JPH04200101A - band elimination filter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a band elimination filter used in microwave band communication equipment.

(Conventional technology) In the conventional band elimination filter, the 10.1
A coaxial resonator with the structure shown in Figure 1 was used.

FIG. 10 is a diagram of the coaxial resonator viewed from the open end side, and FIG. 11 is a cross-sectional view taken along the line AA' in FIG. 10.

In FIG. 10.11, 801 is a hollow dielectric. Conductive layers of an inner conductor 802, an outer conductor 803, and a short-circuit end 805 are formed on the inner peripheral surface, outer peripheral surface, and end surface of this dielectric 801. A metal material (silver, copper, etc.) with low resistivity is used to form the conductor layer. 804 indicates the open end of the coaxial resonator.

As described above, conventional band elimination filters use filters with constant characteristic impedance within a coaxial resonator.

FIGS. 12 and 14 show examples of circuit configurations of conventional band elimination filters.

The above circuit configuration is used in a transmission filter section that requires low insertion loss, such as an antenna duplexer for a car phone or a mobile phone.

The circuit configuration in Fig. 12 is the transmission frequency ftx and reception frequency f.
Models where the frequency relationship of rx is frx (ftx)
Suitable for domestic use as a transmission filter for antenna duplexers).

UIRl, UIR2, and UIR3 in FIG. 12 are number 10.
A coaxial resonator having the structure shown in Fig. 11, one end of capacitors C1, C2, C3 is connected to the inner conductor on the open end side, and the other end of capacitor C1, C2, C3 is connected to the inner conductor on the open end side through capacitors C12, C23. connected in parallel.

FIG. 13 shows the pass characteristics of the band elimination filter having the above circuit configuration.

In addition, Fig. 13 shows the transmission frequency frx20, 912 GHz.
, reception frequency f rx = 0.857 GHz.

Bandwidth is 0.027 GHz, attenuation in the receiving frequency band ff
FIG. 7 is a pass characteristic diagram when a band elimination filter for a transmission filter is configured under the condition of i>40 dB.

The circuit configuration in Fig. 11 is the transmission frequency ftx and reception frequency f.
Models where the rx frequency relationship is frx > ftx (
Suitable for use as a transmission filter for overseas destinations (antenna duplexer).

Coaxial resonators UIR1, UIR2, UIR3 in Figure 14
is a coaxial resonator having the structure shown in Fig. 10.11, and the internal conductor at its open end m1 is equipped with cabaret ci, C2, C3.
one end of which is connected to the adjacent capacitors C1, C2, C
The other ends of 3 are connected in parallel via inductors LL2 and L23.

FIG. 15 shows the pass characteristics of the Bandai IJ Millon filter having the above circuit configuration.

In addition, Fig. 15 shows the transmission frequency f tx = 0.837G H
z, receiving frequency f r x = 0.882 GHz, bandwidth 0.025 GHz, attenuation amount in the receiving frequency band 240
FIG. 6 is a pass characteristic diagram when a mind-elimination filter for a transmission filter is configured under dB conditions.

(Problems to be Solved by the Invention) Consider a case where the band elimination filter described above is used in a transmission filter section of an antenna duplexer for a car phone.

Broadly speaking, there are two functions required of a transmission filter.

One is to reduce the level of noise components in the reception frequency band included in the transmission output, and the other is to reduce the spurious radiation components of the transmission output.

Here, the former function (reducing the level of noise components in the reception frequency band) can be realized by setting the rejection frequency of the band elimination filter to the reception frequency.

However, there is a problem with the latter, as shown in Figures 13 and 15 (this is an integer multiple of the transmission frequency ftx).
The problem is that sufficient attenuation cannot be obtained for spurious radiation generated at frequencies of 2.ftx, 3.ftx, etc.).

This is due to the basic characteristics of the band elimination filter, and is because at frequencies other than the parallel resonance point of the coaxial resonator, no attenuation pole occurs and the frequency becomes a pass region.

In the case of a distributed constant circuit such as a coaxial resonator, it is generally known that there are an infinite number of parallel resonance points, but this has not been able to be used to suppress spurious radiation.

