JPH07321511A - Band pass filter employing dielectric resonator - Google Patents

Abstract

PURPOSE:To provide the band pass filter by which the frequency characteristic is simply improved. CONSTITUTION:Coupling capacitors 12, 13, 14 are connected in series between an input terminal conductor layer 8 and an output terminal conductor layer 9 sequentially. A 1st dielectric resonator 2 is connected between the capacitors 12, 13 and a ground conductor layer 5 and a 2nd dielectric resonator 3 is connected between the capacitors 13, 14 and a ground conductor layer 7. An inductor 10(11) is connected in parallel with the 1st capacitor 13(3rd capacitor 14). The parallel circuit comprising the 1st coupling capacitor 12 and the inductor 10 is formed to suppress a 3rd harmonic. The parallel circuit comprising the 3rd coupling capacitor 14 and the indutctor 11 is formed to suppress a 5th harmonic.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bandpass filter using a dielectric resonator used in mobile phones and the like.

[0002]

2. Description of the Related Art A conventional TEM mode coaxial dielectric resonator for forming a bandpass filter has a cylindrical dielectric having a through hole, an inner conductor provided in the through hole, and an outer peripheral surface of the dielectric. The outer conductor is provided and a short-circuit conductor that connects the inner conductor and the outer conductor at one end surface of the dielectric body.

[0003]

The dielectric resonator as described above not only resonates with the fundamental wave (desired frequency signal) but also has a frequency 3f0 which is three times the fundamental wave frequency f0.
Spurious resonance occurs even at 5 times the frequency of 5f0. Therefore, the harmonic component of the fundamental wave also passes through the filter. If it is necessary to remove harmonic components in a conventional high frequency circuit or if you want to remove other specific frequency components, an independent filter is required to remove them, and the circuit device becomes complicated and large. It was Further, it may be desirable to make the rise and / or the fall of the bandpass width in the bandpass filter steep. In the conventional filter device, individual trap circuits are connected in parallel to the dielectric resonator. This inevitably made the filter complicated and large.

Therefore, an object of the present invention is to simply and compactly construct a bandpass filter device having good characteristics.

[0005]

The present invention for achieving the above object provides a bandpass filter device having a coupling element and a dielectric resonator, and a circuit having an anti-resonance point which also serves as the coupling element. The present invention relates to a bandpass filter device, wherein a resonance frequency of a circuit having the anti-resonance point is set to a specific frequency other than a resonance frequency of a fundamental wave of the dielectric resonator. As set forth in claim 2, the resonance frequency of the circuit having the anti-resonance point is set to a value capable of sharpening the attenuation characteristic of one or both of the low-pass side and the high-pass side of the bandpass filter characteristic. can do.

[0006]

According to the first aspect of the invention, a circuit having an antiresonance point is formed by also using a coupling element, and for example, a frequency component which is an integral multiple of the resonance frequency of the fundamental wave or a specific frequency component other than this is formed. Since the blocking is performed, an independent filter for suppressing a harmonic component or other specific frequency component due to spurious resonance is unnecessary, and the configuration of the filter device can be simplified and downsized. Further, in the invention of claim 2, since the circuit having the anti-resonance point for adjusting the attenuation characteristic is formed by also using the coupling element, the configuration of the filter device is simplified as compared with the method of providing the independent attenuation characteristic adjusting circuit. And downsizing is possible.

[0007]

[First Embodiment] Next, a band-pass filter device according to a first embodiment of the present invention will be described with reference to FIGS. In order to obtain the equivalent circuit of FIG. 3, the filter device 1 has first and second dielectric resonators 2 and 3 and a ground conductor layer formed on the dielectric substrate 4, as shown in FIG. 5, first and second connection conductor layers 6, 7, first and second
Of the terminal conductor layers 8 and 9 and the first and second inductors 10 and 11 and the first, second and third capacitors 12, 13 and 14 mounted on the substrate 4.

The first and second dielectric resonators 2 and 3 of FIG.
As shown in FIG. 2, each of the two is formed into a cylindrical dielectric body 20 made of a dielectric ceramic, and a circular shape formed so as to extend from a first end surface 21 of the dielectric body 20 to a second end surface 22 opposite thereto. Through hole 23 and inner conductor 2 formed in this through hole 23
4 and the outer conductor 26 formed on the outer peripheral surface 25 of the dielectric 20.
A short-circuit conductor 27 formed on the second end face 22 so as to connect the inner conductor 24 and the outer conductor 26, and the first end face 21.
And a terminal conductor 28 formed on a part of the outer peripheral surface 25 and connected to the inner conductor 24. Each conductor 24, 26, 2
Reference numerals 7 and 28 are formed by applying a conductive paste (for example, silver paste) and baking it.

