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In designing SAW dispersive delay lines (DDLs), one usually applies dispersive interdigital transducers with electrode spacing varying according to the frequency-delay time relation of the delay line impulse response. A new method is proposed in the letter, in which a DDL is treated as a bandpass filter with a nonlinear phase response. Such a filter can be synthesised with an IDT having periodic electrodes with apodisation. The experimental result is −40 dB of sidelobe level obtained in a system of two DDLs, one of which is Hamming-weighted.
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