Comparisons of the far-field patterns at cut plane φ = 0° obtained by FPQCM and PO combined with PTD for V _s = 10 ms⁻¹ and δ _w = 0°. (A) is the beam cut under δ _ZA = 0°; (B) is the beam cut under δ _ZA = 15°; (C) is the beam cut under δ _ZA = 30°; (D) is the beam cut under δ _ZA = 45°; (E) is the beam cut under δ _ZA = 60°; (F) is the beam cut under δ _ZA = 75°.