JPH04275711A - Surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To eliminate the occurrence of spurious owing to lateral mode connection occurring between stages, to miniature a filter and to reduce cost in the surface acoustic wave filter of a multiplex mode, which is used for a communication unit and the like. CONSTITUTION:The filter is composed in such a way that an interdigital electrode 2a and an interdigital electrode 2b, where reflecting electrodes 3 are respectively provided on both sides on a piezoelectric substrate are provided by shifting a relative position between the stages in the transmission direction of a surface acoustic wave in a degree that spurious owing to lateral mode connection does not occur. Thus, a feature is not deteriorated the filter is made small and cost is reduced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact multimode surface acoustic wave filter used in communication equipment and the like.

0002

[Prior Art] In recent years, surface acoustic wave filters in which a comb-shaped input electrode and a comb-shaped output electrode are arranged on a piezoelectric substrate have a large insertion loss. Multimode surface acoustic wave filters that utilize the resulting symmetric and antisymmetric modes have been put into practical use.

A conventional vertical dual-mode surface acoustic wave filter will be explained below. As shown in FIG. 2, comb-shaped electrodes 5a, 5b and a reflective electrode 6 are arranged on a piezoelectric substrate 4, and in order to ensure out-of-band attenuation, they are arranged and connected in two vertical stages. There is. 7 is an input electrode, and 8 is an output electrode.

0004

However, in the above-mentioned conventional configuration, when attempting to connect multiple stages, spurious noise occurs between stages due to transverse mode coupling, so it is necessary to provide sufficient distance between stages, and therefore piezoelectric This has the problem that the size of the sexual substrate 4 becomes large and the cost increases.

The present invention solves the above-mentioned conventional problems, and aims to provide a small, low-cost surface acoustic wave filter that is free from spurious waves due to transverse mode coupling.

[0006]

[Means for Solving the Problem] In order to solve this problem, the surface acoustic wave filter of the present invention shifts the relative positions between the stages in the propagation direction of the surface acoustic wave to the extent that spurious noise due to transverse mode coupling does not occur. It has a structure that includes comb-shaped electrodes arranged as follows.

[0007]

[Operation] This configuration eliminates transverse mode coupling,
This will shorten the distance between stages.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the structure is such that comb-shaped electrodes 2a, 2b and a reflective electrode 3 are disposed on a piezoelectric substrate 1. The comb-shaped electrode 2a and the comb-shaped electrode 2b are arranged so that the relative positions between the stages are shifted in the propagation direction of the surface acoustic wave to such an extent that transverse mode coupling does not occur. 7 is an input electrode, and 8 is an output electrode.

With this configuration, it is possible to shorten the distance between the stages of vertical multi-mode surface acoustic wave filters connected in multiple stages without deteriorating the characteristics, and the size of the piezoelectric substrate 1 can be reduced. A small, low-cost surface acoustic wave filter can be obtained.

[0010]Although the area of the piezoelectric substrate 1 increases in the direction in which the comb-shaped electrodes 2a, 2b are shifted, the comb-shaped electrodes 2a, 2b
If the piezoelectric substrate 1 is made into a parallelogram according to the arrangement position of the piezoelectric substrate 2b, the number of piezoelectric substrates 1 to be used in the surface acoustic wave filter can be increased from the piezoelectric substrate 1 as the material source, and the cost can be reduced.

[0011]

As is clear from the above description of the embodiments, the present invention provides comb-shaped electrodes in which the relative positions of the stages are shifted in the direction of propagation of surface acoustic waves to such an extent that transverse mode coupling does not occur. With this configuration, it is possible to realize an excellent surface acoustic wave filter that does not deteriorate its characteristics and can be made small and low cost.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view of essential parts showing the configuration of a surface acoustic wave filter according to an embodiment of the present invention.

[Fig. 2] A schematic plan view of the main parts showing the configuration of a conventional surface acoustic wave filter.

[Explanation of symbols]

1 Piezoelectric substrate 2a, 2b Comb-shaped electrode 3 Reflecting electrode

Claims (2)

[Claims] 1. A vertical multi-mode filter comprising at least two comb-shaped electrodes on a piezoelectric substrate and reflective electrodes on both sides of the comb-shaped electrodes, the comb-shaped electrodes being used to reduce spurious waves due to transverse mode coupling. A surface acoustic wave filter in which the relative positions of the stages are shifted in the direction of propagation of the surface acoustic wave to the extent that this does not occur. 2. The surface acoustic wave filter according to claim 1, wherein a parallelogram-shaped piezoelectric substrate is used to match the arrangement position of the comb-shaped electrodes.