JP2531011B2 - Active filter - Google Patents

Description

TECHNICAL FIELD The present invention relates to an active filter, and more particularly to an active filter used as, for example, a band stop filter (BEF) or a band pass filter (BPF) in the microwave band.

[Prior art]

Referring to FIG. 6, in the conventional BEF type active filter 1, an input signal is given from the input end 2a and transmitted to the output end 2b through the strip lines 3a and 3b. At the connection point 4 between the strip line 3a and the strip line 3b, a λ / 2 strip line resonator 5 whose one end is grounded is electric field coupled by a coupling capacitor Ca. And, between the coupling capacitor Ca and the strip line resonator 5,
The feedback active element loop 6 is field-coupled by the two coupling capacitors Cb and Cc. The feedback active element loop 6 includes a series connection of the phase adjusting strip lines 7 a and 7 b and the amplifier 8.

Further, in the BEF type active filter 1'shown in FIG. 7, one end of the feedback active element loop 6 has a coupling capacitor Cb.
The electric field is coupled to the strip line resonator 5 by the phase adjusting strip line 7b.

6 and 7, the frequency signal in the band corresponding to the resonance frequency of the stripline resonator 5 is greatly attenuated and obtained at the output end 2b.

[Problems to be Solved by the Invention]

In the prior art shown in FIG. 6, the feedback active element loop 6 is used.
The phase of 2 is required to be about 2π, and there is a limit to miniaturization.

Further, in the conventional technique shown in FIG. 7, the phase of the feedback active element loop 6 may be about π, which is advantageous for downsizing, but the stripline resonator 5 and the feedback active element loop 6 are Are arranged close to each other, so that the stripline resonator 5 and the amplifier 8 are undesirably electromagnetically coupled. Therefore, there is a problem in that the electrical characteristics deviate from the design characteristics, resulting in lack of designability.

Therefore, a main object of the present invention is to provide an active filter which can be downsized and has a good design.

[Means for solving the problem]

The present invention relates to an active filter having a substantially U-shaped stripline resonator, a feedback active element loop electrically coupled to both open ends of the stripline resonator, and an input / output terminal coupled to the stripline resonator. Is.

[Action]

The frequency component resonated in the stripline resonator is input to the feedback active element loop by electric field coupling, amplified, and fed back to the input of the stripline resonator by electric field coupling. Therefore, if the input and output ends are connected so as to pass through the stripline resonator, it is configured as BPF, and if the input and output ends are connected to the short-circuit side of the stripline resonator.
Can be configured as BEF.

〔The invention's effect〕

According to the present invention, since the stripline resonator is formed in a substantially U shape, and the feedback active element loop is electric-field-coupled between both open ends of the stripline resonator, the phase in the feedback active element loop is Therefore, the size can be reduced. In addition, since the feedback active element loop is provided at a position on the open end side of the stripline resonator, that is, at a position where it is not electromagnetically coupled to the stripline resonator, the electrical characteristics of the active filter almost always deviate from the design characteristics. It is eliminated and designability is improved.

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

〔Example〕

Referring to FIG. 1, the active filter of this embodiment
10 is used as a BPF in the microwave band, for example, and includes a U-shaped stripline resonator 12. Both open ends 14a and 14b of the stripline resonator 12
A feedback active element loop 16 is electrically coupled between the two. That is, the feedback active element loop 16 is formed by the series connection of the strip line 18 for phase adjustment, the amplifier 20, and the strip line 22 for phase adjustment, and the strip line 18 is field-coupled to the open end 14a by the coupling capacitor C1.
The strip line 22 is field-coupled to the other open end 14b by the coupling capacitor C2.

Note that the coupling capacitors C1 and C2 may be discrete ones, or may utilize the interelectrode distributed capacitance.

An input line 24 and an output line 26 are formed on the opposing straight line portions of the stripline resonator 12 in the outward and orthogonal directions, respectively. The ends of the input line 24 and the output line 26 become the input end 28 and the output end 30, respectively.

When a signal is input to the input terminal 28 of the active filter 10, the stripline resonator 12 passes through the input line 24.
Is input to Then, the frequency component resonated in the stripline resonator 12 is fed back to the stripline resonator 12 through the feedback active element loop 16 by electric field coupling. That is, the resonance frequency component passes through the strip line 18 from the open end 14a through the coupling capacitor C1 and the amplifier
Entered in 20. Then, the frequency component amplified by the amplifier 20 passes through the strip line 22 and is coupled to the coupling capacitor.
It is fed back to the stripline resonator 12 from the open end 14b via C2, passes through the output line 26, and is output to the output end 30.

