JPS6225283B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high frequency bandpass waver. Conventionally, bandpass filters used in microwave integrated circuits (MICs) have two open-ended λg/2 resonators coupled in parallel with an electrical length of 90° (π/2) at the center frequency of the passband, as shown in Figure 1. It consists of Figure 1 shows an example of a two-stage bandpass filter (hereinafter referred to as BPF), where 11 and 12 are input and output lines, and 13 and 14 are TEM
The line resonator is shown, θ ₀₁ and θ ₂₃ are input and output coupling electrical lengths, and θ ₁₂ is the coupling length between the resonators. As mentioned above, this coupling length is, at the passband center frequency,
Select θ ₀₁ = θ ₁₂ = θ ₂₃ = 90°.

Now, let the frequency be the propagation velocity of the electromagnetic wave, Vg be the characteristic admittance of the resonator, Yo be the actual _length of the resonator, and let Yi be the admittance seen from the open end of the resonator, then Yi=jYoton(2πl /Vg). Since the resonance condition is given by Yi=O,
The resonance frequency is 2πl/Vg=nπ (n=1, 2, 3,...). If the lowest resonant frequency is ₀ , this corresponds to n=1, so 2πl/Vg ₀ =π, and if we rewrite the resonance condition using ₀ , we get =n ₀ (n=1, 2, 3,... ), and
Resonance will also occur at integral multiples of ₀ . If we assume that the degree of coupling has no frequency characteristic, the characteristics of the filter shown in FIG. 1 will have spurious responses at 2 ₀ , 3 ₀ , and 4 ₀ as shown in FIG. 2 . In reality, the degree of coupling has frequency characteristics, so FIG. 2 shows the response when the coupling circuit is ideal. FIG. 3 shows an extracted portion of the parallel coupling circuit. If the electrical bond length is θ _c , the characteristics of the degree of coupling K are as shown in Figure 4, and the maximum value is θ _c = π/2 (2m + 1) (m = 0, 1, 2, 3, ...). When θ _c = kπ (1, 2, 3, ...),
It becomes zero.

By the way, the bond electrical length increases in proportion to the frequency, so if you choose the bond electrical length to be 90 degrees at the center frequency of ₀ , the electrical length at ₂₀ , ₃₀ , and ₄₀ will be 180 degrees.
゜, 270゜, 360゜. Therefore, the frequency characteristic of the degree of coupling K in this case is as shown in Fig. 5,
It has a characteristic that the bond disappears at 2 ₀ , 4 ₀ , and 6 ₀ .

As a result of the above, the frequency response of a 90° parallel coupling filter (example shown in FIG. 1) using a normal λg/2 resonator with both ends open is as shown in FIG. 6. That is, 2
₀ , 4 ₀ , 6 ₀ have zero connectivity, so
Even if spurious resonance occurs, the response is small,
This results in large spurious responses centered around ₃₀ and ₅₀ .

Now, one of the reasons why the bond length was conventionally chosen to be 90°
The main reason is that the joint design is easy, and
The main reason is that the change in the degree of bonding is the smallest around ₀ , and the change exhibits symmetrical characteristics around ₀ . By the way, the characteristics of the conventional filter shown in Figure 6 exist as an output component when used as an output filter for an oscillator or amplifier.
It has no effect on the suppression of the next high frequency component.

SUMMARY OF THE INVENTION The present invention aims to provide a high-frequency bandpass filter with a wide _stopband and which reduces the spurious response of conventional filters.

The present invention provides a high-frequency bandpass waver as a TEM line resonator in which a parallel coupling portion is formed by coupling λg/2 resonators with both ends open in parallel, and a coupling electrical length of the parallel coupling portion is 90 degrees. The above object is achieved by providing at least one angle angle of 60 degrees and one angle of 60 degrees.

Another invention is a high-frequency bandpass waver in which a λg/4 resonator with one end open and the other end short-circuited is coupled in parallel to form a parallel coupling part as a TEM line resonator. The above object is achieved by providing at least one bond having an electrical length of 60 degrees.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 8 shows an embodiment of the present invention.
81 and 82 are input/output lines, 83 to 85 are λ ₀ /2 resonators, and θ ₀₁ to _{θ 34} are electrical lengths of the coupling portions. Now, at the electrical length and center frequency, θ ₀₁ = θ ₃₄ = 90°, θ
Consider the case where ₁₂ = θ ₂₃ = 60°. Resonator 8
Since 3 to 85 are of the λg/2 type, spurious resonance occurs at n ₀ (n = 1, 2, 3), but the coupling length θ
₀₁ , θ ₃₄ part has a bond electrical length of 90°, so 2
No bond occurs at ₀ , 4 ₀ , 6 ₀ , θ ₁₂ , θ ₂₃
Since the bond electrical length of the part is 60°, 3 ₀ ,
No bonding occurs at ₆₀ and ₉₀ .

