JPS60165102A - Dielectric filter - Google Patents

Abstract

PURPOSE:To eliminate almost the need for the further adjustment to a resonance frequency shift produced in connecting input/output coupling capacitors by selecting an upper end face of an input/output resonator at both ends of a dielectric block comprising cascade connection of plural resonators lower than the end face of other resonators by a specific value. CONSTITUTION:In an execution of an example where five-stages of resonators 10-14 are provided in cascade to a dielectric block 1', adjacent resonators are coupled by coupling holes 15-18 and coaxial capacitors 19, 20 are used for the coupling between the input/output resonators 10, 14 and an external circuit. The change DELTAh of the length (h) of the resonator when the coupling capacitor with the external circuit is loaded to the open face of the resonator is expressed in equation I with a constant wo=2pif, where wo is a resonance angular frequency, C is a capacitance of a coupling capacitor, V is a characteristic admittance of the resonators and epsilonr is a dielectric constant of the dielectric block. Thus, in manufacturing the height of the resonators 10, 14 at both ends of the dielectric block by DELTAh in advance, the adjusting work after the coupling capacitor is connected is not almost required.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to improvements in dielectric filters used in the construction of telecommunications equipment operating at relatively high frequencies.

fb) Background of the technology and problems with the conventional technology For example, in the production of automobile radio equipment that uses frequencies in the UHF band of several hundred megahertz, a plurality of 11
A so-called dielectric filter in which 1 il resonance holes and coupling holes are alternately provided is widely used because it has relatively low loss, high Q, stable characteristics, and can be manufactured in a small size.

NS Figure 1 shows a conventional example of this type of dielectric filter composed of two-stage resonators, with a plan view fal and Δ-71. (This is shown in (b)), where 1 is a rectangular dielectric block 1.
J 7, 2.2' is the resonance hole, 3 is the coupling hole, and the inner wall of the resonance hole, the side wall of the block, and the bottom surface are covered with metal coatings 4.4', 5
．． 6 is provided. Chip capacitor 7.7゛ for input/output coupling and metal covering 1 on the inner wall of the resonance hole? i4.
4', a metal piece 8.8' is soldered to the upper end of the inner wall of the resonant hole.

In a dielectric filter with such a configuration, the height h of the block determines the resonant frequency, and the length d between the resonant holes and the shape of the coupling hole determine the degree of coupling between both resonators, and therefore the bandwidth of the filter. This is well known.

The illustrated dielectric filter is further sealed in a metal case and is incorporated into equipment for use.

However, in conventional configurations of this type, the coupling capacitor 7.
When 7' is connected, the resonant frequency of each resonator decreases by several percent, and the resonators must be adjusted again.

Generally, this adjustment is performed by cutting 9.9 degrees of the upper side of the resonator with a grinder, but it has to be done by cut and 1-lie with the resonant frequency measurement work, which requires a significant amount of man-hours. This increases production costs.

Furthermore, the work of soldering a metal piece 8.8" to the upper part of the inner wall of the resonator for connecting the coupling chip capacitor 7.7" is not easy and is one of the causes of increased manufacturing costs.

(C1 Object of the Invention The object of the present invention is to provide a novel dielectric filter that eliminates the two drawbacks of the conventional structure.

(d) Snoring! ) Nol\ and the object of the present invention is that the upper end surfaces of the input and output resonators at both ends of a dielectric block formed by cascading a plurality of resonators are
From the end face of the other resonator, the value Δhβp′ υ (J1), IAa is the resonant angular frequency, C is the capacitance of the coupling content, ■ is the speed of light in free space, Yo is the characteristic admittance of the resonator, and εr is the dielectric material. This is achieved by the dielectric filter of the present invention in which the dielectric constant of the block is selected to be low.

Since the resonant frequency f of the resonator is determined by the length of approximately 1/4 wavelength, the length h of the resonator without a coupling capacitor is expressed as.

Next, as shown in the equivalent circuit shown in Figure 2, the coupling capacitor C
is applied to the open surfaces a, a' (b, b' are short-circuit surfaces) of the resonator, the change Δ11 in the length h of the resonator is w
It is shown in the case where o=2πf is constant.

Therefore, the height of the resonators at both ends of the dielectric block is set in advance by Δ1.
), the conventional adjustment work after connecting the coupling capacitor is almost unnecessary, which significantly reduces the number of manufacturing steps and production costs.

(C1 Embodiments of the Invention The gist of the present invention will be specifically explained below with reference to embodiments shown in the drawings. The same reference numerals indicate the same objects throughout the drawings.

FIG. 3 shows a plan view (a
8-Δ side cross-sectional view (indicated by bl). Adjacent resonators are coupled through coupling holes 15 to 18, respectively, and input/output resonators] 0.14 and external circuits. Coaxial capacitors 19 and 20 are used for connection with the resonators 19 and 20, and the difference in resonance frequency due to the connection is made so that the difference in resonance frequency between the two resonators 11) is set to be Δ1] lower than that of the other resonators 11, 12, and 13 in advance.

For example, the resonance frequency is 1000100O, t r -40
, Yo-1/12, Δl=o, 6 dragons. This corresponds to approximately 12 MIIz.

FIG. 4 shows another embodiment of the dielectric filter of the present invention using the chip capacitor 7 shown in FIG. (Indicated by bl.

In this case, the upper end of the metal coating 21 on the inner wall of the resonance hole of the input/output resonator (only one is shown in the figure) is extended to the surface of the dielectric block l'' by applying conductive paint and baking it into a ring shape. The connecting terminal 22 of the capacitor 22 is made of a conductive material to ensure reliable ≦1:χ contact with the chip capacitor 7 for input/output coupling.

(11. Effects of the Invention) As explained in Section 2, the dielectric filter according to the present invention is designed to substantially eliminate the need for subsequent adjustments to the resonant frequency shift that occurs when connecting input/output coupling capacitors. It shows industrial effect.

[Brief explanation of drawings]

Fig. 1 shows an example of a conventional dielectric filter in a plan view and a sectional side view, Fig. 2 shows an equivalent circuit of a resonator when an input/output coupling capacitor is connected, and Fig. 3 shows an example of a conventional dielectric filter. The embodiment is shown in a plan view and a side view, and FIG. 4 shows another embodiment in a perspective view and a side sectional view of the main part. In the figure, 1.1", 1" is a dielectric block, 2.2
"" is a resonance hole, 3 and 15 to 18 are coupling holes, 7.7 is a chip capacitor for input/output coupling, 10 to 14 is a resonator, and 19.20 is a coaxial capacitor for input/output coupling. Number I (θ) Dormitory? Utaken 3 Uta'v-4 Shoutyude/II

Claims (2)

[Claims] (1) The upper end faces of the input/output resonators at both ends of a dielectric block formed by cascading multiple resonators have a value Δh higher than the end faces of other resonators. However, 0 is the resonant angular frequency, and C is the coupling 8 of the capacitor, ■ is the speed of light in free space, Yo is the characteristic admittance of the resonator, and εr is the permittivity of the dielectric block, which is selected to be low. (2) A dielectric filter according to claim 1, characterized in that the inner conductor film of the input/output resonator is extended to the end face surface, and a coupling capacitor is soldered to the extended part.