JPS62140501A - Mic filter - Google Patents

Abstract

PURPOSE:To obtain a filter having an attenuation characteristic extending over a wide band by adding a capacity of a lumped constant to an opening end of at least one or more resonant lines, and also making the length of two or more resonant lines different from each other. CONSTITUTION:When a characteristics impedance of a resonant line, length of the resonant line, length of a coupling point and a short circuit end of a resonator, a capacity of a chip capacitor, and an angular frequency are denoted as Zi, Li, Ii, Ci, and omega, respectively, a resonance condition is expressed by an expression cot betaLi-omegaCiZi=0. Also, when the center frequency, lengths of resonant lines 2a, 2b, and capacities of chip capacitors 6a, 6b are denoted as omega1, L1 and L2, and C1, C2 (C1<C2), respectively, since the resonance is executed by the center frequency omega1, the lengths of the resonant lines become L1>L2, and resonance frequencies of higher order of the resonator to the resonant lines 2a, 2b become omega'2, omega'3... and omega''2, omega''3.... Accordingly, the resonance frequency of the resonator corresponding to the resonant lines 2a, 2b coincides in only the center frequency omega1, and a filter generates no passing band except the frequency omega1. In this way, an attenuation characteristic extending over a wide band can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a MIC filter formed on a dielectric substrate, and particularly to a MIC filter with a wide band of attenuation characteristics.

[Conventional technology]

Conventionally, in a multi-stage MIG filter in which resonators having resonant lines with one end short-circuited and the other end open are coupled by a 174-wavelength line, the length of each resonant line is uniformly 1/4 wavelength.

For example, FIG. 6 shows an example of a conventional MIG filter of this type configured in three stages, where 11 is a dielectric substrate, 12a, 12
b, 12c are co-fivA tracts formed with uniform length, respectively;
13 is a coupling line that couples these resonant lines, 14 is an input/output end, and 15 is a ground conductor. That is, this MIC filter has B, , B2 . . . as shown in FIG. B Yu's resonator 1 no 4
The configuration is such that they are connected by a wavelength line. FIG. 8 shows an equivalent circuit of the resonator of the MIC filter, and the resonance condition is given by the following equation.

tan β(Li-1i) -cot β1i=o
...(1) Here, β is the wave number, Li is the resonant line length, and l
i is the length between the coupling point and the shorted end of the resonator.

From equation (1), βL4=2π/λg XLi=(2n-1)/4 x
π...(2) Here, n is an integer and λg is the wavelength.

Then, with n = 0, L'i is selected to be the minimum, and Li =
Obtain 1/4λg0 (3). λg0 is the center frequency ω of the filter. This is the wavelength corresponding to

[Problem that the invention seeks to solve]

In the above-mentioned conventional MIC filter, as explained above, the length of the resonant line is uniformly 1/4λg0 regardless of its characteristic impedance Zi.

However, from equation (2) above, this resonator satisfies the resonance condition at the wavelength λg7 corresponding to the integer value n, so the filter exhibits spurious responses at frequencies that are odd multiples of the center frequency, resulting in a wide band There is a problem in that effective damping characteristics cannot be obtained over a period of time.

[Means for solving problems]

The MIC filter of the present invention provides a filter having broadband attenuation characteristics.

The MIC filter of the present invention has a configuration in which a lumped constant capacitor is added to the open end of at least one resonant line, and the lengths of the two or more resonant lines are made different.

〔Example〕

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

FIG. 1 shows an embodiment of the present invention, and here an example in which the present invention is applied to a MIC filter composed of three stages of resonators is shown. In the figure, 1 is a dielectric substrate and 2a.

2b and 2a are resonant lines formed on this dielectric substrate 1, and here, the central resonant line 2b is formed to be slightly shorter than the other lines 2a, 2a on both sides thereof. 3 is a 174-wavelength coupling line connecting these resonant lines 2a, 2b, 2a, 4 is an input/output terminal, 5a, 5b is the resonant line 2a,
2b, ground conductor arranged to sandwich 2a, 6a, 6b
, 6a is the ground conductor 5b and each resonant line 2a, 2b, 2
These are chip capacitors inserted between the two terminals a.

