the non-reciprocal circuit element passes the signal to a plurality of second band-pass filters. give.

The second bandpass filter passes signals in an undesired frequency band and reflects signals in a desired frequency band to the irreciprocal circuit element. In this case, the active circuit coupled to the dielectric coaxial resonator in the second bandpass filter becomes a negative resistance, so the Q value of the second bandpass filter becomes large. Therefore, the plurality of second band-pass filters steeply pass undesired frequency bands and steeply reflect desired frequency bands.

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

(Effects of the Invention) According to the present invention, a multiband filter having steep characteristics can be obtained. Moreover, this multiband filter uses a dielectric coaxial resonator instead of a cavity resonator, so it is compact.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

(Embodiment) FIG. 1 is an illustrative diagram showing an embodiment of the present invention. This multiband filter 10 includes a box-shaped case 12 made of metal, for example. For example, a coaxial connector 14 is fixed as an input terminal to one side wall of the case 12 so as to pass through it.

Furthermore, a bandpass filter 16 made of a dielectric coaxial resonator is housed within the case 12.

This bandpass filter 16 filters a desired frequency band (in this example, a band of 835 to 845 MHz and a band of 846 MHz).
5 to 849 MHz (in this example, a band of approximately 820 to 853 MHz).

Therefore, this bandpass filter l6 passes signals in a band including the desired frequency band. An input end 16a of this bandpass filter 16 is connected to the input terminal 14 by, for example, a coaxial cable.

Furthermore, within the case 12, for example, three band rejection filters 18, 20 and 22 are housed. These band-elimination filters 18, 20 and 22 select undesired frequency bands among the bands to be passed by the band-pass filter 16,
That is, the band from 845 to 846.5 MHz, 849 MH
It is for attenuating the band above z and the band below 835 MHz, and is connected in series after the band pass filter l6. That is, the output terminal 16b of the band pass filter l6 is connected to the input terminal 18a of the first stage band rejection filter 18, and the output terminal 16b of the first stage band rejection filter l8 is connected to the input terminal 18a of the first stage band rejection filter 18.
8b is the input terminal 20a of the middle stage band rejection filter 20,
The output end 20b of the middle-stage band-elimination filter 20 is connected to the input end 22a of the final-stage band-elimination filter 22, respectively, by, for example, a coaxial cable.

These band-elimination filters 18, 20, and 22 have similar structures, although the number of stages of the dielectric coaxial resonators used and the attenuation band differ, so the first-stage band-elimination filter 18 will be described in detail.

This first-stage band rejection filter includes a rectangular parallelepiped case 24 made of metal, for example, and the space inside this case 24 is divided into eight partitions by seven partition plates 26 made of metal, for example.
It is divided into storage compartments.

For example, λ/
Four dielectric coaxial resonators 28 and a substrate 30 made of an insulating material such as epoxy resin are housed. In this case, the outer conductor 28a as one end of those dielectric coaxial resonators 28 is grounded to the case 24. Further, the substrates 30 are arranged on the open end sides of the dielectric coaxial resonators 28, respectively.

On this substrate 30, as shown in FIG. 2A, for example, an L-shaped conductor pattern 32 is formed, and one end of this conductor pattern 32 serves as the other end of the dielectric coaxial resonator 28. Inner conductor 28b is connected, for example, with a conductor ribbon 34. Furthermore, a conductor pattern 32 is provided on the substrate 30.
Two electrodes 36a and 36b are provided which cooperate with to create a gap capacitance. These electrodes 36a and 36
An amplifier circuit 40 constituted by, for example, a Si bipolar transistor as an active circuit is connected to the phase adjustment line 38a and 38b. Therefore, this amplifier circuit 40 will be coupled to the dielectric coaxial resonator 28.

Further, this amplifier circuit 40 is configured to have a negative resistance in the operating range of the band rejection filter l8.

Therefore, the apparent Q value of this band-elimination filter 18 becomes large in the operating range of the band-elimination filter I8. Furthermore, a conductor pattern 42 for supplying power to the amplifier circuit 40 is formed on the substrate 30.

On the other hand, one end of a chip-shaped capacitor 44, for example, is soldered to the other end of the conductor pattern 32, and the other end of the capacitor 44 is soldered to a center conductor 46a of a coaxial cable 46 serving as a transmission line. . Therefore, the equivalent circuit of this dielectric coaxial resonator 28 and its surroundings is as shown in FIG. 2B. The dielectric coaxial resonator 28 and the capacitor 44 are selected so that their series resonance frequency is in the band of 845 to 846.5 MHz to be attenuated.

In this band rejection filter 18, the eight stages of dielectric coaxial resonators 28, an amplifier circuit 40, and the like are connected by the above-mentioned coaxial cable 46. Furthermore, both ends of the coaxial cable 46 are connected to an input end 18a and an output end 18b, which pass through one side wall of the case 24, respectively. Therefore, the equivalent circuit of this band rejection filter I8 is as shown in FIG. Moreover, this band rejection filter 1
The frequency characteristics of the sun are as shown in FIG.

