Surface acoustic wave apparatus with a variable amplitude-frequency characteristic

DETAILED DESCRIPTION What is claimed is: 1.
A surface acoustic wave apparatus with a variable amplitude-frequency characteristic comprising an input terminal for receiving an electric input signal; a surface acoustic wave element having an input electrode for converting said electric input signal to a surface acoustic wave and propagating the latter to the surface portion of a piezoelectric substrate and output electrodes for converting said propagated surface acoustic wave again to an electric signal, said input electrode being formed by a first interdigital electrode while said output electrode being formed by internally connected second and third interdigital electrodes and provided at a position where the surface acoustic waves radiated from said first interdigital electrode and reaching said second and third interdigital electrodes respectively do not mutually couple and the delay time characteristic appearing between said first and second interdigital electrodes and the phase characteristic of a filter determined by said first and second interdigital electrodes are the same as the delay time characteristic appearing between said first and third interdigital electrodes and the phase characteristic of a filter determined by said first and third interdigital electrodes, respectively; a variable gain function element connected to said second interdigital electrode; a connection means connected to said third interdigital electrode; and an adder circuit for adding the output signal of said third interdigital electrode derived from said connection means and the output signal of said variable gain function element.
2.
A surface acoustic wave apparatus according to claim 1, wherein the phase characteristic of a filter determined by said first and second interdigital electrodes and that of a filter determined by said first and third interdigital electrodes are linear.
3.
A surface acoustic wave apparatus according to claim 1, wherein said connection means is an amplifier with a constant gain