JPH0430601A - Dielectric filter - Google Patents

Abstract

PURPOSE:To improve the filter characteristic by employing a 1/4 wavelength type integrated dielectric coaxial resonator having plural resonator holes, forming a non-electrode part to a position of an outer face ground electrode corresponding to each resonance hole, providing an island electrode to the inside of the non-electrode part apart from the ground electrode and interconnecting the said island electrodes with a coil. CONSTITUTION:A coupling capacitor 22 is fitted to the inside of a non-electrode part 20 so as not to be in continuity with a ground electrode 16 and the coupling capacitors 22 are interconnected by a coil 26 and the coupling capacitor 22 and an input output terminal 24 are interconnected by the coil 26 respectively. The coupling capacitor 22 may be adhered directly to the non-electrode part 20 or an island electrode is formed in the non-electrode part 20 and the coupling capacitor 22 may be soldered to the island electrode. A low pass filter is formed by the five coils 26 and the coupling capacitor 22 and the capacitance formed by the opposed area comprising the coupling capacitor and inner conductor of resonance hole, and a band stop filter is formed by the combination of each resonance element corresponding to each of the four resonator holes 12 and the said capacitor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a dielectric filter mainly used in the microwave band. More specifically, the low-pass filter section consists of multiple coils and capacitors, and the integrated λ/
This invention relates to a dielectric filter that is combined with a band rejection filter section using a type 4 dielectric resonator.

This filter is widely used in fields such as mobile communications, for example.

[Prior Art] As one of the conventional techniques related to dielectric filters, a plurality of resonator holes and coupler holes are provided alternately in a rectangular parallelepiped dielectric block, and one of the surfaces where the resonator holes are open ( open surface)
There is a structure in which a conductor film is provided on the entire outer surface of the dielectric material except for the resonator hole and on the inner wall surface of the resonator hole.

In this filter, each resonator hole corresponds to a single resonant element, and has a resonant wavelength four times the height of the resonator hole. The resonant elements are coupled through the coupler holes, and function as a band-pass filter.

In mobile microwave communication, bandpass filters with different center resonant frequencies are 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. On the other hand, a receive filter has a center resonance frequency in the receive band and has low insertion loss, and has a characteristic of large attenuation in the transmit band slightly shifted from the center resonant frequency.
By combining the two, you can share the antenna.

[The problem that the invention tries to solve! ! ] In a bandpass filter with an integrated multi-stage structure as described above,
In order to improve the damping characteristics, it is necessary to increase the number of stages (the number of resonator holes). However, if the number of stages is increased, the insertion loss of the filter worsens and the filter becomes larger.

In addition, in the λ/4 type, the fundamental wave mode (fundamental wave center frequency f
o), and also resonates at odd-numbered harmonics of the fundamental wave, producing spurious waves. In particular, the spurious of 3f0 (third harmonic of the fundamental wave f0) is the largest, which poses a problem.

Therefore, in order to prevent the increase in insertion loss and reduce the 3fo spurious, a low-pass filter that cuts the high frequency range of 3f or more may be separately added. In that case, separate low-pass filters and band-pass filters are connected in series to form a transmission filter. This has the disadvantage of further increasing the size.

The object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to provide a small size, low loss, and 3f.

The object of the present invention is to provide a dielectric filter with a new structure that improves the spurious response of the filter and has sufficiently large attenuation characteristics.

[Means for Solving the Problems 1] In the present invention, a quarter-wavelength type integrated dielectric coaxial resonator having a plurality of resonator holes is used. Then, a non-electrode portion is formed at a position corresponding to each resonator hole of the external ground electrode of the resonator, and an island-shaped electrode separated from the ground electrode is provided within the non-electrode portion, and the island-shaped electrodes are connected with a coil. do. A coupling capacitor may be attached instead of the island-shaped electrode. A capacitor is formed between the island-shaped electrode and the inner conductor of the resonator hole, and if a coupling capacitor is used, the structure is such that a coupling capacitor is further added. This results in a configuration in which a low-pass filter section made up of the coil and the capacitor and a band-stop filter section made up of each resonance element etc. are combined.

