SU412670A1 - - Google Patents

Description

one

The invention relates to filters and can be used in various radio devices.

A multichannel filter is known that contains an ultrasonic delay line on which one input and several output electroacoustic transducers are located, made in the form of equidistant arrays of conducting electrodes. In the filter, the number of transducers placed on one duct is equal to the number of channels, and the number of elements in each transducer is determined by the required frequency channel band. However, it is difficult to ensure the prescribed accuracy of mutual frequency arrangement of channels with small relative detuning of neighboring channels, which increases as the absolute value of the operating frequencies of the channels increases.

The aim of the invention is to increase the accuracy of the relative frequency distribution of channels.

This is achieved in that each conductive electrode of the input converter is made with stepwise varying length. The number of steps is equal to the number of channels of the filter, and the difference of the heights of neighboring steps is proportional to the frequency detuning of the channels.

FIG. 1 depicts the proposed

filter; in fig. 2 - the same, in section, with a metallized layer prior to the deposition of converters; in fig. 3 - the same, in a section, after applying converters.

The multichannel filter contains an ultrasonic delay line, made on a suction line I made of a piezoelectric material, on which input 2 and several output 3 electroacoustic transducers, made in the form of equidistant lattices from conducting electrodes with the same spatial periods, are located. The longitudinal axis XX, converters are parallel to each other. Input converter 2 broadband. The narrowband frequency channels of the filter are allocated by output converters 3 having the same spatial period. Each conductive electrode 4 of the input converter 2 is made in length with stepwise varying thickness.

The number of steps is equal to the number of channels of the filter, and the difference of the heights of neighboring steps is proportional to the frequency detuning of the channels.

Let the electrode thickness of the converter of the highest-frequency channel be equal to ftx its longitudinal axis coincides with the direction XX. The thickness of the transducer electrodes, the longitudinal axes of which coincide with the directions and, increases by the value of Ah in accordance with the expression

M i. (,

where / a is the tuning frequency of the first channel; a / - frequency detuning of the channel

regarding the first; VR is the velocity of the Rayleigh wave on the free surface;

K is the slope of the characteristic of the variation of the velocity of the Rayleigh wave as a function of the electrode thickness (determined by the ratio of the elastic constants of the duct material and the metallization and the operating frequency);

fn is the frequency of the th channel setting. This expression was obtained assuming a linear dependence of the change in the velocity of the surface wave on the thickness of the metallization layer. The law of change in the thickness of the metallization layer is selected in accordance with the magnitude of the mutual detuning of the channel frequencies using the above formula.

Different thickness of the transducer electrodes can be obtained if the transducers are manufactured on a metallization layer having a cross sectional profile of the metallized surface of the duct (see Fig. 2). The thickness of the transducer electrodes in FIG. 3 will correspond to the thickness of the steps of the metallization layer shown in FIG. 2

Multi-channel filter works as follows. A signal in the form of a radio pulse with a frequency of filling lying within

The frequency bands of the filter are fed to the input transducer 2. At the output transducers 3, which do not have an electrical contact with each other, the signals with different amplitudes are sent to each other. In this case, the signal of the converter for which the relation

Uk (hi)

f

where Ud (ft, -) is the speed of propagation of the surface wave under the transducer with electrode thickness L ;;

I - the spatial period of the lattice converters.

Thus, knowing the number of the frequency channel at the output of which the signal has the largest value, one can determine the frequency offset of the incoming signal.

Subject invention

A multichannel filter containing an ultrasonic delay line on which one input and several output electroacoustic transducers are arranged, made in the form of equidistant arrays of conductive electrodes, characterized in that, in order to increase the accuracy of the relative frequency distribution of the channels, each conductive electrode of the input transducer the length is made with stepwise varying thickness, with the number of steps being equal to the number of filter channels, and the difference in the heights of adjacent steps is proportional to not the frequency offset of the channels.

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