Very compact IF CDMA filter on GaPO4

In the first part of this paper, SAW properties of GaPO₄ are investigated as a function of cut angles and propagation angle. It is found that singly rotated GaPO₄ is already very promising. Therefore, SAW propagation characteristics such as velocity, coupling coefficient, reflection coefficient, power flow angle, and first and second order temperature coefficients are presented as a function of propagation angle ψ and cut angle θ. Experimental results are presented for two singly rotated cuts. They show good agreement with theoretical results when using a proper set of material constants. The second part of this paper is dedicated to the design and realization of an 85 MHz IF CDMA filter. Low velocity allows for a significant reduction in chip size. Using an advanced SPUDT structure, it was possible to prototype a 85 MHz filter in a 7×5 mm² SMT package. Performances of the filter are similar to specifications of up-to-date filters on ST-Quartz