Here, the cutoff frequency of the low-pass filter section is set to be slightly higher than the stopband of the band-stop filter section.

The frequency of each resonant element of the dielectric resonator can be adjusted by mounting a lumped constant capacitor at the open end of the resonator hole. In addition, the open surface of the dielectric resonator can be used to
Susceptance correction can be performed by providing a pattern or by connecting the frequency@adjustment capacitor and the side ground electrode with a coil.

[Operation 1] A combination of a λ/4 type resonant element formed by a resonator hole and a capacitor located near the resonant element constitutes a band rejection filter section, thereby obtaining large attenuation in a predetermined 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 λ/4 type dielectric resonator is used, spurious components appear in frequency bands that are odd multiples of the fundamental wave center frequency 10. As mentioned above, especially 3 [. spurious is large.

In the present invention, the 3fo spurious is reduced by a low-pass filter section consisting of a combination of a coil and a capacitor.

Furthermore, when the susceptance is corrected by a capacitor pattern or a lumped constant capacitor/coil, the filter characteristics within the band change slightly, and the edges of the attenuation characteristics of the band-stop filter section become steeper.

[Embodiment] FIG. 1 is an exploded perspective view showing an embodiment of a dielectric filter according to the present invention. The λ/4 integrated dielectric resonator 10 is composed of a rectangular parallelepiped dielectric block 12 (for example, a sintered body of barium titanate or the like). Four resonator holes 14 are arranged in parallel at regular intervals in the longitudinal direction, and one of the surfaces where the resonator holes 14 are open (here, the upper surface) is an open surface.
A ground electrode 16 is formed on almost the entire outer surface (the four surfaces and the bottom surface) excluding the open surface, and an inner conductor is formed on the inner wall surface of the resonator hole 14. The earth electrode 16 and the inner conductor are
For example, it is an extremely thin layer of conductive material formed by baking silver paste or the like. However, each resonator hole 14 of the ground electrode 16
The electrodeless portion 20 is left at a position corresponding to (nearby position).

A coupling capacitor 22 is attached inside the electrodeless part 20 so as not to be electrically connected to the ground electrode 16, and between each coupling capacitor 22 and between the coupling capacitor 22 and the input/output terminal 2.
4 through a coil 26. Coupling capacitor 22
may be directly bonded, or an island-like electrode may be formed within the electrodeless portion 22 and soldered thereto.

In this embodiment, a frequency adjustment capacitor 28 is further mounted and connected to the open end of the resonator hole 14. You can attach a ribbon-shaped connection terminal to the open end and place it on it and solder it, or you can add an electrode around the open end and place it on top of it and solder it, or you can put it on top of the electrode. They may be connected by simultaneous baking.

A low-pass filter section is configured by the five coils 26, the coupling capacitor 22, and the capacitance formed by the opposing portion of the coupling capacitor and the inner conductor of the resonator hole.
A band rejection filter section is configured by the combination of the resonant element corresponding to No. 2 and the capacitance.

FIG. 2 shows an equivalent circuit of the dielectric filter shown in FIG. 1. L+, . . . , Ls are the inductances of the coil 26, and Lb, . . . , Lq represent the equivalent inductance of each resonant element. C1..., C4 are the sum of the capacitance due to the coupling capacitor 22 and the dielectric material in its vicinity, the equivalent capacitance of the resonant element, etc.

A dielectric filter with this structure has an extremely small insertion loss and can obtain a sufficiently large amount of attenuation in a predetermined frequency band. When this is used as a transmission filter, the stop band (region with large f!Ii attenuation) becomes the reception band. The transmission band, which is slightly lower than the reception band, has extremely little attenuation (insertion loss is very small), and this is due to the characteristics of the band rejection filter section. The region higher than that is where the effect of the low-pass filter section is effective.

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.

3 to 6 show other embodiments of the invention. Since the basic configuration is the same as that shown in FIG. 1, common parts are given the same reference numerals and explanations thereof will be omitted. In FIG. 3, a dielectric block 30 has a structure in which grooves 32 are formed at both ends thereof. An electrodeless portion 20 is formed in the groove 32, a coupling capacitor 22 is attached, and a coil 26 is connected. In other words, the coupling capacitor 22 and coil 26 are housed within the 11132 to reduce the size and protect these components.