The reason for this is that the attenuation pole due to the high-order parallel resonance points is shifted from the frequency at which spurious radiation occurs, as shown in the attenuation pole Nl (frequency -3·fo) shown in Figs. 13 and 15, and the high-order This is because the frequency liquid of the attenuation pole N1 cannot be arbitrarily controlled.

The frequency of the attenuation pole N1 is determined by the rejection frequency band (reception frequency band) of the band-elimination filter and the amount of attenuation.

As described above, the conventional vanodium filter does not have the function of reducing spurious radiation, so there are problems when using it as a transmission filter.

SUMMARY OF THE INVENTION An object of the present invention is to provide a bar/elimination/junction filter that can solve the above problems.

(Means for Solving the Problem) The gist of the present invention that solves the problem is to connect several resonant circuits each having a coaxial resonator and a cavantor/storage means connected in series using a capacitor/tance means or an inductance means. At the same time, the characteristic impedance of the coaxial resonator was changed from the short-circuited end to the open end t to adjust the high-order parallel resonance frequency of the filter to be approximately equal to the frequency at which spurious radiation occurs. It has a characteristic band elimination filter.

(Function) An example of the structure of a coaxial resonator used in the present invention is shown in FIGS. 1 to 4.

Figure 1 is a diagram of the coaxial resonator seen from the open end side, and the second
The figure is a sectional view taken along line AA' in FIG.

In FIGS. 1 and 2, reference numeral 101 is a hollow dielectric having a step on its inner circumference. An inner conductor 102, an outer conductor 103, and a short-circuit end 1 are provided on the inner peripheral surface, outer peripheral surface, and end surface of this dielectric 101.
A metal material (silver, copper, etc.) with low specific resistance is used to form the conductor layer described above. Reference numeral 104 indicates the open end of the coaxial resonator.

In Figure 1.2, the characteristic impedance of the coaxial resonator is reduced from the short-circuited end to the open end by providing a step on the inner periphery of the hollow dielectric 201 so that the inner periphery on the open end side becomes larger. ing. Incidentally, when the characteristic impedance is increased in the direction from the short-circuited end to the open end, the structure shown in FIGS. 3 and 4 may be adopted.

Figure 3 is a diagram of the coaxial resonator viewed from the open end side, and the fourth
The figure is a sectional view taken along the line AA' in FIG.

In Fig. 3.4, 201 is a hollow dielectric having a step on its inner circumference. The conductor layers that form the inner conductor 2o2, outer conductor 203, and short-circuited end 205 of the inner circumferential surface, outer circumferential surface, and end surface of this dielectric 201 are made of a metal material with a low resistivity (silver, etc.). copper, etc.). 204 indicates the open end of the coaxial resonator.

In Figures 1 to 4, if the characteristic impedance of the line on the short-circuited end side (length Ll) is Zl, and the characteristic impedance of the line on the open end side (length L2> Z2), the parallel resonance condition of the coaxial resonator is jan ( βLl)・jan(βL2)=tan (θ
1)・tan(θ2)=Z2/Z.

β: Phase constant θ1, θ2° electrical length (θ1=βL4, θ2=βL2) You can hail.

In the above equation, for simplicity, L1=L2, that is, θj−
Considering the case of θ22θ, the parallel resonance condition can be expressed as jan”θ=kk, impedance ratio (k=Z2/Zt).

Here, the fundamental resonance frequency is fo, the higher-order parallel resonance frequencies are fSl, fs2..., fsn from the lowest to lowest, and the electrical lengths that are proportional to the resonance frequency are θ0, θ4, θ2..., θ.
sn, and find each electrical length from the relational expression of the parallel resonance condition mentioned above, θo = jan''(k'') θs, = π-jan-'(k'/2) θ52 = yr + tan-' (k1/2) or more results are obtained.

In the case of a distributed constant circuit such as a coaxial resonator, there are countless parallel resonance points as is clear from the resonance conditions, but this explanation would be complicated, so we will explain the parallel resonance points in the frequency range below θs2. .

If we organize the relationship between the fundamental frequency fo and the higher-order parallel resonance frequency from the above electrical length, fsl/fo=θs1/θo:=π/ tan −
' (k!/2) 1 fs2/fo=θs2/θo=π/tan-'
(k1/2)+1 The following relational expression is obtained.

In the above relational expression, the impedance ratio can be arbitrarily set to a value of 40 or more, so the high-order parallel resonance point of the coaxial resonator can be controlled over a wide range.

Furthermore, from the above relational expression, the higher-order resonance frequency fs can be set to any frequency in the frequency range above the fundamental frequency fo, and the higher-order resonance frequency fs2 can be set to any frequency in the frequency range more than three times the fundamental frequency fo. It can be seen that the higher-order parallel resonance frequency increases as the impedance ratio decreases.

The relationship between the impedance ratio and the parallel resonance frequency is expressed as the fifth
As shown in the figure.

Note that the vertical axis in the figure is the high-order parallel resonance frequency fs normalized by the fundamental resonance frequency for.

When a band-elimination dissonance filter is configured using the coaxial resonator, an attenuation pole occurs near the high-order parallel resonance point, so the coaxial resonance is adjusted so that the frequency of the attenuation pole is equal to the frequency at which spurious radiation occurs. Spurious radiation can be reduced by controlling the impedance ratio k of the device.

(Example) Examples of the present invention will be described below.

Embodiment 1 FIG. 6 is a diagram showing an embodiment of a band elimination filter according to the present invention.

In FIG. 6, 5IR1, 5IR2, and 5IR3 are coaxial resonators having a structure in which the characteristic impedance within the coaxial resonators increases or decreases stepwise from the short-circuited end to the open end.

In this example, 5IRI and 54R3 have the structure shown in Figure 3.4 (a coaxial resonator whose characteristic impedance increases from the short-circuited end to the open end), and 5IR2 has the structure shown in Figures 1 and 2 (from the short-circuited end to the open end). A coaxial resonator with a characteristic impedance (a coaxial resonator whose characteristic impedance is reduced) was used.

Zll, Z21, Z31 are coaxial resonators 5IR1, 5I
The impedance of the line on the shorted end side of R2, 5IR3 is
Z12, Z22, Z23 are coaxial resonators 5IRI, 5IR
The impedance of the line on the open end side of 2,5IR3 is shown.

Here, in order to control the high-order parallel resonance frequency of the coaxial resonator, the impedance ratio was set as follows.

Impedance ratio of 5IRI k = 2.55 Impedance ratio of SIR2 k = 0.84 Impedance ratio of SIR3 k = 2.59 Furthermore, 5IRI, 5IR2, 5IR
In No. 3, the line length on the open end side and the line length on the short-circuited end side were set equal.

The open ends of the coaxial resonators 5IRI, 5IR2, and 5IR3 are connected to one end of the capacitor C1, C2, and C3, and the other end of the adjacent capacitor C1, C2, and C3 is connected to the capacitor CI2. , C23.

Transmission frequency ftx=0.912GH with the above circuit configuration
z, reception frequency f rx = 0.857GH2, bandwidth is 0.027GHz, attenuation in reception frequency band Jt > 4
A 3-band band eliminator filter for the transmission filter was constructed under the condition of 0 dB.

The pass characteristic of the band elimination filter is determined by the seventh
Illustrated here.

In FIG. 7, frx represents the reception frequency, ftx represents the transmission frequency, and 2·ftx and 3·ftx represent frequencies at which spurious radiation occurs.

As is clear from FIG. 7, the vanodescent filter according to this embodiment can generate an attenuation pole at the frequency where spurious radiation occurs.

Embodiment 2 FIG. 8 is a diagram showing another embodiment of the band elimination filter according to the present invention.

5IRI, 5IR2, and 5IR3 in FIG. 8 are coaxial resonators, which have a structure in which the characteristic impedance within the coaxial resonators increases from the short-circuited end toward the open end.

In this example, the 3rd and 4th
A coaxial resonator with the structure shown in the figure was used.

Zll, Z21, Z31 are coaxial resonators 5IR1, 5IR
The impedance of the line on the short-circuited end side of 2,5IR3, and Z12, Z22, and Z23 are the coaxial resonators 5IR1, 5IR.
The impedance of the line on the open end side of 2,5IR3 is shown.

Here, the impedance ratio was set as follows to control the high-order parallel resonance frequency of the coaxial resonator.

Impedance ratio of 5IRI k = 3.525 Impedance ratio of IR2 k = 1.375 Impedance ratio of IR3 k = 3.70 Furthermore, 5IRI, 5IR2, 5IR
The line length of the open end 0111 and the line length of the short-circuited end in No. 3 were set equal.

One end of the capacitor C1, C2, C3 is connected to the open end side of the coaxial resonator 5IR1, 5IR2, 5IR3, and the other end of the adjacent capacitor C1, C2, C3 is connected to the inductor L12, L23. Connected via.

The above circuit configuration e Trowel transmission frequency ftx = 0.837
GHz, receiving frequency f r x = 0.882 GH2
, the bandwidth is 0.025 GHz, the attenuation in the receiving frequency band j
A band/domain elimination filter for a transmission filter was constructed under the condition of t > 40 dB.

The ninth pass characteristic of the band elimination filter is
As shown in the figure.

In FIG. 9, frx indicates a reception frequency, ftx indicates a transmission frequency, and 2.ftx and 3.ftx indicate frequencies at which spurious radiation occurs.

As is clear from FIG. 9, the band elimination filter according to this embodiment can generate an attenuation pole at the frequency where spurious radiation occurs.

In the above embodiment, the coaxial resonator has a structure in which a step is provided on the inner circumference of the dielectric material. However, this does not limit the shape of the coaxial resonator, and the characteristics within the coaxial resonator. It is sufficient if the impedance increases or decreases from the short-circuited end to the open end.

For example, a similar effect can be obtained with a coaxial resonator in which the characteristic impedance is changed by providing a two-step difference in the outer circumference of the dielectric and a tapered portion on the inner or outer circumference of the dielectric.

(Effects of the Invention) As described above, according to the present invention, the characteristic impedance of the coaxial resonator is changed from the short-circuited end toward the open end, so that the high-order parallel resonance frequency of the filter is approximately equal to the frequency at which spurious radiation occurs. The spurious radiation component of the transmission output was able to be reduced by making adjustments so that

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a coaxial resonator used in an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the line A-A' in FIG. 1, and FIG.
The figure is a plan view showing another coaxial resonator used in the example.
The figures are a cross-sectional view taken along line A-A' in Figure 3, Figure 5 is a resonance characteristic diagram of the coaxial resonator used in the example, Figure 6 is a circuit diagram of the band elimination filter of Example 1, Fig. 7 is a pass characteristic diagram of the band elimination filter of Example 1, Fig. 8 is a circuit diagram of the band elimination filter of Example 2, Fig. 9 is a pass characteristic diagram of the same embodiment, and Fig. 10 is a conventional filter. Fig. 11 is a cross-sectional view taken along line A and -A' in Fig. 10, Fig. 12 is a circuit diagram of a conventional band-elimination filter, and Fig. 13 is a coaxial resonator used in a band-elimination filter. The pass characteristic diagram of a conventional band-elimination non-uniform Noyon filter, Fig. 14 shows another conventional band-elimination IJ.
The circuit diagram of the Millon filter, Figure M15, is a passage characteristic diagram of the same filter. 101.201.801: Dielectric 102.202.802: Inner conductor 103.203.803: Outer conductor 104.204.804: Open end 105.205.805: Shorted end conductor 5IR1, 5IR2, 5IR3: Coaxial resonator Z11.
Z12. Z21. Z22. 231°Z32
゛Inopida/S C1, C2, C3 Cab/Li L12. L23: Inductor ftx: Transmission frequency frx: Reception frequency 2・ftx, 3・ftx High-order parallel resonance frequency property Applicant Matsushita Electric Industrial Co., Ltd. Representative Patent attorney Haruaki Ko
(and 2 others) Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 7 Fig. 12 Fig. 13 Fig. 14 Fig. 15 Frequency (GHz

Claims (1)

[Claims] 1) A plurality of resonant circuits each having a coaxial resonator and a capacitance means connected in series are connected in parallel using capacitance means or inductance means to form a filter, and the characteristic impedance of the coaxial resonator is changed from the short-circuited end to the open end. A band elimination filter characterized in that the high-order parallel resonance frequency of the filter is adjusted to be approximately equal to the frequency at which spurious radiation occurs.