The outer conductors 26 of the first and second dielectric resonators 2 and 3 are soldered (not shown) to the ground conductor layer 5 of the substrate 4.
Are electrically and mechanically coupled with each terminal conductor 2
Reference numeral 8 is connected to the first and second connection conductor layers 6 and 7 with solder (not shown). First and second connection conductor layers 6,
First and second inductances 10 and 11 made of strip-shaped conductor layers are connected between 7 and the first and second terminal conductor layers 8 and 9. One electrode of each of the first and third capacitors 12 and 14 composed of chip capacitors is the first and second electrodes.
Are connected to the terminal conductor layers 8 and 9 by soldering, and the other electrode is connected to the first and second connecting conductor layers 6 and 7 by soldering. One and the other electrodes of the second capacitor 13, which is a chip capacitor, have first and second connection conductor layers 6 and 7, respectively.
It is connected with solder.

FIG. 3 shows an equivalent circuit of the filter device of FIG. The first and second dielectric resonators 2 and 3 are shown as a parallel circuit of an inductance L and a capacitor C. First, second and third capacitors 12, 1 as coupling elements
Reference numerals 3 and 14 are sequentially connected in series to the signal transmission line between the input terminal T1 and the output terminal T2. The input and output terminals T1 and T2 correspond to the first and second terminals 8 and 9 of FIG. The inductances 10 and 11 are connected in parallel to the first and third capacitors 12 and 14.

FIG. 4 (A) shows the filter characteristics (frequency / gain characteristics) of the two dielectric resonators 2 and 3 shown in FIG. 3, and FIG. 4 (B) shows the anti-resonance point composed of the capacitor 12 and the inductance 10. 4C shows the frequency characteristics of the first LC parallel circuit 31 as a circuit having
Shows frequency characteristics of the second LC parallel circuit 32 as a circuit having an anti-resonance point composed of
FIG. 4D shows the entire frequency characteristic between the input and output terminals T1 and T2 of FIG.

As is apparent from FIG. 4A, only the dielectric resonators 2 and 3 resonate at the fundamental wave frequency f0, and in addition to the frequency 3f0 which is three times the fundamental wave frequency and the frequency 5 which is five times the fundamental wave frequency.
f0 Spurious resonance occurs at higher frequencies. In order to suppress harmonic components, it is necessary to increase the amount of attenuation at frequencies 3f0 and 5f0 at which spurious resonance occurs. In order to obtain this attenuation, in this embodiment, a trap circuit (a circuit having an anti-resonance point) is formed without providing a trap circuit or a filter circuit independently and using the coupling capacitors 12 and 14 in common. That is, the first LC parallel circuit 3
1 is a frequency 3f that is three times as high as the fundamental wave as shown in FIG.
The constant of CL is set so that it resonates at 0 and becomes a large impedance, and a large attenuation is obtained. Also,
As shown in FIG. 4C, the second LC parallel circuit 32 resonates at a frequency 5f0, which is five times the fundamental wave, to become a large impedance, and the CL constant is set so that a large attenuation can be obtained. The total frequency characteristic of the filter of FIG. 3 is shown in FIG. 4 (D) which is a combination of FIGS. 4 (A), (B) and (C). As a result, filter characteristics with large attenuation at 3f0 and 5f0 can be obtained, and harmonic components can be suppressed. In this embodiment, since the coupling capacitors 12 and 14 are also used to suppress the harmonic components, the circuit configuration can be made simple and small.

[0013]

[Second Embodiment] Next, a filter device according to a second embodiment will be described with reference to FIG. However, in FIG. 5, parts that are substantially the same as those in FIG. 3 are assigned the same reference numerals and explanations thereof are omitted. The filter device of FIG. 5 is the same as that of FIG. 3 except that an inductance 30 is connected in parallel to the second coupling capacitor 13 to form an LC parallel circuit 33. This LC parallel circuit 33 is set so as to resonate at a frequency 7f0 which is seven times the fundamental wave. Therefore, the filter device of FIG. 5 can suppress the third-order, fifth-order, and seventh-order harmonic components. The filter device of the second embodiment has the same effects as the filter device of the first embodiment.

[0014]

[Third Embodiment] Next, a filter device according to a third embodiment will be described with reference to FIG. However, since the mechanical structure and electric circuit of the filter device of the third embodiment are the same as those of FIGS. 1 and 3, they will be described with reference to FIG. 6 together with FIGS. The third and first embodiments are the first and second LCs.
The difference is in the setting of the LC constants of the parallel circuits 31 and 32.

FIGS. 6A, 6B, 6C and 6D show the characteristics of the same parts as FIGS. 4A, 4B, 4C and 4D. As shown in FIGS. 6B and 6C, the frequency characteristics of the first and second LC parallel circuits 31 and 32 are attenuated in the rising region and the falling region of the pass band of the band pass filter of FIG. It is set as shown. As a result, the overall frequency characteristic becomes as shown in FIG. 6 (D), and the attenuation characteristics at the rising and falling edges of the pass band can be made steep to improve the attenuation characteristics at the low frequency side and the high frequency side.