Then, the open surface of the dielectric block 30 is covered with a metal cover 34 for grounding. This stabilizes the fill characteristics.

FIG. 4 shows an example in which a susceptance correction conductor pattern 36 is formed between the open end of the resonator hole on the open surface of the dielectric resonator 10 and the side earth electrode 16. Further, FIG. 5 shows an example in which a susceptance correction coil 3B is connected between the frequency adjustment capacitor 2 and the side ground electrode 16. A narrow stepped portion is provided at the bottom of the dielectric block, and a coupling capacitor 22 and a coil 26 are housed there.

Island-like patterns 40 for input/output connections are formed at both ends so that they can be connected to strip lines 42 on the board.

FIG. 6 shows that a non-electrode portion 20 is formed on the short-circuit surface of a dielectric resonator lO, and a coupling capacitor 22 is attached to the coil 2.
This is an example of wiring at 6.

All of the above embodiments have four resonator holes, but the number of resonator holes formed is not limited to four, and in all of the above embodiments, coupling capacitors are attached. However, it is also possible to form island-shaped electrodes and connect the island-shaped electrodes with a coil. In that case, a capacitor is substantially formed between the island-shaped electrode and the conductor in the resonator hole.

[Effects of the Invention] Since the present invention provides a band-elimination filter section in the frequency band where desired attenuation is desired as described above, a sufficiently large amount of attenuation can be obtained even with a dielectric resonator having a small number of resonator holes. Moreover, the spurious signal 3f 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 resonator holes in the band-elimination filter section can be reduced, so that insertion loss can be reduced and the device can be made smaller.

By providing a susceptance correction pattern or a coil, the filter characteristics within the band can be changed and the attenuation characteristics can be made steeper. Furthermore, if the dielectric block is provided with recesses such as steps or grooves to house the coupling capacitors and coils, they can be protected and this is advantageous in terms of miniaturization.

[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 of the dielectric filter,
FIG. 3, FIG. 4, FIG. 5, and FIG. 6 are perspective views showing other embodiments of the present invention. 10... Dielectric resonator, 12... Dielectric block,
14... Resonator hole, 16... Earth electrode, 20...
- Non-electrode part, 22... Coupling capacitor, 26... Coil, 28... Frequency adjustment capacitor, 36...
Susceptance correction pattern, 36... Susceptance correction coil. Patent Applicant: Fuji Electrochemical Co., Ltd. Representative: Shigeru Minoru

Claims (6)

[Claims] 1. A 1/4 wavelength integrated dielectric coaxial resonator having multiple resonator holes is used, and a non-electrode portion is formed at a position corresponding to each resonator hole of the outer ground electrode, and an electrode-free portion is formed inside the non-electrode portion. A dielectric filter in which an island-shaped electrode is provided at a distance from a ground electrode, and a coil is connected between the island-shaped electrodes. 2. A 1/4 wavelength integrated dielectric coaxial resonator having multiple resonator holes is used, and a non-electrode portion is formed at a position corresponding to each resonator hole of the outer ground electrode, and an electrode-free portion is formed inside the non-electrode portion. A dielectric filter in which a coupling capacitor separated from a ground electrode is attached to the capacitor, and a coil is connected between the coupling capacitors. 3. 3. The dielectric filter according to claim 1, further comprising a frequency adjustment capacitor mounted on the open end of the resonator hole on the open surface of the dielectric resonator. 4. 4. The dielectric filter according to claim 3, wherein a recess is formed in the side surface of the dielectric resonator, an electrodeless portion is formed in the recess, and an island-like electrode or a coupling capacitor and a coil are arranged. 5. 4. The dielectric filter according to claim 3, wherein a conductor pattern for susceptance correction is formed between the vicinity of the open end of the resonator hole on the open surface of the dielectric resonator and the side ground electrode. 6. 4. The dielectric filter according to claim 3, further comprising a susceptance correction coil connected between the frequency adjustment capacitor and the side earth electrode.