Narrowband SAW filters for IF applications

The general concerns of narrowband surface acoustic wave (SAW) filtering are reviewed. The specific characteristics of each approach are discussed. The application of these filters in particular IF subsystems such as an anti-jam modem, a satellite transponder, and a direction finder is studied. It is found that SAW filters can be used in a wide variety of narrowband IF applications. Waveguide coupled resonant filters offer the best near-in rejection performance for a given size and insertion loss but are limited to 0.1% bandwidth. When greater bandwidths are called for but low loss is important or near-in rejection is not a concern, the inline coupled resonant filters are effective. Because of their low loss, resonator type filters are often cascaded when greater rejection or steeper shape factors are required. When linear phase is required, reflective array filters can satisfy the specifications provided a larger size and higher insertion loss can be tolerated