JPS62193302A - Band pass filter - Google Patents

Abstract

PURPOSE:To contrive to obtain a small-sized band pass filter without damaging features of a hairpin resonator filter by arranging plural resonators, where capacitance elements are connected to front end parts of approximately U-shaped strip or microstrip lines with both ends opened, so that these resonators are connected in parallel and providing coupling lines in input/output parts. CONSTITUTION:Open ends of approximately U-shaped resonators are connected by capacitance elements 9-12. When the line admittance of resonators 5-8, the electric length of lines, connecting capacitance elements, and the resonance frequency are denoted as Y0, theta, C and Fr respectively, the resonance condition is given by a formula Y0sintheta-4pifrC(1-costheta)=0. For example, theta is 45 deg. if Y0, C, and Fr are 0.02S, 4pF, and 1GHz respectively. If capacitance elements are not connected, that is, C is 0, the line length is shortened to 45 deg./180 deg.=1/4 because of theta=180 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a bandpass filter constructed of string lines or microstrip lines, which is used in various communication devices, measuring instruments, and the like.

2. Description of the Related Art Parallel coupling filters using a half-wavelength resonator are often used as band-pass filters using strip lines or microstrip lines, but in order to miniaturize them, resonators vo1. MTI-20, Al
l, November 1972. P9.719-7
It was announced on the 28th. FIG. 3 shows a conventional example of a three-stage bandpass filter using hairpin resonators.

In FIG. 3, 2 and 2 are input/output terminals, 3.4 is an input/output coupling line, and 5.6.7 is a hairpin resonator.

Since the filter with this structure uses a hairpin resonator, it can be made more compact than when using a linear resonator. It also uses a printed circuit board and has the feature of being repair-free.

Problems to be Solved by the Invention However, even when using the hairpin resonator shown in Figure 3, when the frequency reaches about 10Hz, the resonator itself becomes large, so compared to a coaxial resonator, its size is There were problems in terms of size, and the features that could be realized with printed circuit boards could not be taken advantage of.

The present invention aims to reduce the size of the hairpin resonator filter without losing its characteristics.

Means for Solving the Problems The present invention arranges a plurality of resonators in which capacitive elements are connected to the ends of a substantially U-shaped strip or microstrip line with both ends open so as to be coupled in parallel to each other. In addition, the above object is achieved by providing a coupling line in the input/output section.

Operation The present invention connects the two open ends of a substantially U-shaped resonator with a capacitive element as in the above configuration. Now, the line admittance of the resonator is Yo, the electrical length of the line is θ, and the connected capacitive element is C.
If one resonance frequency is pr, then Yo Sfnθ−4πf
ro (1-house 0) = 0 becomes the resonance conditional expression. For example, Yo = 0.028, C = 4 pF,
If f r = I GI [z, then θ = 45°. When no capacitive element is connected, that is, when C=O, θ
= 180°, so the line length is 45P/18θ = 1/
This has been shortened to 4.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a plan view of a bandpass filter in a first embodiment of the invention.

In FIG. 1, 1.2 is an input/output terminal, 3.4 is an input/output coupling line, 5 to 8 are approximately U-shaped resonators, and 9 to 12 are capacitive elements. It is assumed that the pattern shown in FIG. 1, that is, the input/output coupling lines 3.4 and the resonators 5 to 8, are formed on a printed circuit board (dielectric substrate). Further, the capacitive element may have any description as long as it is a lumped constant element. That is, it may be an external individual element, a gap using a pattern, or an interdigital capacitor formed at the same time as the line. It is also possible to use a trimmer capacitor to adjust the frequency.

FIG. 2 shows a second embodiment of the present invention, and the difference from the configuration in FIG. 1 is that the input/output coupling is not parallel coupling as shown in FIG. 1, but capacitive coupling using capacitive elements 13 and 14. This is suitable for wide bandwidth cases,
This is advantageous when it is difficult to realize a pattern as shown in FIG. 1 due to manufacturing accuracy.

Effects of the Invention As described above, the present invention enables miniaturization of a filter using a conventional hairpin resonator, and can be easily realized using a printed circuit board or a ceramic substrate, and its industrial value is high. Very dog-like.

[Brief explanation of drawings]

1 and 2 are plan views of bandpass filters in first and second embodiments of the present invention, respectively, and FIG. 3 is a plan view of a conventionally known hairpin resonator filter. 1.2... Input/output terminal, 3.4... Input/output coupling line, 5--Resonator, 9-12... Capacitive element. Name of agent Toshio Nakao and one other person Figure 1 Figure 3

Claims (2)

[Claims] (1) A plurality of hairpin-shaped resonators in which capacitive elements are connected to the ends of a substantially U-shaped strip or microstrip line with both ends open are arranged so as to be coupled in parallel to each other, and coupled to the input/output section. A bandpass filter with a line. (2) The bandpass filter according to claim 1, wherein the input/output coupling is parallel coupling or capacitive coupling.