Although not shown, the conductor pattern 4 of each board 30
2 is connected to a power source end 18c passing through the other side wall of the case 24. And, this power supply terminal 18C is connected to the case l.
A DC power supply 48 in the DC power supply 2 is connected, and power is supplied from the DC power supply 48.

The middle-stage band-elimination filter 20 has the same structure as the above-described band-elimination filter l8, but differs in that it includes 10 stages of dielectric coaxial resonators and has an attenuation range of 849 MHz or more.

Furthermore, the final stage band-elimination filter 22 differs from the above-described band-elimination filter 18 in that it includes 18 stages of dielectric coaxial resonators, etc., and that its attenuation range is 835M82 or less.

Power is also supplied from the DC power supply 48 to the power supply terminals 20c and 22c of these band rejection filters 20 and 22.

Further, the output end of the final stage band rejection filter 22 is connected to a coaxial connector 50 serving as an output terminal passing through the side wall of the case 12.

In this multi-band filter 10, the band pass filter l6 passes signals in a band including a desired frequency band, and the band rejection filters 18, 20 and 22 in the succeeding stage pass signals among the signals passed by the band pass filter l6. Signals in undesired frequency bands, that is, in the band from 845 to 846.5 MHz, in the band above 849 MHz, and in the band below 835 MHz, are attenuated steeply. therefore,
This multiband filter 10 has frequency characteristics shown in FIG.

Note that in the above embodiment, in the band rejection filter, λ
Although a /4 dielectric coaxial resonator is used, a λ/2 dielectric coaxial resonator may be used instead of a λ/4 dielectric coaxial resonator.

In this case, for example, as shown in FIGS. 6A and 6B, a λ/2 dielectric coaxial coaxial Fi. Inner conductor 28 of vessel 28
one end side of b is coupled to an amplifier circuit 40 as an active circuit,
Further, for example, a metal cylindrical body 4 is provided on the other end side of the inner conductor 28b.
3 with a conductive adhesive, and both ends of the capacitor 44 are soldered, for example, to the metal cylinder body 43 and the coaxial cable 46 serving as a transmission line.

FIG. 7 is an illustrative view showing another embodiment of the invention. This embodiment is particularly different from the embodiment shown in FIG.
The difference is in the structure of the stage after the bandpass filter 16.

That is, in this embodiment, the l-th bandpass filter l
The output end 16b of 6 is connected to a first terminal 19a of a circulator 19 as a non-reciprocal circuit element.

Furthermore, when the first terminal 19a of this circulator 19 is set as the input side, the second terminal 19b, which becomes the output side, includes:
Input ends 21a, 23a and 25a of the three second bandpass filters 21, 23 and 25 are connected in common.

These second bandpass filters 21, 23 and 25
is the band to be attenuated among the bands to be passed by the bandpass filter l6, for example, 845 to 846.5MHz
, a band of 849 MHz or higher, and a band of 835 MHz or lower, respectively. These second band-pass filters 21, 23 and 25 have similar structures, although the number of stages and passbands of the dielectric coaxial resonators used are different, so especially regarding one second band-pass filter 21, explain.

This second bandpass filter 21 is a dielectric coaxial resonator 28 of λ/4 whose outer conductor 28a is grounded, similar to the bandstop filter 1 in the embodiment shown in FIG.
and a substrate 30 having an amplifier circuit 40 as an active circuit coupled to the dielectric coaxial resonator 28.

The conductive patterns 32 on each substrate 30 are connected to respective electrodes 47 as transmission lines by respective conductive ribbons 45, as shown in FIG. Further, these electrodes 47 are arranged in a row at intervals so that Ganop capacitance is generated between them. Further, the electrodes 47 at both ends are connected to the input end 21a via, for example, Gasop capacitance.
and output terminal 2lb (FIG. 9).

Therefore, this second bandpass filter 21
The equivalent circuit is shown in the figure.

Note that the output end 2lb of this second bandpass filter 21
is left open in this example, but may be connected to a load.

The other second band-pass filter 23 has the same structure as the above-mentioned band-pass filter 2l, but is different in that it includes a 10-stage dielectric coaxial resonator and has a pass band of 849 MHz or more. do.

Still another second band-pass filter 25 is different from the above-described band-pass filter 2l in that it includes 18 stages of dielectric coaxial resonators and has a pass band of 835 MHz or less.

Note that the amplifier circuit in each second bandpass filter is as follows:
The second bandpass filter is configured to have negative resistance in its operating range.

On the other hand, the third terminal 19C, which is the output side when the second terminal 19b of the circulator 19 is the input side, is connected to the coaxial connector 50 as an output terminal.

