JPH01143402A - Mic filter - Google Patents

Abstract

PURPOSE:To obtain a broad band attenuation characteristic by varying the length of at least >=two resonance lines and adding a capacitor to an open end of at least >=one resonance line. CONSTITUTION:The filter consists of a dielectric board 1, resonance lines 2a, 2b whose line length differs from each other, a coupling line 3 of a 1/4 wavelength, chip capacitors 5a, 5b connected to the open end of the resonance lines 2a, 2b respectively and a ground conductor 6. Since the resonance frequency of the resonator corresponding to the resonance lines 2a, 2b is coincident with the center frequency omega0 only and the filter has no pass band caused except the frequency omega0, the broad band attenuation characteristic is obtained.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides an MIC (microwave t
C) Regarding filters.

[Conventional technology]

Conventionally, in MIC filters constructed using MICs on dielectric substrates, especially multi-stage MIC filters in which resonators with both ends open are coupled via a 1/4 wavelength line, the length of the resonant line is uniformly 1/2 wavelength. It became.

FIG. 8 shows a conventional three-stage MTC filter, where ▪ is a dielectric plate, 2 is a resonant line, 3 is a coupling line, and 4 is an input/output terminal. The equivalent circuit of such a filter can be expressed as shown in FIG. 9, and has a circuit configuration in which a resonator formed by a resonant line is coupled by a quarter wavelength line.

[Problem that the invention seeks to solve]

In the above-mentioned MIC filter, considering each resonator, the equivalent circuit of each resonator is as shown in FIG. 10, and the resonance condition is given by the following equation.

tanβL,, = O-(+) β is the wave number, and Lo is the resonant line length.

From equation (1), βLot=2'yr/λ9 ・Lo, -(n+1)π・
...(2) n: integer, λ9: wavelength.

Here, with n=o, select Lot to be the minimum and Lo==
t/2·λ9° (3) λ9°: Center frequency ω of the filter. Obtain the wavelength corresponding to .

This resonant line having a length of 1/2·λ9° satisfies the resonance condition even at a wavelength λ9n corresponding to the integer value of equation (2). For this reason, conventional filters of this type exhibit spurious responses at frequencies that are integral multiples of the center frequency, making it difficult to obtain wideband attenuation.

The present invention is an MIS that can obtain broadband attenuation characteristics.
The purpose is to provide filters.

[Means for solving problems]

The MIC filter of the present invention uses one resonant line with both ends open.
/4 The lengths of at least two or more resonant lines of a multistage MIC filter coupled by a wavelength line are changed, and at least one
The configuration is such that a capacitance is added to the open end of the above resonant line.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which a three-stage MIC filter is shown. In the figure, 1 is a dielectric substrate, 2a and 2b are resonant lines with different line lengths,
3 is a 1/4 wavelength coupling line, 4 is an input/output end, 5a, 5b
are resonant lines 2a, respectively.

A chip capacitor is connected to the open end of 2b, and 6 is a ground conductor.

The equivalent circuit of a resonator with capacitance added to the open end is shown in Figure 2, and the resonance condition is expressed by the following formula: %Zo: Characteristic impedance of the resonant line.

C8: Capacitance of chip capacitor Here, the center frequency of the MIC filter in Fig. 1 is ω. ,
Z is the characteristic impedance of the resonant lines 2a and 2b. l+Z
O2, the respective line lengths as LOI+Log, and the capacitances of the chip capacitors 5a and 5b as CI and Cz (CI<Cm), tan βL0. ．． tan βL OZ +
The frequency change of ωCIZ(11, ωC2zoz is as shown in FIG. 3, and based on the resonance condition of equation (4), the resonance line 2a.

The resonators corresponding to 2b resonate at frequencies where tanβLOI=−ωC+ZoI tanβLOZ=(L′C2zoz).

Here, since CI>Cz, the center frequency ω.

In order to resonate at , the resonant line length is L o+ > L oz
Therefore, the higher-order resonant frequencies of the resonators corresponding to the resonant lines 2a and 2b are CI Z '+ ω3'...
・And ω2 and ω,′, ω2′, ω,′, and so on.

Therefore, as can be seen from FIG. 3, the resonant lines 2a, 2
The resonant frequency of the resonator corresponding to b coincides with the center frequency ω. and the filter has a frequency ω. Since no other passband is generated, wideband attenuation characteristics can be obtained.

In this example, capacitance was added to all three stages of resonators, but
As shown in FIG. 4, even when a resonant line 2b to which a capacitance consisting of a chip capacitor 5b is added and a resonant line 2a to which no capacitance is added are mixed, a broadband attenuation characteristic can be similarly obtained.

Also, for a filter with N stages (N≧2.integer) in -S, wideband attenuation characteristics can be obtained by changing the lengths of at least two or more resonant lines and adding capacitance to at least one resonator. It will be done.

In the above embodiment, the additional capacitance was realized by a chip capacitor for the sake of explanation, but as shown in FIG.
, 2b, 2c are connected by bonding wires 8 to single-plate capacitors 7a, 7b.

The capacity may be realized with 7c.

In addition, as shown in FIG.
The lengths of b, 2c, 2d, and 2e are made different, and single-plate capacitors 7a, 7b, and 7c are connected to these resonant lines.
, 7d, and 7e may be added.

Furthermore, as shown in FIG. 7, even if capacitors consisting of chip capacitors 5b+ and 5bz are added to both open ends of the resonant line 2b, a broadband attenuation characteristic can be obtained in the same way as described above.

〔Effect of the invention〕

As explained above, the present invention changes the length of at least two or more resonant lines of a multi-stage MIC filter,
Since a capacitor is added to the open end of at least one resonant line, it is possible to eliminate spurious responses and obtain a filter having broadband attenuation characteristics.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an embodiment of the MIC filter of the present invention;
Figure 2 is an equivalent circuit diagram of a resonator with a capacitance added to the open end.
FIG. 3 is a diagram explaining the resonant frequency of the resonator of the filter in FIG. 1, FIGS. 4 to 7 are plan views of different embodiments of the present invention, and FIG. 8 is a plan view of a conventional MIC filter. , FIG. 9 is an equivalent circuit diagram thereof, and FIG. 10 is an equivalent circuit diagram of one unit of the resonator. 1... Dielectric substrate, 2.2a to 2e... Resonant line,
3...Coupling line, 4...I/O terminal, 5a to 5C...
・Chip capacitor, 6... Ground conductor, 7a to 7e・
・Single plate capacitor. Figure 1 2a, 2b Send $14 group i 5a, 5b,
-;, + Buko Tenotsu Figure 2 Figure 4 Figure 5 Figure 8 Figure 9 Figure 10

Claims (1)

[Claims] (1) In a multi-stage MIC filter in which resonant lines with both ends open are coupled by a 1/4 wavelength line, the lengths of at least two or more resonant lines are changed and a capacitance is added to the open end of at least one resonant line. A MIC filter that is characterized by: