JPH03181205A - Dielectric filter - Google Patents

Abstract

PURPOSE:To obtain a large attenuation factor by inserting the resin part of a resin terminal produced by converting the outside of a terminal pin with a resin material into a resonator hole of each 1/4 wavelength type dielectric coaxial resonator and connecting each terminal part to the corresponding capacitor pattern of a substrate. CONSTITUTION:A band stop filter part is formed with a combination of plural 1/4 wavelength type dielectric coaxial resonators 10, the resin terminals 14 put into the resonance holes 12 of the resonators 10, and the capacitors consisting of capacitor patterns 26 on a substrate 24. In such a constitution, a large attenuation factor is obtained at a prescribed frequency band. In case of a band stop filter, a stop band (a frequency band where a large attenuation factor is secured) is set to a reception band. On the other hand, the stop band is set to a transmission band in case of a reception filter respectively. In other words, the stop band filter part is provided in a frequency area where a desired attenuation factor is obtained. Thus it is possible to obtain a large attenuation factor with smaller number of attenuators 10.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a dielectric filter used in high frequency bands such as microwaves, and more specifically, a low-pass filter section consisting of a plurality of coils and a capacitor, This invention relates to a dielectric filter that is combined with a band-stop filter section having a quarter-wavelength dielectric coaxial resonator.

[Prior Art] Filters using dielectric ceramics such as barium titanate have characteristics such as low loss and can be miniaturized, and are widely used in microwave band mobile communication systems such as car telephones.

As a conventional technique related to dielectric filters, a plurality of resonator holes and coupler holes are provided alternately at predetermined intervals in a rectangular parallelepiped dielectric block, and one of the surfaces where the resonator holes are open is A structure is known in which the outer surface of the dielectric block except for the open surface and the inner surface of the resonator hole are metallized.

In such a filter, each resonator hole corresponds to an individual resonant element, and has a resonant wavelength four times the height of the resonator hole, and the resonant elements are coupled by a coupler hole,
It functions as a band pass filter (BPF...band pass filter).

In mobile microwave communication, this type of bandpass filter with different center resonance frequencies is used for transmission and reception. The transmission filter has a center resonant frequency in the transmission band and has a small insertion loss, and has a characteristic of having a large attenuation in the reception band slightly shifted from the center resonance frequency. Conversely, a reception filter has a center resonant frequency in the reception band and exhibits characteristics of low insertion loss, and a transmission band slightly shifted from the center resonance frequency, which exhibits a large attenuation amount.By combining these two, it is possible to share the antenna.

[Problems to be Solved by the Invention] In the above-mentioned integrated multistage structure bandpass filter,
In order to improve the damping characteristics, it is necessary to increase the number of stages (the number of resonator holes). However, as the number of stages increases, the insertion loss of the filter worsens and the filter becomes larger.

In addition, in a 174-wavelength resonator, in addition to resonating in the fundamental wave mode (fundamental wave center frequency fo), it also resonates in odd-numbered harmonics of the fundamental wave, producing spurious waves. In particular, the spurious of 3r0 (third harmonic of the fundamental wave center frequency f0) is the largest and becomes a problem.

Therefore, in order to reduce spurious at 3fo, 3f,
It was necessary to add a separate low-pass filter to cut the above-mentioned high frequency range. In other words, a separate low-pass filter and band-pass filter are connected in series to form a transmission filter. For this reason, further enlargement was inevitable.

The purpose of the present invention is to eliminate the drawbacks of the prior art as described above, and to provide a dielectric filter with a new structure that is small, has low loss, improves the 3f6 spurious response, and has a sufficiently large attenuation characteristic. There is a particular thing.

[Means for Solving the Problems] The present invention, which can achieve the above object, includes a low-pass filter section in which a plurality of capacitor patterns are formed on a substrate and the capacitor patterns are connected by a coil, and a plurality of capacitor patterns are arranged in parallel. The resin part of the resin terminal, which has a 1/4 wavelength type dielectric coaxial resonator and the outer side of the terminal pin is covered with a resin material, is inserted into each resonator hole, and each terminal part is connected to the corresponding capacitor of the board. This is a dielectric filter connected to a pattern. Here, the cutoff frequency of the low-pass ill filter section is designed to be slightly higher than the stopband of the band-stop filter section formed by the plurality of resonators.

It is also effective in terms of attenuation characteristics to provide a polarized pattern near the capacitor pattern on the substrate and to couple between stages.

[Function] A band rejection filter section is configured by a combination of a plurality of 1/4 wavelength type dielectric coaxial resonators, resin terminals inserted into the resonator holes, and capacitors formed by the capacitor pattern on the board. Obtain large attenuation in the frequency band. For example, in the case of a transmission filter, its stopband (frequency band where large attenuation can be obtained) is set as the reception band, and conversely, in the case of a reception filter, the stopband is set as the transmission band.

When a 1/4 wavelength type dielectric resonator is used, spurious components appear in frequency bands that are odd multiples of the fundamental wave center frequency r0. As mentioned above, the 3fo spurious is especially large. In the present invention, the 3fo spurious is reduced by a low-pass filter consisting of a combination of a coil and a capacitor formed by a capacitor pattern on the substrate.

In addition, if a polar pattern is provided near the capacitor pattern on the board and coupled between stages, a characteristic with an attenuation pole (polar type) can be obtained, which results in the edge part of the attenuation filter characteristic of the band-stop filter section. can be made steeper.

[Embodiment] FIG. 1 is an exploded perspective view showing an embodiment of a dielectric filter according to the present invention. Four quarter-wavelength dielectric coaxial resonators 10 are arranged in parallel, and resin terminals 14 are inserted into their resonator holes 12. Here, the resonator 10 is made of a sintered body 16 of a dielectric material (for example, barium titanate, etc.) in the shape of a rectangular column, with a resonator hole 12 penetrating through the center thereof, and a surface where the resonator hole I2 is open. One of the surfaces (here, the top surface) is an open surface, and a metallized layer 18 is formed on the other outer surfaces (the four surfaces and the bottom surface) and the inner surface of the resonator hole 12. The metallized layer 18 is an extremely thin conductive film formed by baking silver paste or the like, for example.

The resin terminal 14 has a structure in which a part of the outer side of the terminal pin 20 is covered with a resin material in a cylindrical shape.The upper end of the resin part 22 has a flange shape, and the resin terminal 14 is inserted into the resonator hole 12 up to the flange part. The resin parts of the two resin terminals closer to the center are longer than the resin terminals at both ends (therefore, the terminal pins are also longer).
It has a large capacity.

The substrate 24 located above them is made of glass, epoxy, etc. or alumina, etc. On the surface side, four capacitor patterns 26 are formed with the same pinch as the resonator 10, and terminal patterns 28 are formed on both ends. Furthermore, a polar pattern 30 is formed on one side. Polar pattern 30
In this embodiment, two lines are provided so as to connect the vicinity of the two left and right capacitor patterns. These patterns are conductive films formed by etching, screen printing, or the like. The back surface of the substrate 24 (first
The bottom surface (in the figure) is a full-surface conductor pattern. A through hole 32 is provided at the center of the capacitor pattern 26, into which the terminal pin 24 of the resin terminal 14 is inserted.

Input/output terminals 34 are connected to the terminal patterns 28 located at both ends. 26 capacitor patterns and a coil 36 between capacitor pattern 26 and terminal pattern 28
Connect with. The board 24 is attached so that the terminal pin 20 is inserted into the through hole 32, and the capacitor pattern 26 is used to connect by soldering. The top of them is metal cover 3
Covered by 8.

The metal cover 38 is a pressed product, bent into a U-shape, has holes 40 at both ends of the top for inserting input/output terminals, and long holes 42 for fixing solder on both sides. . The metal cover 38 is for preventing the magnetic field from leaking to the outside, and is used to protect each resonator 10 and the metal cover 3.
8 is fixed by soldering using an elongated hole 42 formed on the side surface.

FIG. 2 shows an equivalent circuit of the dielectric filter assembled according to FIG. 1. *L I + . . . , I4 represents the equivalent inductance of the resonator 10, and L.

..., I9 represents the inductance of the coil 36. C1, ..., Ca is capacitor pattern 2
6, the capacitance due to the resin terminal 14, and the equivalent capacitance of the resonator 10. Cs and Ch represent connections by the polar pattern 30.

Figure 3 shows the characteristics obtained with the dielectric filter configured as above. In this example, three resonators are arranged in parallel, and the coil between the capacitors is 6 turns, and the input and output coils are 5 turns. This is an example. However, no polar pattern is formed.This result shows that the insertion loss is extremely small and that a sufficiently large amount of attenuation can be obtained in a predetermined frequency band. When this is used as a transmission filter, the stop band a (region with large t2 attenuation) becomes the reception band, as shown in the figure.

The transmission band, which is slightly lower than the reception band a, has extremely little attenuation (insertion loss is very small), and this is due to the characteristics of the band rejection filter section. The area indicated by symbol C is an area where the effect of the low-pass filter section is effective.

Examining the filter characteristics shown in FIG. 3, it can be seen that the insertion loss is about 1.9 dB in the conventional band rejection filter, but can be reduced to about 1.3 to 1.4 dB in the present invention.

Also, when comparing the amount of attenuation, in order to obtain the amount of attenuation shown in Figure 3, it is necessary to use 5 to 6
However, in the present invention, only three stages are necessary, which means that the size can be significantly reduced.

By using two dielectric filters as described above having different center resonance frequencies and combining one as a transmitting filter and the other as a receiving filter, an antenna duplexer used in a car phone or the like can be constructed.

Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to only such a configuration.

Although the polar pattern is provided only on one side in the above embodiment, it can also be provided on both sides. By forming a polar pattern, the mating attenuation characteristics can be improved, which is advantageous for miniaturization.

The number of installed Wi-Fi devices and low J! The number of sections of coils and capacitors constituting the 1iiffi overfilter section may be changed as appropriate, and the phase can be changed by varying the inductance of the first stage coil.

[Effects of the Invention] As described above, the present invention provides the band M-band rejection filter section in the frequency region where desired attenuation is desired, so that a sufficiently large amount of attenuation can be obtained even with a small number of resonators. Moreover, the 3f0 spurious can be suppressed by the low-pass filter section, and the filter characteristics are improved as a whole.

Furthermore, the present invention is a combination of a band-elimination filter section and a low-pass filter section, and the number of resonators in the band-elimination filter section can be reduced, so that insertion loss can be reduced and the device can be made smaller.

Since the capacitor and coil are formed on the substrate, they are extremely easy to manufacture and stable. Furthermore, if a polar pattern is formed, the attenuation characteristics will be improved and the insertion loss will be reduced.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view showing an embodiment of a dielectric filter according to the present invention, FIG. 2 is an equivalent circuit diagram thereof, and FIG. 3 is an example of filter characteristics obtained by the dielectric filter according to the present invention. It is a graph. DESCRIPTION OF SYMBOLS 10... Resonator, 12... Resonator hole, 14... Resin terminal, 20... Terminal pin, 22... Resin part, 24
... Board, 26... Capacitor pattern, 30.
...Polar pattern, 32...Through hole, 36...Coil.

Claims (2)

[Claims] 1. It has a low-pass filter section in which multiple capacitor patterns are formed on the board and the capacitor patterns are connected by a coil, and a plurality of 1/4 wavelength dielectric coaxial resonators arranged in parallel. A dielectric filter characterized in that a resin portion of a resin terminal covered with a resin material is inserted into each resonator hole, and each terminal portion is connected to a corresponding capacitor pattern on a substrate. 2. 2. The dielectric filter according to claim 1, further comprising a polar pattern provided near the capacitor pattern on the substrate.