Application of a stopband multistrip coupler in a SAW resonator filter

Experimental and theoretical results are presented for the amplitude frequency responses of a SAW two-pole resonator filter with a stopband multistrip coupler (SMSC). Two resonators are placed side-by-side and the SMSC is formed by connecting open aluminium strips of reflectors. As compared with ordinary MSC, application of a SMSC makes the resonators shorter. Therefore, the two nearest longitudinal modes are moved away, and better rejection is obtained near the passband. The filter was fabricated on the ST-cut quartz at the center frequency of about 300 MHz. For a single SMSC, the insertion loss at the center frequency was about -20 dB (in a 50 Ω system) and a stopband rejection was about -40 dB