Obtaining the fundamental and harmonic radiation conductances of a reflective SAW interdigital transducer

The fundamental and harmonic radiation conductances of a solid-electrode uniform reflective SAW Interdigital transducer (IDT) are derived by applying the IDT reflection coefficient as a weighting function to modify the nominal (sin(X)/X)² radiation conductance. The IDT radiation conductance is derived from the single-tap SAW amplitude response function μ_s(f,η)≈μ_s(f₀,η) sin[(πf)/(2f₀)]P_n(cos ηπ), where P_n =nth Legendre polynomial, together with IDT reflectivity as obtained from single-tap charge distribution analysis. The method is demonstrated for the fundamental and third-harmonic radiation conductances of a highly-reflective 100-MHz solid-electrode IDT using 41 electrodes with η=0.25, on 128° YX-LiNbO₃. The results obtained by this approximate method are in good agreement with those published by Morgan (1998), using a quasi-static analysis applied to a reflective array model (RAM)