SAW ring filters with insertion loss of 1 dB

This paper presents low loss ring SAW filters on 49°YX, 64°YX, 128°YX LiNbO₃ with reflective multistrip couplers (RMSCs). Using the RMSCs with 3 electrodes per λ (λ is the SAW wavelength at the center frequency) and the self-matching approach, when the static capacitance of the IDT is compensated by the acoustic radiation susceptance, the ring filters have shown very low insertion loss of 0.8-1 dB, 3-dB fractional bandwidth of 2-5% with very low ripple of 0.1 dB, stopband attenuation over 50 dB at 10-33% offset from the center frequency of 45 MHz. In a 50 ohm system, 148, 164, 172 MHz ring filters on 128°YX for low power transceivers have provided an insertion loss of 1 dB, 1 dB bandwidth of 1.8-2 MHz, stopband attenuation over 55 dB at ±25 MHz offset from the center frequency. Two cascaded filters at 164.5 MHz have shown insertion losses below 3 dB and stopband attenuation over 90 dB at ±25 MHz, offset from the center frequency. The chip size is 5×4×0.7 mm