Theoretical and Experimental Results of Flat Phase Linear-Wide Band -Loss Filters Using Dispersive Unidirectional Interdigital Transducers

Dispersive transducers have sharp cut-off and flat wide band frequency characteristics. Moreover phase linear and the very low loss characteristics are obtained by combining down-chirp and up-chirp unidirectional dispersive transducers (DUDIDT and UUDIDT). In this paper, DUDIDT and UUDIDT were investigated using TeO₂ thin film gratings with the large impedance ratios. The impedance ratio of r = Ze/Zg (Ze: with shorted thin film and Zg: without open thin film) were investigated using TeO₂ thin films. The results showed the large impedance ratio, r = 0.96 at the thickness of Hlambda = 0.01 on TeO₂/128deg Y-X LiNbO₃. These grating are applied for DUDIDT and UUDIDT. The very low insertion loss of 0.2 dB and flat wide band of 10% and the very sharp cut-off characteristics were theoretically obtained and the experimental results showed the insertion loss of 0.6 dB at 400 MHz.