Dual-T SAW tunable band elimination filter and its application to wideband UHF VCSO

Widely tunable dual-T SAW BEF (band elimination filter) and its application to VCSO (voltage controlled SAW oscillator) operating in UHF range are discussed. It is shown theoretically that owing to very low capacitance ratio (γ ~ 4) of utilised SAW resonators, the notch frequency of the dual-T SAW BEF can be tuned for about 10% at 1 GHz. The designed voltage controlled current adder works properly for the dualT SAW BEF, although the tuning frequency range is narrowed to about 4% by gain and phase dependence on control voltage. To check validity of the circuit design concept, a 430 MHz VCSO was fabricated by using a couple of narrow band SAW resonator of which resonant frequencies are 433.42 and 433.92 [MHz], respectively. The oscillation frequency could be continuously controlled from 433.56 to 433.65 [MHz]. Measured phase noise was -120 dBc/Hz at 10 kHz offset.