JPH073681Y2 - Helical filter - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention is capable of adjusting the resonance frequency with a capacitive element, and the coupling coefficient between the input side and output side coupling coils and the helical coil makes it possible to adjust the resonance frequency at the high frequency side. The present invention relates to a helical filter that can set the position of an attenuation pole.

[Prior art]

The helical filter is usually constructed by electromagnetically coupling a plurality of helical coils each having one end open and the other end grounded. Specifically, each of the helical coils is wound around a bobbin in a metal case, and the side surfaces of the plurality of cases are fixed by solder or an adhesive. Also, a plurality of helical coils are provided on a common base. There is a case where it is wound around a bobbin and covered with a case having a partition wall between the helical coils.

Each helical coil constitutes one resonator, and its resonance frequency is adjusted by changing the distributed capacitance between the helical coil and the case around it. The distributed capacitance equivalently connected in parallel with the helical coil changes by moving the dielectric between the helical coil and the case, or by moving a metal screw electrically connected to the case near the helical coil.

The resonance frequencies of the respective resonators are made equal, and the filter resonates with respect to the input signal of this resonance frequency. The pass band width of the filter is set by the coupling state between the resonators. This coupling state is usually changed depending on the size of the side surface of the case between the helical coils and the opening of the partition wall.

〔Task〕

However, since the position of the attenuation pole outside the pass band cannot be set in the helical filter, when it is necessary to provide the attenuation pole in the vicinity of it, especially on the high frequency side of the resonance frequency, another filter for trapping should be used as the helical filter. You have to connect. Also, as the frequency increases, the resonant frequency changes even if the distributed capacitance changes slightly.Therefore, the method of adjusting the resonant frequency by changing the distributed capacitance by moving the dielectric or screw as described above has a high frequency. Naturally, there is a limit in accuracy.

At higher frequencies, changing the distributed capacitance also changes the bandwidth, making it difficult to independently adjust only the resonant frequency.

An object of the present invention is to provide a helical filter that can adjust the resonance frequency without using a method of moving a dielectric or the like and can set the position of the attenuation pole.

[Means for Solving the Problems]

That is, the helical filter of the present invention is characterized in that it has a variable capacitance element that is connected in parallel to a plurality of helical coils that form the helical filter through the intermediate taps thereof, or is coupled in parallel using a coupling coil. To do.

〔Example〕

An embodiment of the helical filter of the present invention will be described below with reference to FIG. 1, which is a connection diagram.

In FIG. 1, 1 is a helical coil whose one end is open and the other end is grounded, 2 is a trimmer capacitor, which is attached to the base of the bobbin of the helical coil,
One end is connected to the intermediate tap of the helical coil 1 and the other end is grounded via a terminal pin implanted in the base. Reference numeral 3 is an input-side and output-side coupling coil that is coupled to each of the two helical coils 1. Reference numeral 4 denotes a metal case that covers these coils and capacitors, and an opening 7 is provided in the partition wall of the two resonators. The case 4 and one end of the coupling coil 3 are grounded. Reference numerals 5 and 6 denote an input terminal and an output terminal, respectively, which are connected to the coupling coil 3.

A resonator is composed of the helical coil 1 and a trimmer capacitor 2 connected in parallel to the ground side portion by a tap, and the resonance frequency is adjusted by the capacitance value of this capacitor.

Further, the position of the attenuation pole on the higher frequency side than the resonance frequency can be set by the coupling coefficient between the coupling coil 3 and the helical coil 1. The coupling coefficient can be adjusted by winding a set of helical coil 1 and coupling coil 3 on the same bobbin and adjusting the spacing, or by winding the helical coil 1 and coupling coil 3 in different winding grooves of the same bobbin, respectively. It may be adjusted according to the thickness of the collar in between.

The coupling coefficient between the helical coils 1-1 is case 4
The size of the opening 7 is adjusted. FIG. 5 is a partially cutaway front view showing an embodiment of the helical filter of the present invention. The symbols in the figure are the same as those in FIG. 1 and their detailed description is omitted.

Since the resonance frequency of the helical filter configured as described above can be adjusted by the trimmer capacitor 2, the helical filter can be made finer than when the object is moved to change the distributed capacitance. Further, since there is no mechanical portion, other characteristics, such as the bandwidth, are not influenced and changed when the resonance frequency is adjusted.

The setting of the position of the attenuation pole when the coupling coefficient between the coupling coil 3 and the helical coil 1 is adjusted is shown in the characteristic diagrams of FIGS. 2 and 3.

The coupling coefficient in Fig. 2 is 0.4, the coupling coefficient in Fig. 3 is about 0.8, and the resonance frequency is 400 MHz in all cases. The attenuation pole on the higher frequency side than the resonance frequency is near 500 MHz in the case of FIG. 2, but has moved to around 650 MHz in the case of FIG. The attenuation pole on the low frequency side of the resonance frequency hardly changes.

In this way, it is possible to freely change the attenuation pole on the high frequency side.
This is convenient because it is not necessary to connect a filter for trap separately.

FIG. 4 is a connection diagram showing another embodiment of the helical filter of the present invention.

The trimmer capacitor 2 is coupled to the helical coil 1 by the coupling coil 11. Similar to the case of connecting by tap in FIG. 1, parallel connection is equivalently made. The set of helical coil 1, coupling coil 11, and trimmer capacitor 2 constitutes a resonator. The other parts have the same structure as in FIG.

Even with such a configuration, the resonance frequency can be changed independently and the position of the attenuation pole can be changed as in the case of FIG.
However, the configuration shown in FIG. 4 requires one extra coil for constructing the resonator as compared with FIG.

Although the trimmer capacitor 2 is used as the capacitance element in FIGS. 1 and 4, a variable capacitance diode may be used.

These capacitors are attached to the bobbin around which the helical coil is wound, but may be connected to a circuit board or the like outside the case.

〔effect〕

As described above, the helical filter of the present invention adjusts the resonance frequency by connecting the resonance frequency to the helical coil in parallel via the intermediate tap, or by adjusting the capacitance with the capacitive element coupled in parallel using the coupling coil. It can be set by the coupling coefficient between the input and output coupling coils and the helical coil.

Compared with the case of adjusting the resonance frequency by moving the dielectric or the like, the capacitance value connected in parallel with the helical coil can be finely changed. It can also be adjusted independently without affecting other properties.

Further, since the position of the attenuation pole can be set freely, there is an advantage that the trap filter can be saved.

In this way, the present invention can obtain a helical filter suitable for use at high frequencies.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an embodiment of the helical filter of the present invention, FIGS. 2 and 3 are characteristic diagrams of the helical filter shown in FIG. 1, and FIG. 4 is a connection diagram showing another embodiment. FIG. 5 is a partially cutaway front view of an embodiment of the helical filter of the present invention. 1: Helical coil, 2: Trimmer capacitor 3: Coupling coil, 4: Case

Claims (1)

[Scope of utility model registration request] 1. A plurality of helical coils, one end of which is an open end and the other end of which is grounded, are coupled through an opening of a partition wall provided between the helical coils of a case accommodating the helical coil, and an input side and an output side. Of a helical filter that is coupled to the side helical coil and has one end grounded and the other end an input / output terminal and a coupling coil for input and output, and the case is grounded, between the middle tap and the ground of the helical coil. A helical filter having a variable capacitance element connected to either of the other end of a coupling coil, which is electromagnetically coupled to the helical coil and one end of which is grounded, and the ground.