Transversal SAW filters are extremely general: any linear bandpass filter may be synthesized, with arbitrary amplitude and phase, limited only by line width and substrate size. Resonator SAW filters are minimum phase designs with low loss. Both devices are small, rugged, very stable, and capable of high volume low cost production.
Delay lines are simply transversal bandpass filters with additional separation between the transducers to achieve the desired insertion delay.
Applications of bandpass filters include anti-aliasing, digital communications, MSK modulation, channel selection, matched filtering, TV broadcast, cable headend, channel processors, RADAR matched filtering, EW matched multi-channel receivers, and filter banks.
Adjustment of electrode length and position allows the SAW designer to synthesize any finite impulse response. For filters specified in the frequency domain, FIR digital filter design techniques are used to find the initial optimum, i.e. shortest, time response. Filters may also be specified directly in the time domain. Filters may be specified by defining templates or mathematical functions in the frequency or time domains.
|Center frequency fo MHz||20 – 1000||10 – 2500||100 – 1000||50 – 2500|
|PassBandWidth B*100/fo for Quartz||.5 – 5||.1 – 10||.05-.1||.025-.2|
|for Lithium tantalate||5 – 10||1 – 20||—||.5-5|
|for Lithium niobate||10 – 30||10 – 150||—||1-15|
|Amplitude ripple in B dB pp||>1||.2||>1||.5|
|Phase ripple in B degrees pp||>10||2||—||—|
|StopBand rejection dB in SB<2|f-fo|<fo||-40||-60||-40||-60|
|Min insertion loss IL in B dB||>25||10||>5||2|
|Return loss in B dB||none||14||none||14|
|Time spurious dB||2*IL||-60||—||—|
|Max response length or Delay us||<10||100||—||—|