The feedback active element loop 16 of this embodiment is connected to the stripline resonator 12, that is, both open ends 14a and 1a.
Since the phase is opposite in 4b, the phase of the feedback active element loop 16 may be about π. Further, the stripline resonator 12 and the feedback active element loop 16 need only be brought close to each other at their coupling parts, and the amplifier 20 and the like can be arranged at positions apart from the stripline resonator 12, so that between them. There is no unnecessary electromagnetic coupling as in the prior art.

Further, in the manufacturing process, the feedback active element loop 16 and the stripline resonator 12 are separately processed and then appropriately combined to form a filter, which improves the mass productivity.

The positions of the input line 24 and the output line 26, which are coupled to the stripline resonator 12, differ depending on the bandwidth of the frequency signal to be passed, and when the bandwidth is widened, it is close to the open ends 14a and 14b, and the bandwidth On the contrary, when narrowing the distance, the distance should be increased.

Another embodiment of active filter 10 'shown in FIG.
Is configured as a BEF and the input / output line 32 is magnetically coupled to the short-circuit side of the stripline resonator 12. This embodiment is basically the same as the embodiment shown in FIG.
When the signal is transmitted from the output terminal 30 to the output terminal 30 through the input / output line 32, the signal in the resonance frequency band of the stripline resonator 12 is significantly attenuated. When the attenuation band width is widened, the space between the input / output line 32 and the strip resonator 12 is widened, and when the band width is narrowed, the space between them may be narrowed.

Although the stripline resonator 12 is U-shaped in each of the above-described embodiments, it may be U-shaped as shown in FIG. 3A. In addition, as a U-shaped modification, as shown in FIG. 3B, the outer peripheral corner is chamfered, and as shown in FIG. 3C, the inner peripheral corner and the outer peripheral corner are both chamfered. May be. Furthermore, as shown in FIG. 3D, a physical length of the stripline resonator may be shortened by inserting a capacitor between both open ends of the stripline resonator.

The active filter 10 'shown in FIG. 2 is, for example, a BEF34 of a receiver of a mobile communication base station as shown in FIG.
Can be effectively used as.

Generally, in a receiving device of a mobile communication base station, unnecessary signals other than the used band are removed by inserting a BPF between the antenna and the receiver, but this used band becomes complicated and unnecessary signals are generated. When mixed in the used band, it cannot be removed only by BPF. Therefore, as shown in FIG. 4, between the antenna 36 and the receiver 38, a BPF 4 including a passive filter such as a dielectric filter is used.
By inserting a composite filter in which 0 and a narrow band and large attenuation amount according to the embodiment of FIG. 2 are combined, unnecessary signals other than the used band are removed and only complicated used frequencies are passed. Can be made.

A passive filter such as a dielectric filter may be used as the BEF 34, but if the active filter 10 ′ is used as the BEF 34, the size can be reduced as compared with the case of using other filters.

By the way, the function of BEF34 and BPF40 will be explained with reference to FIG. 5. When it is desired to extract two bands W1 and W2 as used frequencies, first, the frequency of band W is extracted by BPF40 and then the band W3 is extracted by BEF40. Remove the frequency. As a result, only frequencies in the bands W1 and W2 are input to the receiver 38.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. FIG. 2 is a circuit diagram showing another embodiment of the present invention. FIG. 3A to FIG. 3D are schematic views showing modifications of the stripline resonator. FIG. 4 is a block diagram showing a front end in a receiver of a mobile communication base station in which the present invention can be used. FIG. 5 is a waveform diagram showing an example of the used band in FIG. FIG. 6 and FIG. 7 are circuit diagrams showing different conventional techniques. In the figure, 10 and 10 'are active filters, 12 is a stripline resonator, 14a and 14b are open ends, 16 is an active element loop for feedback, 24 is an input line, 26 is an output line, 28 is an input end, and 30 is An output terminal, 32 is an input / output line, and C1 and C2 are coupling capacitors.

Claims (1)

(57) [Claims] 1. A substantially U-shaped stripline resonator, a feedback active element loop electrically coupled to both open ends of the stripline resonator, and an input / output terminal coupled to the stripline resonator. , Active filter.