Surface Acoustic Wave Filter (SAWF) is an integrated filter which uses the principle of "piezoelectricity" and "anti piezoelectric" to transmit signals. The ability of different frequency signals to transfer energy in SAWF is different, thus forming a filtering function for different frequency signals.
(1). Structure of Surface Acoustic Wave Filter (SAWF)
Saw filter is composed of piezoelectric crystal substrate, input transducer and output transducer. Piezoelectric crystals are usually made of lithium niobate, and transducers are interdigitated. They convert voltage signals into mechanical waves, and then convert mechanical waves into voltage signals. The size and shape of the interdigital transducer determine the passband characteristics of the filter.
The characteristic of surface acoustic wave filter (SAWF) is: 1)Good selectivity, the absorption depth can reach 35~ 1 40dB;
2)The amplitude frequency characteristic and the phase frequency characteristic are good, and need not be adjusted;
3)The temperature stability is good, the aging is not easy, the overload ability is strong, it will not cause the change of frequency characteristic because of the size of the transmission signal.
But it also has disadvantages such as large insertion loss, low transmission efficiency and three reflections.
(2). Main parameters of surface acoustic wave filter (SAWF)
The main parameters of surface acoustic wave filter (SAWF) include central frequency, bandwidth, rectangle coefficient, insertion loss, maximum out of band suppression, amplitude fluctuation, linear phase shift and so on.