Also in this embodiment, the coupling capacitors 12 and 14 are
Since the frequency characteristic is improved by also using, the simplification and miniaturization of the circuit device can be achieved.

[0017]

MODIFICATION The present invention is not limited to the above-mentioned embodiments, and the following modifications are possible. (1) When it is necessary to remove only the third harmonic component, the first and second LC parallel circuits 31 and 32 of FIG.
Can have the same resonance frequency of 3f0. (2) The first, second and third capacitors 12, 13,
Inductance can be connected in parallel to only one of 14 to suppress the harmonic component or to make the attenuation characteristics of the low-pass side or the high-pass side of the bandpass filter or both of them steep. (3) Input terminal T1 and output terminal T
As a circuit having an anti-resonance point which is also used as a coupling element (for example, a capacitor) connected between 2 and 1, a first parallel circuit of the capacitor C1 and the inductance L1 and a second parallel circuit of the capacitor C2 and the inductance L2 shown in FIG. A circuit in which parallel circuits are connected in series, or a capacitor C as shown in FIG.
A circuit in which an inductance L2 or a capacitor C2 is connected in series to a parallel circuit of 1 and the inductance L1,
Alternatively, as shown in FIG. 9, a circuit in which an inductance L2 and a capacitor C2 are connected in series to a C1 L1 parallel circuit, or an inductance L2 is connected in series to a C1 L1 parallel circuit as shown in FIG. It is possible to form a circuit in which a capacitor C2 is connected in parallel to the whole. In short, it is sufficient that at least one LC parallel circuit is included. (4) The present invention can also be applied to a filter having three or more stages using three or more dielectric resonators. (5) It is possible to use one of the plurality of coupling capacitors for suppressing the harmonic component and another for improving the attenuation characteristic. (6) The inductance may be a separate coil component, or the capacitors 12, 13 and 14 may be formed on the substrate 4 so as to face a pair of conductor layers. (7) When an inductance is provided instead of the capacitor as the coupling element, a capacitor can be connected in parallel to this to form a circuit having an anti-resonance point. (8) When the coupling element is an inductance, the circuit in which the capacitor 13 is omitted from the circuit of FIG. 5 can be formed. (9) It is possible to form a circuit having an anti-resonance point so as to block a predetermined frequency component other than the fundamental wave, similarly to blocking a high frequency component.

[Brief description of drawings]

FIG. 1 is a plan view showing a bandpass filter device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a dielectric resonator in a portion corresponding to line AA in FIG.

FIG. 3 is an equivalent circuit diagram showing the filter device of FIG.

FIG. 4 is a diagram showing frequency characteristics of each part of FIG.

FIG. 5 is an equivalent circuit diagram showing a bandpass filter device according to a second embodiment.

FIG. 6 is a diagram showing frequency characteristics of respective parts of the bandpass filter according to the second embodiment.

FIG. 7 is a circuit diagram showing a modified example of a circuit having an anti-resonance point.

FIG. 8 is a circuit diagram showing another modification of the circuit having an anti-resonance point.

FIG. 9 is a circuit diagram showing still another modification of the circuit having the anti-resonance point.

FIG. 10 is a circuit diagram showing another modification of the circuit having the anti-resonance point.

[Explanation of symbols]

 2, 3 Dielectric resonator 10, 11 Inductance 12, 13, 14 Coupling capacitor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhisa Sato 6-16-20 Ueno, Taito-ku, Tokyo Taiyo Denki Co., Ltd. (72) Inventor Makoto Inoue 6-16-20 Ueno, Taito-ku, Tokyo Taiyo Inductor Co., Ltd. (72) Inventor Takeshi Kosaka 6-16-20 Ueno, Taito-ku, Tokyo Taiyo Induction Co., Ltd.

Claims (2)

[Claims] 1. A bandpass filter device having a coupling element and a dielectric resonator, wherein a circuit having an anti-resonance point is provided, which also serves as the coupling element.
A bandpass filter device, wherein a resonance frequency of a circuit having the anti-resonance point is set to a specific frequency other than a resonance frequency of a fundamental wave of the dielectric resonator. 2. A bandpass filter device having a coupling element and a dielectric resonator, wherein a circuit having an anti-resonance point is provided which also serves as the coupling element,
The resonance frequency of the circuit having the anti-resonance point is such that the resonance frequency of the dielectric resonator is one or both of the low-pass side and the high-pass side of the bandpass filter configured by the dielectric resonator The bandpass filter device is characterized in that it is set to a value that can sharpen.