JPH0211001A - Dielectric filter - Google Patents

Abstract

PURPOSE:To decrease the cost of the die for shaping for ceramic burning and to improve a filter manufacturing yield by using two coaxial parallel coupling filters of the same construction, capacity-coupling the section between filters and constituting the filter of a 2N step. CONSTITUTION:For a 2N step band pass filter, two N step filters of the completely same construction are combined and two filters are capacity-coupled. Namely, for dielectric blocks 101 and 102, the construction is the completely same, respective blocks have central conductors 103-108 of a resonator and holes 116-118 for adjusting the coupling between resonators, and for the dielectric blocks 101 and 102, the surface is metallized and they are capacity-coupled by a coupling capacity 113. Thus, for the die for shaping a dielectric block, the size is halved and the yield of the dielectric block after burning is far improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a dielectric filter using a dielectric block used in RF circuits of wireless communication devices, measuring instruments, etc. used in the UHF band.

Background of the Invention In recent years, mobile communication devices such as car phones, MCA radios, personal radios, and cordless telephones have become significantly smaller and lighter, and there is also a demand for smaller and lower cost filters used in these devices. It's getting stronger. In order to reduce the size of filters, a filter having a coaxial structure using a dielectric block having low loss and high dielectric constant is known, as disclosed in Japanese Patent Laid-Open No. 58-51601. First, an explanation will be given using FIG. 5, which is an example of a conventional method.

Figure 5 shows an example of a filter with 6 stages, and in the figure 1
01 is a dielectric block, 103-108 bars are a quarter wavelength resonator with one end shorted and the other end open, inner conductor, 109, 11
0 is an input/output terminal, 111. 112 is input/output coupling capacitance;
Reference numerals 116 to 120 indicate through holes for adjusting interstage coupling. The dielectric block 101 is entirely metalized except for the open end face of the resonator. Furthermore, the inner peripheral surfaces of the resonators 103 to 108 are also metallized.

By using a dielectric, the resonator length can be reduced to 1/JE r
(Er: dielectric constant), it is possible to downsize, and since the dielectric is a sintered ceramic, it can be integrally fired, vibration resistance is improved, and costs can be reduced.

Problems to be Solved by the Invention Filters using dielectric blocks have various features, but as the number of stages in the filter increases, the cost of the mold for filter shaping increases and the manufacturing yield also deteriorates. It has the following problems. Furthermore, in terms of electrical performance, the attenuation characteristics in the stopband below the center frequency are worse than those above the center frequency, and the characteristics also have the disadvantage of being asymmetrical with respect to the center frequency.

An object of the present invention is to solve the cost problem or the asymmetry problem of attenuation characteristics of a coaxial filter having a dielectric block structure.

Means for Solving the Problems The basic structure of the present invention is 2N (N=2.3°4,
) stage dielectric block structure bandpass filter (
BPF) focuses on the fact that when it is divided into two parts at the center of the N-stage and N+1-stage, the boundary is used as a plane of symmetry and is completely symmetrical both structurally and electrically. This is a combination of N-stage filters, and the coupling between the filters is realized by capacitive coupling.

Operation By adopting this configuration of the present invention, the size of the mold for shaping the dielectric block is halved, and the yield of the dielectric block after firing is also greatly improved. In addition, by providing capacitive coupling between the filters, the asymmetry of the attenuation characteristics can be improved, whereas in the conventional configuration all magnetic field coupling is involved.

Note that with this configuration, only an even number of stages, 2N stages, can be realized, but 2N-1 (N = 3° 4.5...
・) stage filter characteristics can be achieved with a 2N stage filter, so electrical characteristics are not a problem.

Embodiment FIG. 1 shows a first embodiment of the present invention. FIG. 1 is a perspective view of a six-stage dielectric band pass filter in a first embodiment of the present invention. In the figure, 101. 102
are dielectric blocks and have exactly the same structure. 103~
108 is the center conductor of the resonator, and 116 to 118 are holes for adjusting the coupling between the resonators. Dielectric block 101. 10
No. 2 has metallized surfaces except for one open end surface and the inner circumferential surface of the coupling adjustment hole. 113 is a coupling capacitance for coupling the two filter blocks 101 and 102; 112. 113 is the input and output capacitor, 1
09. 110 is an input and output terminal. Further, the two filter blocks are arranged and fixed so that the corresponding resonator center conductors and coupling adjustment holes face each other.