Figure 2 shows the equivalent circuit of the resonator of the MIC filter, where Zi is the characteristic impedance of the resonant line, Li is the length of the resonant line, li is the length of the connecting point and shorted end of the resonator, and Ci is the capacitance of the chip capacitor. , ω is the angular frequency.

The resonance condition of this resonator is expressed by the following equation.

cotβLi-ωC1zi-0...(4) Also, the first
In the figure, the center frequency is C1, and the characteristic impedance of the resonant lines 2a and 2b is Z.

Z! , the lengths of the resonant lines 'la and 2b are L1°LZs, respectively.
The capacitances of the chip capacitors 6a and 6b are respectively C, , Ct(
However, if cl<cl), then cotβL,,
cotβLz+ω(1z1.0JC1Zt The frequency changes are as shown in Fig. 3, and from the above formula (4), the resonators corresponding to the resonant lines 2a and 2b are cotβL1 and ωC
, Z, and the frequency of the intersection of cotβL2 and ωCtZz, respectively.

Now, since C1<C1, in order to resonate at the center frequency ω1, the resonant line length becomes LI > Lt, and the resonant line 2a
, 2b, the higher-order resonant frequencies of the resonator are ωt,
ω′1. ω′4. ...and ω''2.ω゛'3...

Therefore, as can be seen from FIG. 3, the resonant lines 2a, 2b
The resonant frequencies of the resonators corresponding to C1 and C1 match only at the center frequency ω1, and the filter does not generate a passband other than the frequency C1, and can obtain a wideband attenuation characteristic.

Here, in the present invention, instead of the chip capacitor, the capacitor may be constructed of single plate capacitors 7a, 7b, 7a and bonding wires 8 as shown in FIG. In addition, there is no need to add lumped constant capacitance to all three stages of resonators;
As shown in the figure, the resonant line 2b to which the lumped constant capacitor 7 is added and the resonant lines 2a, 2a to which the lumped constant capacitor 7 is not added may be mixed, and in this configuration as well, broadband attenuation characteristics can be obtained as in the previous embodiment.

Furthermore, in general, for N-stage (N≧2; integer) filters, broadband attenuation characteristics can be achieved by adding a lumped constant capacitor to at least one resonator and by making at least two or more resonant line lengths different. Obtainable.

〔Effect of the invention〕

As explained above, the present invention adds a lumped constant capacitor to the open end of at least one resonant line, and makes the lengths of the two or more resonant lines different, so that the MIC has broadband attenuation characteristics. You can get filters.

[Brief explanation of drawings]

Fig. 1 is a plan configuration diagram of an embodiment of the present invention, Fig. 2 is an equivalent circuit diagram, Fig. 3 is a graph showing resonance frequency characteristics, Fig. 4 is a plan configuration diagram of a modified example, and Fig. 5 is a further FIG. 6 is a plan view of another modified example, FIG. 6 is a plan view of the conventional configuration, FIG. 7 is a schematic view of the configuration, and FIG. 8 is an equivalent circuit diagram thereof. 1... Dielectric substrate, 2a, 'lb... Resonant line, 3
...Coupling line, 4...Input/output terminal, 5a, 5b...
- Ground conductor, 5a, 5b... Chip capacitor (lumped constant capacitor), 7... Single plate capacitor, 8... Bonding wire, 11-... Dielectric substrate, 12a, 12b
, 12cm resonant line, 13...coupled line, 14...
Input/output terminal, 15...ground conductor.

Claims (1)

[Claims] 1. In a MIC filter having a multi-stage configuration in which resonators each having a resonant line with one end short-circuited and the other end open-circuited are coupled by a 1/4 wavelength line, at least one open end of the resonant line is A MIC filter characterized in that a lumped constant capacitor is added and two or more of the resonant lines have different lengths. 2. The MIC filter according to claim 1, wherein a lumped constant capacitor is connected to the open ends of all the resonant lines.