SAW dispersive delay line utilising apodised IDT with periodic electrodes

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.