JPS632403A - Filter - Google Patents

Abstract

PURPOSE:To equivalently raise the Q of a filter and, at the same time, to miniaturize the shape of the filter as a whole, by electrically coupling an active element which shows a negative resistance when a resonator is in a resonant state with the resonator. CONSTITUTION:A strip line-resonator 3 is a 1/4-wavelength resonator and one end of the resonator 3 is short-circuited and connected with a varactor diode D. The other end is opened and a positive feedback loop containing an amplifier 4 and phase regulator 5 connected with each other by means of gap capacities C1 and C2 is formed at the opened end. Since the amplifier 4 shows a negative resistance when the resonator 3 is set to a resonant state, energy is supplied to the resonator 3 from the amplifier 4. As a result, losses at the diode D connected with the resonator 3, etc., are compensated and the Q of this filter is equivalently raised. Moreover, it becomes unnecessary to couple filters in multiple stages in order to obtain a steep damping characteristic and the shape of this filter can be miniaturized as a whole.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a filter in which a variable capacitance diode is connected to a resonator so that the center frequency can be shifted.

<Prior Art> A circuit diagram of this type of filter realized by a stripline resonator is shown in FIG. 4, and its equivalent circuit is shown in FIG. 5. In the same figure, l is an input circuit, 2 is an output circuit, and 3 is a stripline B device. This stripline resonator 3
is grounded via a variable capacitance diode D. Note that the voltage control circuit for the variable capacitance diode D is omitted in the figure.

Then, by controlling the terminal voltage of the variable capacitance diode D and changing its capacitance VC, for example, as shown in FIG. 6, the center frequency f of the stripline filter is
0 can be shifted to '.'.

<Problems to be Solved by the Invention> However, the conventional stripline filter described above has a problem in that the filter sharpness Q is small in the high frequency range because the variable capacitance diode has a large loss in the high frequency range. Similar problems are also pointed out with respect to filters using other resonators.

The present invention has been made in view of the above circumstances, and an object of the present invention is to improve the Q of a filter in which a variable capacitance diode is connected to a resonator so that the center frequency can be shifted.

<Means for Solving the Problems> In order to achieve the above object, the present invention has the following features.

That is, the present invention provides a filter in which a variable capacitance diode is connected to a resonator so that the center frequency can be shifted, and an active element that exhibits negative resistance when the resonator is in a resonant state.
It is characterized in that it is electrically coupled to the resonator.

<Effect> Since energy is supplied from the active element to the resonator when the resonator is in a resonant state, the loss of the variable capacitance diode, etc. is compensated for, and the Q of the filter can be increased isometrically. can.

<Embodiment> FIG. 1 is a circuit diagram of a stripline filter according to an embodiment of the present invention. In FIG. 0, the same parts as in FIG. 4 are indicated by the same symbols. The strip line resonator 3 is
It is a λ/4 resonator whose - end is short-circuited and the other end is open, and a variable capacitance diode D is connected to the short-circuited end.

On the other hand, at the open end of the stripline resonator 3, a positive feedback loop including an amplifier 4 and a phase adjuster 5 is formed, which are coupled by gap capacitances C, , C,.

In the stripline filter as described above, when the stripline resonator 3 enters a resonant state, the amplifier 4 exhibits negative resistance, so that energy is supplied from the amplifier 4 to the stripline resonator 3.

As a result, the loss in the variable capacitance diode D etc. connected to the stripline resonator 3 is compensated, and the Q of the filter is isometrically increased. Note that even if Q is increased isometrically in this way, the amount of frequency shift that can be controlled by the variable capacitance diode D does not change.

In the embodiment shown in FIG. 1, the positive feedback loop is capacitively coupled to the open end of the stripline resonator 3, but this is inductively coupled between the stripline resonator 3 and the variable capacitance diode D. You can also get the same effect.

Further, in the above embodiment, the stripline resonator 3 is λ/
Although the explanation has been made assuming that there are 4 resonators, this may also be a λ/2 resonator. Fig. 2 shows an example using a λ/2 resonator, that is, a strip line resonance according to this example. The device 6 has a variable capacitance diode D interposed between two electrode blocks 6a and 6b to form one λ/2 resonator.

A positive feedback loop including an amplifier 4 and a phase adjuster 5 is capacitively coupled to the open end side of the resonator 6. In the embodiment shown in FIG. 2, the positive feedback loop can also be coupled between the pole block and the variable capacitance diode D.

Furthermore, although the above embodiments have been explained using a bandpass filter as an example, the present invention can also be applied to a bandstop filter. FIG. 3 shows an example of application to a band rejection filter. In the figure, a stripline resonator 7
One end is connected to the main strip line 8 via the gab capacity 1tC3.
The other end of the resonator 7 is grounded via a variable capacitance diode D. A positive feedback loop including an amplifier 4 and a phase adjuster 5 is connected between the variable capacitance diode D and the stripline resonator 7.

In the above embodiments, a filter using one resonator has been described, but it goes without saying that the present invention can also be applied to a multi-stage filter.

<Effects of the Invention> As is clear from the above description, the filter according to the present invention electrically couples to the resonator an active element that exhibits negative resistance when the resonator is in a resonant state. Losses in capacitive diodes and the like are compensated for by the energy supplied by the active element, thereby making it possible to increase the Q of the filter isometrically. As a result, if the filter according to the present invention is used, there is no need to combine filters in multiple stages in order to obtain steep attenuation characteristics, so the filter as a whole can be made smaller in size, which is a different effect.

[Brief explanation of drawings]

Figure 1 shows a first example using a λ/4 stripline resonator.
A circuit diagram of the embodiment, FIG. 2 is a circuit diagram of a second embodiment using a λ/2 strip line resonator, and FIG. 3 is a circuit diagram of a third embodiment showing an example of application to a band rejection filter. FIG. 4 is a circuit diagram of a conventional stripline filter, FIG. 5 is an equivalent circuit diagram thereof, and FIG. 6 is an explanatory diagram of the operation of the conventional stripline filter. 1... Input circuit, 2... Output circuit, 3, 6.7...
・Strip line resonator, 4... amplifier circuit, 5...
・Phase adjustment circuit, C,,C! ...gap capacity, D.
...Variable capacitance diode.

Claims (1)

[Claims] In a filter in which a variable capacitance diode is connected to a resonator so that the center frequency can be shifted, an active element exhibiting negative resistance when the resonator is in a resonant state is electrically coupled to the resonator. Featured filters.