Surface Acoustic Wave (SAW) Filter is a frequency filter whereby the electrical input signal is converted to a acoustic wave by so-called interdigital transducers (IDTs) on a piezoelectric substrate such as quartz. The space between the IDTs, across which the surface acoustic wave will propagate, is known as the delay-line. The delayed outputs are recombined to produce a direct analog implementation of a finite impulse response filter. This hybrid filtering technique is also found in an analog sampled filter. SAW filters are limited to frequencies from about 50 MHz up to 3GHz.

Surface Acoustic Wave (SAW) Filter DesignThe most common group of SAW-filters are bandpass filters, which are in very widespread use in radio systems (including mobile phone handsets and base stations) and in domestic TV. There are many types with differing advantages, such as low shape factor, low insertion loss, small size, or high-frequency operation. The wide variety of types is possible because almost arbitrary shapes can be defined on the surface with very high precision.

SAW Filters Applications

Surface acoustic wave filters play a key role in telecommunications. Because of their special features various products are being used more and more in different transmission systems:

  • Passband filter typically as RF or IF filters for data processing in communication systems. A few examples for these applications are mobile phone basestations, point to multipoint systems, radio link systems, Professional Mobile Radio (PMR) systems and Wireless Local Loop (WLL) systems.
  • Clock recovery SAW filters for digital regeneration in fiber-optic systems, e.g. FDDI, ISDN, LAN, WLAN, etc.
  • Digital TV Reception & Broadcasting – Nyquist and Vestigial sideband filters in television transmission systems in TV transmitters and high quality receivers, modulators/demodulators, and converters of CATV head-ends, etc.
  • Passband filters for basestations include filters for all worldwide standards (TDMA, CDMA, GSM, and W-CDMA). Filters for WLL systems are available for products based on CDMA, W-CDMA, DECT, GSM, and proprietary standards. Trunked radio filters for PMR basestation, mobile and handheld applications are offered for the digital standard TETRA.
  • Other applications of SAW filters include: GPS Location and Navigation Equipment, Cordless Phones, Bluetooth, RFID, Land Mobile Radios, ETC, RKE, WLAN, etc.