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The propagation characteristics of surface acoustic waves (SAW) and piezoelectric leaky surface waves in KNbO/sub 3/ single crystal have been investigated theoretically and experimentally. The results show that the electromechanical coupling coefficient k/sup 2/ of the surface wave propagating along the X-axis of the rotated Y-cut plate is very large with k/sup 2/=0.53. This is about 10 times as large as that of LiNbO/sub 3/ in the surface wave branch. Experimental results for wideband SAW filters show low loss and temperature stable characteristics. The bandwidth is about 20%, and insertion losses are less than 2 to 6 dB. Simulation results for a ladder type filter using Y-cut KNbO/sub 3/ indicate that a bandwidth of 40% should be possible. The KNbO/sub 3/ substrates exhibit zero temperature coefficient of frequency (TCF) around 20/spl deg/C in rotated Y-cut substrates.