FIG. 7 shows the frequency characteristics of the degree of coupling K when the electrical coupling length is selected to be 60° at the center frequency of ₀ . Since the electrical length is 60° at ₀ , it becomes 180° at 30 _° , and at this time, the degree of coupling K becomes zero as shown in Figure 4.

Therefore, as shown in FIG. 9, the response of the filter having the configuration shown in FIG. 8 can reduce the spurious responses of 2 ₀ , 3 ₀ , and 4 ₀ and achieve a wide stop band.

Note that although a three-stage filter has been described in the embodiment, the present invention is not related to the number of stages and can be applied to a filter with any number of stages. Furthermore, if at least one of the bond lengths is 90° and 60°, the spurious response can be reduced.

Next, another aspect of the present invention will be explained.

FIG. 10 shows another embodiment of the present invention. This embodiment shows a case where the present invention is applied to a four-stage interdigital type filter. 101 and 102 are input/output coupling circuit parts, 103 to 106 are λg/4 resonators with one end open and the other end short-circuited, and θ _c is the electrical length of the parallel coupling part. Conventionally, θ _c is selected to be 90° in the design, but in the present invention, it is selected to be 60° to provide a characteristic that reduces spurious response by _30° .

The admittance seen from the open end of the λg/4 resonator is Yi=jYocot(2πl/Vg). (l: resonator length, Vg: velocity of electromagnetic wave,
Yo: resonator characteristic admittance) Since Yi= _{O is the resonance condition, the spurious resonance becomes = (2n + 1) 0 (} n = 1, 2, 3, ...) with the fundamental resonance frequency as 0, and 3 ₀ , 5 ₀ ,7 ₀ . . generates spurious signals. Also, if the bond electrical length is chosen to be 90°,
As shown in Fig. 5, ₃₀ , ₅₀ , ₇₀ ...
..., the degree of coupling is maximum, so the response of the filter in this case is as shown in Figure 11, and spurious responses occur at odd multiples of ₀ .

When θ _c =60° is selected as in the present invention, the frequency characteristic of the degree of coupling becomes as shown in Fig. 7, where no coupling occurs at 30 _° , and the response of the filter also has a stopband up to _50° as shown in Fig. 12. Expanding.

In the case of interdigital type filters, magnetic field coupling is often used for input/output coupling as shown in FIG. 10, so the present invention can be applied to filters with two or more stages.

As described above, the present invention provides a high-frequency bandpass waver in which a parallel coupling portion is formed by coupling λg/2 resonators with both ends open in parallel as a TEM line resonator. The bond electrical length is
A high-frequency band formed by providing at least one 90-degree and one 60-degree resonator, or by parallel coupling λg/4 resonators with one end open and the other end short-circuited as a TEM line resonator to form a parallel coupling part. By providing at least one of the parallel coupling parts with a coupling electrical length of 60 degrees in the pass wave device, the spurious response at 30 _° C is reduced, the stopband is expanded, and the output of the oscillator and amplifier is It has extremely high utility value as a filter.

[Brief Description of the Drawings] Figure 1 is a diagram showing the configuration of a conventional filter using a λg/2 resonator, and Figure 2 is a diagram showing the frequency response of the filter in Figure 1 when the degree of coupling has no frequency. , Fig. 3 is an explanatory diagram of the parallel coupling part, Fig. 4 is a diagram showing the relationship between the degree of coupling and the electrical length of the coupling, and Fig. 5 is the degree of coupling K when the electrical coupling length is chosen to be 90° at the center frequency ₀ .
Figure 6 shows the frequency response of the filter in Figure 1 when the coupling length is 90°, and Figure 7 shows the frequency response of the filter in parallel coupling when the coupling length is 60°. Figure 8 is a diagram showing the frequency characteristics of the coupling degree, Figure 8 is a diagram showing the configuration of a high frequency bandpass waver according to an embodiment of the present invention, Figure 9 is a diagram showing the frequency response of the configuration shown in Figure 8, and Figure 10 is a diagram showing the frequency response of the configuration shown in Figure 8. A configuration diagram of another embodiment of the invention,
FIG. 11 is a diagram showing the response of a conventional interdigital filter, and FIG. 12 is a diagram showing the frequency response of the filter of the present invention. 81, 82...Input/output lines, 83-85...
λg/2 resonator, θ ₀₁ to _{θ 34} ... Electrical length of coupling section, 1 01, 102 ... Input/output coupling circuit section, 103 to 1
06...λg/4 resonator, _θc ...electrical length of parallel coupling part.

Claims (1)

[Scope of Claims] 1. In a high-frequency bandpass waver formed by coupling λg/2 resonators with both ends open in parallel to each other as a TEM line resonator to form a parallel coupling part, the coupling part of the parallel coupling part A high-frequency bandpass transducer having at least one electrical length of 90 degrees and 60 degrees. 2. In a high-frequency bandpass resonator in which λg/4 resonators with one end open and the other end short-circuited are coupled in parallel to each other to form a parallel coupling part as a TEM line resonator, the coupling electrical length of the parallel coupling part is High-frequency bandpass waver with at least one 60-degree angle.