FIG. 2 is a plan view of a dielectric filter in a second embodiment of the invention. It is basically the same as the embodiment of FIG. 1, and the same numbers as in FIG. 1 have the same functions. In this embodiment, between the opposing resonators, that is, the resonators 103 and 108 (1
the resonators 104 and 107 (the second and fifth stages) at 115. An auxiliary coupling circuit 114 for slight coupling using a capacitor, inductor, etc. is provided to form a polarized filter that produces an attenuation pole in the filter's stop band. Note that 113 is a coupling capacitance that determines the pass characteristics of the filter as in FIG. Generally, polar filters are 2N
1 stage and 2N (N>2) stages of filters, 2 stages and 2N-
1 stage (N>3), 3 stages and 2N-2 stages (N>4),...
Since the auxiliary coupling circuit is provided in the filter, the two-block structure filter of the present invention has a structure suitable for a polarized filter.

FIG. 3 is a perspective view of a dielectric filter in a third embodiment of the present invention. This shows an embodiment of a four-stage BPF, consisting of two dielectric filter blocks 101 .
102 are arranged and connected. 103 to 106 are resonator center conductors, 116. 117 is a coupling adjustment hole;
109. 110 is an input/output terminal, 111 and 112 are input/output coupling capacitances, and 113 is an inter-filter coupling capacitance.

As can be seen in this example, by making the filter into two parts, it is possible to arrange the filters in parallel or in series.
Since two filter blocks can be completely separated and connected by a coupling capacitor 113 to form a single filter, a filter with an extremely large degree of freedom in configuration can be created.

FIG. 4 shows a fourth embodiment of the present invention, in which stepped impedance resonators (SIR) 200 to 203 are applied to the resonators. This resonator has a structure in which the outer conductor is circular in order to lower the line impedance near the open end of the center conductor. In this resonator structure, since the coupling length between the resonators is 9 CI' or less, the coupling adjustment holes required in the first to third embodiments are not required, and there is an advantage that spurious characteristics are improved.

Effects of the Invention As described above, the present invention reduces the cost of shaping molds for ceramic firing and improves filter manufacturing yield by dividing 2N stages (N≧5) into two filter blocks of the same structure. In addition, the filters can be arranged in parallel, in series, or completely separated, which increases the degree of freedom in mounting, and in the case of parallel arrangement, a polarized filter can be easily constructed. In addition, since the coupling between the filter blocks is capacitive, the interstage coupling includes a mixture of magnetic field coupling and electric field coupling, so it is possible to achieve electrical characteristics such as symmetrical attenuation characteristics of a band pass filter. Therefore, its industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a dielectric filter according to a first embodiment of the present invention, FIG. 2 is a plan view of a dielectric filter according to a second embodiment of the invention, and FIGS. A perspective view of a dielectric filter in the fourth embodiment, and FIG. 5 is a perspective view of a conventional dielectric block filter. 101, 102...dielectric filter block, 1
03-108... Center conductor, 116-119... Coupling degree adjustment hole, 109, 110... Input/output terminal, 11
1. 112... Input/output coupling capacitor, 113...
・Coupling capacity, 114. 115...Auxiliary coupling circuit. Name of agent: Patent attorney Toshi Nakao, male and 1 other person / 701 Ino Fufuguchi Schiff / /b2 Rikitsou Tab Book D 7

Claims (3)

[Claims] (1) Two coaxial parallel coupling filters with the same structure using a dielectric block in which N pieces (N≧2) of coaxial resonators are arranged.
1. A dielectric filter characterized in that a 2N-stage filter is constructed by capacitively coupling the filters using a coupling capacitance. (2) The dielectric filter according to claim 1, wherein the two unit dielectric block filters are arranged in parallel, in series, or completely separated. (3) Arrange two unit dielectric block filters in parallel in the same row, capacitively couple the N stage and N+1 stage, and capacitively couple the 1st stage and 2N stage, and the 2nd stage and 2N-1 (N≧ 3),
3rd stage and 2N-2 (N≧4), 4th stage and 2N-3 (N≧4)
2. The dielectric filter according to claim 1, further comprising an auxiliary coupling circuit made of an inductor or a capacitor between the resonators of item 5), and an attenuation pole provided in the stop band of the filter.