In this multiband filter 10, the first bandpass filter l6 passes a signal in a band including a desired frequency band to the first terminal 19a of the circulator 19. This circulator 19 then provides the signal to input ends 21a, 23a and 25a of three second bandpass filters 21.23 and 25.

One second band-pass filter 2l has a pass band in the undesired frequency band of 845 to 846.5 MHz, so it steeply reflects signals in other bands and passes the signal to the second terminal 19b of the circulator 19. give to Similarly, the other second band pass filter 23 steeply reflects signals in bands other than 849 MHz and above to pass through the circulator 19.
Further, another second bandpass filter 25 steeply reflects signals in bands other than 835 MHz and applies the reflected signals to the second terminal 19b of the circulator 19. Therefore, the second terminal 19b of the circulator 19 is given a signal in a desired frequency band. Therefore, the third terminal 19 of the circulator l9
A signal in a desired frequency band is output from c, and the signal is applied to the output terminal 50. Therefore, this multi-band filter 10 also provides frequency characteristics similar to those of the embodiment shown in FIG.

In the embodiment shown in FIG. 7, a λ/4 dielectric coaxial resonator is used in the second bandpass filter, but a λ/2 dielectric coaxial resonator may be used instead of the λ/4 resonator. may be used. In this case, as shown in Figure 10, λ/2
One end of the dielectric coaxial resonator 28 may be coupled to the amplifier circuit 4o as an active circuit, and the other end may be connected to the electrode 47 as a transmission line.

Further, each of the above-mentioned embodiments has the characteristic of passing two different bands, but in the present invention, a multi-band filter having the characteristic of passing three or more different bands is used. It's okay. In this case, for example, in the embodiment shown in FIG. 1, three or more band-stop filters having mutually different attenuation bands are provided after the band-pass filter, or in the embodiment shown in FIG. Three or more second bandpass filters having mutually different passbands may be connected to the circuit.

[Brief explanation of the drawing]

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 band rejection 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 band rejection filter used in the embodiment of FIG. 1. FIG. 4 is a graph showing the frequency characteristics of the band rejection filter shown in FIG. FIG. 5 is a graph showing the frequency characteristics of the embodiment shown in FIG. FIG. 6A is an illustrative diagram showing the main part of another example of the band rejection filter used in the embodiment of FIG. 1, and FIG. 6B is an equivalent circuit diagram of the main part. FIG. 7 is an illustrative view showing another embodiment of the invention. FIG. 8 shows the second band if! used in the embodiment of FIG. !
FIG. 2 is an illustrative diagram showing the main parts of a filter. FIG. 9 is an equivalent circuit diagram of the second bandpass filter used in the embodiment of FIG. 7. FIG. 10 is an equivalent circuit diagram showing another example of the second bandpass filter used in the embodiment of FIG. 7. FIGS. 11 and 12 are graphs that form the background of the present invention and show required frequency characteristics, respectively. In the figure, 10 is a multi-band filter, 14 is a coaxial connector as an input terminal, 16 is a band-pass filter, 18, 20 and 22 are band-stop filters, 19 is a circulator, and 21, 23 and 25 are second band-pass filters. a filter, 28 a dielectric coaxial resonator, 40 an amplifier circuit,
50 indicates a coaxial connector as an output terminal.

Claims (1)

[Claims] 1. A multiband filter in which a desired frequency band is in its pass band and an undesired frequency band is in its attenuation band, comprising: an input terminal; the input terminal is connected to the input terminal; , a bandpass filter for passing a band including the passband, a plurality of bandstop filters connected in series after the bandpass filter for attenuating the attenuation band, and a plurality of bandstop filters for attenuating the attenuation band. The band-elimination filter includes an output terminal connected to a subsequent stage, and the band-elimination filter includes a dielectric coaxial resonator and an active circuit that is coupled to the dielectric coaxial resonator and has a negative resistance in the operating range of the band-elimination filter. Including multi-band filters. 2. A multi-band filter in which a desired frequency band is in its pass band and an undesired frequency band is in its attenuation band, the input terminal being connected to the input terminal and including the pass band. a first band-pass filter for passing a band; a non-reciprocal circuit element whose first terminal is connected to the output terminal of the first band-pass filter; and when the first terminal is set as an input side. a plurality of second bandpass filters whose input terminals are commonly connected to a second terminal of the nonreciprocal circuit element serving as an output side, and whose passbands are in the attenuation range; and the second terminal. includes an output terminal connected to the third terminal of the non-reciprocal circuit element which becomes the output side when the input side is set to the input side, and the second bandpass filter includes: a dielectric coaxial resonator; and the dielectric coaxial resonator. an active circuit coupled to the filter and having a negative resistance in the operating range of the second bandpass filter;
Multiband filter.