Abstract: This article reports the design and construction of SAW bandpass filters consisting of two apodized transducers and a multiscrip coupler. The multiscrip coupler (MSC) is somewhat different from what have been reported in the previous literatures. It consists of a number of strips which are equal to those in the perfect transfer coupler. However a modified quantity a has been introduced to the relative position between the input and output transducers so as to reduce the effect of diffraction and beam deviation. In fact this MSC is no longer a perfect transfer coupler.
In addition with the aim of reducing the wavefront distortion and the effect of broken fingers, a pair of split fingers at the same sampling point are electrically connected, moreover the gaps between the adjacent pair of split fingers, corresponding to the space between an active finger and the passive one, are connected in the same way.
Filters with different specifications have been prepared using the technique stated above. The center frequency ranges from 30MHz to 70MHz with the bandwidth of 11%-40% f₀, the shape factor of 1.24-1.45, in-band ripple of ±0.2dB-0.4dB (peak to peak) and sidelobe rejection of 42dB-49dB.