JPS62292002A - Filter circuit - Google Patents

Abstract

PURPOSE:To obtain a stable HPF having a few amount of dispersion, by connecting a stripline type inductor having a length of <=lambdag/4, whose stripline length can be adjusted by a movable metal, between two chip type capacitors. CONSTITUTION:Chip type capacitors 4a and 4b are arranged on striplines SL2a-2c provided on a dielectric substrate 1. An Sh type inductor 5 having the length of <=lambdag/4 is connected between the SL2, and an earth electrode 6 connecting to the earth 3 passing through a through hole 7. A part between the appropriate intermediate point 5c of the SL of the inductor 5, and the electrode 6, is soldered with a movable metallic piece 8. Therefore, since the inductance value of the inductor 5 is decided by a length between 5a and 5c, the shape of the inductor 5 is formed in a zigzag pattern, and it is possible to change the inductance value, and to adjust the cut off frequency of the HPF by moving the metallic piece 8, and changing the position of the intermediate point 5c. In this way, unrequired radiation is reduced, and an enough attenuating quantity can be obtained, and the HPF easy to be adjusted and with high reliability, can be obtained.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention Industrial Application Field The present invention relates to a T-type no-pass filter for high frequencies, particularly a bypass filter for the UHF band or the frequency band of 1 GHz or higher. It is useful as

BACKGROUND OF THE INVENTION FIG. 2 shows an example of a conventional T-type bypass filter. Figure a shows a plan view, and figure b shows a front view.

In the figure, 1 is a dielectric substrate such as Teflon or Gala Evo, 3 is a back ground electrode, 2a to 2C are SOΩ strip lines, and 6 is a ground electrode having a through hole 7.

Two chip capacitors 4a and 4b are arranged on the strip lines 2a to 2C, and a coil type inductor 9 is arranged between the strip line 2b and the ground electrode 6, thereby forming a T-shaped bypass filter. Capacitors 42L, 4b and inductor 9 are soldered. 10.11 is an input/output terminal.

FIG. 3 shows an isochoric circuit of a bypass filter.

Bypass filter cutoff frequency f0, f o
From the relational expression c 1 / n, adjustment of L, that is, adjustment of opening and closing of the air-core coil 9 in FIG. 2, is performed while absorbing variations in the chip capacitors 4a and 4b.

Problems to be Solved by the Invention A bypass filter having such a structure causes the following problems. First, radio waves transmitted on strips and plines are likely to be radiated from the coil-type inductor 9 and may not be sufficiently attenuated. Second, after a long period of time after delicate adjustments are made by opening and closing the coil-type inductor 9, the cutoff frequency may shift slightly, resulting in a lack of reliability. Thirdly, the coil type inductor 9 is susceptible to vibration. These problems become more serious as the number of stages of the T-type bypass filter increases or as the frequency becomes higher.

Means for Solving the Problems In order to solve the above problems, the present invention connects one end of a strip line inductor with a length of 4 or less between two chip capacitors, and The IJ tube line length can be adjusted using a movable metal piece.

Function The present invention uses a variable stripline type inductor made of movable metal pieces as described above, thereby providing a filter that is stable in terms of radiation, reliability, vibration, variation, etc.

Embodiment FIG. 1 shows an example of the bypass filter of the present invention,
4 shows a plan view, and b shows a front view.

In this figure, parts having the same functions as those in FIG. 2 are denoted by the same reference numerals.

The difference in FIG. 1 from the conventional example shown in FIG. 1 is that the air-core coil for adjustment is a variable strif brine type inductor. As shown in FIG. 1, the strip line inductor 6 has a length of λi74 or less, and one end 6b thereof is grounded to the ground electrode 6 with a through pole 7.
The other end 5a is connected to a 50Ω stripline 2b, and a movable metal piece 8 is soldered between a ground electrode 6 and a suitable midpoint 5c of the high impedance stripline forming the inductor.

Therefore, the inductance value of the strip line inductor 6 is determined by the length between 5 & -50. Here, by making the shape of the strip line type inductor 6 into a zigzag pattern as shown in FIG. 1, for example, and moving the movable metal piece 8 to change the position of the intermediate point 5C, the inductance value also changes, and the bypass filter is cut. Off frequency etc. can be adjusted.

For example, when designing a bypass filter for a high frequency band around 1 GHz band, the capacitor is several PF, the inductor is several nH, and in the case of the coil type inductor 9, the wire diameter is Q.
, 5M, coil diameter of 2.0mm, and 1 to 2 turns, which are very small values.If you replace this with a stripline type inductor 5 and configure it with a movable metal piece 8 for adjustment, the variation will be reduced. This makes it a stable filter in various aspects such as reliability.

Effects of the Invention As is clear from the above examples, according to the present invention,
It is possible to realize a bypass filter that reduces unnecessary radiation, provides sufficient attenuation, is easy to adjust, has improved reliability, is resistant to vibration, has little variation, and is extremely stable. Further, the present invention is particularly effective when used in a high frequency band.

[Brief explanation of drawings]

Figures 1a and b are a plan view and a front view of an embodiment of the filter circuit of the present invention, Figures 2a and b are a plan view and a front view of a conventional filter circuit, and Figure 3 is a new bus filter. This is the equivalent circuit of 1...Dielectric substrate, 2a-2c...6o
Ω strip line, 3... Back ground electrode, aa
, 4b... Chi knob type capacitor, 5...
・・Stripline type inductor, 6・・・・・・
Ground electrode, 7...Through hole, 8...
Movable metal piece. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure (α) (b) Figure 2 (ωu)

Claims (1)

[Claims] A filter circuit in which one end of a stripline inductor having a length of λg/4 or less is connected between two chip capacitors, and the stripline length of the inductor can be adjusted by a movable metal piece.